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Stefano FRABBONI

Professore Ordinario
Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica


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Pubblicazioni

2022 - Challenging Point Scanning across Electron Microscopy and Optical Imaging using Computational Imaging [Articolo su rivista]
Kallepalli, Akhil; Viani, Lorenzo; Stellinga, Daan; Rotunno, Enzo; Bowman, Richard; Gibson, Graham M.; Sun, Ming-Jie; Rosi, Paolo; Frabboni, Stefano; Balboni, Roberto; Migliori, Andrea; Grillo, Vincenzo; Padgett, Miles J.
abstract


2022 - Enhancing Electron Computational Ghost Imaging Using Artificial Neural Networks [Articolo su rivista]
Viani, Lorenzo; Rosi, Paolo; Rotunno, Enzo; Frabboni, Stefano; Balboni, Roberto; Grillo, Vincenzo
abstract


2022 - Generation of electron vortex beams with over 1000 orbital angular momentum quanta using a tunable electrostatic spiral phase plate [Articolo su rivista]
Tavabi, A. H.; Rosi, P.; Roncaglia, A.; Rotunno, E.; Beleggia, M.; Lu, P. -H.; Belsito, L.; Pozzi, G.; Frabboni, S.; Tiemeijer, P.; Dunin-Borkowski, R. E.; Grillo, V.
abstract

We report the use of an electrostatic micro-electromechanical systems-based device to produce high quality electron vortex beams with more than 1000 quanta of orbital angular momentum (OAM). Diffraction and off-axis electron holography experiments are used to show that the diameter of the vortex in the diffraction plane increases linearly with OAM, thereby allowing the angular momentum content of the vortex to be calibrated. The realization of electron vortex beams with even larger values of OAM is currently limited by the breakdown voltage of the device. Potential solutions to overcome this problem are discussed.


2022 - Highly-Packed Proximity-Coupled DC-Josephson Junction Arrays by a Direct-Write Approach [Articolo su rivista]
Porrati, F.; Jungwirth, F.; Barth, S.; Gazzadi, G. C.; Frabboni, S.; Dobrovolskiy, O. V.; Huth, M.
abstract

Focused ion beam induced deposition (FIBID) is a direct-write technique enabling the growth of individual nanostructures of any shape and dimension with high lateral resolution. Moreover, the fast and reliable writing of periodically arranged nanostructures can be used to fabricate devices for the investigation of collective phenomena and to design novel functional metamaterials. Here, FIBID is employed to prepare dc-Josephson junction arrays (dc-JJA) consisting of superconducting NbC dots coupled through the proximity effect via a granular metal layer. The fabrication is straightforward and allows the preparation of dc-JJA within a few seconds. Microstructure and composition of the arrays are investigated by transmission electron microscopy and energy dispersive X-ray spectroscopy. The superconductor-to-metal transition of the prepared dc-JJA is studied in a direct way, by tuning the Josephson junction resistance in 70 nm-spaced superconducting NbC dots. The observed magnetoresistance oscillations with a period determined by the flux quantum give evidence for the coherent charge transport by paired electrons. Moreover, the measured resistance minima correspond to two fundamental matching configurations of fluxons in the dc-JJA, caused by magnetic frustration. The robust properties of the prepared dc-JJA demonstrate the opportunities for a fast preparation of complex device configurations using direct-write approaches.


2022 - Pre-treatment of Selective Laser Melting (SLM) surfaces for thermal spray coating [Articolo su rivista]
Bolelli, G.; Bonilauri, M. F.; Sassatelli, P.; Bruno, F.; Franci, R.; Pulci, G.; Marra, F.; Paglia, L.; Gazzadi, G. C.; Frabboni, S.; Lusvarghi, L.
abstract

In this work, we investigated the deposition of thermal spray coatings onto additively manufactured parts obtained by Selective Laser Melting (SLM). SLM is indeed replacing conventional subtractive machining to produce diverse industrial parts; hence, it will become increasingly frequent to apply thermal spray coatings onto SLM surfaces. Whilst grit-blasting is the most widely accepted process to prepare a conventionally machined part for a thermal spray coating, the unique surface texture of SLM surfaces might open new possibilities. As a case study, we chose High Velocity Oxygen-Fuel (HVOF) spraying of WC-10%Co4%Cr onto AISI 316 L SLM surfaces in three different conditions: “as built”, pickled, or grit-blasted. We also examined SLM surfaces grown along different directions: parallel, perpendicular, or inclined with respect to the build platform. The references were a machined and grit-blasted SLM part, and a grit-blasted stainless steel bulk. Dense coatings were obtained on every surface regardless of its roughness and pre-treatment. Electrochemical corrosion testing confirmed the low porosity of the layers. Tensile adhesion/cohesion strength was >70 MPa on both SLM and reference surfaces, but the presence of an oxide scale on as-built surfaces degraded the adhesion strength to some extent. Although TEM analysis showed occasional evidence of diffusion bonding between the coating and the oxide scale, cyclic impact tests revealed that the scale itself broke. Particularly strong adhesion was achieved with pickled surfaces; indeed, failure was only cohesive (i.e. within the coating) in both tensile and impact tests. In addition to mechanical interlocking to the rough surface profile, TEM showed widespread diffusion bonding to the clean metal. An SLM part might therefore need chemical activation but no subtractive machining before application of a thermal spray coating. The coating also exerts a levelling action toward the SLM surface, i.e. the coated surface is smoother than the as built one.


2022 - Theoretical and practical aspects of the design and production of synthetic holograms for transmission electron microscopy [Articolo su rivista]
Rosi, P.; Venturi, F.; Medici, G.; Menozzi, C.; Gazzadi, G. C.; Rotunno, E.; Frabboni, S.; Balboni, R.; Rezaee, M.; Tavabi, A. H.; Dunin-Borkowski, R. E.; Karimi, E.; Grillo, V.
abstract

Beam shaping-the ability to engineer the phase and the amplitude of massive and massless particles-has long interested scientists working on communication, imaging, and the foundations of quantum mechanics. In light optics, the shaping of electromagnetic waves (photons) can be achieved using techniques that include, but are not limited to, direct manipulation of the beam source (as in X-ray free electron lasers and synchrotrons), deformable mirrors, spatial light modulators, mode converters, and holograms. The recent introduction of holographic masks for electrons provides new possibilities for electron beam shaping. Their fabrication has been made possible by advances in micrometric and nanometric device production using lithography and focused on ion beam patterning. This article provides a tutorial on the generation, production, and analysis of synthetic holograms for transmission electron microscopy. It begins with an introduction to synthetic holograms, outlining why they are useful for beam shaping to study material properties. It then focuses on the fabrication of the required devices from theoretical and experimental perspectives, with examples taken from both simulations and experimental results. Applications of synthetic electron holograms as aberration correctors, electron vortex generators, and spatial mode sorters are then presented.


2021 - Alignment of electron optical beam shaping elements using a convolutional neural network [Articolo su rivista]
Rotunno, E.; Tavabi, A. H.; Rosi, P.; Frabboni, S.; Tiemeijer, P.; Dunin-Borkowski, R. E.; Grillo, V.
abstract

A convolutional neural network is used to align an orbital angular momentum sorter in a transmission electron microscope. The method is demonstrated using simulations and experiments. As a result of its accuracy and speed, it offers the possibility of real-time tuning of other electron optical devices and electron beam shaping configurations.


2021 - Convolutional neural network as a tool for automatic alignment of electron optical beam shaping devices [Articolo su rivista]
Rotunno, Enzo; Tavabi, Amir; Rosi, Paolo; Frabboni, Stefano; Tiemeijer, Peter; Dunin-Borkovski, Rafal; Grillo, Vincenzo
abstract


2021 - Experimental Demonstration of an Electrostatic Orbital Angular Momentum Sorter for Electron Beams [Articolo su rivista]
Tavabi, Amir H.; Rosi, Paolo; Rotunno, Enzo; Roncaglia, Alberto; Belsito, Luca; Frabboni, Stefano; Pozzi, Giulio; Gazzadi, Gian Carlo; Lu, Peng-Han; Nijland, Robert; Ghosh, Moumita; Tiemeijer, Peter; Karimi, Ebrahim; Dunin-Borkowski, Rafal E.; Grillo, Vincenzo
abstract

The component of orbital angular momentum (OAM) in the propagation direction is one of the fundamental quantities of an electron wave function that describes its rotational symmetry and spatial chirality. Here, we demonstrate experimentally an electrostatic sorter that can be used to analyze the OAM states of electron beams in a transmission electron microscope. The device achieves postselection or sorting of OAM states after electron-material interactions, thereby allowing the study of new material properties such as the magnetic states of atoms. The required electron-optical configuration is achieved by using microelectromechanical systems technology and focused ion beam milling to control the electron phase electrostatically with a lateral resolution of 50 nm. An OAM resolution of 1.5. is realized in tests on controlled electron vortex beams, with the perspective of reaching an optimal OAM resolution of 1. in the near future.


2021 - Focused ion beam fabrication of Janus bimetallic cylinders acting as drift tube Zernike phase plates for electron microscopy [Articolo su rivista]
Rosi, P.; Gazzadi, G. C.; Frabboni, S.; Grillo, V.; Tavabi, A. H.; Dunin-Borkowski, R. E.; Pozzi, G.
abstract

Modern nanotechnology techniques offer new opportunities for fabricating structures and devices at the micrometer and sub-micrometer level. Here, we use focused ion beam techniques to realize micrometer-sized Janus bimetallic cylinders acting as drift tube devices, which are able to impart a controlled phase shift to an electron wave. The phase shift results from the presence of contact potentials in the cylinders, in a similar manner to the electrostatic Aharonov-Bohm effect in bimetallic wires. We use electron Fraunhofer interference to demonstrate that such bimetallic structures introduce phase shifts that can be tuned to desired values by varying the dimensions of the pillars, in particular their heights. Such devices are promising for electron beam shaping and for the realization of electrostatic Zernike phase plates (i.e., devices that are able to impart a constant phase shift between an unscattered and a scattered electron wave) in electron microscopy, in particular, cryo-electron microscopy.


2020 - Combination of Electron Energy-loss Spectroscopy and Orbital Angular Momentum Spectroscopy. Applications to Electron Magnetic Chiral Dichroism, Plasmon-loss, and Core-loss [Articolo su rivista]
Bertoni, G.; Rotunno, E.; Tavabi, A.; Zanfrognini, M.; Rosi, P.; Frabboni, S.; Karimi, E.; Dunin-Borkowski, R.; Grillo, V.
abstract


2020 - Design, Realization and Challenges of an Orbital Angular Momentum Sorter: A New Instrument for Phase Microscopy [Articolo su rivista]
Tavabi, Amir; Rosi, Paolo; Pozzi, Giulio; Roncaglia, Alberto; Frabboni, Stefano; Rotunno, Enzo; Lu, Peng Han; Nijland, Robert; Tiemeijer, Peter; Ghosh, Moumita; Karimi, Ebrahim; Dunin-Borkowski, Rafal; Grillo, Vincenzo
abstract


2020 - Dynamical diffraction effects in STEM orbital angular momentum resolved electron energy-loss magnetic chiral dichroism [Articolo su rivista]
Zanfrognini, M.; Rotunno, E.; Rusz, J.; Dunin Borkowski, R. E.; Karimi, E.; Frabboni, S.; Grillo, V.
abstract

In this paper, we explore the properties of dynamical diffraction coefficients in orbital angular momentum resolved electron energy-loss magnetic chiral dichroism spectra, in a scanning transmission electron microscopy setup. We demonstrate that for basic zone axis geometries with fourfold or threefold symmetry the coefficients are constrained to have simplified forms. By exploiting these properties, we show how a dichroism spectrum accessible using this technique is only weakly dependent on sample thickness and, more generally, on dynamical diffraction effects. Our results indicate that in such cases it is possible to determine the orbital and spin components of atomic magnetic moments approximately from experimental spectra without the need for additional dynamical diffraction calculations.


2020 - Efficient molecule discrimination in electron microscopy through an optimized orbital angular momentum sorter [Articolo su rivista]
Troiani, F.; Rotunno, E.; Frabboni, S.; Ravelli, R. B. G.; Peters, P. J.; Karimi, E.; Grillo, V.
abstract

We reformulate the single-molecule analysis in an electron microscope in terms of a quantum-state discrimination problem, and discuss its implementation through electron-beam shaping. Our approach relies on the use of new electron-optical elements to efficiently extract the "which-molecule"information from the state of each electron. The optimal observables are formally derived, and subsequently implemented by suitably designed phase elements in a generalized orbital angular momentum sorter. As a representative example, we simulate the discrimination between model proteins and benchmark the performance of the sorter against that of the best known real-space approach.


2020 - How the observation in a new custom basis based on orbital angular momentum space could improve our dose effective reconstruction of the protein structure [Articolo su rivista]
Troiani, F.; Rotunno, E.; Frabboni, S.; Ravelli, R.; Peters, P.; Karimi, E.; Grillo, V.
abstract


2020 - Near-4D STEM with an Orbital Angular Momentum Sorter: Advantages and Challenges [Articolo su rivista]
Rotunno, Enzo; Tavabi, Amir; Rosi, Paolo; Roncaglia, Alberto; Nijland, Robert; Ghosh, Moumita; Tiemeijer, Peter; Frabboni, Stefano; Dunin-Borkowski, Rafal; Grillo, Vincenzo
abstract


2019 - Electron-Beam Shaping in the Transmission Electron Microscope: Control of Electron-Beam Propagation Along Atomic Columns [Articolo su rivista]
Rotunno, E.; Tavabi, A. H.; Yucelen, E.; Frabboni, S.; Dunin Borkowski, R. E.; Karimi, E.; Mcmorran, B. J.; Grillo, V.
abstract

We present a detailed analysis of the propagation of high-energy electron beams that have different shapes in a crystal of [100]-oriented zincblende GaN. Our study primarily focuses on Bessel beams and makes use of reformulated Bloch wave and multislice simulations. As a result of the simplicity of the momentum spectrum of a Bessel beam and the symmetry of the crystal, its propagation in the material can be described in a free-space representation, providing a deeper understanding of channeling phenomena and of probe intensity oscillation in the propagation direction. We also consider aperture-limited and Gaussian beams. The latter probes are shown to be optimal for coupling to 1s Bloch states and achieving minimal spreading along atomic columns.


2019 - Orbital Angular Momentum and Energy Loss Characterization of Plasmonic Excitations in Metallic Nanostructures in TEM [Articolo su rivista]
Zanfrognini, Matteo; Rotunno, Enzo; Frabboni, Stefano; Sit, Alicia; Karimi, Ebrahim; Hohenester, Ulrich; Grillo, Vincenzo
abstract

Recently, a new device to measure the orbital angular momentum (OAM) electronic spectrum after elastic/inelastic scattering in a transmission electron microscope has been introduced. We modified the theoretical framework needed to describe conventional low-loss electron energy loss spectroscopy (EELS) experiments in transmission electron microscopes (TEM) to study surface plasmons in metallic nanostructures, to allow for an OAM post selection and devise new experiments for the analysis of these excitations in nanostructures. We found that unprecedented information on the symmetries and on the chirality of the plasmonic modes can be retrieved even with limited OAM and energy resolutions.


2019 - Orbital angular momentum resolved electron magnetic chiral dichroism [Articolo su rivista]
Rotunno, E.; Zanfrognini, M.; Frabboni, S.; Rusz, J.; Dunin Borkowski, R. E.; Karimi, E.; Grillo, V.
abstract

We propose to use the recently introduced orbital angular momentum spectrometer in a transmission electron microscope to perform electron magnetic chiral dichroism experiments, dispersing the inelastically scattered electrons from a magnetic material in both energy and angular momentum. The technique offers several advantages over previous formulations of electron magnetic chiral dichroism as it requires much simpler experimental conditions in terms of specimen orientation and thickness. A simulation algorithm, based on the multislice description of the beam propagation, is used to anticipate the advantages of the approach over current electron magnetic chiral dichroism implementations. Numerical calculations confirm an increased magnetic signal to noise ratio with in plane atomic resolution.


2019 - The Young-Feynman controlled double-slit electron interference experiment [Articolo su rivista]
Tavabi, Amir H; Boothroyd, Chris B; Yücelen, Emrah; Frabboni, Stefano; Gazzadi, Gian Carlo; Dunin-Borkowski, Rafal E; Pozzi, Giulio
abstract

The key features of quantum mechanics are vividly illustrated by the Young-Feynman two-slit thought experiment, whose second part discusses the recording of an electron distribution with one of the two slits partially or totally closed by an aperture. Here, we realize the original Feynman proposal in a modern electron microscope equipped with a high brightness gun and two biprisms, with one of the biprisms used as a mask. By exciting the microscope lenses to conjugate the biprism plane with the slit plane, observations are carried out in the Fraunhofer plane with nearly ideal control of the covering of one of the slits. A second, new experiment is also presented, in which interference phenomena due to partial overlap of the slits are observed in the image plane. This condition is obtained by inserting the second biprism between the two slits and the first biprism and by biasing it in order to overlap their images.


2018 - Combined HREM and theoretical analysis of SiC/Si interfaces [Capitolo/Saggio]
Grillo, V.; Frabboni, S.; Cicero, G.; Savini, G.; Catellani, A.
abstract

We performed molecular dynamics simulations to study the atomic structure of the β-SiC/Si(001) and (111) interfaces. The wide lattice mismatch between the two materials (?20%) introduces an array of misfit dislocations along the interface, responsible for releasing almost all the strain which would be present in a pseudomorphic structure. The interface termination, its stoichiometry and the core dislocation structures are discussed here; for the most stable heterostructures, the simulated HREM images are presented, and the features connected to the peculiar interface reconstructions shown.


2018 - Comparison of Cliff-Lorimer-Based Methods of Scanning Transmission Electron Microscopy (STEM) Quantitative X-Ray Microanalysis for Application to Silicon Oxycarbides Thin Films [Articolo su rivista]
Parisini, Andrea; Frabboni, Stefano; Gazzadi, Gian Carlo; Rosa, Rodolfo; Armigliato, Aldo
abstract

In this work, we compare the results of different Cliff-Lorimer (Cliff & Lorimer 1975) based methods in the case of a quantitative energy dispersive spectrometry investigation of light elements in ternary C-O-Si thin films. To determine the Cliff-Lorimer (C-L) k-factors, we fabricated, by focused ion beam, a standard consisting of a wedge lamella with a truncated tip, composed of two parallel SiO2 and 4H-SiC stripes. In 4H-SiC, it was not possible to obtain reliable k-factors from standard extrapolation methods owing to the strong CK-photon absorption. To overcome this problem, an extrapolation method exploiting the shape of the truncated tip of the lamella is proposed herein. The k-factors thus determined, were then used in an application of the C-L quantification procedure to a defect found at the SiO2/4H-SiC interface in the channel region of a metal-oxide field-effect-transistor device. As in this procedure, the sample thickness is required, a method to determine this quantity from the averaged and normalized scanning transmission electron microscopy intensity is also detailed. Monte Carlo simulations were used to investigate the discrepancy between experimental and theoretical k-factors and to bridge the gap between the k-factor and the Watanabe and Williams ζ-factor methods (Watanabe & Williams, 2006).


2018 - Holographically Probing Longitudinal Magnetic Fields with Electron Vortex Beams [Abstract in Rivista]
Harvey, Tyler R.; Grillo, Vincenzo; Venturi, Federico; Pierce, Jordan S.; Yasin, Fehmi S.; Chess, Jordan J.; Frabboni, Stefano; Karimi, Ebrahim; Mcmorran, Benjamin J.
abstract


2018 - Magnetic characterization of cobalt nanowires and square nanorings fabricated by focused electron beam induced deposition [Articolo su rivista]
Venturi, Federico; Gazzadi, Gian Carlo; Tavabi, Amir H; Rota, Alberto; Dunin-Borkowski, Rafal E; Frabboni, Stefano
abstract

The magnetic properties of nanowires (NWs) and square nanorings, which were deposited by focused electron beam induced deposition (FEBID) of a Co carbonyl precursor, are studied using off-axis electron holography (EH), Lorentz transmission electron microscopy (L-TEM) and magnetic force microscopy (MFM). EH shows that NWs deposited using beam energies of 5 and 15 keV have the characteristics of magnetic dipoles, with larger magnetic moments observed for NWs deposited at lower energy. L-TEM is used to image magnetic domain walls in NWs and nanorings and their motion as a function of applied magnetic field. The NWs are found to have almost square hysteresis loops, with coercivities of ca. 10 mT. The nanorings show two different magnetization states: for low values of the applied in-plane field (0.02 T) a horseshoe state is observed using L-TEM, while for higher values of the applied in-plane field (0.3 T) an onion state is observed at remanence using L-TEM and MFM. Our results confirm the suitability of FEBID for nanofabrication of magnetic structures and demonstrate the versatility of TEM techniques for the study and manipulation of magnetic domain walls in nanostructures.


2018 - Transmission electron microscopy study of helium implanted silicon [Capitolo/Saggio]
Frabboni, Stefano; Corni, Federico; Tonini, Rita; Nobili, Carlo Emanuele; Ottaviani, Giampiero
abstract

The structural evolution of helium-related extended defects in silicon, formed after intermediate dose helium implantation and annealing, has been investigated. It is found that the highest helium concentration (annealing at 300°C) is associated with clusters of bubbles arranged in a platelet-like morphology. At 500°c the helium concentration markedly decreases and clusters of cavities formed by a central, large cavity surrounded by small cavities (planetarylike structures) are detected. Thermal treatment at 900°c accomplishes complete helium effusion from the sample leaving behind empty cavities i.e. voids.


