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DIPENDENTE ALTRO ENTE DI RICERCA presso: Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica

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2021 - Green Fabrication of (6,5)Carbon Nanotube/Protein Transistor Endowed with Specific Recognition [Articolo su rivista]
Berto, M.; Di Giosia, M.; Giordani, M.; Sensi, M.; Valle, F.; Alessandrini, A.; Menozzi, C.; Cantelli, A.; Gazzadi, G. C.; Zerbetto, F.; Calvaresi, M.; Biscarini, F.; Bortolotti, C. A.

A general single-step approach is introduced for the green fabrication of hybrid biosensors from water dispersion. The resulting device integrates the semiconducting properties of a carbon nanotube (CNT) and the functionality of a protein. In the initial aqueous phase, the protein (viz., lysozyme [LZ]) disperses the (6,5)CNT. Drop-casting of the dispersion on a test pattern (a silicon wafer with interdigitated Au source and drain electrodes) yields a fully operating, robust, electrolyte-gated transistor (EGT) in one step. The EGT response to biorecognition is then assessed using the LZ inhibitor N-acetyl glucosamine trisaccharide. Analysis of the output signal allows one to extract a protein-substrate binding constant in line with values reported for the free (without CNT) system. The methodology is robust, easy to optimize, redirectable toward different targets and sets the grounds for a new class of CNT-protein biosensors that overcome many limitations of the technology of fabrication of CNT biosensors.

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

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 - 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

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 - 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

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.

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.

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

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

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

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 - 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

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

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.

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

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.

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

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.

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.

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

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

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

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 - 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

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.

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

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

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 - Electron Interference via a 4096-Pixel <newline/>MAPS Detector Designed for <newline/>High-Energy Physics Experiments [Articolo su rivista]
Balbi, G.; Frabboni, S.; Gabrielli, A.; Gazzadi, gian carlo; Giorgi, F. M.; Matteucci, G.; Semprini, N.; Villa, M.; Zoccoli, A.

A conventional transmission electron microscope is used as a versatile optical bench in a setup where a pixel recording system, sensitive to single electrons, replaces the final viewing screen. Our detector is based on a custom CMOS chip of 4096 monolithic active pixels designed for applications in vertex detectors of future collider experiments. The chip is equipped with a fast read-out chain able to manage up to 10(6) frames per second. This capability permitted to collect high statistics samples of single electron events within a time interval where the stable operations and the coherence conditions of the microscope were guaranteed. The microscope was configured with an accelerating potential of 60 kV, hence leading to 60 keV electrons. The large fraction of empty events made possible to obtain measurements of the time distribution of electron arrivals and this is what really characterizes this work. In fact, for the first time, conventional interference patterns have been split into single-electron frames according to the time of arrival. In particular, the 4096-pixel sensor has been used to collect diffraction patterns of a single wire, a carbon grating and eventually to reproduce the Young-Feynman two-slit experiment with single electrons instead of light. The experiment has been carried out by inserting two nanometric slits-two 100 x 1500 nm slits, 500 nm spaced apart-in the microscope that provided the electron beam source and the electro-optical lenses for projecting and focusing the pattern on the sensor. The fast readout of the sensor allowed us to record single-electron frames, spaced by several empty frames, and this is an improvement over past single-electron interference works. In this way the time distribution of the single electron arrivals has been measured with a timing resolution of 160 mu s. This research might also open new detector investigation and development and characterization of pixel sensors.

2013 - Mechanism of lustre formation in scheelite-based glazes [Articolo su rivista]
Gualtieri, Alessandro; Canovi, Lorenzo; Viani, Alberto; Bertocchi, Paolo; Corradini, Cecilia; Gualtieri, Eva Magdalena; Gazzadi, gian carlo; Zapparoli, Mauro; Berthier, Serge

This work elucidates the mechanism responsible for the lustre effect of scheelite-based glazes for single-firing wall tiles. The surface decoration is obtained with a thin film composed of a Si–Ca–Zn–Al–K–B frit and 10 wt% WO3 on zircon-engobed substrates for single-firing wall tiles (maximum temperature of 1130 °C for 50 min). The observed lustre effect is sub-adamantine and pearlescent. It is sub-adamantine because scheelite nanocrystals at the surface, with a relatively high refractive index (n = 1.93), cause considerable reflection of light. The lustre is also weakly pearlescent because the nano-crystals oriented with the (004) plane parallel to the surface give interference with the underlying glassy layer (n ≈ 1.5), where randomly dispersed scheelite crystals occur. This model apparently applies to the glazes decorated with ceria, although the latter exhibits iridescence due to the high refractive index of ceria (n = 2.05) which yields stronger interference effect with the underlying glassy substrate.

