Nuova ricerca

Raffaella CAPELLI

Professore Associato
Dipartimento di Ingegneria "Enzo Ferrari"

Home | Curriculum(pdf) | Didattica |


Pubblicazioni

2023 - Growth Dynamics of Ultrathin Films of Benzo[1,2-b:4,5-b']dithiophene Derivatives on Au(111): A Photoelectron Spectroscopy Investigation [Articolo su rivista]
Stummo, Angelo; Montecchi, Monica; Parenti, Francesca; Vanossi, Davide; Fontanesi, Claudio; Capelli, Raffaella; Pasquali, Luca
abstract

: Ultrathin films of a stereoisomeric mixture of benzo[1,2-b:4,5-b']dithiophene derivatives were grown by thermal evaporation in vacuum on Au(111), and they were studied in situ by photoelectron spectroscopy. X-ray photons from a non-monochromatic Mg Kα conventional X-ray source and UV photons from a He I discharge lamp equipped with a linear polarizer were used. He I photoemission results were compared with density functional theory (DFT) calculations: density of states (DOS) and 3D molecular orbital density distribution. Au 4f, C 1s, O 1s, and S 2p core-level components suggest a surface rearrangement as a function of film nominal thickness, with the variation of the molecular orientation, from flat-laying at the initial deposition to tilted toward the surface normal at coverages exceeding 2 nm. Eventually, the DFT results were exploited in assigning of the valence band experimental structures. Moreover, polarization-dependent photoemission confirmed the tilted arrangement of the molecules, starting at 2 nm. A variation of the work function of 1.4 eV with respect to the clean substrate was measured, together with a valence band offset of 1.3 eV between the organic layer and gold.

2023 - Influence of chirality on the aggregation of a new A-π-D-π-A small molecule with a benzodithiophene core: Spectroscopic and morphological investigations [Articolo su rivista]
Parenti, Francesca; Capelli, Raffaella; Mucci, Adele; Mortalò, Cecilia; Paolicelli, Guido; Pigani, Laura; Vanossi, Davide; Caselli, Monica
abstract

2022 - Electrical conduction and noise spectroscopy of sodium-alginate gold-covered ultrathin films for flexible green electronics [Articolo su rivista]
Barone, Carlo; Maccagnani, Piera; Dinelli, Franco; Bertoldo, Monica; Capelli, Raffaella; Cocchi, Massimo; Seri, Mirko; Pagano, Sergio
abstract

: Green electronics is an emerging topic that requires the exploration of new methodologies for the integration of green components into electronic devices. Therefore, the development of alternative and eco-friendly raw materials, biocompatible and biodegradable, is of great importance. Among these, sodium-alginate is a natural biopolymer extracted from marine algae having a great potential in terms of transparency, flexibility, and conductivity, when functionalized with a thin gold (Au) layer. The electrical transport of these flexible and conducting substrates has been studied, by DC measurements, from 300 to 10 K, to understand the interplay between the organic substrate and the metallic layer. The results were compared to reference bilayers based on polymethyl-methacrylate, a well-known polymer used in electronics. In addition, a detailed investigation of the electric noise properties was also performed. This analysis allows to study the effect of charge carriers fluctuations, providing important information to quantify the minimum metallic thickness required for electronic applications. In particular, the typical noise behavior of metallic compounds was observed in samples covered with 5 nm of Au, while noise levels related to a non-metallic conduction were found for a thickness of 4.5 nm, despite of the relatively good DC conductance of the bilayer.

2021 - Analysis of Resonant Soft X-ray Reflectivity of Anisotropic Layered Materials [Articolo su rivista]
Pasquali, Luca; Mahne, Nicola; Giglia, Angelo; Verna, Adriano; Sponza, Lorenzo; Capelli, Raffaella; Bonfatti, Matteo; Mezzadri, Francesco; Galligani, Emanuele; Nannarone, Stefano
abstract

We present here a method for the quantitative prediction of the spectroscopic specular reflectivity line-shape in anisotropic layered media. The method is based on a 4 × 4 matrix formalism and on the simulation from the first principles (through density functional theory—DFT) of the anisotropic absorption cross-section. The approach was used to simulate the reflectivity at the oxygen K-edge of a 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) thin film on Au(111). The effect of film thickness, orientation of the molecules, and grazing incidence angle were considered. The simulation results were compared to the experiment, permitting us to derive information on the film geometry, thickness, and morphology, as well as the electronic structure.