2017 - Alloy multilayers and ternary nanostructures by direct-write approach [Articolo su rivista]
Porrati, F.; Sachser, R.; Gazzadi, G. C.; Frabboni, S.; Terfort, A.; Huth, M.
abstract

The fabrication of nanopatterned multilayers, as used in optical and magnetic applications, is usually achieved by two independent steps, which consist in the preparation of multilayer films and in the successive patterning by means of lithography and etching processes. Here we show that multilayer nanostructures can be fabricated by using focused electron beam induced deposition (FEBID), which allows the direct writing of nanostructures of any desired shape with nanoscale resolution. In particular, [Co2Fe/Si]n multilayers are prepared by the alternating deposition from the metal carbonyl precursors, HFeCo3 (CO)12 and Fe (CO)5, and neopentasilane, Si5H12. The ability to fabricate nanopatterned multilayers by FEBID is of interest for the realization of hyperbolic metamaterials and related nanodevices. In a second experiment, we treated the multilayers by low-energy electron irradiation in order to induce atomic species intermixing with the purpose to obtain ternary nanostructured compounds. Transmission electron microscopy and electrical transport measurements indicate that in thick multilayers, (n = 12), the intermixing is only partial, taking place mainly in the upper part of the structures. However, for thin multilayers, (n = 2), the intermixing is such that a transformation into the L21 phase of the Co2FeSi Heusler compound takes place over the whole sample volume.


2017 - Measuring the orbital angular momentum spectrum of an electron beam [Articolo su rivista]
Grillo, Vincenzo; Tavabi, Amir H.; Venturi, Federico; Larocque, Hugo; Balboni, Roberto; Gazzadi, gian carlo; Frabboni, Stefano; Lu, Peng Han; Mafakheribashmagh, Erfan; Bouchard, Frédéric; Dunin Borkowski, Rafal E.; Boyd, Robert W.; Lavery, Martin P. J.; Padgett, Miles J.; Karimi, Ebrahim
abstract

Electron waves that carry orbital angular momentum (OAM) are characterized by a quantized and unbounded magnetic dipole moment parallel to their propagation direction. When interacting with magnetic materials, the wavefunctions of such electrons are inherently modified. Such variations therefore motivate the need to analyse electron wavefunctions, especially their wavefronts, to obtain information regarding the material's structure. Here, we propose, design and demonstrate the performance of a device based on nanoscale holograms for measuring an electron's OAM components by spatially separating them. We sort pure and superposed OAM states of electrons with OAM values of between-10 and 10. We employ the device to analyse the OAM spectrum of electrons that have been affected by a micron-scale magnetic dipole, thus establishing that our sorter can be an instrument for nanoscale magnetic spectroscopy.


2017 - Observation of nanoscale magnetic fields using twisted electron beams [Articolo su rivista]
Grillo, Vincenzo; Harvey, Tyler R.; Venturi, Federico; Pierce, Jordan S.; Balboni, Roberto; Bouchard, Frédéric; Gazzadi, Gian Carlo; Frabboni, Stefano; Tavabi, Amir H.; Li, Zi-An; Dunin-Borkowski, Rafal E.; Boyd, Robert W.; Mcmorran, Benjamin J.; Karimi, Ebrahim
abstract

Electron waves give an unprecedented enhancement to the field of microscopy by providing higher resolving power compared to their optical counterpart. Further information about a specimen, such as electric and magnetic features, can be revealed in electron microscopy because electrons possess both a magnetic moment and charge. In-plane magnetic structures in materials can be studied experimentally using the effect of the Lorentz force. On the other hand, full mapping of the magnetic field has hitherto remained challenging. Here we measure a nanoscale out-of-plane magnetic field by interfering a highly twisted electron vortex beam with a reference wave. We implement a recently developed holographic technique to manipulate the electron wavefunction, which gives free electrons an additional unbounded quantized magnetic moment along their propagation direction. Our finding demonstrates that full reconstruction of all three components of nanoscale magnetic fields is possible without tilting the specimen.


2017 - Phase retrieval of an electron vortex beam using diffraction holography [Articolo su rivista]
Venturi, Federico; Campanini, Marco; Gazzadi, Gian Carlo; Balboni, Roberto; Frabboni, Stefano; Boyd, Robert W.; Dunin-Borkowski, Rafal E.; Karimi, Ebrahim; Grillo, Vincenzo
abstract

In both light optics and electron optics, the amplitude of a wave scattered by an object is an observable that is usually recorded in the form of an intensity distribution in a real space image or a diffraction image. In contrast, retrieval of the phase of a scattered wave is a well-known challenge, which is usually approached by interferometric or numerical methods. In electron microscopy, as a result of constraints in the lens setup, it is particularly difficult to retrieve the phase of a diffraction image. Here, we use a "defocused beam" generated by a nanofabricated hologram to form a reference wave that can be interfered with a diffracted beam. This setup provides an extended interference region with the sample wavefunction in the Fraunhofer plane. As a case study, we retrieve the phase of an electron vortex beam. Beyond this specific example, the approach can be used to retrieve the wavefronts of diffracted beams from a wide range of samples.


2017 - Realization of electron vortices with large orbital angular momentum using miniature holograms fabricated by electron beam lithography [Articolo su rivista]
Mafakheribashmagh, Erfan; Tavabi, A. H.; Lu, P. H.; Balboni, R.; Venturi, Federico; Menozzi, Claudia; Gazzadi, G. C.; Frabboni, Stefano; Sit, A.; Dunin Borkowski, R. E.; Karimi, E.; Grillo, V.
abstract

Free electron beams that carry high values of orbital angular momentum (OAM) possess large magnetic moments along the propagation direction. This makes them an ideal probe for measuring the electronic and magnetic properties of materials, as well as for fundamental experiments in magnetism. However, their generation requires the use of complex diffractive elements, which usually take the form of nano-fabricated holograms. Here, we show how the limitations of the current fabrication of such holograms can be overcome by using electron beam lithography. We demonstrate experimentally the realization of an electron vortex beam with the largest OAM value that has yet been reported to the first diffraction order (L = 1000 ℏ), paving the way for even more demanding demonstrations and applications of electron beam shaping.


2017 - Towards a holographic approach to spherical aberration correction in scanning transmission electron microscopy [Articolo su rivista]
Grillo, Vincenzo; Tavabi, Amir H.; Yucelen, Emrah; Lu, Peng-Han; Venturi, Federico; Larocque, Hugo; Jin, Lei; Savenko, Aleksei; Gazzadi, Gian Carlo; Balboni, Roberto; Frabboni, Stefano; Tiemeijer, Peter; Dunin-Borkowski, Rafal E.; Karimi, Ebrahim
abstract

Recent progress in phase modulation using nanofabricated electron holograms has demonstrated how the phase of an electron beam can be controlled. In this paper, we apply this concept to the correction of spherical aberration in a scanning transmission electron microscope and demonstrate an improvement in spatial resolution. Such a holographic approach to spherical aberration correction is advantageous for its simplicity and cost-effiectiveness.


2016 - Experimental realization of the Ehrenberg-Siday thought experiment [Articolo su rivista]
Pozzi, Giulio; Boothroyd, Chris B.; Tavabi, Amir H.; Yücelen, Emrah; Dunin Borkowski, Rafal E.; Frabboni, Stefano; Gazzadi, gian carlo
abstract

In 1949, at the end of a paper dedicated to the concept of the refractive index in electron optics, Ehrenberg and Siday noted that wave-optical effects will arise from an isolated magnetic field even when the rays themselves travel in magnetic-field-free space. They proposed a two-slit experiment, in which a magnetic flux is enclosed between interfering electron beams. Now, through access to modern nanotechnology tools, we used a focused ion beam to open two nanosized slits in a gold-coated silicon nitride membrane and focused electron beam induced deposition to fabricate a thin magnetic bar between the two slits. We then performed Fraunhofer experiments in a transmission electron microscope equipped with a field emission gun and a Lorentz lens. By tilting the specimen in the objective lens field of the electron microscope, the magnetization of the bar could be reversed and the corresponding change in the phase of the electron wave observed directly in the form of a shift in the interference fringe pattern.


2016 - Fabrication of FeSi and Fe3Si compounds by electron beam induced mixing of [Fe/Si]2 and [Fe3/Si]2 multilayers grown by focused electron beam induced deposition [Articolo su rivista]
Porrati, F.; Sachser, R.; Gazzadi, Gian Carlo; Frabboni, Stefano; Huth, M.
abstract

Fe-Si binary compounds have been fabricated by focused electron beam induced deposition by the alternating use of iron pentacarbonyl, Fe(CO)5, and neopentasilane, Si5H12 as precursor gases. The fabrication procedure consisted in preparing multilayer structures which were treated by low-energy electron irradiation and annealing to induce atomic species intermixing. In this way, we are able to fabricate FeSi and Fe3Si binary compounds from [Fe/Si]2 and [Fe3/Si]2 multilayers, as shown by transmission electron microscopy investigations. This fabrication procedure is useful to obtain nanostructured binary alloys from precursors which compete for adsorption sites during growth and, therefore, cannot be used simultaneously.


2016 - Generation and application of bessel beams in electron microscopy [Articolo su rivista]
Grillo, Vincenzo; Harris, Jérémie; Gazzadi, Gian Carlo; Balboni, Roberto; Mafakheribashmagh, Erfan; Dennis, Mark R.; Frabboni, Stefano; Boyd, Robert W.; Karimi, Ebrahim
abstract

We report a systematic treatment of the holographic generation of electron Bessel beams, with a view to applications in electron microscopy. We describe in detail the theory underlying hologram patterning, as well as the actual electron-optical configuration used experimentally. We show that by optimizing our nanofabrication recipe, electron Bessel beams can be generated with relative efficiencies reaching 37±3%. We also demonstrate by tuning various hologram parameters that electron Bessel beams can be produced with many visible rings, making them ideal for interferometric applications, or in more highly localized forms with fewer rings, more suitable for imaging. We describe the settings required to tune beam localization in this way, and explore beam and hologram configurations that allow the convergences and topological charges of electron Bessel beams to be controlled. We also characterize the phase structure of the Bessel beams generated with our technique, using a simulation procedure that accounts for imperfections in the hologram manufacturing process.


2016 - Nondestructive Measurement of Orbital Angular Momentum for an Electron Beam [Articolo su rivista]
Larocque, Hugo; Bouchard, Frédéric; Grillo, Vincenzo; Sit, Alicia; Frabboni, Stefano; Dunin Borkowski, Rafal E.; Padgett, Miles J.; Boyd, Robert W.; Karimi, Ebrahim
abstract

Free electrons with a helical phase front, referred to as "twisted" electrons, possess an orbital angular momentum (OAM) and, hence, a quantized magnetic dipole moment along their propagation direction. This intrinsic magnetic moment can be used to probe material properties. Twisted electrons thus have numerous potential applications in materials science. Measuring this quantity often relies on a series of projective measurements that subsequently change the OAM carried by the electrons. In this Letter, we propose a nondestructive way of measuring an electron beam's OAM through the interaction of this associated magnetic dipole with a conductive loop. Such an interaction results in the generation of induced currents within the loop, which are found to be directly proportional to the electron's OAM value. Moreover, the electron experiences no OAM variations and only minimal energy losses upon the measurement, and, hence, the nondestructive nature of the proposed technique.


2015 - Elastic and inelastic electrons in the double-slit experiment: A variant of Feynman's which-way set-up [Articolo su rivista]
Frabboni, Stefano; Gazzadi, Gian Carlo; Grillo, Vincenzo; Pozzi, Giulio
abstract

Modern nanotechnology tools allowed us to prepare slits of 90 nm width and 450 nm spacing in a screen almost completely opaque to 200 keV electrons. Then by covering both slits with a layer of amorphous material and carrying out the experiment in a conventional transmission electron microscope equipped with an energy filter we can demonstrate that the diffraction pattern, taken by selecting the elastically scattered electrons, shows the presence of interference fringes, but with a bimodal envelope which can be accounted for by taking into account the non-constant thickness of the deposited layer. However, the intensity of the inelastically scattered electrons in the diffraction plane is very broad and at the limit of detectability. Therefore the experiment was repeated using an aluminum film and a microscope also equipped with a Schottky field emission gun. It was thus possible to observe also the image due to the inelastically scattered electron, which does not show interference phenomena both in the Fraunhofer or Fresnel regimes. If we assume that inelastic scattering through the thin layer covering the slits provides the dissipative process of interaction responsible for the localization mechanism, then these experiments can be considered a variant of the Feynman which-way thought experiment. (C) 2015 Elsevier B.V. All rights reserved.


2015 - Holographic generation of highly twisted electron beams [Articolo su rivista]
Grillo, Vincenzo; Gazzadi, Gian Carlo; Mafakheribashmagh, Erfan; Frabboni, Stefano; Karimi, Ebrahim; Boyd, Robert W.
abstract

Free electrons can possess an intrinsic orbital angular momentum, similar to those in an electron cloud, upon free-space propagation. The wave front corresponding to the electron's wave function forms a helical structure with a number of twists given by the angular speed. Beams with a high number of twists are of particular interest because they carry a high magnetic moment about the propagation axis. Among several different techniques, electron holography seems to be a promising approach to shape a conventional electron beam into a helical form with large values of angular momentum. Here, we propose and manufacture a nanofabricated phase hologram for generating a beam of this kind with an orbital angular momentum up to 200h. Based on a novel technique the value of orbital angular momentum of the generated beam is measured and then compared with simulations. Our work, apart from the technological achievements, may lead to a way of generating electron beams with a high quanta of magnetic moment along the propagation direction and, thus, may be used in the study of the magnetic properties of materials and for manipulating nanoparticles.


2015 - Influence of Grain Size on the Thermoelectric Properties of Polycrystalline Silicon Nanowires [Articolo su rivista]
Suriano, F.; Ferri, M.; Moscatelli, F.; Mancarella, F.; Belsito, L.; Solmi, S.; Roncaglia, A.; Frabboni, Stefano; Gazzadi, Gian Carlo; Narducci, D.
abstract

The thermoelectric properties of doped polycrystalline silicon nanowires have been investigated using doping techniques that impact grain growth in different ways during the doping process. In particular, As- and P-doped nanowires were fabricated using a process flow which enables the manufacturing of surface micromachined nanowires contacted by Al/Si pads in a four-terminal configuration for thermal conductivity measurement. Also, dedicated structures for the measurement of the Seebeck coefficient and electrical resistivity were prepared. In this way, the thermoelectric figure of merit of the nanowires could be evaluated. The As-doped nanowires were heavily doped by thermal doping from spin-on-dopant sources, whereas predeposition from POCl3 was utilized for the P-doped nanowires. The thermal conductivity measured on the nanowires appeared to depend on the doping type. The P-doped nanowires showed, for comparable cross-sections, higher thermal conductivity values than As-doped nanowires, most probably because of their finer grain texture, resulting from the inhibition effect that such doping elements have on grain growth during high-temperature annealing.


2015 - Silicon de novo: Energy filtering and enhanced thermoelectric performances of nanocrystalline silicon and silicon alloys [Articolo su rivista]
Narducci, Dario; Frabboni, Stefano; Zianni, Xanthippi
abstract

Second-phase precipitation in nanocrystalline silicon may lead to improved thermoelectric power factors (up to ≈15 mW K-2 m-1 at room temperature) and high figures of merit. In this review, energy filtering is shown to provide an explanatory framework for these findings, helping predict strategies to further improve nanocrystalline silicon efficiency in thermal harvesters.


2015 - Structural transitions in electron beam deposited Co-carbonyl suspended nanowires at high electrical current densities [Articolo su rivista]
Gazzadi, gian carlo; Frabboni, Stefano
abstract

Suspended nanowires (SNWs) have been deposited from Co-carbonyl precursor (Co-2(CO)(8)) by focused electron beam induced deposition (FEBID). The SNWs dimensions are about 30-50 nm in diameter and 600-850 nm in length. The as-deposited material has a nanogranular structure of mixed face-centered cubic (FCC) and hexagonal close-packed (HCP) Co phases, and a composition of 80 atom % Co, 15 atom % O and 5 atom % C, as revealed by transmission electron microscopy (TEM) analysis and by energydispersive X-ray (EDX) spectroscopy, respectively. Current (I)-voltage (V) measurements with current densities up to 10(7) A/cm(2) determine different structural transitions in the SNWs, depending on the I-V history. A single measurement with a sudden current burst leads to a polycrystalline FCC Co structure extended over the whole wire. Repeated measurements at increasing currents produce wires with a split structure: one half is polycrystalline FCC Co and the other half is graphitized C. The breakdown current density is found at 2.1 x 10(7) A/cm(2). The role played by resistive heating and electromigration in these transitions is discussed.


2015 - Structured quantum waves [Articolo su rivista]
Harris, Jérémie; Grillo, Vincenzo; Mafakheribashmagh, Erfan; Gazzadi, Gian Carlo; Frabboni, Stefano; Boyd, Robert W.; Karimi, Ebrahim
abstract

The study of structured optical waves has enhanced our understanding of light and numerous experimental methods now enable the control of the angular momentum and radial distributions. Recently, these wavestructuring techniques have been successfully applied to the generation and shaping of electron beams, leading to promising practical and fundamental advances. Here, we discuss recent progress in the emerging field of electron beam shaping, and explore the unique attributes that distinguish electron beams from their photonic analogues.


2014 - Controlled growth of Ni/NiO core–shell nanoparticles: Structure, morphology and tuning of magnetic properties [Articolo su rivista]
D'Addato, Sergio; Spadaro, MARIA CHIARA; Luches, Paola; Grillo, V.; Frabboni, Stefano; Valeri, Sergio; Ferretti, A. M.; Capetti, E.; Ponti, A.
abstract

We performed a detailed study of Ni/NiO core–shell nanoparticles (NP) obtained with a gas aggregation source. The NP oxide shells were produced by oxidizing the NP with different procedures: deposition in oxygen atmosphere, post-annealing in air, sequential deposition of (a) first NiO layer, (b) Ni NP and (c) third NiO Layer. X-ray photoelectron spectroscopy from Ni 2p core-level gave information about the chemical state of Ni in the core and in the oxide shell, while scanning electron microscopy was used for investigation of the NP morphology. High quality scanning transmission electron microscopy in high angle annular dark field mode data demonstrated core–shell structure also for NiO/Ni NP/NiO samples. Fieldcooled/ zero-field-cooled magnetization curves and field-cooled isothermal hysteresis cycles at T = 5 K were recorded by a SQUID magnetometer. In this way, the relation between magnetic properties and oxide shell structure was assessed, showing the role played by the control of the formation of oxide on the exchange bias and interparticle magnetic interaction.


2014 - Enhancement of the power factor in two-phase silicon-boron nanocrystalline alloys [Articolo su rivista]
Narducci, D; Lorenzi, B.; Zianni, X.; Neophytou, N.; Frabboni, Stefano; Gazzadi, Gc; Roncaglia, A.; Suriano, F.
abstract

In previous publications it was shown that the precipitation of silicon boride around grain boundaries may lead to an increase of the power factor in nanocrystalline silicon. Such an effect was further explained by computational analyses showing that the formation of an interphase at the grain boundaries along with high boron densities can actually lead to a concurrent increase of the electrical conductivity σ and of the Seebeck coefficient S. In this communication we report recent evidence of the key elements ruling such an unexpected effect. Nanocrystalline silicon films deposited onto a variety of substrates were doped to nominal boron densities in excess of 1020cm-3 and were annealed up to 1000°C to promote boride precipitation. Thermoelectric properties were measured and compared with their microstructure. A concurrent increase of σ and S with the carrier density was found only upon formation of an interphase. Its dependency on the film microstructure and on the deposition and processing conditions will be discussed.


2014 - Experiments and Potentialities for the use of Bessel Beam in Superresolution STEM [Relazione in Atti di Convegno]
Grillo, Vincenzo; Karimi, Ebrahim; Balboni, Roberto; Carlo Gazzadi, Gian; Frabboni, Stefano; Mafakheri, Erfan; Boyd, Robert W.
abstract

In light optics holographic beam shaping has been largely used to obtain complicated wavefronts [1] and vortex beams. In the last years holograms have been used in the electron vortex beam generation [2]. We have recently improved the technology of hologram fabrication by means of “phase hologram” [3] replacing the amplitude hologram so far used. Phase holograms appropriately change the phase of the incident wavefront by a modulation of thickness in a silicon nitride thin membrane. Beyond vortex generation, holograms can have a large range of applications. As an example in this work we report on the production of a Bessel beam in the Fresnel diffraction regime [4]. Bessel beams have many interesting properties most of which derived from being the Fourier transform of a ring. In this sense they can be considered as the extreme case of hollow cone illumination. However while the production of hollow cone probes requires a strong reduction of the electron beam current by the use of an obstructing aperture, the holographic approach permits to produce high quality Bessel beams with only marginal intensity losses. In particular by the use of phase holograms we could demonstrate up to 40% efficiency. In these conditions the generated beam is competitive with normal aperture limited approaches in terms of intensity. Fig 1a shows the FIB-nanofabricated hologram that has been positioned in the second condenser aperture of a FEI Tecnai F20 operated at 200 kV. Fig 1b is an image of the logarithm of the intensity of the Bessel beam showing the characteristic fringes aside from the central peak. The obtained probe size is in this case 0.5 nm. But we will show that the beam can be potentially scaled to 0.1 nm for larger convergences. In Fig 1c the Fraunhofer diffraction of the hologram is also shown demonstrating that the probe is the Fourier transform of a tiny ring. The calculated convergence is here 1.9 mrad. This beam can be exploited in many applications. One of the main advantages of this is that the probe shape is, to large extent, independent from spherical aberration, chromatic aberration and from defocus; the other is that for the given convergence Bessel beam provide the minimal probe size regardless of spherical aberration. Fig 2a shows the transfer function of a microscope with a conventional probe (with and without aberration) with convergence 15 mrad and with a Bessel probe. Clearly the Bessel probe can produce advantages in the high frequency region. Fig 2b is a simulation of STEM-HAADF images for a Au particle with the two kinds of probes as in fig 2a. Using the Bessel beams in fig 1a we obtained the STEM image in fig 2c that demonstrates that, in spite of the presence of other diffraction peaks, a good quality scan of a sample (a Si-SiO STI structure) can be obtained with a resolution better than 2nm (measured as the blurring of the contrast features). In fact the transmitted and other diffraction beam are completely delocalized and do not contribute significantly to the contrast.