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

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 - Origin of Hydrophobicity in FIB-Nanostructured Si Surfaces [Articolo su rivista]
ROTA, Alberto; TRIPATHI, MANOJ; GAZZADI, gian carlo; VALERI, Sergio

Surface morphology has been demonstrated to influence the tribological properties at different scales, but the phenomena which occur at the nano-scale have not been completely understood. The present study reports on the effect of Focused Ion Beam nano-patterning on coefficient of friction (CoF) and adhesion of Si(001) surface covered by native oxide. Regular arrays of nano-grooves reduce both CoF and adhesion, related to a hydrophobic character of the patterned surface, but this effect disappears as soon as the separation among the nano-structures approaches the microscopic scale. The dependence of this hydrophobic effect on the pitch is not linked to the corresponding contact area. It has been found that each nano-structure is surrounded by a low-friction region which extends some hundreds nm from it. For pitch of 125 and 250nm these low-friction regions completely overlap, generating a consistent decrease in CoF and adhesion, while for pitch of 500 and 1000nm its effect is negligible. The low-friction regions were not observed in humidity free ambient, indicating that they are the origin of patterns hydrophobicity.

2013 - Tribology of patterned Si surface from the nano-to the micro-scale [Articolo su rivista]
Rota, A.; Tripathi, M.; Gazzadi, G. C.; Valeri, S.

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

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.

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

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 - 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

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 - 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

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 - Laterally confined magnetic nanometric structures [Capitolo/Saggio]
Valeri, Sergio; DI BONA, Alessandro; Gazzadi, gian carlo

Basic and applied aspects of magnetic nanostructures are presented and discussed, with emphasis on the state of the art fabrication methods and modeling.

2010 - Hydrophobic effect of surface patterning on Si surface [Articolo su rivista]
Marchetto, Diego; Rota, Alberto; L., Calabri; Gazzadi, Gian Carlo; Menozzi, Claudia; Valeri, Sergio

Adhesion and friction force between flat Si tip and nano-patterned Si surface have been investigated byatomic force microscopy (AFM) in air and high vacuum conditions (10−5 Torr) at room temperature (RT) and at 180 ◦C. The pattern consists of parallel grooves realized on a Si(0 0 1) single crystal by focused ion beam (FIB) milling. The FIB technique was also used to modify a commercial AFM Si probe in order to obtain a flat tip, suitable for tribological characterization of patterned surfaces, since it presents an extended contact area. In high vacuum the coefficient of friction (CoF) on the pristine surface is about 64% lower than in ambient condition, related to the presence of a water meniscus. The situation is completely different on the patterned surface where CoF does not change appreciably in the different analyzed conditions. The adhesive force related to the presence of a water layer is lower on the patterned surface with respect to the pristine surface. These findings suggest that patterning induces a hydrophobic character to the Si surface. © 2009 Elsevier B.V. All rights reserved.

2007 - Focused ion beam patterned Hall nano-sensors [Articolo su rivista]
Candini, A.; Gazzadi, G. C.; di Bona, A.; Affronte, M.; Ercolani, D.; Biasiol, G.; Sorba, L.

By means of focused ion beam milling, we fabricate Hall magnetometers with active areas as small as 100 × 100 nm2. The constituent material can either be metallic (Au), semimetallic (Bi) or doped bulk semiconducting (Si doped GaAs). We experimentally show that Au nano-probes can work from room temperature down to liquid helium with magnetic flux sensitivity &lt; 10- 1 Φ0. © 2006 Elsevier B.V. All rights reserved.

1997 - Early stage in low-energy ion-induced damage on InP(110) surface [Articolo su rivista]
Valeri, Sergio; Gazzadi, gian carlo; Rota, Alberto; DI BONA, Alessandro

The change in the short-range order created by ion milling in the near surface region of InP single crystals wasinvestigated by primary beam diffraction modulated electron emission (PDMEE). The very early stage of the damagecreation by low energy (0.6-1 keV) Ar ions in normal and oblique incidence was studied. A simple model based on theweighted combination of perfectly crystalline and completely amorphous regions was used to model the experimental results.Evidence of a subsurface nucleation of the amorphization process was found. We also found that the total sputtering yield ismarkedly dependent on the ion dose, being on the undamaged surface much larger than its steady state value. Low energyelectron diffraction (LEED) measurements were also performed to correlate long-range and short-range order removal by ionbombardment. Finally, the ion damage on the GaAs and InP surfaces was comparatively discussed.