2021 - Electric transport in gold-covered sodium–alginate freestanding foils [Articolo su rivista]
Barone, C.; Bertoldo, M.; Capelli, R.; Dinelli, F.; Maccagnani, P.; Martucciello, N.; Mauro, C.; Pagano, S.
abstract

The electric transport properties of flexible and transparent conducting bilayers, realized by sputtering ultrathin gold nanometric layers on sodium–alginate free-standing films, were studied. The reported results cover a range of temperatures from 3 to 300 K. In the case of gold layer thicknesses larger than 5 nm, a typical metallic behavior was observed. Conversely, for a gold thickness of 4.5 nm, an unusual resistance temperature dependence was found. The dominant transport mechanism below 70 K was identified as a fluctuation-induced tunneling process. This indicates that the conductive region is not continuous but is formed by gold clusters embedded in the polymeric matrix. Above 70 K, instead, the data can be interpreted using a phenomenological model, which assumes an anomalous expansion of the conductive region upon decreasing the temperature, in the range from 300 to 200 K. The approach herein adopted, complemented with other characterizations, can provide useful information for the development of innovative and green optoelectronics.

2021 - Enhanced gold adhesion on sodium alginate films for green electronics: study of the role of oxygenated functional groups [Poster]
Lorenzi, Francesco; Capelli, Raffaella; Mortalò, Cecilia; Mucci, Adele; Parenti, Francesca
abstract

Sodium alginate (SA) is a natural widespread polysaccharide whose constitutional repeating unit is made of alternating mannuronic and guluronic moieties. Transparent, freestanding and flexible films can be obtained from aqueous solutions of SA, making this green polymer very appealing for several uses [1]. When green electronic components are concerned, a thin gold conducting layer with outstanding adhesion can be deposited on SA flexible substrates by sputtering techniques [2]. In fact, as evidenced by a scotch tape test, the adhesion of the metal layer on SA is much stronger than that observed when the thermal evaporation technique is used for Au deposition. To gain insights on the origin of this strong interaction and to understand if it is more of a chemical or physical nature, here we synthesize a series of hydrophobically modified SAs bearing amide or ester groups in place of the carboxyl and/or the hydroxyl groups of the backbone, which are supposed to form complexes with gold. After thoroughly characterization of the polymers, by IR, 1H and 13C NMR spectroscopies, thermogravimetric and elemental analysis, we obtained modified SAs films which were covered whit a thin gold layer by sputtering techniques. [1] X. Guo et al. Int. J. Biol. Macromol. 162 (2020) 618–628. [2] P. Maccagnani et al. Adv. Sustainable Syst. 1900001 (2019).

2021 - Fully Recyclable OLEDs Built on a Flexible Biopolymer Substrate [Articolo su rivista]
Cocchi, M.; Bertoldo, M.; Seri, M.; Maccagnani, P.; Summonte, C.; Buoso, S.; Belletti, G.; Dinelli, F.; Capelli, R.
abstract

This is the “mobile” era, characterized by a growing demand of flexible substrates for novel products such as curved screens, folding smartphones, and wearable devices. In this framework, plastic electronics represents a suitable technology to replace silicon-based electronics. However, up to now, little attention has been devoted to rendering this technology more environmentally sustainable. It is thus necessary to develop new eco-designed devices that allow recycling of all the components and recovering the valuable materials through sustainable methods. For the first time, we report the fabrication of organic light emitting diodes made on an as-cast biopolymeric flexible substrate. Sodium alginate is a natural biodegradable polymer derived from brown algae; it is water-soluble and easy to manipulate for the realization of flat and transparent foils using an environmentally friendly process. Thus, the active stack can be directly deposited on the biopolymer substrate in a bottom-up architecture with no need for a pretreatment or a buffer layer. In addition, the devices can be disassembled and all of the valuable materials almost entirely recovered. This result opens up new and exciting opportunities for the fabrication of electronic and optoelectronic devices with a green platform for an ambient sustainable circular economy.