2014 - Generation of Nondiffracting Electron Bessel Beams [Articolo su rivista]
Vincenzo, Grillo; Ebrahim, Karimi; Gazzadi, gian carlo; Frabboni, Stefano; Mark, R. Dennis; Robert, W. Boyd
abstract

Almost 30 years ago, Durnin discovered that an optical beam with a transverse intensity profile in the form of a Bessel function of the first order is immune to the effects of diffraction. Unlike most laser beams, which spread upon propagation, the transverse distribution of these Bessel beams remains constant. Electrons also obey a wave equation (the Schrodinger equation), and therefore Bessel beams also exist for electron waves. We generate an electron Bessel beam by diffracting electrons from a nanoscale phase hologram. The hologram imposes a conical phase structure on the electron wave-packet spectrum, thus transforming it into a conical superposition of infinite plane waves, that is, a Bessel beam. We verify experimentally that these beams can propagate for 0.6 m without measurable spreading and can also reconstruct their intensity distributions after being partially obstructed by an obstacle. Finally, we show by numerical calculations that the performance of an electron microscope can be increased dramatically through use of these beams.


2014 - Highly efficient electron vortex beams generated by nanofabricated phase holograms [Articolo su rivista]
Vincenzo, Grillo; Gian Carlo, Gazzadi; Ebrahim, Karimi; Mafakheribashmagh, Erfan; Robert W., Boyd; Frabboni, Stefano
abstract

We propose an improved type of holographic-plate suitable for the shaping of electron beams. The plate is fabricated by a focused ion beam on a silicon nitride membrane and introduces a controllable phase shift to the electron wavefunction. We adopted the optimal blazed-profile design for the phase hologram, which results in the generation of highly efficient (25%) electron vortex beams. This approach paves the route towards applications in nano-scale imaging and materials science.


2014 - Innovative Phase Plates for Beam Shaping [Relazione in Atti di Convegno]
Grillo, Vincenzo; Karimi, Ebrahim; Balboni, Roberto; Carlo Gazzadi, Gian; Frabboni, Stefano; Mafakheri, Erfan; Boyd, Robert W.
abstract

In light optics the use of holographic beam shaping has been largely used to obtain complicated wavefronts [1] and vortex beams but recently holograms have been used in the electron vortex beam generation [2]. We show here our recent improvement in the technology of hologram fabrication by means of “phase hologram” [3] replacing the amplitude hologram so far used. Phase hologram appropriately changes the phase of the wavefront by a modulation of thickness in a Silicon nitride thin membrane. By means of phase hologram we could produce different beam shape in both Fresnel and Fraunhofer regime. Moreover we engineered the hologram shape to obtain high efficiency on the generated wavefunction. Presently we could demonstrate an efficiency of 40% in the generation efficiency for a single beam. This is the best performance ever shown and is much higher than amplitude hologram so far used. The particular holographic technique consists in creating a grating of Si3N4 and modulating the periodicity with the desired wavefront shape. In general many order of diffraction of the grating are generated while only the first order is typically interesting for application with a clear loss of intensity. However if the groove of the grating is a ramp spanning an appropriate thickness corresponding exactly to 2π phase in the electron path (also dubbed “blazed” profile) a single diffraction with the relevant beam can be obtained. Using this principle we generated by FIB a close to ideal hologram. The experimental thickness profile (as calculated by EELS) is shown in fig 1a. In the inset a profile in a line is extracted and compared with the “ideal” blazed pattern. The full pattern for the generation of a Bessel beam is shown in fig 1b while the resulting series of beam in a Fresnel plane is shown in fig 1c. In particular the experimental pattern (up) is compared with the simulated one based Fresnel integral of the hologram in fig 1a [3]. The very good agreement means that the simulated phase is also correct. Therefore the figure in the inset that represents intensity and phase of the simulated beam can be considered as a realistic representation of the actual phase.


2014 - Nanovoid Formation and Dynamics in He+-Implanted Nanocrystalline Silicon [Articolo su rivista]
Lorenzi, Bruno; Frabboni, Stefano; Gazzadi, gian carlo; Tonini, Rita; Ottaviani, Giampiero; Narducci, Dario
abstract

Helium implantation in single crystal silicon is known to lead, after a proper thermal treatment, to the formation of voids with diameters ranging between 10 nm and 30 nm. Formation of voids is governed by the coalescence of vacancies created by implantation, initially trapping helium atoms. At high temperatures (), helium leaves the nanobubbles and outdiffuses, while the now empty voids grow in size and eventually change their shape to form tetrakaidecahedra (Wulff construction). In this communication, we report how He+ implantation in heavily boron-doped nanocrystalline silicon shows a completely different dynamics. Annealing at leads to the formation of large voids, located around grain boundaries, along with a large number of nanovoids with an average diameter of 2-4 nm and an estimated density of distributed throughout the grains. Annealing at higher temperature (up to ) also induces a decrease of the void size with a change in their density, finally accounting to . The high temperature annealing also causes vacancy evaporation down to a depth of 80-100 nm from the outer surface. The possibility of obtaining a stable, uniform distribution of nanometer-sized voids is of major relevance as a novel tool for phonon and electron engineering in thermoelectric materials.


2014 - Paradoxical Enhancement of the Power Factor of Polycrystalline Silicon as a Result of the Formation of Nanovoids [Articolo su rivista]
Lorenzi, B.; Narducci, D.; Tonini, Rita; Frabboni, Stefano; Gazzadi, G. C.; Ottaviani, Giampiero; Neophytou, N.; Zianni, X.
abstract

Hole-containing silicon has been regarded as a viable candidate thermoelectric material because of its low thermal conductivity. However, because voids are efficient scattering centers not just for phonons but also for charge carriers, achievable power factors (PFs) are normally too low for its most common form, i.e. porous silicon, to be of practical interest. In this communication we report that high PFs can, indeed, be achieved with nanoporous structures obtained from highly doped silicon. High PFs, up to a huge 22 mW K-2 m(-1) (more than six times higher than values for the bulk material), were observed for heavily boron-doped nanocrystalline silicon films in which nanovoids (NVs) were generated by He+ ion implantation. In contrast with single-crystalline silicon in which He+ implantation leads to large voids, in polycrystalline films implantation followed by annealing at 1000A degrees C results in homogeneous distribution of NVs with final diameters of approximately 2 nm and densities of the order of 10(19) cm(-3) with average spacing of 10 nm. Study of its morphology revealed silicon nanograins 50 nm in diameter coated with 5-nm precipitates of SiB (x) . We recently reported that PFs up to 15 mW K-2 m(-1) could be achieved for silicon-boron nanocomposites (without NVs) because of a simultaneous increase of electrical conductivity and Seebeck coefficient. In that case, the high Seebeck coefficient was achieved as a result of potential barriers on the grain boundaries, and high electrical conductivity was achieved as a result of extremely high levels of doping. The additional increase in the PF observed in the presence of NVs (which also include SiB (x) precipitates) might have several possible explanations; these are currently under investigation. Experimental results are reported which might clarify the reason for this paradoxical effect of NVs on silicon PF.


2014 - Power Factor Enhancement by Inhomogeneous Distribution of Dopants in Two-Phase Nanocrystalline Systems [Articolo su rivista]
Neophytos, Neophytou; Xanthippi, Zianni; Hans, Kosina; Frabboni, Stefano; Bruno, Lorenzi; Dario, Narducci
abstract

In this work, we describe a novel idea that allows for high thermoelectric power factors in two-phase materials that are heavily doped with an inhomogeneous distribution of dopants. We show that a concurrent increase of the electrical conductivity and Seebeck coefficient and a consequent increase of the power factor can be achieved in such systems. To explain the concept, we employ a semiclassical one-dimensional model that considers both electron and phonon transport through a series connection of two-phases of the material. We discuss microscopic characteristics of the material and the formation of the two phases (grains and grain boundaries in our case) by the inhomogeneous distribution of dopants in the polycrystalline material. Our theoretical investigation reveals that: (1) the improvement in the Seebeck coefficient can be attributed to carrier filtering due to the energy barriers at the grain boundaries, and to the difference in the lattice thermal conductivity of the grains and grain boundaries, and (2) the improvement in the electrical conductivity is a result of a high Fermi level in the grains. This allows high energy carriers to contribute to transport, which increases the impurity scattering limited mean-free-path, and increases the conductivity in the grains and thus in the whole material. Such an unexpected concurrent increase of the electrical conductivity and the Seebeck coefficient was recently observed in heavily boron-doped polycrystalline silicon of grain sizes <100 nm in which a silicon-boride phase is formed around the grain boundaries. We provide a simple 1D model that explains the behavior of this system, indicating processes that can take place in heavily doped nanocrystalline materials.


2013 - A 4096-pixel MAPS detector used to investigate the single-electron distribution in a Young–Feynman two-slit interference experiment [Articolo su rivista]
Gabrielli, A.; Giorgi, F. M.; Semprini, N.; Villa, M.; Zoccoli, A.; Matteucci, G.; Pozzi, G.; Frabboni, Stefano; Gazzadi, gian carlo
abstract

A monolithic CMOS detector, made of 4096 active pixels developed for HEP collider experiments, has been used in the Young-Feynman two-slit experiment with single electrons. The experiment has been carried out by inserting two nanometric slits in a transmission electron microscope that provided the electron beam source and the electro-optical lenses for projecting and focusing the interference pattern on the sensor. The fast readout of the sensor, in principle capable to manage up to 10(6) frames per second, allowed to record single-electron frames spaced by several empty frames. In this way, for the first time in a single-electron two-slit experiment, the time distribution of electron arrivals has been measured with a resolution of 165 mu s. In addition, high statistics samples of single-electron events were collected within a time interval short enough to be compatible with the stability of the system and coherence conditions of the illumination.


2013 - Build-up of interference patterns with single electrons [Articolo su rivista]
Giorgio, Matteucci; Michele, Pezzi; Giulio, Pozzi; Gian Luigi, Alberghi; Filippo, Giorgi; Alessandro, Gabrielli; Nicola Semprini, Cesari; Mauro, Villa; Antonio, Zoccoli; Frabboni, Stefano; Gazzadi, gian carlo
abstract

A conventional transmission electron microscope, equipped with a fast recording system able to measure the electron arrival time and the position of single electrons, is used to show the build-up of interference patterns. Two experiments are presented. The first is the electron version of the Grimaldi and Young experiments performed with light, where single electrons strike on an opaque thin wire. Interference fringes are observed in the geometrical shadow of the wire and diffraction effects are clearly displayed at the wire edges. The second, original experiment reports the build-up of two-slit interference patterns with single electrons.


2013 - Controlled co-deposition of FePt nanoparticles embedded in MgO: a detailed investigation of structure and electronic and magnetic properties [Articolo su rivista]
D'Addato, Sergio; V., Grillo; A., di Bona; P., Luches; Frabboni, Stefano; Valeri, Sergio; P., Lupo; F., Casoli; F., Albertini
abstract

Films of FePt nanoparticles (NP) embedded in MgO were obtained by controlled co-deposition of FePt NP pre-formed by a gas aggregation source and of Mg evaporated in Oxygen atmosphere. Control over the deposition rate permitted to pass from FePt@MgO core-shell morphology to a film of MgO embedding FePt NP. Transmission Electron Microscopy (TEM) and High Resolution-TEM revealed the core-shell structure of the NP, with FePt core (of average diameter <d>= 4.75 nm) presenting a multi-twinned icosahedral structure, and MgO partially in crystalline form. The functional effect of MgO shell in shielding the FePt core from external oxidation was shown with XPS. Upon controlled annealing transition from A1 to L10 ordering could be obtained, with structural and morphological re-arrangement. The magnetic hysteresis loops obtained from Alternating Gradient Field Magnetometry at room temperatures show a “wasp-waist” shape, with small values of coercive field (Hc=300-1400 Oe), decreasing at increasing amount of co-deposited MgO.


2013 - FIB Preparation of a NiO Wedge-Lamella and STEM X-Ray Microanalysis for the Determination of the Experimental k(O-Ni) Cliff-Lorimer Coefficient [Articolo su rivista]
Aldo, Armigliato; FRABBONI, Stefano; Gian Carlo, Gazzadi; Rodolfo, Rosa
abstract

A method for the fabrication of a wedge-shaped thin NiO lamella by focused ion beam is reported. The starting sample is an oxidized bulk single crystalline, < 100 > oriented, Ni commercial standard. The lamella is employed for the determination, by analytical electron microscopy at 200 kV of the experimental k(O-Ni) Cliff-Lorimer (G. Cliff & G. W. Lorimer, J Microsc 103, 203-207, 1975) coefficient, according to the extrapolation method by Van Cappellen (E. Van Cappellen, Microsc Microstruct Microanal 1, 1-22, 1990). The result thus obtained is compared to the theoretical k(O-Ni) values either implemented into the commercial software for X-ray microanalysis quantification of the scanning transmission electron microscopy/energy dispersive spectrometry equipment or calculated by the Monte Carlo method. Significant differences among the three values are found. This confirms that for a reliable quantification of binary alloys containing light elements, the choice of the Cliff-Lorimer coefficients is crucial and experimental values are recommended.


2013 - Morphological and mechanical characterization of composite calcite/SWCNT–COOH single crystals [Articolo su rivista]
Matteo, Calvaresi; Giuseppe, Falini; Luca, Pasquini; Michela, Reggi; Simona, Fermani; GAZZADI, gian carlo; FRABBONI, Stefano; Francesco, Zerbetto
abstract

A growing number of classes of organic (macro) molecular materials have been trapped into inorganic crystalline hosts, such as calcite single crystals, without significantly disrupting their crystalline lattices. Inclusion of an organic phase plays a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals. Here we report the synthesis and mechanical characterization of composite calcite/SWCNT-COOH single crystals. Once entrapped into the crystals SWCNT-COOH appeared both as aggregates of entangled bundles and nanoropes. Their observation was possible only after crystal etching, fracture or FIB (focused ion beam) cross-sectioning. SWCNT-COOHs occupied a small volume fraction and were randomly distributed into the host crystal. They did not strongly affect the crystal morphology. However, although the Young's modulus of composite calcite/SWCNT-COOH single crystals was similar to that of pure calcite their hardness increased by about 20%. Thus, SWCNT-COOHs provide an obstacle against the dislocation-mediated propagation of plastic deformation in the crystalline slip systems, in analogy with the well-known hardness increase in fiber-reinforced composites.


2013 - Simultaneous increase in electrical conductivity and Seebeck coefficient in highly boron-doped nanocrystalline Si [Articolo su rivista]
Neophytos, Neophytou; Xanthippi, Zianni; Hans, Kosina; Frabboni, Stefano; Bruno, Lorenzi; Dario, Narducci
abstract

A large thermoelectric power factor in heavily boron-doped p-type nanograined Si with grain sizes similar to 30 nm and grain boundary regions of similar to 2 nm is reported. The reported power factor is similar to 5 times higher than in bulk Si. It originates from the surprising observation that for a specific range of carrier concentrations, the electrical conductivity and Seebeck coefficient increase simultaneously. The two essential ingredients for this observation are nanocrystallinity and extremely high boron doping levels. This experimental finding is interpreted within a theoretical model that considers both electron and phonon transport within the semiclassical Boltzmann approach. It is shown that transport takes place through two phases so that high conductivity is achieved in the grains, and high Seebeck coefficient by the grain boundaries. This together with the drastic reduction in the thermal conductivity due to boundary scattering could lead to a significant increase of the figure of merit ZT. This is one of the rare observations of a simultaneous increase in the electrical conductivity and Seebeck coefficient, resulting in enhanced thermoelectric power factor.


2013 - Single electron interference and diffraction experiments with a high energy physics detector [Relazione in Atti di Convegno]
Alberghi, G. L.; Don, R.; Gabrielli, A.; Giorgi, F.; Matteucci, G.; Cesari, N. S.; Villa, M.; Zoccoli, A.; Frabboni, S.; Gazzadi, G.
abstract

The Young-Feynman two-slit experiment for single electrons was carried out by inserting two nanometric slits and a fast recording system, capable of detecting the electron arrival-time, in a conventional transmission electron microscope. The sensor, designed for experiments at future high energy colliders, is based on a custom 4096 Monolithic Active Pixels CMOS chip, is equipped with a fast readout chain and can manage up to 106 frames per second, allowing the collection of high statistic samples of single electron events within a time interval compatible with the stability of the experimental setup and the coherence conditions of the illumination. For the first time in a single electron two-slit experiment, the time distribution of electron arrivals was obtained.


2012 - Assembly and structure of Ni/NiO core–shell nanoparticles [Articolo su rivista]
D'Addato, Sergio; Vincenzo, Grillo; Altieri, Salvatore; Frabboni, Stefano; Valeri, Sergio
abstract

In this work it is reported a detailed investigation of the structure in Ni/NiO core–shell nanoparticles (NP). An experimental set-up was realized for the preparation and the study of pre-formed NP films. NiO shell was obtained with controlled dosing of O2 gas in the experimental system. A comparison of HR-TEM experimental images with theoretical simulations shows that the Ni NP core has a regular multitwinned icosahedral structure, composed with single crystal tetrahedra with (1 1 1) faces. NiO phase is clearly observed forming islands on the NP surface. In order to better investigate the oxide shell, the exit wave reconstruction method was applied to the images. It was found evidence of oxide island formation with direct or opposite (twinned) stacking on Ni (1 1 1) surfaces.


2012 - Convergent beam electron-diffraction investigation of lattice mismatch and static disorder in GaAs/GaAs1−xNx intercalated GaAs/GaAs1−xNx:H heterostructures [Articolo su rivista]
Frabboni, Stefano; V., Grillo; Gazzadi, gian carlo; R., Balboni; R., Trotta; A., Polimeni; M., Capizzi; F., Martelli; S., Rubini; G., Guzzinati; F., Glas
abstract

Hydrogen incorporation in diluted nitride semiconductors dramatically modifies the electronic and structural properties of the crystal through the creation of nitrogen-hydrogen complexes. We report a convergent beam electron-diffraction characterization of diluted nitride semiconductor- heterostructures patterned at a sub-micron scale and selectively exposed to hydrogen. We present a method to determine separately perpendicular mismatch and static disorder in pristine and hydrogenated heterostructures. The roles of chemical composition and strain on static disorder have been separately assessed.