2021 - Production Strategies of TiNx Coatings via Reactive High Power Impulse Magnetron Sputtering for Selective H2 Separation [Articolo su rivista]
Mortalò, Cecilia; Deambrosis, Silvia Maria; Montagner, Francesco; Zin, Valentina; Fabrizio, Monica; Pasquali, Luca; Capelli, Raffaella; Montecchi, Monica; Miorin, Enrico
abstract

This scientific work aims to optimize the preparation of titanium nitride coatings for selective H-2 separation using the Reactive High Power Impulse Magnetron Sputtering technology (RHiPIMS). Currently, nitride-based thin films are considered promising membranes for hydrogen. The first series of TiNx/Si test samples were developed while changing the reactive gas percentage (N-2%) during the process. Obtained coatings were extensively characterized in terms of morphology, composition, and microstructure. A 500 nm thick, dense TiNx coating was then deposited on a porous alumina substrate and widely investigated. Moreover, the as-prepared TiNx films were heat-treated in an atmosphere containing hydrogen in order to prove their chemical and structural stability; which revealed to be promising. This study highlighted how the RHiPIMS method permits fine control of the grown layer's stoichiometry and microstructure. Moreover, it pointed out the need for a protective layer to prevent surface oxidation of the nitride membrane by air and the necessity to deepen the study of TiNx/alumina interface in order to improve film/substrate adhesion.

2021 - Resonant Soft X-ray Reflectivity in the Study of Magnetic Properties of Low-Dimensional Systems [Articolo su rivista]
Verna, Adriano; Capelli, Raffaella; Pasquali, Luca
abstract

In this review, the technique of resonant soft X-ray reflectivity in the study of magnetic low-dimensional systems is discussed. This technique is particularly appealing in the study of magnetization at buried interfaces and to discriminate single elemental contributions to magnetism, even when this is ascribed to few atoms. The major fields of application are described, including magnetic proximity effects, thin films of transition metals and related oxides, and exchange-bias systems. The fundamental theoretical background leading to dichroism effects in reflectivity is also briefly outlined.

2019 - Flexible Conductors from Brown Algae for Green Electronics [Articolo su rivista]
Maccagnani, Piera; Bertoldo, Monica; Dinelli, Franco; Murgia, Mauro; Summonte, Caterina; Ortolani, Luca; Pizzochero, Giulio; Verucchi, Roberto; Collini, Cristian; Capelli, Raffaella
abstract

In this paper a novel approach is presented to prepare flexible and transparent conducting films, whose components can be separated and recovered via a recycling process. The fabrication method is based on low power sputtering of ultrathin gold layers on sodium alginate free-standing films. The resulting foils are thin, easy to handle, and shape, while showing good conductive properties. In particular, they show excellent resistance to mechanical stress, like bending or rubbing, and are highly stable in ambient atmosphere over several months. Therefore they may represent a very promising candidate to be employed in green electronics, thanks to the reduced energy consumption required for their fabrication, the absence of toxic components or chemicals that are derived from oil, and the possibility to disassemble the devices at the end of their life in environmentally friendly conditions.

2019 - Interpretation of linear dichroism at S L2,3 x-ray absorption edges of small organic molecules at surfaces [Articolo su rivista]
Capelli, Raffaella; Pasquali, Luca
abstract

Resonant soft x-ray absorption was applied at the S L2,3 (2p) edges of thin films of 1,4-benzenedimethanethiol (BDMT) on gold and of sexithiophene (6 T) on flat and patterned CaF2 surfaces. Linear dichroism effects were clearly observed depending on the orientation of the electric field vector of the incoming radiation. They were related to the organization of the molecules. For the interpretation of the angular dependencies of the spectral features, density functional theory (DFT) simulations of the absorption cross sections were calculated. It was possible to confirm the generally accepted chemisorption geometry of BDMT on Au(111), composed of molecules nearly vertical at the surface with one of the S atoms participating in the bonding with Au and the other left pending at the outermost surface and contributing mostly to the measured x-ray absorption. For 6 T on CaF2 a new chemisorption phase was identified on ridge-patterned CaF2(110), coexisting with a previously known phase given by 6 T crystallites highly oriented along the ridges. The new phase being composed of molecules oriented perpendicular to the ridges and lying on their edges.

2019 - Quantitative resonant soft x-ray reflectivity from an organic semiconductor single crystal [Articolo su rivista]
Capelli, R.; Da Como, E.; Kociok-Köhn, G.; Fontanesi, C.; Verna, A.; Pasquali, L.
abstract

Resonant soft X-ray reflectivity at the carbon K-edge was applied to a trigonal tetracene single crystal. The angular resolved reflectivity was quantitatively simulated describing the tetracene crystal in terms of its dielectric tensor, which was derived from the anisotropic absorption cross section of the single molecule, as calculated by density functional theory. A good agreement was found between the experimental and theoretically predicted reflectivity. This allows us to assess the anisotropic optical constants of the organic material, probed at the carbon K-edge, in relation to the bulk/surface structural and electronic properties of the crystal, through empty energy levels.

2019 - Understanding adhesion of gold conductive films on sodium-alginate by photoelectron spectroscopy [Articolo su rivista]
Capelli, Raffaella; Maccagnani, Piera; Dinelli, Franco; Murgia, Mauro; Bertoldo, Monica; Montecchi, Monica; Doyle, Bryan P.; Carleschi, Emanuela; Pasquali, Luca
abstract

Ultrathin layers of gold, from 2 to 25 nm of nominal coverage, have been deposited on sodium-alginate biopolymer foils applying two alternative approaches: low power sputtering and thermal evaporation. The morphology of the deposited layers was obtained by means of atomic force microscopy. In the early stages of growth, thermal evaporation gives rise to a top surface resembling the underlying substrate, whereas low power sputtering produces a topography characterized by smoother areas. This indicates that the film growth occurs in different ways. X-ray photoelectron spectroscopy with two photon energies, corresponding to Al Kα and Ag Lα photons, was used to get information on the chemistry at the interface and on the degree of intermixing between Au and sodium-alginate. While no chemical modifications with respect to the bare materials could be detected, the evolution of the intensities of the relevant core levels of Au and sodium alginate (Au 4f and Na 1s in particular) indicated a strong intermixing in the case of films deposited by low power sputtering. This is further supported by optical measurements. The observed behaviour can be correlated with the enhanced adhesion of sputtered films compared to thermally evaporated ones.

2018 - 3D reconstruction of pentacene structural organization in top-contact OTFTs via resonant soft X-ray reflectivity [Articolo su rivista]
Capelli, Raffaella; Nardi, Marco Vittorio; Toccoli, Tullio; Verucchi, Roberto; Dinelli, Franco; Gelsomini, Carolina; Koshmak, Konstantin; Giglia, Angelo; Nannarone, Stefano; Pasquali, Luca
abstract

Herein, we describe the use of soft X-ray reflectivity at the carbon K-edge to study the molecular organization (orientation, structure, and morphology) of pentacene active films in a top-contact transistor geometry. This technique is not affected by sample charging, and it can be applied in the case of insulating substrates. In addition, the sampling depth is not limited to the near-surface region, giving access to buried device interfaces (metal/organic and dielectric/organic). Spectral lineshape simulations, based on ab-initio calculations using a realistic 3D layer-by-layer model, allow us to unravel the details of the molecular organization in all the specific and crucial areas of the active film, overcoming the limitations of conventional approaches. The tilt angle of the long molecular axis in the whole film is found to progressively decrease with respect to the substrate normal from 25° to 0° with the increasing film thickness. A full vertical alignment, optimal for in-plane charge hopping, is reached only after the complete formation of the first five monolayers. Remarkably, starting from the first one in contact with the dielectric substrate, all the monolayers in the stack show a change in orientation with the increasing thickness. On the other hand, at the buried interface with a gold top-contact, the molecules assume a flat orientation that only propagates for two or three monolayers into the organic film. Top-contact devices with the highest performances can thus be obtained using films of at least ten monolayers. This explains the observed thickness dependence of charge mobility in pentacene transistors.