2012 - Growth and characterization of EBID-fabricated suspended nanostructures [Capitolo/Saggio]
G. C., Gazzadi; Frabboni, Stefano
abstract

While the standard beam-induced deposition approach is to grow deposits on a substrate, deposition of self-supporting suspended structures can be obtained by slowly moving the beam laterally from an elevated edge, in order to grow an overhanging deposit behind the beam path. An example of nanofabrication by lateral-EBID is given in fig. 1, where a suspended nanowire has been deposited across two vertical pillars. The structure is obtained (fig. 1c) by moving the electron beam from the top of left pillar toward the right one with a scan speed of 33 nm/s, at steps of 5 nm, under a Pt-metallorganic gas flow. As indicated by the lateral dimensions in fig. 1a and fig. 1b, an advantage of this deposition method is the high lateral resolution because of the lack of secondary emissions from the substrate, that enlarge the deposit footprint well above the beam spotsize.The growth mechanism at the basis of lateral deposition, as proposed by Liu and co-workers, is depicted in fig. 2, where a gaussian electron beam, positioned over a thin edge and then moved to the right, is considered. On the first spot, the beam generates a gaussian deposit above (A) and below (B) the edge (because of the deep electron penetration), having a volume and gaussian width which are proportional to the beam dwell time and also depend on the beam shape. When the beam is shifted laterally it falls on a point of the deposit that may be above (O1a), at the same level of (O2), or below (O3b) the edge, depending on the amplitude of the shift, and thus give rise to upward (A1B1), parallel (A2B2) or downward (A3B3) growth, respectively. If the lateral shift is much larger than the deposit width, lateral growth doesn’t take place. The process is ruled by the interplay of several parameters, such as the deposition rate, the beam dwell time, the lateral shift amplitude and the beam shape. In most studies, these are often resumed into the beam shift speed which is also a reasonable parameter for a given beam shape and gas flux. A major capability offered by lateral deposition is the three-dimensional (3D) nanofabrication. Matsui and co-workers demonstrated the potentiality of the technique with several examples of both functional (nanocoils, electrical circuit elements, nanogrippers) and artwork shapes (nanoglass) produced with IBID of carbon precursor. In the case of EBID, Ooi and co-workers presented the fabrication of tools and probes based on suspended nanowires for the manipulation and observation, with SNOM microscopy, of DNA fibers. The structures were realized by lateral-EBID of carbon-contamination gas. Another noteworthy example are the 10 nm-size nanotweezers, with a gap of 25 nm, fabricated at the ends of conventional Si microtweezers by lateral-EBID of C contamination by Boggild et al. Several works were devoted to the study of the growth mechanism and material properties. EBID of 3D freestanding nanostructures from a Cu precursor was explored by Utke et al.. Suspended horizontal nanorods were used as a support for the growth of vertical pillars, and it was found that the reduced thermal conductivity with respect to a bulk substrate, resulted in a thermal decomposition of the precursor with higher crystallinity of the Cu deposit. Fujita et al. fabricated 5 nm-width suspended nanowires by lateral-EBID of C contamination with a SEM. They compared the suspended growth with the one of vertical pillars and concluded that the higher resolution in the former was due to the reduced secondary electrons generation within the structure. Liu and co-workers studied the lateral deposition of W precursors with TEM high energy electrons (200keV), deriving the growth model presented in fig. 2. Lateral EBID has been also investigated on bulk substrates. By varying the lateral scan speed, the inclination of pillars deposited from Au and Mo precursors [ ] and the periodicity of arch-like structures grown from Cu precurs


2012 - High figures of merit in degenerate semiconductors. Energy filtering by grain boundaries in heavily doped polycrystalline silicon [Relazione in Atti di Convegno]
Narducci, Dario; Selezneva, Ekaterina; Cerofolini, Gianfranco; Frabboni, Stefano; Ottaviani, Giampiero
abstract

Heavily boron-doped polycrystalline silicon has been reported to be characterized by somewhat unexpectedly high power factor. High Seebeck coefficients are however unexpected in materials with high carrier densities. A semi-quantitative model was proposed, showing that the potential barrier structure at grain boundaries, along with the nanometric grain size, leads to an unusual mechanism of carrier filtering, named adiabatic energy filtering. Actually, the presence of potential barriers associated with segregated boron disables charge transport by holes in the band deep tail. This leads to a decrease of the actual carrier density, as in the case of standard energy filtering. However, the nanometric grain size along with the inefficiency of the hole-hole relaxation mechanism in degenerate semiconductors actually prevents carriers from relaxing, causing an increase of the average (macroscopic) drift mobility. Thus, in spite of the decrease of drifting hole density the electrical conductivity is found to increase. In this communication a refinement of the model is presented, that will be discussed and corroborated with an extended body of experimental data gathered by several authors on degenerate polycrystalline silicon films.


2012 - Impact of energy filtering and carrier localization on the thermoelectric properties of granular semiconductors [Articolo su rivista]
Dario, Narducci; Ekaterina, Selezneva; Gianfranco, Cerofolini; Frabboni, Stefano; Ottaviani, Giampiero
abstract

Energy filtering has been widely considered as a suitable tool to increase the thermoelectric performances of several classes of materials. In its essence, energy filtering provides a way to increase the Seebeck coefficient by introducing a strongly energy-dependent scattering mechanism. Under certain conditions, however, potential barriers may lead to carrier localization, that may also affect the thermoelectric properties of a material. A model is proposed, actually showing that randomly distributed potential barriers (as those found, e.g., in polycrystalline films) may lead to the simultaneous occurrence of energy filtering and carrier localization. Localization is shown to cause a decrease of the actual carrier density that, along with the quantum tunneling of carriers, may result in an unexpected increase of the power factor with the doping level. The model is corroborated toward experimental data gathered by several authors on degenerate polycrystalline silicon and lead telluride


2012 - The Young-Feynman two-slits experiment with single electrons: Build-up of the interference pattern and arrival-time distribution using a fast-readout pixel detector [Articolo su rivista]
Frabboni, Stefano; Alessandro, Gabrielli; Gian Carlo, Gazzadi; Filippo, Giorgi; Giorgio, Matteucci; Giulio, Pozzi; Nicola Semprini, Cesari; Mauro, Villa; Antonio, Zoccoli
abstract

The two-slitsexperimentforsingleelectronshasbeencarriedoutbyinsertinginaconventionaltransmissionelectronmicroscopeathicksamplewithtwonano-slitsfabricatedbyFocusedIonBeamtechniqueandafastrecordingsystemabletomeasuretheelectronarrival-time.Thedetector,designedfor experimentsinfuturecolliders,isbasedonacustomCMOSchipequippedwithafastreadoutchainable tomanageupto106 frames persecond.Inthisway,highstatisticsamplesofsingleelectroneventscan becollectedwithinatimeintervalshortenoughtomeasurethedistributionoftheelectronarrival-times andtoobservethebuild-upoftheinterferencepattern.


2012 - Using evidence from nanocavities to assess the vibrational properties of external surfaces [Articolo su rivista]
G. F., Cerofolini; CORNI, Federico; FRABBONI, Stefano; OTTAVIANI, Giampiero; E., Romano; TONINI, Rita; D., Narducci
abstract

Internal surfaces of nanocavities are an exceptionally useful laboratory wherein one can spotlight the factors ruling the intricate interplay between morphology and chemistry at silicon surfaces. At the same time, they offer unparalleled opportunities to validate the assignment of vibrational signals of silicon-terminating species under almost ideal experimental conditions. In the case of hydrogen, evidence will be provided of the detailed evolution of H-related species at surfaces depending on their orientation. Also, preliminary results concerning nitrogen at and around nanocavity surfaces will be reported.


2011 - Application of a HEPE-oriented 4096-MAPS to time analysis of single electron distribution in a two-slits interference experiment [Articolo su rivista]
A., Gabrielli; F., Giorgi; N., Semprini Cesari; M., Villa; A., Zoccoli; G., Matteucci; G., Pozzi; Frabboni, Stefano; Gazzadi, gian carlo
abstract

The Young-Feynman two-slit experiment for single electrons has been carried out by inserting in a conventional transmission electron microscope two nanometric slits and a fast recording system able to measure the electron arrival-time. The detector, designed for experiments in future colliders, is based on a custom CMOS chip of 4096 monolithic active pixels equipped with a fast readout chain able to manage up to 106 frames per second. In this way, high statistic samples of single electron events can be collected within a time interval short enough to guarantee the stability of the system and coherence conditions of the illumination. For the first time in a single electron two-slit experiment, the time distribution of electron arrivals has been measured.


2011 - Assembly and Fine Analysis of Ni/MgO Core/Shell Nanoparticles [Articolo su rivista]
D'Addato, Sergio; Vincenzo, Grillo; Altieri, Salvatore; Frabboni, Stefano; Francesca, Rossi; Valeri, Sergio
abstract

We obtained assemblies of Ni/MgO core/shell nanoparticles (NPs) by using a special experimental setup, in which a beam of preformed Ni nanoclusters, obtained by sputtering and aggregation, is co-deposited with evaporated Mg on a substrate, in a controlled O(2) atmosphere. In situ X-ray photoelectron spectroscopy (XPS) and ex situ energy-filtered transmission electron microscopy (EF-TEM) show that the Ni core remains metallic, whereas Mg, located in the shell, is completely oxidized. Detailed high-resolution transmission electron microscopy and geometric phase analyses reveal the multitwinned icosahedral structure of the Ni core and details the arrangement of the MgO shell. This combined effort of controlled assembly of NPs and fine analysis offers intriguing possibilities in the design of nanoscale materials.


2011 - Characterization of a new cobalt precursor for focused beam deposition of magnetic nanostructures [Articolo su rivista]
Gazzadi, gian carlo; J. J. L., Mulders; P., Trompenaars; Ghirri, Alberto; Rota, Alberto; Affronte, Marco; Frabboni, Stefano
abstract

The electrical and magnetic properties of nanowires deposited from cobalt tricarbonyl nitrosyl (Co(CO)(3)NO) precursor by focused electron beam- and focused ion beam-induced deposition (FEBID and FIBID) have been investigated. As-deposited nanowires have similar Co content, around 50-55 at.%, but different electrical behaviour: FEBID nanowire is highly resistive (6.3 m Omega cm at RT) and non-metallic at low T, while the FIBID one has much lower resistivity (189 mu Omega cm at RT) and it is metallic. The magnetic properties, tested with magnetoresistance measurements, reveal a non-magnetic behaviour for both nanowires. After 400 degrees C annealing in vacuum FEBID wire is much less resistive (62 mu Omega cm at RT) and recovers the metallic behaviour at low T, and both FEBID and FIBID wires display ferromagnetic behaviour. Structural analysis by low energy-scanning transmission electron microscopy (LE-STEM) suggests that coarsening and interconnection of the Co nanograins are responsible for the improvement in electrical and magnetic properties.


2011 - Effect of Nanocavities on the Thermoelectric Properties of Polycrystalline Silicon [Relazione in Atti di Convegno]
Ekaterina, Selezneva; Andrea, Arcari; Gilles, Pernot; Elisabetta, Romano; Gianfranco, Cerofolini; Rita, Tonini; Frabboni, Stefano; Giampiero, Ottaviani; Ali, Shakouri; Dario, Narducci
abstract

Nanostructuring has opened new ways to increase the thermoelectric performance of a host of materials, mainly by decreasing their thermal conductivity κ while preserving the Seebeck coefficient S and electrical conductivity σ. The thermoelectric properties of degenerated polycrystalline silicon films with nanocavities (NCs) have been studied as a function of annealing temperature upon isochronous annealings in argon carried out every 50 °C in the range 500-1000°C which were used to modify the shape of the NCs. We found that presence of the NCs had no negative effect on the electronic properties of the system. The measured values of S and σ were close to those previously reported for the blank polycrystalline silicon films with the same doping level. The thermal conductivity was also found to be close to the value measured on the blank sample, about half of the reported value in polycrystals. This led to a power factor of 15.2 mWm -1K -2 and a figure of merit of 0.18 at 300 K.


2011 - Focused Electron Beam Deposition of Nanowires from Cobalt Tricarbonyl Nitrosyl (Co(CO)(3)NO) Precursor [Articolo su rivista]
Gazzadi, gian carlo; Mulders, H.; Trompenaars, P.; Ghirri, A.; Affronte, Marco; Grillo, V.; Frabboni, Stefano
abstract

Nanowires deposited by focused electron beam-induced deposition (FEBID) of cobalt tricarbonyl nitrosyl (Co(CO)(3)NO) precursor have been thoroughly characterized from an electrical, magnetic, and structural point of view. Deposit composition and deposition yield have been studied as a function of beam energy and current. Atomic concentrations are weakly dependent on beam parameters and have average values of 49 at % for Co, 27 at % for O, 14 at % for N, and 10 at % for C. Deposition yield decreases as the beam energy increases, and strong enhancement (67x) is observed for deposition at 130 degrees C substrate temperature. FEBID nanowires are highly resistive (rho = 6.3 m Omega cm at RT), and resistivity increases as T decreases with a power law behavior typical of metal-insulator (M-I) nanogranular systems. Nonmagnetic behavior is revealed by magnetoresistance (MR) measurements. After 400 degrees C vacuum annealing, conductivity of the nanowire is greatly improved (rho = 62 mu Omega cm at RT), and a metallic-like resistivity is fully recovered. MR angular plots display a (cos theta)(2) dependence typical of anisotropic MR (AMR) in ferromagnets, with AMR values of 0.85%. Co concentration in the deposit is not significantly increased though. TEM structural analysis reveals that before annealing the deposit has a CoO fcc structural phase with nanograins size around 1 nm. After annealing, a new Co hcp phase shows up beside CoO fcc, and coarsening (10 - 15 nm) and interconnection of the Co nanograins are observed, providing the conditions for ferromagnetism and metallic electrical transport.


2011 - HRTEM and HAADF analysis of Ni Multi-Twinned Nanoparticles [Articolo su rivista]
V., Grillo; D'Addato, Sergio; Altieri, Salvatore; Frabboni, Stefano; Valeri, Sergio
abstract

In this work, we report our HR-TEM results on Ni and Ni/NiO core shell nanoparticles.


2011 - Structure and stability of nickel/nickel oxide core-shell nanoparticles [Articolo su rivista]
D'Addato, Sergio; V., Grillo; Altieri, Salvatore; R., Tondi; Valeri, Sergio; Frabboni, Stefano
abstract

The results of a combined x-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HR-TEM) study of Ni nanoparticles (NP), before and after oxidation, are presented. An experimental set-up was realized for the preparation and study of pre-formed NP films, concentrating the attention on Ni NP in the diameter range between 4 and 8 nm. The XPS data were taken in situ from NPs after different stages of oxidation, including controlled dosing of O(2) gas in the experimental system and exposure to the atmosphere. The Ni 2p structure is a combination of spectra from metallic Ni in the NP core and from the oxide shell. The signal from the NP core was observed even for samples after exposure to air. From the comparison of HR-TEM experimental images with theoretical simulations, it was found that the Ni NP core has a regular multitwinned icosahedral structure, composed of single-crystal tetrahedra with (111) faces. The NiO phase is clearly observed forming islands on the NP surface.


2011 - Two and three slit electron interference and diffraction experiments [Articolo su rivista]
Frabboni, Stefano; Frigeri, Cesare; Gazzadi Gian, Carlo; Pozzi, Giulio
abstract

Current nanotechnology techniques make possible the preparation of slits in the submicrometer range so that electron interference and diffraction experiments can be done even with a conventional electron microscope. If the instrument is also equipped with a field emission source, it is possible to follow almost in real time the transition from the image of the slits to their Fraunhofer pattern through the intermediate Fresnel diffraction images. We discuss our results for the two-slit experiment and illustrate them for the three-slit case.


2010 - A Tool for the Spectroscopic Investigation of Hydrogen-Silicon Interaction [Articolo su rivista]
E., Romano; G. F., Cerofolini; D., Narducci; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita
abstract

The preparation of an array of nanocavities (NCs) in silicon via thermal treatments of high-fluence heliumimplantedsilicon is a well established process. The NCs have oered a powerful tool for the preparation of welldefined and ordered internal silicon surface, enabling the experimental investigation of its free energy. Here,instead, we interpret the NCs as an ideal nanolaboratory for the study of the adsorption and desorption of H2on silicon. We will present the determination of the internal pressure through the equilibrium abundances ofmono-hydride dimers and dihydrides obtained with infrared spectroscopy.


2010 - Adsorption equilibria and kinetics of H2 at nearly ideal (2 x 1) Si(1 0 0) inner surfaces [Articolo su rivista]
G. F., Cerofolini; E., Romano; D., Narducci; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita
abstract

Silicon nanocavities can be terminated with hydrogen by wet chemical etching. Their infrared spectra can to a large extent be interpreted in terms of silicon monohydrides on H(7 x 7) Si(1 1 1), H(1 x 1) Si(1 1 1) and H(2 x 1) Si(1 0 0), and of silicondihydrides on H(1 x 1) Si(1 0 0). The time evolution under isothermal conditions (600 °C) of the (1 0 0) faces admits a description in terms of transformation from H(1 x 1) Si(1 0 0) into (2 x 1) Si(1 0 0) with simultaneous H2 adsorption onto (2 x 1) Si(1 0 0) neat dimers. In so doing the inner H2 pressure decreases by about one order of magnitude from the initial value of 3000 Torr. The unique properties of nanocavities allow their use as nanoreactors; this has led to the determination of the sticking coecient for H2 adsorption in conditions of pressure, temperature and adventitious contamination otherwise not achievable.


2010 - Four slits interference and diffraction experiments [Articolo su rivista]
Frabboni, Stefano; Frigeri, C.; Gazzadi, Gc; Pozzi, G.
abstract

By means of a focused ion beam apparatus slits about 90 nm in width, 1500 nm in length and with a pitch of 430 nm were prepared on a gold film of 100 nm in thickness. The diffraction and interference experiments carried out in a transmission electron microscope equipped with a field emission gun are an amazing and impressive demonstration of the wave behaviour of the electrons.


2010 - Ion and electron beam nanofabrication of the which-way double-slit experiment in a transmission electron microscope [Articolo su rivista]
Frabboni, Stefano; Gian Carlo, Gazzadi; Giulio, Pozzi
abstract

We have realized a which-way experiment closely resembling the original Feynman’s proposal exploiting focused ion beam milling to prepare two nano-slits and electron beam induced deposition to grow, selectively over one of them, electron transparent layers of low atomic number amorphous material to realize a which way detector for high energy electrons. By carrying out the experiment in an electron microscope equipped with an energy filter, we show that the inelastic scattering of electron transmitted through amorphous layers of different thicknesses provides the control of the dissipative interaction process responsible for the localization phenomena which cancels out the interference effects.


2009 - Current-driven structural transitions in suspended Pt/C nanowires grown by EBID [Abstract in Atti di Convegno]
Frabboni, Stefano; Gian Carlo, Gazzadi
abstract

Electron beam-induced deposition (EBID) [1] performed by lateral shift of the beam from an elevated edge is a powerful method to obtain suspended nanowires (SNWs), [2] because of the lack of secondary emissions from the substrate. Here we will show an in-situ electrical characterization of Pt/C SNWs by means of a two-probe system and live SEM video recorded during the I-V measurement. TEM analysis of the transformed SNWs will be also presented. SNWs about 20nm in diameter, are connecting the tips of Pt/C pillars grown on opposite Au electrodes, patterned by FIB-lithography on a thin membrane. The gap between the electrodes (200-600nm wide), below the SNW bridge, is realized by opening a slit into the membrane in order to enable TEM observation of the wires and to avoid on-substrate deposition (Fig. 1a).I-V measurements within a range of few hundreds of mV show an ohmic behavior, with typical resistivity of about 8-10 x 10-5 Ω m. As the voltage range exceeds 1 V, current departs from the linear trend, Fig. 1b, and structural evolution becomes dramatically evident. Transition consists of a sudden coalescence of the Pt nanocrystals (from 2-3nm to 20nm), separated by even wider gaps, embedded within the carbonaceous matrix.[3] When voltage is further increased, migration of the grains from the centre of the SNW to the ends is observed, transforming the SNWs in carbonaceous structures (Fig. 2). After this evolution SNWs can carry currents up ~ 50 – 80 μA, corresponding to current densities of the order of 107 A/cm2, and when they eventually brake they remain stiff. Similar electrical characteristics have been reported in literature for amorphous carbon wires [4] undergoing transition to graphitic phase by the injection and alternated motion of metal nanoparticles. TEM observation of the transformed SNWs shows sheet-and ring-like structures consistent with a graphitization-like process (Fig.3).


2009 - Evidence for H-2 at high pressure in the silicon nanocavities after dipping in HF solution [Articolo su rivista]
Romano, E.; Cerofolini, G. F.; Narducci, D.; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita
abstract

The immersion in HF solutions of silicon containing nanocavities (produced by the annealing at high temperature, 950 degrees C, of silicon implanted with helium at high fluence, 2 X 10(16) cm(-2)) results in the injection of hydrogen in an infrared-mute state (most likely HA into the nanocavities. The pressure achieved in the cavities is sufficiently high to stabilize the hydrogen coverage of the inner surfaces at: temperatures exceeding by 200 degrees C the one of complete desorption from the outer surface.


2009 - Hydrogen injection and retention in nanocavities of single-crystalline silicon [Articolo su rivista]
G. F., Cerofolini; E., Romano; D., Narducci; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita
abstract

The control of the chemical state of the inner surfaces of nanocavities (NCs) produced by the annealing of helium-implanted silicon has influence on lifetime control, gettering and wafer bonding. In this work it is demonstrated that the etching in HFaq of (1 0 0) silicon containing a buried array of NCs produces a giant injection of hydrogen with the consequent passivation of the inner surfaces, mainly via the formation of silicon monohydride at (1 1 1) faces and monohydride dimers at 2 × 1 reconstructed (1 0 0) faces. These terminations are very stable and survive heat treatments at 700 °C.


2009 - Il microscopio ottico a proiezione come modello per introdurre la microscopia elettronica in trasmissione [Articolo su rivista]
Corni, Federico; Frabboni, Stefano; G., Tigano; V., Pagani
abstract

Viene presentato un percorso composto di attività di laboratorio e di simulazione, indirizzato agli studenti di scuola secondaria di secondo grado, sul microscopio ottico a proiezione allo scopo di introdurre alla comprensione elementare del funzionamento e della formazione delle immagini del microscopio elettronico in trasmissione. Le attività sono progettate in stretta analogia con quello che si svolge al microscopio elettronico; il percorso termina con l’analisi di immagini reali acquisite su un campione di alluminio policristallino in modalità bright field, dark field e alta risoluzione.


2009 - Image charge screening: A new approach to enhance magnetic ordering temperatures inultrathin correlated oxide films [Articolo su rivista]
S., Altieri; M., Finazzi; H. H., Hsieh; M. W., Haverkort; H. J., Lin; C. T., Chen; Frabboni, Stefano; G. C., Gazzadi; Rota, Alberto; Valeri, Sergio; L. H., Tjeng
abstract

We have tested the concept of image charge screening as a new approach to restore magnetic orderingtemperatures and superexchange interactions in correlated oxide ultrathin films. Using a three-monolayerNiO100 film grown on Ag100 and an identically thin film on MgO100 as model systems, we observedthat the Néel temperature of the NiO film on the highly polarizable metal substrate is 390 K while that of thefilm on the poorly polarizable insulator substrate is below 40 K. This demonstrates that screening by highlypolarizable media may point to a practical way toward designing strongly correlated oxide nanostructures withgreatly improved magnetic properties.