2018 - Gold Nanoparticles on Sodium Alginate: Simulation of Optical Properties [Relazione in Atti di Convegno]
Summonte, C.; Maccagnani, P.; Desalvo, A.; Bolognini, G.; Ortolani, L.; Sanmartin, M.; Capelli, R.; Bertoldo, M.; Dinelli, F.
abstract

UV-visible spectrophotometric properties of gold nanoparticles fabricated by magnetron sputtering on freestanding sodium alginate (SA) membranes have been recorded and simulated. The simulation implied the tuning of the collision frequency as well as the introduction of the Local Surface Plasmon (LSP) resonance in optical constants of the nanostructured material, which are based on a Drude- Lorentz model. The nanostructured film is treated by means of the Effective Medium Approximation. The film stack is simulated using the Generalized Transfer Matrix Method. The results show that the actual material can properly be treated, and quantitative results are obtained. A red shift in the LSP spectral position is observed for more interconnected material.

2017 - Controlling In-Plane Isotropic and Anisotropic Orientation of Organic Semiconductor Molecules on Ionic Fluoride Dielectrics [Articolo su rivista]
Jiang, Tingming; Koshmak, Konstantin; Giglia, Angelo; Banshchikov, Alexander; Sokolov, Nikolai S.; Dinelli, Franco; Capelli, Raffaella; Pasquali, Luca
abstract

alpha-Sexithiophene (6T) ultrathin films have been grown on CaF2(111)/Si(111) planar surfaces and on CaF2(110)/Si(001) ridged surfaces by molecular beam epitaxy. The growth mode has been studied by means of atomic force microscopy (AFM), photoemission, and near edge X-ray absorption fine structure (NEXAFS). AFM reveals a substantial difference in the film morphology on the two substrates: on CaF2(111) large islands with flat terraces form with no in-plane preferential growth direction; on CaF2(110) narrow and elongated islands develop following the substrate corrugation. Photoemission and X-ray absorption at Ca L-2,L-3 and F K edges indicate that the interaction with the substrate is negligible. Near-edge X-ray absorption (NEXAFS) flanked by DFT calculations of the angular-resolved absorption cross section of 6T at the carbon K-edge reveal that the molecules on both substrates have their long axis vertically oriented with respect to the substrate plane. In addition, in-plane anisotropy of the molecular orientation has been observed on CaF2(110), and it has been interpreted in terms of well aligned molecules in the elongated islands.

2016 - Chapter One - Interference of Light and of Material Particles: A Departure from the Superposition Principle [Articolo su rivista]
Castañeda, R; Matteucci, G; Capelli, R
abstract

Interference of light and material particles is described in this chapter with a unified model, which does not need to assume the superposition principle. A moving particle is associated with a region of spatial correlated points called a coherence cone. Its geometry depends on photon or material particle momentum and on the parameters of the experimental setup. The coherence cone geometry causes the spatial distribution of particles in preferential directions. After propagation, particles accumulate on the final observation plane to form interference peaks. In the context given here, the wave front superposition principle, wave–particle duality, and wave collapse are no longer significant. In addition, the present model describes light and material particle distributions in near- and far-field regions and in paraxial and nonparaxial approximations so that the paraxial Fourier and Wigner optics are included, as particular cases, in our more general model. Fits of observed single-electron and single-molecule interference patterns, together with the simulations of expected near-field molecule interferences, demonstrate the model validity. An interference experiment is suggested to realize molecular nanostructures with a vacuum sublimation process controlled by a shadow mask. A new scenario is envisaged to miniaturize electronic devices and to realize individual noninteracting nanodomains of well-chosen thickness.