2009 - Multiple beam interference and diffraction with FIB fabricated nano-slits [Abstract in Atti di Convegno]
Frabboni, Stefano; Cesare, Frigeri; Gian Carlo, Gazzadi; Giulio, Pozzi
abstract

The recent advances in nanotechnology and electron microscopy are making today possible the realization of experiments of diffraction and interference at multiple slits which formerly were carried out with extremely skilled specimen preparation techniques and dedicated electron optical apparatus [1]. Recently we have used the focused ion beam (FIB) to fabricate two slits on a commercial silicon nitride membrane (500 nm thick) suspended on a 100x100m2 silicon frame 200m thick. In that case the Fraunhofer image was observed in a conventional TEM-JEOL 2010 [2].Here we adopt a less expensive support for nano-slits fabrication, consisting of a commercial continuous carbon film on a standard copper grid, which was subsequently coated with a gold layer about 120 nm in thickness. The slits (nominally 80nm wide, 420 nm spaced) were fabricated with a 9 pA, 30keV, Ga+ beam of a FEI Strata235M Dual Beam. The quality of the slits is very good, as shown in Fig. 1(a) and Fig.1(b), that display two and three slits, respectively. An additional advantage of these samples with respect to the previous ones, is that they can be inserted in almost all FEG-TEM specimen holders. The diffraction and interference experiments were carried out with a JEM-2200FS electron microscope. Owing to the larger coherence of the FEG with respect to the thermionic source, it has been possible to record interference and diffraction images with exposure times of few seconds.The three-slit case is illustrated in Fig. 2 where the in focus image (a), and the images taken at a nominal defocus of -10 mm (b), -20 mm (c) and -40 mm (d), are reported. This sequence shows the transition from the nearly separated Fresnel diffraction images of the single slits, (b), to their subsequent overlapping as the defocus increases, displaying interference phenomena, (c), and finally to a nearly Fraunhofer image, (d).Fig. 3 displays the true Fraunhofer image, taken at a nominal defocus of -53 mm, which clearly shows the secondary minima between the more intense maxima. In the same figure the single slit Fraunhofer images corresponding to the longer side of the slits can also be observed.


2009 - Nanocavities in silicon: An infrared investigation of internal surface reconstruction after hydrogen implantation [Articolo su rivista]
E., Romano; D., Narducci; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita; G. F., Cerofolini
abstract

The preparation of tetrakaidecahedron-shaped nanocavities in silicon via thermal treatments of high-fluence helium-implanted silicon is a well established process. When the mean distance between Such cavities is on the length scale of the exciton diameter, they are expected to modulate the silicon band structure. This property, however, can hardly be exploited due to the large number of dangling bonds remaining on the cavity inner surface at the end of the process. An easy way to reduce their amount is to passivate them with hydrogen. To investigate the interaction of hydrogen with (i) bulk silicon and (ii) the inner surface of the nanocavities, hydrogen was implanted in silicon on preformed nanocavity arrays and the evolution of the Si-H complexes after isochronal annealings in the temperature range 150-80 degrees C was sensed by infrared spectroscopy in multiple internal reflection geometry. In contrast with previous findings, we will provide evidence that there is no measurable redistribution from bulk defects to inner surface during the thermal treatments. Thus, within the limits of experimental sensitivity. surface passivation was proved to occur upon implantation. Annealing eliminates first the most reactive species (SiH3 and SiH2 above 500 and 550 degrees C, respectively): at higher temperatures only signals related to the remaining H passivation of the ideal reconstructed H (1 x 1)-Si(111). H (7 x 7)-Si(111), and H (2 x 1)-Si(100) Surfaces are observed.


2009 - Structural evolution and graphitization of metallorganic-Pt suspended nanowires under high-current-density electrical test [Articolo su rivista]
G. C., Gazzadi; Frabboni, Stefano
abstract

We present a real-time investigation of the dramatic structural evolution occurring in metallorganic-Pt suspended nanowires (SNWs) (20 nm size) under high-current-density electrical test. SNWs are fabricated by electron beam-induced deposition and consist of Pt nanograins (2-3 nm) embedded in a carbonaceous matrix. As current increases, the Pt-C granular material transforms into Pt-depleted, graphitized C with a two-stage process. First, Pt coalescence into big grains (10-15 nm) is observed, then, for current density approaching 10(7) A/cm(2), grains are depleted by Pt electro- and thermomigration, leaving a graphitized C matrix. The graphitic-C wire eventually breaks forming a nanosize gap.


2008 - Electrical characterization of suspended Pt nanowires grown by EBID with water vapour assistance [Articolo su rivista]
G. C., Gazzadi; Frabboni, Stefano; C., Menozzi; L., Incerti
abstract

Suspended nanowires (SNWs), 600 nm-long, 20 nm-wide and 30 nm-thick, were grown by electron beam-induced deposition of metallorganic Pt, with and without water vapour assistance, and electrically characterized at room temperature. SNWs have Ohmic behaviour in the (-0.1, 0.1 V) range, and show conductivity improvement and structural evolution as subsequent I-V cycles are applied; both effects being enhanced by water vapour assistance. Typical resistivities after two I-V cycles are 1-3 x 10(-4) Omega m and 6-8 x 10(-5) Omega m, for Pt and (Pt + water) depositions, respectively. Structural evolution consists of a progressive coalescence of the Pt nanocrystals into large (15-20 nm) and separated grains, leaving wide regions essentially made of carbon material. I-V characteristics over an extended (-2, 2 V) range show a non-linear behaviour outside the (-0.4, 0.4 V) interval, with currents up to similar to 90 mu A at 2 V, corresponding to current densities of similar to 1 x 10(7) A/cm(2). (C) 2008 Elsevier B.V. All rights reserved.}


2008 - Electron diffraction with ten nanometer beam size for strain analysis of nanodevices [Articolo su rivista]
A., Armigliato; Frabboni, Stefano; G. C., Gazzadi
abstract

A method to perform nanobeam diffraction (NBD) in a transmission electron microscope with high spatial resolution and low convergence angle is proposed. It is based on the use of a properly fabricated condenser aperture of 1 mu m in diameter, which allows an electron beam about 10 nm in size to be focused on the sample, with a convergence angle in the 0.1 mrad range. Examples of NBD patterns taken in an untilted < 110 > cross section of a silicon device are shown. Their quality is adequate for spot position determination and hence to obtain, in principle, quantitative strain information. (C) 2008 American Institute of Physics. {[}DOI: 10.1063/1.3003581]}


2008 - Nanofabrication and the realization of Feynman's two-slit experiment [Articolo su rivista]
Frabboni, Stefano; Gian Carlo, Gazzadi; Giulio, Pozzi
abstract

Two nanosized slits are opened by focused ion beam milling in a membrane to observe, with a transmission electron microscope, electron interference fringes. Then, on the same sample, one of the slits is closed by focused ion beam induced deposition and the corresponding transmitted intensity is recorded. The comparison between the two measurements provides an impressive experimental evidence of the probability amplitude of quantum mechanics following step by step the original idea proposed by Feynman {[}The Feynman Lectures on Physics (Addison-Wesley, Reading, MA, 1966), Vol. 3, Chap. 1]. (C) 2008 American Institute of Physics.}


2008 - Quantitative strain mapping in nano electronic silicon dvices by convergent beam electron diffraction [Capitolo/Saggio]
A., Armigliato; R., Balboni; Frabboni, Stefano; A., Spessot
abstract

Lattice deformations which are generated in thedifferent process steps of the current technology fornanoelectronic devices can affect either positively ornegatively their electrical performances. In both casesquantitative information on strains at the nanometerscale are necessary, and presently this can only beachieved by convergent beam electron diffraction(CBED), a technique available in any moderntransmission electron microscope (TEM). In this paper the basic principles of CBED, the method to extract the local strain tensorfrom an experimental diffraction pattern and its application to twodimensional strain mapping in the active silicon region of ultra-scaled isolation structures are reported. The limitations of this method, particularly in the case of high strain gradients along a direction perpendicular to the plane of the device TEM cross section, are discussed. Possible solutions to obtain the displacement field distribution, with reference to a practical case, are described.


2007 - Il FIB come strumento nella sintesi, preparazione e caratterizzazione di materiali e dispositivi [Capitolo/Saggio]
Frabboni, Stefano; G. C., Gazzadi; C., Menozzi
abstract

In questo capitolo vengono descritte alcune tra le metodologie di analisi e fabbricazione disponibili su una classe relativamente recente di microscopi a scansione come il Focusd Ion Beam (FIB) e gli strumenti a doppia colonna FIB+SEM. Sul versante analisi verranno descritti metodi per l’osservazione in pianta e sezione trasversale con i microscopi a scansione e metodi per la preparazione di campioni da aree selezionate per la microscopia elettronica in trasmissione in sezione trasversale. Per quanto concerne la fabbricazione saranno riportati esempi relativi alla nano-strutturazione di superfici, la modifica di punte per microscopia a sonda e la deposizione assistita da fascio (sia ionico che elettronico).


2007 - Method for determination of the displacement field in patterned nanostructures by TEM/CBED analysis of split high-order Laue zone line profiles [Articolo su rivista]
A., Spessot; Frabboni, Stefano; R., Balboni; A., Armigliato
abstract

A method to extract accurate information on the displacement field distribution from split high-order Laue zones lines in a convergent-beam electron diffraction pattern of nanostructures has been developed. Starting from two-dimensional many beam dynamical simulation of HOLZ patterns, we assembled a recursive procedure to reconstruct the displacement field in the investigated regions of the sample, based on the best fit of a parametrized model. This recursive procedure minimizes the differences between simulated and experimental patterns, taken in strained regions, by comparing the corresponding rocking curves of a number of high-order Laue zone reflections. Due to its sensitivity to small displacement variations along the electron beam direction, this method is able to discriminate between different models, and can be also used to map a strain field component in the specimen. We tested this method in a series of experimental convergent-beam electron diffraction patterns, taken in a shallow trench isolation structure. The method presented here is of general validity and, in principle, it can be applied to any sample where not negligible strain gradients along the beam direction are present.


2007 - Microaanalisi a raggi X e microdiffrazione a fascio convergente: apllicazioni al silicio [Capitolo/Saggio]
A., Armigliato; R., Balboni; Frabboni, Stefano; R., Rosa; A., Spessot
abstract


2007 - Structural properties of reactively sputtered W-Si-N thin films [Articolo su rivista]
Vomiero, A; Marchi, Eb; Quaranta, A; DELLA MEA, G; Brusa, Rs; Mariotto, G; Felisari, L; Frabboni, Stefano; Tonini, Rita; Ottaviani, G; Mattei, G; Scandurra, A; Puglisi, O.
abstract

Tungsten-silicon-nitrogen, W-Si-N, ternary thin films have been reactively sputter deposited from W5Si3 and WSi2 targets using several nitrogen partial pressures. The films have been thermal annealed in the 600-1000 degrees C temperature range and a wide region of the W-Si-N ternary phase diagram has been explored by changing the N-2/Ar ratio during the deposition. Multitechnique approach was adopted for the analysis of the samples. Composition has been determined via ion beam analysis; chemical states were investigated using x-ray photoelectron spectroscopy (XPS); crystalline structure was studied using transmission electron microscopy (TEM) and x-ray diffraction (XRD) and surface morphology by scanning electron microscope. The films deposited in pure argon atmosphere are tungsten rich and approach the target contents as N2/Ar ratio is varied during deposition. Tungsten enrichment in the films is caused by resputtering of silicon which can be inhibited by the formation of silicon nitride, allowing films with Si/W ratio closer to the target compositions. The higher capability to form nitrides with silicon than with tungsten favors enhancement of nitrogen. content in samples deposited from the silicon rich target (WSi2). The samples with excess nitrogen content have shown losses of this element after thermal treatment. XPS measurements show a break of W-N bonds caused by thermal instability of tungsten nitrides. TEM and XRD revealed the segregation of tungsten in form of metallic or silicide nanoclusters in samples with low nitrogen content (W58Si21N21 and W24Si42N34). High amounts of nitrogen were revealed to be highly effective in inhibiting metallic cluster coalescence. Measurements of electrical resistivity of as deposited films were performed using four point probe technique. They were found to lie in the range between 0.4 and 79 m Omega cm depending on sample composition. (c) 2007 American Institute of Physics.


2007 - Suspended nanostructures grown by electron beam-induced deposition of Pt and TEOS precursors [Articolo su rivista]
GAZZADI G., C; Frabboni, Stefano; Menozzi, C.
abstract

Suspended nanostructures ( SNSs) are grown by electron beam-induced deposition ( EBID) of Pt and tetra-ethyl-ortho-silicate ( TEOS) gas precursors on nanopillar tips, by lateral shifting of a scanning electron microscope beam. Shape evolution of SNSs is characterized as a function of electron energy ( 5, 10, 15 keV) and electron charge deposited per unit length ( CDL, 1 - 9 pC nm(-1) range) along the beam track. Pt SNSs grow as single nanowires, evolving from thin ( 15 - 20 nm) and horizontal to thick ( up to 70 nm) and inclined ( up to 60 degrees.) geometry as CDL increases. TEOS SNSs consist of multiple nanowires arranged in a stack: horizontal and parallel along the beam shift direction and aligned on top of each other along the beam incidence axis. As the CDL increases, the number of nanowires increases and the top edge of the stack progressively inclines, taking the form of a hand-fan. Deposition yield and overall size of SNSs are found to be proportional to CDL and inversely proportional to electron energy for both Pt and TEOS precursors. As an example of 3D nanoarchitectures achievable by this lateral EBID approach, a 'nano-windmill' TEOS structure is presented.


2007 - TEM study of annealed Pt nanostructures grown by electron beam induced deposition [Articolo su rivista]
Frabboni, Stefano; G. C., Gazzadi; A., Spessot
abstract

In this paper we report on the microstructural characterization of Pt nanostructures fabricated by electron beam-induced deposition in a dual beam system and subsequently annealed in furnace. The as-deposited natiostructures are made of a mixture of nanocrystalline Pt and amorphous carbon. We show by transmission electron microscopy and electron energy loss spectroscopy that the annealing in presence of oxygen at 550 degrees C for 30 min is able to remove the amorphous carbon from the nanostructure, leaving polycrystalline Pt grains. (c) 2006 Elsevier B.V. All rights reserved.


2007 - Young's double-slit interference experiment with electrons [Articolo su rivista]
Frabboni, Stefano; Gazzadi, Gc; Pozzi, G.
abstract

In this short Note we report a method for producing samples containing two nano-sized slits suitable for demonstrating to undergraduate and graduate students the double-slit electron interference experiment in a conventional transmission electron microscope. (C) 2007 American Association of Physics Teachers.


2006 - Convergent beam electron diffraction investigation of strain induced by Ti self-aligned silicides in shallow trench Si isolation structures [Articolo su rivista]
Armigliato, A; Spessot, A; Balboni, R; Benedetti, A; Carnevale, G; Frabboni, Stefano; Mastracchio, G; Pavia, G.
abstract

The deformation induced onto silicon by the formation of Ti self-aligned silicides (salicides) in shallow trench isolation structures has been investigated by the convergent beam electron diffraction technique (CBED) in the transmission electron microscope (TEM). The splitting of the high order Laue zone (HOLZ) lines in the CBED patterns taken in TEM cross sections close to the salicide/silicon interface has been explained assuming that the salicide grains induce a local bending of the lattice planes of the underlying matrix. This bending, which affects in opposite sense the silicon areas below adjacent grains, decreases with the distance from the interface, eventually vanishing at a depth of 300-400 nm. The proposed strain field has been implemented into a fully dynamical simulation of the CBED patterns and has proved to be able to reproduce both the asymmetry of the HOLZ line splitting and the associated subsidiary fringes. This model is confirmed by the shift of a Bragg contour observed in large angle CBED patterns, taken in a cross section cut along a perpendicular direction. The whole experimental results cannot be explained by just a strain relaxation of the TEM cross section, induced by the salicide film onto the underlying silicon.


2006 - Electrical characterization and Auger depth profiling of nanogap electrodes fabricated by I2-assisted focused ion beam [Articolo su rivista]
G. C., Gazzadi; E., Angeli; AND P., Facci; Frabboni, Stefano
abstract

Iodine (I-2)-assisted, 30 keV Ga+ focused ion beam (FIB) has been employed to fabricate nanogap Au electrodes and has been compared to conventional FIB milling. Electrical characterization shows that I-2 assistance improves insulation resistance from 300-400 G Omega to 20-50 T Omega. Auger depth profiling reveals that the Ga concentration profile in FIB-milled samples has a peak value of 25 at. % at 7 nm and extends, with a decreasing Gaussian tail, down to 40 nm, whereas in I-2-processed samples Ga concentration is reduced below 5 at. %. I-2 assistance is found to increase minimum gap size from 8 to 16 nm and to markedly roughen Au surface morphology. (c) 2006 American Institute of Physics.


2006 - Fabrication by electron beam induced deposition and transmission electron microscopic characterization of sub-10-nm freestanding Pt nanowires [Articolo su rivista]
Frabboni, Stefano; Gazzadi, Gc; Felisari, L; Spessot, A.
abstract

We present a method to reduce the size and improve the crystal quality of freestanding nanowires grown by electron beam induced deposition from a platinum metal organic precursor in a dual beam system. By freestanding horizontal growth and subsequent electron irradiation in a transmission electron microscope, sub-10-nm polycrystalline platinum nanowires have been obtained. A combined transmission electron microscopy-electron energy loss analysis has shown that the amorphous carbon, mixed to nanocrystalline platinum in the as-deposited material, is removed from the wires during irradiation. The same treatment progressively transforms nanocrystals dispersed in the amorphous matrix in a continuous polycrystalline platinum wire.


2006 - Single-crystal silicon coimplanted by helium and hydrogen: Evolution of decorated vacancy like defects with thermal treatments [Articolo su rivista]
C., Macchi; S., Mariazzi; G. P., Karwasz; R. S., Brusa; P., Folegati; Frabboni, Stefano; Ottaviani, Giampiero
abstract

Si p-type (100) samples were coimplanted at room temperature with He+ ions at 30 keV with a dose of 1×1016 ions/cm2 and successively with H+ ions at 24 keV with a dose of 1×1016 ions/cm2. A series of samples was thermally treated for 2 h from 100 to 900 °C at 100 °C steps to study the evolution of pointlike and extended defects by two complementary techniques: positron Doppler broadening spectroscopy and transmission electron microscopy. Depth profiling the samples with a positron beam led to the identification of five different traps and the evolution of their profile distributions with thermal treatments. The positron traps were identified as decorated vacancy clusters of different sizes. Their decoration by implanted ions and in some case by oxygen was probed by coincidence Doppler broadening spectroscopy. Up to 300 °C annealing temperature positrons probe three distributions of different decorated defects covering regions of the sample down to 400–450 nm. Starting from 300 °C annealing temperature no defects were revealed by positrons in the region next to the peak of the implanted ions distributions positioned around 280 nm, where extended defects are expected; this indicates complete filling of the defects by H and He. From 300 to 600 °C decorated vacancy clusters of different sizes appear progressively in the region below 280 nm, with a distribution moving deeper into the sample. Comparison with previous measurements on He-implanted samples points out the chemical action of H. Hydrogen atoms interact with the previous damage by He, producing more stabilized vacancylike defects distributed through the damage region of the sample. Electron microscopy shows the transformation of the extended defects from platelets to blisters and cavities.


2006 - Strain field reconstruction in shallow trench isolation structures by CBED and LACBED [Articolo su rivista]
A., Spessot; Frabboni, Stefano; A., Armigliato; R., Balboni
abstract

Using a combination of the CBED and the LACBED techniques in the transmission electron microscopy (TEM), we have investigated the strain field in the silicon active region of a shallow trench isolation structure, underlying a TiSi2 layer. Starting from the analysis of the deformation in a sample, thinned for TEM analysis, we have reconstructed the displacement field, simulating the split HOLZ lines visible in the experimental CBED patterns. From the comparison between the experimental LACBED patterns, taken in a suitable sample orientation to evidence the stressors distribution in the polycrystalline silicide layer, and the corresponding dynamically simulated ones, we have reproduced the strain field in the unthinned, bulk sample. (c) 2006 Elsevier B.V. All rights reserved.


2006 - Transmission Electron Microscopy characterization and sculpting of sub-1 nm Si-O-C freestanding nanowires grown by electron beam induced deposition [Articolo su rivista]
Frabboni, Stefano; G. C., Gazzadi; A., Spessot
abstract

The authors present a transmission electron microscopy characterization and sculpting of freestanding Si-O-C nanowires, fabricated by electron beam induced deposition from a tetraethylorthosilicate precursor, in a dual beam system. Electron energy loss spectroscopy and near edge structure analyses performed on as deposited wires show the formation of amorphous silicon dioxide with extra oxygen and carbon content. Subsequent electron beam sculpting by 200 keV transmission electron microscope irradiation decreases carbon and oxygen contents leaving the silicon oxidation state unchanged and narrows Si-O-C wire width to less than 1 nm. (c) 2006 American Institute of Physics.


2005 - Fabrication of 5 nm gap pillar-electrodes by electron-beam Pt deposition [Articolo su rivista]
Gazzadi, G. C.; Frabboni, Stefano
abstract

Using a focused ion beam (FIB)-scanning electron microscope (SEM) workstation, free-standing nanoelectrodes were grown by SEM-assisted Pt deposition between FIB-patterned Au pads. Two pillar electrodes were first grown with opposite-tilted geometries up to a spacing of 120 nm. By SEM scanning over the pillar tips, under a precursor gas flow, gap reduction down to 5 nm was monitored in live imaging mode. As shown by transmission electron microscopy (TEM) analysis, the deposit consisted of Pt crystallites embedded in amorphous- C. Local annealing by high-current TEM irradiation increased the size of the Pt grains, which produced clear diffraction rings. The annealing procedure did not affect the overall shape of the tips, indicating good mechanical stability of the pillars. We show how this FIB-SEM approach is suitable to fabricate multielectrode nanostructures by depositing a third pillar electrode below the gap of the tilted electrodes.


2005 - Improving spatial resolution of convergent beam electron diffraction strain mapping in silicon microstructures [Articolo su rivista]
Armigliato, A.; Balboni, R.; Frabboni, Stefano
abstract

Despite the use of nanometer-sized probes in field emission transmission electron microscopes, the spatial resolution in strain analysis performed by convergent beam electron diffraction is limited in one direction by the need for tilting the cross-sectional sample in the electron microscope off the vertical &lt;110&gt; direction. We demonstrate that it is possible to improve this resolution by using the &lt;340&gt; zone axis, instead of the &lt;230&gt; one, which has recently become of common use in the analysis of silicon microdevices. Quantitative strain information with good sensitivity and accuracy can be obtained in the new axis. An example of application to the two-dimensional strain mapping in shallow trench isolation structures, obtained with a scanning attachment and a high-angle annular dark-field detector, is reported. (C) 2005 American Institute of Physics.


2005 - Single-metalloprotein wet biotransistor [Articolo su rivista]
Alessandrini, Andrea; Salerno, M.; Frabboni, Stefano; Facci, P.
abstract

Metalloproteins are redox molecules naturally shuttling electrons with high efficiency between molecular partners. As such, they are candidates of choice for bioelectronics. In this work, we have used bacterial metalloprotein azurin, hosted in a nanometer gap between two electrically biased gold electrodes, to demonstrate an electrochemically gated single-molecule transistor operating in an aqueous environment. Gold-chemisorbed azurin shows peaks in tunneling current upon changing electrode potential and a related variation in tunneling barrier transparency which can be exploited to switch an electron current through it. These results suggest the wet approach to molecular electronics as a viable method for exploiting electron transfer of highly specialized biomolecules. ©2005 American Institute of Physics


2004 - Analysis of localised strains by convergent beam electron diffraction [Capitolo/Saggio]
A., Armigliato; R., Balboni; A., Benedetti; Frabboni, Stefano
abstract


2004 - Combined HREM and theoretical analysis of SiC/Si interfaces [Relazione in Atti di Convegno]
Grille, V.; Frabboni, S.; Cicero, G.; Savini, G.; Catellani, A.
abstract

We performed molecular dynamics simulations to study the atomic structure of the β-SiC/Si(001) and (111) interfaces. The wide lattice mismatch between the two materials (∼20%) introduces an array of misfit dislocations along the interface, responsible for releasing almost all the strain which would be present in a pseudomorphic structure. The interface termination, its stoichiometry and the core dislocation structures are discussed here; for the most stable heterostructures, the simulated HREM images are presented, and the features connected to the peculiar interface reconstructions shown.


2004 - Effects of thermal annealing on the structural properties of sputtered W-Si-N diffusion barriers [Articolo su rivista]
Vomiero, A.; Marchi, Eb; Frabboni, Stefano; Quaranta, A.; Della Mea, G.; Mariotto, G.; Felisari, L.; Butturi, M.
abstract

W-Si-N thin films were deposited via rf-magnetron sputtering from a W5Si3 target in Ar/N-2 reactive gas mixtures over a large range of compositions, obtained by varying the partial flow of nitrogen within the reaction chamber. The samples of each set were then thermally annealed in vacuum at different temperatures up to 980 degreesC. Film composition was determined by Rutherford backscattering spectrometry (RBS), surface film morphology by scanning electron microscopy (SEM), micro-structure by transmission electron microscopy (TEM), vibrational properties by FT-IR absorption and Raman scattering spectroscopy, and electrical resistivity by four-point probe measurements. Independently of the deposition conditions, all the as-deposited films have an amorphous structure, while their composition varies, showing an increase of Si/W ratio from 0.1 up to 0.55 when the nitrogen concentration in the films increases from 0 to 60 at%. Thermal treatments in vacuum induce an important loss of nitrogen in the nitrogen-rich samples, especially at temperatures higher than 600 degreesC. Samples with high nitrogen content preserve their amorphous structure even at the highest annealing temperature, despite the chemical bonding ordering observed by means of FTIR measurements. Raman spectroscopy of as-deposited films rich in nitrogen suggests the presence of an important amorphous silicon nitride component, but fails to detect any structural rearrangement either within the composite matrix of film or within silicon nitride component. Segregation of metallic tungsten was detected by TEM in the annealed sample with lowest nitrogen content (W58Si21N21). Finally, the resistivity of the films increases with the N content, while the loss of nitrogen accompanies the decrease of resistivity especially of samples with high nitrogen content.


2004 - Nanovoid formationin helium-implanted single-crystal silicon studied by in situ techniques [Articolo su rivista]
Frabboni, Stefano; Corni, Federico; Nobili, Carlo Emanuele; Tonini, Rita; Ottaviani, Giampiero
abstract

In situ transmission electron microscopy and thermal desorption spectrometry have been employed to observe the evolution of vacancy-type extended defects and the corresponding helium state in helium implanted single crystal silicon during thermal ramping annealing. The structural evolution starting with the formation of a platelike cluster of high pressurized helium bubbles and ending in an empty nanovoid is performed conserving tha total volume of vacancy-type extended defects forming each cluster. Structural adjstements occur by surface diffusion inside each cluster following a migration and coalescence mechanism in presence of high pressure helium for 350°C /T/570°C. A conservative Ostwald ripening is observed for 570/T/700°C in presence of helium desorption.


2004 - Strain mapping in deep sub-micron Si devices by convergent beam electron diffraction in the STEM [Articolo su rivista]
Armigliato, A; Balboni, R; Frabboni, Stefano
abstract

The principles of the convergent beam electron diffraction technique, which is a point-to-point method for local strain analysis of thin crystals in the transmission electron microscope, are briefly outlined. The availability in modern instruments of scanning attachments coupled with high-angle annular dark-field detectors (STEM/HAADF) has recently enabled the automatic acquisition of diffraction patterns ill a large number of points, selected by digitally rastering the probe in a two dimensional region of the sample. As the components of the strain tensor can be calculated at each point, 2D strain mapping has thus become possible. An example of application of the technique to deep sub-micron shallow-trench isolation structures in silicon is reported.


2004 - Structural and functional characterization of W-Si-N sputtered thin films for copper metallizations [Relazione in Atti di Convegno]
Frabboni, Stefano; Alberto, Vomiero; ENRICO BOSCOLO, Marchi; Alberto, Quaranta; GIANANTONIO DELLA, Mea; Gino, Mariotto; Laura, Felisari
abstract

Ternary W-Si-N thin films have been reactively sputter-deposited from a W5Si3 target at different nitrogen partial pressures. The composition has been determined by 2.2 MeV 4He+ beam, the structure by x-ray diffraction and transmission electron microscope, the chemical bonds by Fourier transform – infrared spectroscopy and the surface morphology by scanning electron microscopy. The film as-deposited is amorphous with the Si/W ratio increasing from about 0.1 up to 0.55 with the nitrogen content going from 0 to 60 at%. The heat treatments up to 980 oC induce a loss of nitrogen in the nitrogen rich samples. Segregation of metallic tungsten occurs in the sample with low nitrogen content (W58Si21N21). Samples with high nitrogen content preserve the amorphous structure, despite of the precipitation of a more ordered phase inferred by FT-IR absorbance spectrum of the layer treated at highest temperature. The surface morphology depends upon the nitrogen content; the loss of nitrogen induce the formation of blistering and in the most nitrogen rich sample the formation of holes.


2004 - Transmission Electron Microscopy study of Helium Implanted Silicon [Relazione in Atti di Convegno]
Frabboni, S.; Corni, F.; Tonini, R.; Nobili, C.; Ottaviani, G.
abstract

The structural evolution of helium related extended defects in silicon, formed after intermediate dose helium implantation and annealing has been investigated. It is found that the highest helium concentration (annealing at 300ºC) is associated to clusters of bubbles arranged in a platelet-like morphology. At 500ºC the helium concentration markedly decreases and clusters of cavities formed by a central, large cavity surrounded by small cavities (planetary like structures) are detected. The thermal treatment at 900ºC accomplishes the complete helium effusion from the sample leaving behind empty cavities i.e. voids.


2004 - Transmission electron microscopy study of blisters in high-temperature annealed He and H co-implanted single-crystal silicon [Articolo su rivista]
Frabboni, Stefano; Gc, Gazzadi; L., Felisari; Tonini, Rita; Corni, Federico; Ottaviani, Giampiero
abstract

Transmission electron microscopy has allowed us to draw the three-dimensional structure of blisters formed after high-temperature annealing of He-H co-implanted silicon by combining the unique capability of site-selective cross sectioning of the focused ion beam with conventional plan view images. It has been shown that blisters are formed by crystalline lamellae strongly bended, plastically deformed, and suspended over buried empty cavities. The volume of the protruding blister surface is almost equal to the buried empty volumes, thus suggesting a mechanism for blister formation based on H and He precipitation and migration of silicon atoms toward the surface.


2003 - Application of convergent beam electron diffraction to two-dimensional strain mapping in silicon devices [Articolo su rivista]
A., Armigliato; R., Balboni; Gp, Carnevale; G., Pavia; D., Piccolo; Frabboni, Stefano; A., Benedetti; Ag, Cullis
abstract

A method of obtaining quantitative two-dimensional (2D) maps of strain by the convergent beam electron diffraction technique in a transmission electron microscope is described. It is based on the automatic acquisition of a series of diffraction patterns generated from digital rastering the electron spot in a matrix of points within a selected area of the sample. These patterns are stored in a database and the corresponding strain tensor at each point is calculated, thus yielding a 2D strain map. An example of application of this method to cross-sectioned cells fabricated for the 0.15 mum technology of flash memories is reported.


2003 - Combined HREM and theoretical analysis of SiC/Si interface [Relazione in Atti di Convegno]
V., Grillo; Frabboni, Stefano; G., Cicero; G., Savini; AND A., Catellani
abstract

We performed molecular dynamics simulations to study the atomic structure of the β-SiC/Si(001) and (111) interfaces. The wide lattice mismatch between the two materials (~ 20%) introduces an array of misfit dislocations along the interface, responsible for releasing almost all the strain which would be present in a pseudomorphic structure. The interface termination, its stoichiometry and the core dislocation structures are here discussed; for the most stable heterostructures, the simulated HREM images are presented, and the features connected to the peculiar interface reconstructions evidenced.


2003 - Physical-Chemical Evolution of Hf-aluminates upon Thermal Treatments [Relazione in Atti di Convegno]
B., Crivelli; M., Alessandri; S., Alberici; D., Brazzelli; A. C., Elbaz; Frabboni, Stefano; G., Ghidini; J. W., Maes; G., Ottaviani; G., Pavia; C., Wiemer
abstract

This study presents an investigation on physical-chemical stability of (HfO2)x(Al2O3 )1-x alloys upon prolonged post-deposition annealings. Two different Hf-aluminates were deposited by ALCVDTM, containing 34% and 74% Al2O3 mol% respectively. Post-deposition annealings (PDA) were carried out in O2 or N2 atmosphere, at 850°C and 900°C for 30 minutes. Interfacial layer (IL) increase after PDA was detected on all the samples, but with small differences between N2 and O2 treatments. Stack composition was characterized by means of XRR, XRF, RBS and TOF-SIMS. Growth of interface layer was justified by limited oxygen incorporation from external ambient. Silicon diffusion from the substrate into high-k material and aluminum/hafnium redistribution were observed and associated to annealing temperature. XRD and planar TEM analysis evidenced first grain formation and then, in the case of Hf-rich samples, almost complete crystallization. Overall, Hf-aluminates were found to remain XRD amorphous during high temperature prolonged treatments up to 900°C for 74% and 850°C for 34% alloys respectively. Differently from HfO2, (HfO2)0.66(Al2O3 )0.34 alloy was observed to crystallized in orthorhombic phase. Hf-aluminates were also electrically characterized by means of C(V) and I(V) measurements on basic capacitors. Variations in material electrical properties were found consistent with change in physical-chemical film structure. Increase in k value up to 30 was observed on Hf-rich samples crystallized in orthorhombic phase.


2003 - Strain Determination in Silicon Microstructures by Combined TEM/CBED, Process Simulation and micro-Raman Spectroscopy [Articolo su rivista]
V., Senez; A., Armigliato; I., De Wolf; G. P., Carnevale; R., Balboni; Frabboni, Stefano; A., Benedetti
abstract

Test structures consisting of shallow trench isolation (STI) structures are fabricated using advanced silicon (Si) technology. Different process parameters and geometrical features are implemented to investigate the residual mechanical stress in the structures. A technology computer aided design homemade tool, IMPACT, is upgraded and optimized to yield strain fields in deep submicron complementary metal-oxide-semiconductor devices. Residual strain in the silicon substrate is measured with micro-Raman spectroscopy (mu-RS) and/or convergent beam electron diffraction (CBED) for large (25 mum) and medium size (2 mum), while only CBED is used for deep submicron STI (0.22 mum). We propose a methodology combining CBED and technology computer aided design (TCAD) with mu-RS to assess the accuracy of the CBED measurements and TCAD calculations on the widest structures. The method is extended to measure (by CBED) and calculate (by TCAD) the strain tensor in the smallest structures, out of the reach of the mu-RS technique. The capability of determining, by both measurement and calculation, the strain field distribution in the active regions of deep submicron devices is demonstrated. In particular, it is found that for these structures an elastoplastic model for Si relaxation must be assumed. (C) 2003 American Institute of Physics.


2003 - Techniques for mechanical strain analysis in sub-micrometer structures: TEM/CBED, micro-Raman spectroscopy, X-ray microdiffraction and modeling [Articolo su rivista]
I., De Wolf; V., Senez; R., Balboni; A., Armigliato; Frabboni, Stefano; A., Cedola; S., Lagomarsino
abstract

In this paper, three techniques are discussed that provide information on process-induced local mechanical stress in silicon: the convergent beam electron diffraction technique of transmission electron microscopy, X-ray micro-diffraction and micro-Raman spectroscopy. We discuss the principles of these techniques, their spatial resolution, the ease-of-use, the information that can be obtained, the required sample preparation, the measurement time, and the complementarities of these techniques. We demonstrate this for stress induced by shallow trench isolation and correlate the results to finite element analysis results.


2002 - LATTICE STRAIN AND STATIC DISORDER IN HYDROGEN IMPLANTED AND ANNEALED SINGLE CRYSTAL SILICON AS DETERMINED BY LARGE ANGLE CONVERGENT BEAM ELECTRON DIFFRACTION [Articolo su rivista]
Frabboni, Stefano
abstract

The large-angle convergent-beam electron-diffraction technique, available in a conventional transmission electron microscope, has been employed in order to characterize the defective layer present in heavily damaged high-dose hydrogen-implanted and low-temperature annealed (Tless than or equal to500 degreesC) single-crystal silicon in terms of lattice strain and static disorder. These quantities have been measured to determine the mean relaxation volume and atomic concentration of defect clusters present in the implanted layers in order to investigate the structural features causing the reverse annealing phenomena observed in ion channeling measurements. In particular, the mean relaxation volume detected in the 300 degreesC 2-h annealed sample (0.1 nm(3)) results in a factor three times higher than that measured in the as-implanted sample; on the contrary the mean atomic concentration of clusters does not vary appreciably after this thermal treatment. This experimental evidence suggests a nonconservative growth of clusters in the low-temperature annealing regime. After annealing at 500 degreesC for 2h, an increase of the relaxation volume and a significant decrease of the mean concentration is found, thus suggesting that only after this thermal treatment, producing in the meantime intrinsic defects with extended internal surfaces, defects seem to follow a conservative ripening.


2002 - Strain Induced by Ti Salicidation in Sub-quarter-micron CMOS Devices, as Measured by TEM/CBED [Articolo su rivista]
Benedetti, A.; Cullis, A. G.; Armigliato, A.; Balboni, R.; Frabboni, Stefano; Mastracchio, G. F.; Pavia, G.
abstract

The use of TiSi2 layers as ohmic contacts in complementary MOS (CMOS) devices is expected to introduce large distortions in the underlying silicon which may degrade the device performances. In this work, the TEM technique known as convergent beam electron diffraction (CBED) has been employed to map the strain distributions across (1 1 0) cross-sectional specimens of sub-quarter-micron CMOS structures. Different experimental set-ups in terms of energy filtering, liquid nitrogen cooling and zone axis have been explored and compared to each other by using three differently equipped microscopes. The strain induced on silicon by TiSi2 layers has then been investigated. quantified and compared with that due to the presence of an oxide isolation trench. Also, the effects of depositing a TEN capping layer on TiSi2 have been analysed. Our results show that its presence results in a more tensile strain without altering the strain distribution trend. (C) 2002 Elsevier Science B.V. All rights reserved.


2002 - Strain analysis in submicron electron devices by convergent beam electron diffraction [Relazione in Atti di Convegno]
A., Armigliato; R., Balboni; Frabboni, Stefano; A. BENEDETTI AND A. G., Cullis
abstract


2002 - Strain characterisation at the nm scale of deep sub-micron devices by convergent-beam electron diffraction [Relazione in Atti di Convegno]
Armigliato, A; Balboni, R; Benedetti, A; Carnevale, Gp; Cullis, Ag; Frabboni, Stefano; Piccolo, D.
abstract

The convergent beam electron diffraction (TEM/CBED) technique has been applied to 0.2 mum wide active stripes in STI structures for non volatile memories, which have been prepared for electrical characterisations. Details on the improved procedure to obtain the components of strain from experimental CBED patterns are given. With respect to the previous methods, this improvement includes the increase in spatial resolution by both reducing the projection effects, through a reduction in the specimen tilt angle, and increasing the acceleration voltage; moreover a newly developed software allows the strain tensor to be obtained in a semi-automatic way.


2001 - Strain analysis in sub-micron silicon devices by TEM/CBED [Relazione in Atti di Convegno]
Armigliato, A; Balboni, R; Frabboni, Stefano; Benedetti, A; Cullis, Ag; Pavia, G.
abstract

The main aspects of the convergent beam electron diffraction technique (CBED) in a transmission electron microscope (TEM) for the quantitative strain analysis of silicon nanoregions are described. The presently employed procedure to obtain the components of the strain tensor from an experimental CBED pattern is detailed. The method has been applied to the analysis of strain in 0.22 mum active stripes of shallow trench isolation (STI) structures for non volatile memories. The strain distribution along cutlines parallel to the padoxide/Si interface in STI structures with different morphologies can be related to the different technological steps.


2001 - Strain characterisation of shallow trench isolation structures on a nanometer scale by convergent beam electron diffraction [Articolo su rivista]
Armigliato, A; Balboni, R; Frabboni, Stefano; Benedetti, A; Cullis, Ag; Carnevale, Gp; Colpani, P; Pavia, G.
abstract

The convergent beam electron diffraction (CBED) technique of transmission electron microscopy (TEM) has been applied to [110] cross-sections of shallow trench isolation structures in silicon, in order to evaluate the strain field distribution in 0.22 mum wide active areas. Different spot sizes (1 and 10 nm) and sample temperatures (room temperature with energy filtering, liquid nitrogen cooling without filtering) have been employed. It has been found that the regions of the active area closer than about 100 nm to the padoxide/substrate interface can be analysed only by using a 1 nm spot size. Moreover, the use of an energy filter to reduce the inelastic scattering improves the contrast of the diffraction lines in the CBED pattern, thus allowing the analysis to be performed at room temperature. (C) 2001 Elsevier Science Ltd. All rights reserved.


2000 - A novel Monte-Carlo based method for quantitative thin film X-ray microanalysis [Articolo su rivista]
Armigliato, A; Balboni, R; Frabboni, Stefano; Rosa, R.
abstract

A novel approach to the quantitative analysis of thinned samples, which exploits the finite and variable width of the incident beam of an analytical electron microscope (AEM), is reported. For a binary alloy AB, the method requires two measurements of the I(AK alpha)/l(BK alpha) X-ray intensity ratios, obtained with two different beam diameters. The digital image of the beam is also recorded by a slow-scan CCD camera; its pixel intensities are converted into probability densities by our Monte Carlo code, which has been modified to simulate the electron trajectories crossing the vertical boundaries of the sample. The result of the simulation consists of two thickness t vs concentration C matrices for the two different spot sizes; the unique t-C combination, corresponding to the analyzed region, is obtained through the convergence routine described in our previous papers, This method has been applied to the analysis of Si-Ge alloys in AEM cross sections of Si/Si1-xGex/Si heterostructures. The Ge concentrations obtained by this method on samples of different composition and thickness are in agreement with those deduced from other experimental techniques.


2000 - Dynamical simulation of LACBED patterns in cross-sectioned heterostructures [Articolo su rivista]
Wu, F; Armigliato, A; Balboni, R; Frabboni, Stefano
abstract

The Large Angle Convergent Beam Electron Diffraction (LACBED) technique has been applied to determination of the tetragonal mismatch in coherent Si/Si1-xGex/Si heterostructures. Two-dimensional (2D) dynamical simulation of the LACBED patterns has been performed and compared with the corresponding experimental ones. A good agreement is found in the whole simulated area, particularly as regards the splining of the Bragg contours, due to the strain field present in the TEM cross-sections. (C) 2000 Elsevier Science Ltd. All rights reserved.