2016 - Quantitative resonant soft x-ray reflectivity of ultrathin anisotropic organic layers: Simulation and experiment of PTCDA on Au [Articolo su rivista]
Capelli, R.; Mahne, N.; Koshmak, K.; Giglia, A.; Doyle, B. P.; Mukherjee, S.; Nannarone, S.; Pasquali, Luca
abstract

Resonant soft X-ray reflectivity at the carbon K edge, with linearly polarized light, was used to derive quantitative information of film morphology, molecular arrangement, and electronic orbital anisotropies of an ultrathin 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) film on Au(111). The experimental spectra were simulated by computing the propagation of the electromagnetic field in a trilayer system (vacuum/PTCDA/Au), where the organic film was treated as an anisotropic medium. Optical constants were derived from the calculated (through density functional theory) absorption cross sections of the single molecule along the three principal molecular axes. These were used to construct the dielectric tensor of the film, assuming the molecules to be lying flat with respect to the substrate and with a herringbone arrangement parallel to the substrate plane. Resonant soft X-ray reflectivity proved to be extremely sensitive to film thickness, down to the single molecular layer. The best agreement between simulation and experiment was found for a film of 1.6 nm, with flat laying configuration of the molecules. The high sensitivity to experimental geometries in terms of beam incidence and light polarization was also clarified through simulations. The optical anisotropies of the organic film were experimentally determined and through the comparison with calculations, it was possible to relate them to the orbital symmetry of the empty electronic states.

2015 - Multilayer structure of an OLET transistor [Brevetto]
Capelli, R
abstract

The present invention refers to a multilayer structure of an OLET transistor. More specifically the invention relates to a multilayer structure of an OLET transistor realized on at least one substrate, comprising at least one emissive organic layer and provided with a first and a second injection electrode and a control electrode. The invention also refers to an elementary emissive unit or sub-pixel comprising, as emissive element, an OLET transistor and to a display comprising a matrix configuration of such elementary emissive units. The invention relates, in particular but not exclusively, to a multilayer structure of an OLET transistor designed to form a viewing screen or display realized using organic technology, and the description below is provided with reference to this application sector with the sole aim of simplifying illustration thereof.

2014 - Architettura di cella fotovoltaica basata su materiale organico [Brevetto]
Capelli, R
abstract

La presente invenzione fa riferimento ad una architettura di cella fotovoltaica. Più specificatamente l'invenzione si riferisce ad una architettura di cella fotovoltaica a struttura planare comprendente una regione attiva realizzata su un substrato mediante una sovrapposizione di almeno un primo ed un secondo strato organico sovrapposti ed in contatto in corrispondenza di almeno una regione di interfaccia ed avente almeno un primo ed un secondo elettrodo di raccolta di buche ed elettroni, rispettivamente. L'invenzione fa altresì riferimento ad un pannello fotovoltaico piano.

2014 - ITO-Free Organic Light-Emitting Transistors with Graphene Gate Electrode [Articolo su rivista]
Soldano, C; Stefani, A; Biondo, V; Basiricò, L; Turatti, G; Generali, G; Ortolani, L; Morandi, V; Veronese, G P; Rizzoli, R; Capelli, R; Muccini, M
abstract

n this work, we report on the fabrication and characterization of organic light-emitting transistors (OLETs) within an indium–tin-oxide (ITO)-free platform, using graphene-based transparent conductive electrodes in place of ITO as gate electrode. A direct comparison between twin bottom-gate/top-contacts OLETs, where a standard ITO layer is replaced with a film made of a few graphene layers, shows that comparable electrical characteristics can be obtained along with a clear improvement in the electroluminescence generation characteristics. Our experimental findings pave the way to the exploitation of graphene-based transparent conductive electrodes within this class of emerging devices on flexible substrates, further promoting the novel era of flexible organic electronics.

2014 - Interface Functionalities in Multilayer Stack Organic Light Emitting Transistors (OLETs) [Articolo su rivista]
Capelli, R.; Dinelli, F.; Gazzano, M.; D’Alpaos, R.; Stefani, A.; Generali, G.; Riva, M.; Montecchi, Monica; Giglia, A.; Pasquali, Luca
abstract