2000 - Hydrogen and helium bubbles in silicon [Articolo su rivista]
G. F., Cerofolini; Corni, Federico; Frabboni, Stefano; Nobili, Carlo Emanuele; Ottaviani, Giampiero; Tonini, Rita
abstract

Hydrogen is a quite common impurity in semiconductor-silicon technology: it is unintentionally but unavoidably added to the silicon after crystal growth during wafer processing, and continues to be present during wet oxidation, film depositions, etching and annealing steps. The effects of hydrogen in single crystal silicon at low concentration have been the subject of many papers, books and conference proceedings. Much less considered is the case of hydrogen at massive concentration. One Anal effect of heavy hydrogen loading is the formation of cavities and bubbles, with size up to 100 nm. Cavities and bubbles are also observed after helium loading by high-fluence ion implantation. This article reviews the basic mechanisms responsible for the formation and growth of such structures in single-crystalline silicon. In particular, starting from the loading (ion implantation) and having in mind the formation of the cavities, this paper will cover: the effects of substrate temperature, the interaction of vacancies and self-interstitials with the impurity, the mechanisms of gas segregation inside the cavities, the pressure which arises because of the segregation and the subsequent displacement field in the crystal, the stability against heat treatments of the gas in the cavities and of the cavities themselves. The understanding of the physical processes should lead to gain more insight in the processes of cleavage of the Si-Si bond and vacancy agglomeration which can induce not only the formation of cavities and bubbles, but also planar cutting or explosion. (C) 2000 Published by Elsevier Science S.A. All rights reserved.


2000 - Large angle convergent beam electron diffraction strain measurements in high dose helium implanted silicon [Articolo su rivista]
Gambetta, Francesca; Frabboni, Stefano; Tonini, Rita; Corni, Federico
abstract

Large angle convergent beam electron diffraction (LACBED) technique has been applied to <110> TEM cross section of silicon samples implanted with 2x1016 cm-2 He ions at an energy of 20 KeV in order to evaluate the stress/strain field in the implanted layer. The stress/strain field depends on the mismatch between the lattice of the silicon substrate and the one of the defective layer which contains clusters of point defects and small He bubbles. Lattice mismatch causes changes in the spacing and inclination of diffraction planes producing a shift and a rotation of diffraction intensity lines (Bragg contours (BC)) visible in LACBED patterns. In particular, when the electron beam is parallel to the rotation axis, the BC simply rotate. This is the case of mismatches observed with (333) BC when the electron beam is incident on the sample along a direction close to <110> zone axis. Measurements show a peak of the stress/strain field (intensity 1.5 GPa) at a depth close to the helium projected range, where small bubbles occasionally form aggregate oriented along <011> direction.


2000 - TEM/CBED determination of strain in silicon-based submicrometric electronic devices [Articolo su rivista]
Armigliatoa, A; Balboni, R; Balboni, S; Frabboni, Stefano; Tixier, A; Carnevale, Gp; Colpani, P; Pavia, G; Marmiroli, A.
abstract

The convergent beam electron diffraction technique (CBED) of the transmission electron microscopy (TEM) has been employed to determine the strain distribution along a cutline parallel to the padoxide/Si interface in a 0.80 mu m wide recessed-LOGOS structure, The values of the components of the strain tensor so obtained have been compared with those computed by two simulator codes. It has been found that both the LOCOS morphology and the strain distribution deduced from TEM images and TEM/CBED patterns, respectively, were in agreement with the simulation results, if some oxidation-related parameters were modified. (C) 2000 Elsevier Science Ltd. All rights reserved.


2000 - Thermal desorption spectra from cavities in helium-implanted silicon [Articolo su rivista]
Cerofolini, Gf; Calzolari, G; Corni, Federico; Frabboni, Stefano; Nobili, Carlo Emanuele; Ottaviani, Giampiero; Tonini, Rita
abstract

Thermal desorption spectra at constant ramp rate have been determined after helium implantation into bare silicon prepared for a large set of experimental conditions. The spectra can phenomenologically be classified as composed by two peaks: the alpha peak, centered on a temperature of 750-800 degrees C with a shoulder extending to lower temperature (down to 550 degrees C), and the beta peak, centered on a lower temperature depending on the implantation-annealing conditions. The alpha peak is attributed to the emission from cavities, while the beta peak is attributed to the emission from vacancylike defects. A detailed theory describing helium effusion from stable cavities as controlled by the interatomic helium-helium potential is proposed and found to reproduce accurately most of the alpha peaks. The postimplantation of hydrogen into samples displaying a pure beta emission results in an alpha peak which can be described by the same model as above provided that the cavities are unstable and shrink during desorption in such a way as to maintain constant the concentration of contained helium.


1999 - Helium-implanted silicon: A study of bubble precursors [Articolo su rivista]
Corni, Federico; Calzolari, G; Frabboni, Stefano; Nobili, Carlo Emanuele; Ottaviani, Giampiero; Tonini, Rita; Cerofolini, Gf; Leone, D; Servidori, M; Brusa, Rs; Karwasz, Gp; Tiengo, N; Zecca, A.
abstract

The interaction of helium atoms with the radiation damage imparted to (100) silicon single crystal by He+ implantation at 5 x 10(15) cm(-2), 20 keV, and liquid-nitrogen temperature is investigated by means of various complementary techniques during and after thermal treatments. Thermal programmed desorption was used to study the dissociation kinetics of helium from the defects and to plan suitable heat treatments for the other techniques. The helium profiles were determined by 8 MeV N-15(2+) elastic recoil detection, quantitative data on damage were obtained by channeling Rutherford backscattering spectrometry, double crystal x-ray diffraction, and positron annihilation spectroscopy. Isothermal treatments at 250 degrees C produce first helium redistribution and trapping in vacancy-like defects, rather than helium desorption from traps. The process is thermally activated with an effective activation energy, dispersed in a band from 1.1 to about 1.7 eV. For higher temperature treatments (2 h at 500 degrees C) the traps are almost emptied and at 700 degrees C all vacancy-like defects are annealed out. No bubbles or voids are observed by transmission electron microscopy, either in the as-implanted or in annealed samples. (C) 1999 American Institute of Physics. [S0021-8979(99)00903-2].


1999 - Influence of the first preparation steps on the properties of GaN layers grown on 6H-SiC by MBE [Articolo su rivista]
Lantier, R; Rizzi, A; Guggi, D; Luth, H; Neubauer, B; Gerthsen, D; Frabboni, Stefano; Coli, G; Cingolani, R.
abstract

The Gan heteroepitaxy on 6H-SiC is affected by the bad morphology of the substrate surface. We performed a hydrogen etching at 1550 degrees C on the 6H-SiC(0001) substrates to obtain atomically flat terraces. An improvement of the structural properties of GaN grown by MBE on such substrates after deposition of a LT-AlN buffer layer is observed. A value of less than 220 arcsec of the FWHM of the XRD rocking curve, showing a reduced screw dislocations density, is comparable with the best results reported until now for thick GaN samples. Photoluminescence showed a structured near band edge emission spectrum with evidence of the A, B and C free exciton recombinations.


1999 - Investigation of strain distribution in LOCOS structures by dynamical simulation of LACBED patterns [Articolo su rivista]
Wu, F; Armigliato, A; Balboni, R; Frabboni, Stefano
abstract

Large-angle convergent beam electron diffraction (LACBED) dynamical simulations have been applied to the investigation of the strain distribution in the silicon region underlying a local oxidation of silicon (LOCOS) structure. This distribution is revealed through the modification of the profile of the (0 0 8) Bragg contour in the [1 2 0] projection of a [1 1 0] TEM cross-sectioned structure. If one assumes a strain field independent on the direction normal to the cross section, a contrast in the LACBED pattern is obtained only if a rotation of the lattice planes in the silicon region under stress is taken into account. The experimental patterns, taken on a submicron recessed-LOGOS, are in fair agreement with those calculated assuming, for the strain field, an analytical model based on the planar stress approximation (C) 1999 Published by Elsevier Science B.V. All rights reserved.


1999 - Lattice strain and static disorder determination in Si/Si1-xGex/Si heterostructures by convergent beam electron diffraction [Articolo su rivista]
Frabboni, Stefano; Gambetta, F; Armigliato, A; Balboni, R; Balboni, S; Cembali, F.
abstract

Lattice strain and static disorder present in Si1-xGex alloys forming Si/Si1-xGex/Si heterostructures with a Ge atomic fraction x equal to 0.1, 0.2, and 0.3, have been studied by convergent beam electron diffraction and large-angle convergent beam electron diffraction. These techniques have been used in order to perform structural analysis of the alloys with a spatial resolution comparable with the dimensions involved in Si/SiGe applications. Strain values along directions both perpendicular and parallel to the sample surface have been determined from a single high-order Laue zone deficiency lines pattern. The resulting relaxed alloy lattice constant has been found to depend on the Ge atomic fraction following a nearest-neighbor model alloy, where die Si-Si, Ge-Ge, and Si-Ge bond lengths combine themselves with a negligible dependence on the Ge atomic fraction. From lattice strain values, both the strain-induced bond bend in the plane of the interface, and the strain-induced bond stretch have been determined. Static disorder measurements, performed by comparing the integrated intensity of high-angle diffracted beams in the silicon substrate and in the SiGe layers, allow the determination of the atomic mean-square displacements produced by the presence in the same coordination shell of Si-Si, Ge-Ge, and Si-Ge atomic pairs with different bond lengths. The measured atomic displacements are greater than the ones predicted by both. the nearest-neighbor solution model (which only accounts for the different bond lengths, and not for both band trend and strain) and a relaxed alloys structure Monte Carlo simulation (which accounts for differences in bond lengths and bond bend, but neglects the effect of strain). The component of the atomic displacement related to the macroscopic strain has been determined as the difference between the experimental values and those computed by Monte Carlo code. A linear correlation between the strain-induced atomic displacement and the strain-induced bond bend in the plane of the interface has been found. [S0163-1829(99)04343-X].


1999 - Strain determination in submicron isolation structures by TEM/CBED [Relazione in Atti di Convegno]
Armigliato, A; Balboni, R; Balboni, S; Frabboni, Stefano; Tixier, A; Carnevale, Gp; Colpani, P; Pavia, G; Marmiroli, A.
abstract

The convergent beam electron diffraction (CBED) technique in a transmission electron microscope (TEM) has been employed to determine the strain distribution along a cutline parallel to the padoxide/Si interface in a 0.80 mum wide recessed-LOGOS (LOCal Oxidation of Silicon) structure. The values of the components of the strain tensor so obtained have been compared with those computed by two process simulation codes. It has been found that both the LOGOS morphology and the strain distribution, experimentally determined, were in agreement with the simulation results, if some oxidation-related parameters were modified.


1999 - Vacancy-gettering in silicon: Cavities and helium-implantation [Articolo su rivista]
Corni, Federico; Tonini, Rita; Frabboni, Stefano; Nobili, Carlo Emanuele; Calzolari, G; Masetti, S; Tamarozzi, P; Pavia, G; Cerofolini, Gf
abstract

Cavities in single crystalline silicon are shown to act as gettering centers for the vacancies produced during an ion implantation process: the effect of the gettering is observed as an increase of their total volume. Helium implantation at 20 keV with a dose of 2 x 10(16) cm(-2) plus a heat treatment at 850 degrees C for 3 hours produces the cavities; vacancies are supplied by a subsequent 0.8 x 10(16) cm(-2) helium implant. In this case the vacancy-gettering efficiency, i.e. average increase of vacancies involved in stable voids per helium ion, is found to be 0.53 vacancies ion(-1); about 4 times more compared to the case when the same 0.8 x 10(16) cm(-2) implant is performed on a virgin crystal. A further effect is the peculiar helium behavior which acts as a stabilizer of the vacancies produced during the implantation. The differential vacancy-gettering efficiency is found to increase with the helium dose: about 0.13 vacancies ion(-1) at 0.8 x 10(16) cm(-2), 0.4 vacancies ion(-1) at 2 x 10(16) cm(-2), and 3.8 vacancies ion(-1) at 2.8 x 10(16) cm(-2) .


1998 - Determination of bulk mismatch values in transmission electron microscopy cross-sections of heterostructures by convergent-beam electron diffraction [Articolo su rivista]
Balboni, R; Frabboni, Stefano; Armigliato, A.
abstract

The relaxation which occurs along the thinning direction of transmission electron microscopy (TEM) cross-sections of heterostructures is still poorly known. This has so far prevented the accurate determination of the corresponding bulk mismatch values from convergent-beam electron diffraction (CBED) patterns. In this paper it is demonstrated that, by using elasticity theory, it is possible to deduce a simple relationship for (001) heterostructures which relates the lattice mismatches along the different crystallographic directions of the TEM specimen, as deduced from a single CBED pattern, to the bulk value. Both [001] and [110] orientations of the TEM cross-sections are considered. However, to obtain accurate results: the validity of the kinematical approach used to deduce mismatches from high-order Laue zone line patterns must be critically checked; it depends on the crystallographic projection, on the beam voltage and, in the case of Si1-xGex heterostructures: on the Ge concentration. It is found that the best results are obtained at 100 kV, working in the [013] projection, and for Ge concentrations up to 20 at.%. The method has been applied to both uniform and graded Si1-xGex/Si heterostructures, as well as to a B+-implanted, epitaxially regrown Si wafer. Good agreement is found between the CBED results and the bulk values obtained from double-crystal X-ray diffractometry.


1998 - Growth kinetics of a displacement field in hydrogen implanted single crystalline silicon [Articolo su rivista]
D., Bisero; Corni, Federico; Frabboni, Stefano; Tonini, Rita; Ottaviani, Giampiero; R., Balboni
abstract

The growth of a displacement field in single crystal silicon resulting from high dose hydrogen implantation and subsequent heat treatments has been investigated by MeV He-4(+) Rutherford backscattering in channeling conditions, double crystal x-ray diffraction, and transmission electron microscopy. The results obtained in samples annealed for various times in the temperature range 220-350 degrees C have been explained in terms of a kinetic model which assumes the formation of clusters of hydrogen molecules. The growth of the displacement field is thermally activated with an activation energy of 0.50+/-0.05 eV, suggesting that the limiting process could be the release of hydrogen atoms bounded to defects created by ion implantation.


1998 - High-dose helium-implanted single-crystal silicon: Annealing behavior [Articolo su rivista]
Tonini, Rita; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Cerofolini, G. F.
abstract

The modifications induced in single-crystal silicon by implanted helium have been investigated by ion beam techniques. The damage has been detected by 2 MeV 4He+ backscattering in channeling conditions and the helium in-depth distribution by 7 and 8 MeV 15N++ elastic recoil scattering. The samples prepared by implanting 2×1016 cm−2 helium ions at 20 keV in silicon wafers held either at 77 K (LNT sample) or at 300 K (RT sample) have been heat treated for 2 h in the 100–800 °C temperature range. In the as-implanted LNT sample the damage maximum is at 130±20 nm and shifts in-depth to 180±10 nm after annealing at 200 °C, in the as-implanted RT sample, the damage maximum is already located at 180±10 nm. In the 250–500 °C temperature range, the LNT and RT samples follow the same annealing path with only slight differences in the temperature values; in both cases, the dechanneling signal increases and reaches a maximum value of nonregistered silicon atoms of 2.2–2.5×1022 at/cm3. In the same temperature range, the helium signal becomes narrower, builds up in a region centered on 220±20 nm and no appreciable loss of helium can be detected. The growth of the damage is consistent with the creation of cracks and a etherogenous distribution of bubbles filled with high pressure helium which stress the lattice; for the channeling Rutherford backscattering technique, their action is similar to silicon interstitials. At temperatures above 500 °C, helium is released from the samples; this process is associated with a decrease of the damage and the formation and increase in size of voids. At 900 °C empty voids with a diameter around 20 nm are found.


1998 - On the spatial resolution in analytical electron microscopy [Articolo su rivista]
Armigliato, A; Howard, Dj; Balboni, R; Frabboni, Stefano; Caymax, Mr
abstract

The effect on spatial resolution of the spherical aberration of the objective prefield of a Philips CM30 (S)TEM has been investigated. For this purpose, the lattice mismatch of a 20 nm thick Si-Ge film in a cross-sectioned Si/Si0.9Ge0.1/Si heterostructure has been determined by convergent beam electron diffraction (CBED), performed at 100 kV with a spot size of 20 nm. It has been found that, if the disk of minimum confusion is focused onto the specimen plane: the measurement is not affected by a change in the size of the condenser-2 aperture. Therefore, the mismatch information is contained within the Gaussian part of the electron probe. In strain profile determinations by CBED, this allows one to use higher beam intensities (larger C2-apertures) with improved signal/noise ratios and reduced sample drift due to shorter acquisition times.


1998 - Static disorder depth profile in ion implanted materials by means of large angle convergent beam electron diffraction [Articolo su rivista]
Frabboni, Stefano; F., Gambetta
abstract

A new experimental method for static disorder depth profile in ion implanted crystalline materials is presented. Large angle convergent beam electron diffraction patterns of high angle reflections are used to directly compare, on a depth scale of the order of 10 nm, the integrated intensity coming from the undamaged crystal and from different slabs of the damaged layer. The case of high dose hydrogen implanted single crystal silicon wafers is studied. The results agree with the static disorder depth profile expected in both the as-implanted and the low temperature annealed samples. [S0031-9007(98)07270-6].


1998 - The effect of biaxial stress on the solid phase epitaxial crystallization of GexSi((1-x)) films [Articolo su rivista]
Corni, Federico; Frabboni, Stefano; Tonini, Rita; Leone, D; de Boer, W; Gasparotto, A.
abstract

Two fully-strained, Si rich, GexSi((1-x)) alloys deposited on (100) Si by CVD were amorphized including part of the substrate. and recrystallized at different temperatures in the range 500-620 degrees C. The amorphous-crystal interfaces remain flat during crystallization, and the films grow coherently with the substrate producing crystalline, defect-free, strained heteroepitaxial layers. The kinetics of the process, compared with literature data of the corresponding relaxed alloys, are affected by the presence of the in-plane stress at the interface, resulting in a decrease of the velocity, in quantitative agreement with the predictions of the activation strain model in the case of biaxial stress.


1997 - Effects of static disorder on LACBED patterns of single crystal silicon implanted with hydrogen [Relazione in Atti di Convegno]
Frabboni, Stefano; Gambetta, F; Tonini, Rita; Balboni, R; Armigliato, A.
abstract

The LACBED technique has been applied to &lt;110&gt; TEM cross-sections of Si sample implanted with H to study the effect of the static disorder on the Rocking Curves (RC) of high angle diffracted beams in presence of platelets and cavities. This effect has been revealed by comparing the RC originating from the perfect crystal and from the implanted layer, respectively. The results are consistent with an atomic root mean square displacement of the order of 10(-2) nm which compares quite well with x-ray measurements performed in the Bragg-symmetric geometry.


1997 - Strain in silicon below Si3N4 stripes, comparison between SUPREM IV calculation and TEM/CBED measurements [Articolo su rivista]
Armigliato, A; Balboni, R; Frabboni, Stefano; Tixier, A; Carnevale, Gp; Colpani, P; Marmiroli, A.
abstract

The convergent beam electron diffraction technique (CBED) and SUPREM IV simulation have been applied to determine the lattice strain in a silicon region underlying a Si3N4 stripe. The width and thickness of the stripe are 870 and 194 nm, respectively. These strips are the masks which define the pattern of the LOGOS isolation structure, before thermal oxidation. The silicon nitride film has been deposited onto a (100) silicon wafer through a 21 nm thick pad oxide. The resulting profiles of the components of the stress tensor, converted into strain, along a direction perpendicular to the direction of the stripe, have been deduced from SUPREM IV simulations and compared with the corresponding values, obtained by convergent beam electron diffraction (CBED), performed in different points of TEM cross sections of the same structure. It has been found that a suitable choice of the SUPREM IV parameters is needed in order to fit the experimental data to the simulated ones.


1997 - Strain measurements in thin film structures by convergent beam electron diffraction [Articolo su rivista]
Armigliato, A; Balboni, R; Benedetti, A; Frabboni, Stefano; Tixier, A; Vanhellemont, J.
abstract

The Convergent Beam Electron Diffraction technique (CBED) has been applied to determine the lattice strain in Si1-xGex/Si heterostructures and below patterned films on silicon substrates. The well known problem of the stress relaxation which occurs in thinned TEM samples has been overcome, in the case of the heterostructures, by applying the isotropic elasticity theory to the lattice constants measured along different crystallographic directions through the shift of the High Order Laue Zone (HOLZ) lines in the central disk of the CBED patterns. In this way bulk strain values. have been obtained, in good agreement with values deduced from independent techniques. In patterned structures, the high spatial resolution of the CBED technique has been applied to determine the distribution of the components of the strain tensor induced into oxidized silicon substrates by Si3N4 stripes. A good agreement with the results obtained using numerical computations has been found.


1996 - Bulk mismatch values of heterostructures as determined from convergent beam electron diffraction on thin cross sections [Articolo su rivista]
Balboni, R; Armigliato, A; Frabboni, Stefano
abstract

High order Laue zone lines present in the central disk of convergent beam electron diffraction patterns have been used to determine the bulk mismatch in thinned, cross-sectioned heterostructures, where a relaxation occurs along the thinning direction. The position of these lines is sensitive to lattice parameters along different crystallographic directions, so that information on the residual strain along the growth and the thinning directions can be extracted from a single diffraction pattern. This information has been properly combined using the isotropic elasticity theory to give the bulk mismatch. The results are in good agreement with independently obtained bulk measurements.


1996 - Silicon interstitials generation during the exposure of silicon to hydrogen plasma [Articolo su rivista]
Tonini, Rita; Monelli, A; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Queirolo, G.
abstract

Interstitials in silicon can be produced by hydrogen ions through chemical action and physical impact. To establish the relative importance of the two processes, wafers of single crystal silicon kept at a temperature of 250 degrees C were exposed to a hydrogen plasma, with and without an accelerating voltage (500 V). As gettering centers interstitial-type dislocation loops were made, before H exposure, by implanting 1.9 x 10(15) at. cm(-2) 110 keV P atoms and annealing at 1000 degrees C for 30 s. The analysis was performed using MeV ion channeling, elastic recoil detection analysis and cross-section transmission electron microscopy. The results suggest that H is captured by the defects: in the case of unbiased plasma, H goes in the region of the extrinsic defects, while in the case of biased plasma, H is trapped near the surface where the defects are produced by the energetic H ions themselves. In both cases the data are consistent with the formation of hydrogen nanoblisters with the subsequent breaking of silicon bonds and injection of silicon interstitials. The migration of interstitials occurs at a temperature as low as 250 degrees C.


1996 - Stress and interface morphology contributions in the crystallization kinetics of a GexSi1-x thin layer on (100)Si [Articolo su rivista]
Corni, Federico; Frabboni, Stefano; Tonini, Rita; Ottaviani, Giampiero; Queirolo, G.
abstract

A study of the solid phase epitaxial growth from amorphous phase of a strained GexSi1-x thin layer made by Ge-74(+) ion implantation of (100) Si is presented. Ge peak concentration is 6.4 at. %. Principally employed techniques are time-resolved reflectivity for crystallization rate measurements and cross sectional transmission electron microscopy (TEM) for interface morphology imaging. The kinetics is heavily affected by the mismatch stress induced by the Ge; the experimental data cannot however be explained considering only the average stress along the amorphous-crystal interface and another mechanism is required. Cross sectional TEM observations of partially crystallized samples reveal the tendency of the interface to roughen with an evolution reflected in the crystallization activation energy Such roughness is assumed to affect the kinetics by locally enhancing the interface stress.


1996 - Transmission Electron diffraction techniques for nm scale measurement in semiconductors [Relazione in Atti di Convegno]
J., Vanhellemont; K. G. F., Janssens; Frabboni, Stefano; R., Balboni; A., Armigliato
abstract


1995 - ANALYTICAL ELECTRON-MICROSCOPY OF SI1-XGEX/SI HETEROSTRUCTURES AND LOCAL ISOLATION STRUCTURES [Articolo su rivista]
Armigliato, A; Balboni, R; Corticelli, F; Frabboni, Stefano; Malvezzi, F.
abstract

The convergent beam electron diffraction (CBED) technique has been applied to determine the lattice strain in Si1-xGex/Si heterostructures and in local isolation structures. Both plan and cross-sections have been investigated by transmission electron microscopy. In the heterostructures, the strain value obtained by CBED along the growth direction epsilon(CBED) is affected by ii relaxation induced by the thinning process in a direction normal to the cross-section plane, being generally smaller than the bulk tetragonal value epsilon(T). This effect can be overcome using the large angle CBED technique on plan sections. In addition, in the heterostructures the Ge concentration has been determined by energy dispersive X-ray spectrometry: allowing the pseudomorphicity of the samples to be evaluated. All the values of strain and Ge concentration thus obtained ale in good agreement with those deduced from Rutherford backscattering spectrometry. In isolation structures, the CBED technique has been applied to determine the distribution of the components of the strain tensor along a line parallel to the pad oxide/substrate interface. The values obtained are in agreement with the predictions of a previously reported simple model.


1995 - Hydrogen precipitation in highly oversaturated single-crystalline silicon [Articolo su rivista]
Cerofolini, Gf; Balboni, R; Bisero, D; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita; Brusa, Rs; Zecca, A; Ceschini, M; Giebel, G; Pavesi, L.
abstract

A review of high concentration Hydrogen in Silicon is presented.


1995 - Influence of experimental parameters on the determination of tetragonal distortion in heterostructures by LACBED [Articolo su rivista]
Armigliato, A; Balboni, R; Corticelli, F; Frabboni, Stefano
abstract

The LACBED technique has been applied to the determination of the tetragonal distortion in Si1-xGex/Si heterostructures, which are of great interest in the device technology. The strain determination has been performed on plan sections in an analytical electron microscope. The agreement between this strain value and the tetragonal distortion is influenced mainly by the local sample flatness and the acceleration voltage.


1994 - ELECTRON AND ION-BEAM ANALYSIS OF COMPOSITION AND STRAIN IN SI1-XGEX SI HETEROSTRUCTURES [Articolo su rivista]
Armigliato, A; Govoni, D; Balboni, R; Frabboni, Stefano; Berti, M; Romanato, F; Drigo, Av
abstract

Si1-xGex heterostructures have been grown by molecular beam epitaxy, with nominal compositions of 10 and 15 at %. Analytical electron microscopy, Rutherford backscattering spectrometry and ion channeling have been used in order to determine film thickness, Ge molar fraction and tetragonal distortion. The actual Ge concentrations were found to be smaller than the nominal ones. For all the SiGe films a coherent growth was found, with a small deviation from the perfect tetragonal distortion. The good agreement found between the results obtained by each analytical technique demonstrate that these methods of characterization are powerful tools for the control of the epitaxial layer parameters.


1994 - X-RAY-EMISSION MODULATION BY ELECTRON CHANNELING AND SITE OCCUPANCY IN GARNETS [Articolo su rivista]
Balboni, R; Frabboni, Stefano; Rinaldi, R; Spigarelli, S.
abstract

Axial channelling effects in a pyrope garnet for three zone axis orientations: [111], [211], and [311] have been investigated. The variations of the characteristic X-ray emission under the [111] zone axis diffracting conditions was correlated with dynamical n-beam calculations. Site occupancies determinations obtained by comparing X + Z and Y sites have been made using ALCHEMI techniques.


1993 - DETERMINATION OF LATTICE STRAIN IN LOCAL ISOLATION STRUCTURES BY ELECTRON-DIFFRACTION TECHNIQUES AND MICRO-RAMAN SPECTROSCOPY [Relazione in Atti di Convegno]
Armigliato, A; Barboni, R; Dewolf, I; Frabboni, Stefano; Janssens, Kgf; Vanhellemont, J.
abstract

To investigate the stress fields in local isolation structures, convergent beam electron diffraction (CBED), electron diffraction contrast imaging (EDCI) and micro-Raman spectroscopy (mu RS) have proved to be powerful, complementary techniques. CBED and EDCI have a higher spatial resolution with respect to mu RS but need elaborate sample preparation procedures to obtain thin cross sections of the structure. On the other hand mu RS can measure stresses in the silicon substrate provided the overlayers are transparent; moreover, the recorded Raman shift is a convolution of shifts due to different stress components. The results of preliminary experiments performed on LOPOS structures having linewidths in the range 0.5-5 mu m are reported and critically compared.


1993 - Giant radiation damage produced by the impact of heavy molecular ions onto silicon single crystal [Articolo su rivista]
Cerofolini, Gf; Bertoni, S; Meda, L; Balboni, R; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita; Para, Af
abstract

The giant radiation damage imparted to single-crystalline silicon by the impact of Re2(CO)2+ at 140 keV is studied by conventional and high-resolution transmission electron microscopy. Evidence for damage produced by the correlated motion of the atoms initially forming the molecular ion is presented.


1993 - On the assessment of local stress distribution in integrated circuits [Articolo su rivista]
J., Vanhellemont; I., DE WOLF; Kfg, Janssens; Frabboni, Stefano; R., Balboni; A., Armigliato
abstract

The possibilities and limitations of micro Raman spectroscopy (muRS), convergent beam electron diffraction (CBED) and electron diffraction contrast imaging (EDCI) for the study of localised stress fields in semiconductor substrates are discussed and illustrated with results obtained on local isolation structures in silicon. MuRS has the advantage of being non-destructive but has a spatial resolution which is limited by the wavelength of the laser and which is typically of the order of 1 mum. Other drawbacks are that stresses in the silicon substrate can only be measured through transparent layers and that the recorded Raman shift is a convolution of shifts due to different stress components. The two transmission electron microscopy techniques have a much higher spatial resolution (nm scale) but suffer from the drawback that they are destructive and require elaborated specimen preparation. Furthermore, the preparation of the thin foils suitable for TEM inspection leads to relaxation of the strains in the direction perpendicular to the image plane which has to be taken into account for the interpretation of the results. Nevertheless, useful, complementary information on the strain distributions can be deduced from the combined use of these three techniques. This opens interesting perspectives in the correlation between local stress and electrical properties of microelectronic devices.


1992 - HYDROGEN-RELATED COMPLEXES AS THE STRESSING SPECIES IN HIGH-FLUENCE, HYDROGEN-IMPLANTED, SINGLE-CRYSTAL SILICON [Articolo su rivista]
Cerofolini, Gf; Meda, L; Balboni, R; Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita; Anderle, M; Canteri, R.
abstract

This work is devoted to the characterization of the Si:H system obtained by high-fluence, low-energy, hydrogen implantation into single-crystal silicon. The implanted hydrogen profile and the ones resulting after thermal annealing in the range 100-800-degrees-C are detected by secondary-ion mass spectrometry and elastic-recoil detection analysis. The displacement field in the crystal, measured by channeling Rutherford-backscattering spectrometry, is found to depend on the direct radiation damage, the extended defects formed after ion implantation (revealed by transmission electron microscopy), and the implanted species. The contribution to the displacement field due to hydrogen-related defects has a characteristic reverse annealing in the range 100-400-degrees-C, essentially due to their formation kinetics.


1992 - Processing high-quality silicon for microstrip detectors [Articolo su rivista]
Nava, Filippo; Ottaviani, Giampiero; Tonini, Rita; Frabboni, Stefano; A., Alberigi Quaranta; P., Cantoni; P. L., Frabetti; L., Stagni; G., Queirolo; P. F., Manfredi
abstract

An investigation has been made into the behaviour of high-purity silicon (HP-Si) during the fabrication of microstrip detectors. The resistivity of the silicon used is 3 k-OMEGA cm. The investigation is centred on standard bipolar processes based on ion implantation. It is found that, comparing the processes used, the best diode characteristics are achieved when a heat treatment at 600-degrees-C is used after the ion-implantation step, whereas the worst results from an implantation and a 900-degrees-C heat treatment. Thus it is shown that if integration of the electronic circuitry and the detector on a single chip is required, then the high-temperature heat treatments must be done before the ion-implantation step needed for detector fabrication.


1992 - SOLID-PHASE EPITAXIAL-GROWTH OF GE-SI ALLOYS MADE BY ION-IMPLANTATION [Articolo su rivista]
Corni, Federico; Frabboni, Stefano; Ottaviani, Giampiero; Queirolo, G; Bisero, D; Bresolin, C; Fabbri, R; Servidori, M.
abstract

Solid-phase epitaxial growth was studied in germanium-implanted <100> silicon wafers as a function of germanium fluence, annealing temperature, and time. MeV He Rutherford backscattering in channeling conditions, cross-sectional transmission electron microscopy, double-crystal x-ray diffraction, and secondary-ion mass spectroscopy techniques were used to characterize the samples. At low fluences, up to 1 x 10(15) cm-2 at 130 keV, the crystallization kinetics is similar to that measured on self-amorphized silicon. In the high-dose samples, prepared by multiple implants with a total dose of 3.12 x 10(16) cm-2, the growth rate at fixed temperatures decreases. A comparison with literature data, obtained by similar experiments performed on amorphized uniform GexSi100-x films prepared by molecular-beam epitaxy or chemical-vapor deposition, reveals that the concentration gradient, unavoidable in implanted samples mainly at the end of the ion range region, is strictly connected with the observed decrease.


1992 - STRUCTURAL AND ANALYTICAL CHARACTERIZATION OF SI(1-X)GEX/SI HETEROSTRUCTURES BY RUTHERFORD BACKSCATTERING SPECTROMETRY AND CHANNELING, ANALYTICAL ELECTRON-MICROSCOPY AND DOUBLE CRYSTAL X-RAY-DIFFRACTOMETRY [Articolo su rivista]
Armigliato, A; Servidori, M; Cembali, F; Fabbri, R; Rosa, R; Corticelli, F; Govoni, D; Drigo, Av; Mazzer, M; Romanato, F; Frabboni, Stefano; Balboni, R; Iyer, Ss; Guerrieri, A.
abstract

Thin film Si1-xGex alloys have been grown on silicon by molecular beam epitaxy with nominal composition, x, between 10 and 20 at %. These heterostructures have several applications in band-engineering and in the field of device structures. Film thicknesses, germanium atomic fractions and tetragonal distortion were determined by three different techniques, i.e. Rutherford Backscattering Spectrometry-Channeling, Analytical Electron Microscopy and Double Crystal X-ray Diffractometry. The good agreement found between the various analytical results demonstrates that each technique is capable of a high level of accuracy and consistency. These characterization methods are therefore powerful tools for the precise control of the epitaxial layer growth parameters for the fabbrication of different device structures.


1991 - CBED STRAIN-MEASUREMENTS IN BORON IMPLANTED SILICON [Articolo su rivista]
Balboni, R; Frabboni, Stefano
abstract

Strain measurements were performed by convergent-beam electron diffraction on both plan-view sample and cross-sections of silicon wafers, boron implanted at liquid nitrogen temperature. In the plan-view specimens, the strain value measured in the boron-doped layer agrees with previous X-ray double crystal diffraction analyses. In the cross-sectioned specimens, a profile of the strain was obtained, showing a difference between the boron-doped layer and the end-of-range, interstitial-rich layer. In the latter samples the quantitative agreement with X-ray measurements is reached when extra-relaxation along the thinning direction is taken into account.


1991 - Electon spectroscopic imaging of dopant precipitation and segregation in silicon [Articolo su rivista]
Frabboni, Stefano; Lulli, G; MERLI P., G; Migliori, A; Bauer, R.
abstract

Conventional, high-resolution electron microscopy and electron spectroscopy imaging methods have been applied to the characterization of furnace-annealed B-implanted Si and self-annealed As-implanted Si. The combination of these techniques allowed us to point out the presence of a coherent precipitation in the SiBx system and the segregation of As at the (111) surfaces of octahedral cavities produced during self-annealing implantation of Si. A simple ideal structural model of the voids with segregated As is proposed.


1991 - INFLUENCE OF IMPLANT DOSE AND TARGET TEMPERATURE ON CRYSTAL QUALITY AND JUNCTION DEPTH OF BORON-DOPED SILICON LAYERS [Articolo su rivista]
Fabbri, R; Servidori, M; Solmi, S; Frabboni, Stefano; Ottaviani, Giampiero; Tonini, Rita; Canteri, R.
abstract

30 keV boron ions are implanted at doses of 2 x 10(14) and 2 x 10(15) cm-2 in <100> silicon wafers kept at room or liquid-nitrogen temperatures. The samples are analyzed by double-crystal X-ray diffraction, transmission electron microscopy and secondary ion-mass spectrometry before and after furnace annealing at 800-degrees-C. The low-dose implant does not amorphize the substrate at any of the temperatures, and residual defects together with a remarkably enhanced boron diffusion are observed after annealing. The high-dose implant amorphizes the substrate only at low temperature. In this case, unlike the room-temperature implant, the absence of any residual defect, the incorporation of the dopant in substitutional position and a negligible profile braodening of boron are obtained after annealing. In principle, this process proves itself a promising step for the fabrication of p+/n shallow junctions with good electrical characteristics.


1991 - Low temperature dopant activation of BF2 implanted silicon [Articolo su rivista]
G., Queirolo; C., Bresolin; D., Robba; M., Anderle; R., Canteri; A., Armigliato; Ottaviani, Giampiero; Frabboni, Stefano
abstract

Boron activation and carrier mobility were measured after low temperature furnace heat treatments, in silicon layers implanted with BF2+ ions at 60 keV and at fluence in the 1 - 5 x 10(15) ions cm-2 range. These quantities were correlated with boron and fluorine chemical depth profiles obtained with secondary ion mass spectrometry (SIMS), and with the lattice defects revealed by transmission electron microscopy (TEM). High dopant activation, well above the extrapolated boron solid solubility, was found for all the fluences investigated after a thermal treatment of 20 min at 600-degrees-C. In the high fluence implanted samples, the solid phase epitaxial regrowth of the amorphous layer induces a severe fluorine redistribution which causes the formation of a defective band at the sample surface containing microtwins and small precipitates; a decrease in both the activated dopant concentration and carrier mobility was found in this region. The comparison with dopant activation data obtained in samples diffused at higher temperature (from 900 to 1000-degrees-C) shows that twins are electrically active only when they are decorated by isolated impurities and/or in presence of very small precipitates.


1990 - DOPANT ACTIVATION, CARRIER MOBILITY, AND TEM STUDIES IN POLYCRYSTALLINE SILICON FILMS [Articolo su rivista]
Queirolo, G; Servida, E; Baldi, L; Pignatel, G; Armigliato, A; Frabboni, Stefano; Corticelli, F.
abstract

Polycrystalline silicon films, deposited by low-pressure chemical vapor deposition at 570° and 620°C, and doped withphosphorus by ion implantation, have been studied in terms of: dopant activation, carrier Hall mobility, and microstructure,as a function of the annealing temperature. Higher activation and carrier mobility were obtained on samples depositedat lower temperature, which were amorphous [by x-ray diffraction and transmission electron microscopy (TEM)] afterthe deposition step, in contrast with those deposited at higher temperature, which were polycrystalline. Transmissionelectron microscopy observations on a cross section showed a better recrystallization of the amorphous films during ahigh-temperature step, and mean grain size values which agree qualitatively with those calculated from grain boundarymobilities.


1989 - Temperature dependence of damage in boron implanted silicon [Relazione in Atti di Convegno]
G., Ottaviani; F., Nava; R., Tonini; Frabboni, Stefano; G. F. CEROFOLINI AND P., Cantoni
abstract

abstract


1988 - Contrast of small SiX particles in silicon by computed HREM images [Articolo su rivista]
Armigliato, A; Bourret, A; Frabboni, Stefano; Parisini, A.
abstract

The contrast in HREM images of small spherical coherent precipitates in silicon, having a hypothetical sphalerite structure and an SiX composition, is computed by the multislice method; X represents a dopant (or impurity) atom, ranging from boron up to platinum. The particles are assumed to have a diameter of 2 nm and to exert different amounts of in situ strain ϵ on the silicon matrix. The ideal case of no misfit (ϵ = 0) is also considered. For in situ strains 0 < ϵ < 2%, the maximum contrast, corresponding to the optimum defocus, depends mainly on the atomic number of the element X. For larger strains, which can occur in some cases if the Si[BOND]X bond length in the SiX particle is determined by the covalent radius of the impurity atom X, the strain contrast dominates over the structure factor contrast.


1988 - On the silicon dioxide/polycrystalline silicon interface width measurement [Articolo su rivista]
G., Queirolo; S., Manzini; L., Meda; M., Anderle; R., Canteri; A., Armigliato; Frabboni, Stefano
abstract

The apparent width of the SiO2[BOND]Si interface was evaluated with Auger electron spectrometry, secondary ions mass spectrometry and transmission electron microscopy for thin silicon dioxide films grown at temperature ranging from 900 to 1100°C, both on single- and poly-crystalline silicon (polysilicon), with the aim of finding the meaning of this kind of measurement for this particular system. The width of the transition between SiO2 and polysilicon was found to depend on both the oxidation temperature and polysilicon doping method, being lower for ion implanted than for gas phase (POCl3) doped samples and for oxides grown at higher temperature. The possible causes for the differences in the interface width are discussed and attributed, in the present case, to the oxide thickness non-uniformity. This is due, in turn, to the lower oxide growth rate, particularly for the lower oxidation temperature, on the silicon grains protruding out of the surface.


1987 - Observations of electrostatic field by electron holography: the case of reverse-biased p-n junctions [Articolo su rivista]
Frabboni, Stefano; G. MATTEUCCI AND G., Pozzi
abstract

The technique of electron holography is applied to the investigation of microelectric fields such as those associated with reverse-biased p-n junctions. Suitable electron-optical conditions were adopted in order to minimize the effect of the electrostatic fringing field on the reference wave. The electron holograms were optically processed by the method of differential interferometry.


1987 - On the visibility of small SiAs particles in silicon by HREM [Relazione in Atti di Convegno]
A., Armigliato; A., Bourret; Frabboni, Stefano; A., Parisini
abstract

Abstract


1985 - Electron holographic observations of the electrostatic field associated with thin reverse-biased p-n junctions [Articolo su rivista]
Frabboni, Stefano; Matteucci, G; Pozzi, G; Vanzi, M.
abstract

A new method has been devised for investigation by TEM of th electrostatic microfield associated with reverse biase p-n junctions. By means of electron holography and optical inteferometry it is possible to obtain on the reconstructed images two-dimensional representations of the projected potential distribution inside and outside the specimen