Herein is described a multidisciplinary approach to understand the per- formance limitations of small molecule organic light emitting transistors (OLETs) based on a layered architecture, an innovative architecture poten- tially competitive with the state of the art and more flexible for spectral emis- sion control. The processes of charge injection and field-effect transport at metal/organic and organic/organic interfaces are analysed using microscopic and spectroscopic techniques in coordination. Atomic force microscopy and ultrasonic force microscopy are employed to characterize the interface mor- phology and the initial growth stages of organic films where charge transport actually occurs. X-ray diffraction and near edge X-ray dichroic absorption with linearly polarised light allow to determine the unit cell packing and the molecular orientation at the active organic interfaces, as well as the amount of non-ordered domains. Moreover, chemical reactivity at the interfaces are measured by X-ray photoelectron spectroscopy. It is found that a strong reac- tion occurs at the metal-organic interfaces, with molecular fragmentation. Additionally, the transport properties strongly depend on the nature of the materials forming the organic stack. Specifically, amorphous conjugated films as bottom layers can promote an increased molecular disorder in the upper active layer, with a concomitant deterioration of the conduction properties.

2014 - Mapping of Charge Distribution in Organic Field-Effect Transistors by Confocal Photoluminescence Electromodulation Microscopy [Articolo su rivista]
Koopman, W A; Toffanin, S; Natali, M; Troisi, S; Capelli, R; Biondo, V; Stefani, A; Muccini, M
abstract

A novel method for mapping the charge density spatial distribution in organic field-effect transistors based on the electromodulation of the photoluminescence is demonstrated. In field-effect transistors exciton quenching is dominated by exciton–charge carrier interaction so that it can be used to map the charge distribution in different operating conditions. From a quantitative analysis of the photoluminescence quenching, the thickness of the charge carrier accumulation layer is derived. The injection of minority charge carriers in unipolar conditions is unexpectedly evidenced, which is not displayed by the electrical characteristics.

2014 - Perfluoroalkyl-Functionalized Thiazole–Thiophene Oligomers as N-Channel Semiconductors in Organic Field-Effect and Light-Emitting Transistors [Articolo su rivista]
Usta, H; Sheets, W C; Denti, M; Generali, G; Capelli, R; Lu, S; Yu∥, X; Muccini, M; Facchetti, A
abstract

Despite their favorable electronic and structural properties, the synthetic development and incorporation of thiazole-based building blocks into n-type semiconductors has lagged behind that of other π-deficient building blocks. Since thiazole insertion into π-conjugated systems is synthetically more demanding, continuous research efforts are essential to underscore their properties in electron-transporting devices. Here, we report the design, synthesis, and characterization of a new series of thiazole–thiophene tetra- (1 and 2) and hexa-heteroaryl (3 and 4) co-oligomers, varied by core extension and regiochemistry, which are end-functionalized with electron-withdrawing perfluorohexyl substituents. These new semiconductors are found to exhibit excellent n-channel OFET transport with electron mobilities (μe) as high as 1.30 cm2/(V·s) (Ion/Ioff > 106) for films of 2 deposited at room temperature. In contrary to previous studies, we show here that 2,2′-bithiazole can be a very practical building block for high-performance n-channel semiconductors. Additionally, upon 2,2′- and 5,5′-bithiazole insertion into a sexithiophene backbone of well-known DFH-6T, significant charge transport improvements (from 0.001–0.021 cm2/(V·s) to 0.20–0.70 cm2/(V·s)) were observed for 3 and 4. Analysis of the thin-film morphological and microstructural characteristics, in combination with the physicochemical properties, explains the observed high mobilities for the present semiconductors. Finally, we demonstrate for the first time implementation of a thiazole semiconductor (2) into a trilayer light-emitting transistor (OLET) enabling green light emission. Our results show that thiazole is a promising building block for efficient electron transport in π-conjugated semiconductor thin-films, and it should be studied more in future optoelectronic applications.

2014 - Structure–property relationships in multifunctional thieno(bis)imide-based semiconductors with different sized and shaped N-alkyl ends [Articolo su rivista]
Melucci, M; Durso, M; Bettini, C; Gazzano, M; Maini, L; Toffanin, S; Cavallini, S; Cavallini, M; Gentili, D; Biondo, V; Generali, G; Gallino, F; Capelli, R; Muccini, M
abstract

The relationships between the molecular structure, packing modalities, charge mobility and light emission in organic thin films is a highly debated and controversial issue, with both fundamental and technological implications in the field of organic optoelectronics. Thieno(bis)imide (TBI) based molecular semiconductors provide an interesting combination of good processability, tunable self-assembly, ambipolar charge transport and electroluminescence, and are therefore an ideal test base for fundamental studies on the structure–property correlation in multifunctional molecular systems. Herein, we introduce a new class of thieno(bis)imide quaterthiophenes having alkyl side chains of different shapes (linear, cyclic, branched) and lengths (C1–C8). We found that contrarily to what is generally observed in most molecular semiconductors, the length of the alkyl substituent does not affect the optical, self-assembly and charge transport properties of TBI materials. However, different electroluminescence powers are observed by increasing the alkyl side, this suggesting a potential tool for the selective modulation of TBI functionalities. A deep experimental and theoretical investigation on this new family of TBI materials is provided.

2014 - Struttura integrata di un dispositivo fotosensore basato su materiale organico e relativa architettura circuitale di pixel [Brevetto]
Capelli, R
abstract

La presente invenzione fa riferimento ad una struttura integrata di un dispositivo fotosensore basato su materiale organico. Più specificatamente l'invenzione si riferisce ad una struttura integrata di un dispositivo fotosensore comprendente un core attivo multistrato nella forma di un’eterogiunzione organica comprendente la sovrapposizione di almeno un primo ed un secondo strato organico attivo ed almeno un primo ed un secondo elettrodo di controllo denominati di source e drain, rispettivamente, in contatto con almeno uno di detti primo e secondo strato organico attivo. L'invenzione fa altresì riferimento ad una architettura circuitale di pixel comprendente almeno un dispositivo fotosensore realizzato mediante una tale struttura integrata. L'invenzione riguarda in particolare, ma non esclusivamente, un dispositivo fotosensore adatto a realizzare matrici di pixel per dispositivi di acquisizione di immagini e la descrizione che segue è fatta con riferimento a questo campo di applicazione con il solo scopo di semplificarne l'esposizione.

2014 - Struttura multistrato di un transistore OLET [Brevetto]
Capelli, R
abstract

La presente invenzione fa riferimento ad una struttura multistrato di un transistore OLET. Più specificatamente l'invenzione si riferisce ad una struttura multistrato di un transistore OLET realizzata su almeno un substrato, comprendente almeno uno strato organico emissivo e dotata di un primo e di un secondo elettrodo di iniezione e di un elettrodo di controllo. L'invenzione fa altresì riferimento ad una unità emissiva elementare o sub-pixel comprendente come elemento emissivo un transistore OLET e ad un display comprendente una configurazione a matrice di unità emissive elementari siffatte. L'invenzione riguarda in particolare, ma non esclusivamente, una struttura multistrato di un transistore OLET adatta a realizzare uno schermo di visualizzazione o display in tecnologia organica e la descrizione che segue è fatta con riferimento a questo campo di applicazione con il solo scopo di semplificarne l'esposizione.

2013 - A time-temperature integrator based on fluorescent and polymorphic compounds [Articolo su rivista]
Gentili, D; Durso, M; Bettini, C; Manet, I; Gazzano, M; Capelli, R; Muccini, M; Melucci, M; Cavallini, M
abstract

2013 - Effects of constant voltage stress on p- and n-type organic thin film transistors with poly(methyl methacrylate) gate dielectric [Articolo su rivista]
Wrachien, N; Cester, A; Bari, D; Capelli, R; D’Alpaos, R; Muccini, M; Stefani, A; Turatti, G; Meneghesso, G
abstract

We performed constant voltage stress on oligothiophene-based p- and n-type organic thin-film-transistors, in the accumulation regime. The stress induced charge trapping, mobility degradation and defect generation. The specific kinetics depends not only on the applied bias value and polarity, but also on the semiconductor type. Stress on PMMA capacitors (without the semiconductor film) revealed that most of the degradation is largely originated by the interaction with the semiconductor layer, which enhances charge injection

2013 - Molecular tailoring of new thieno(bis)imide-based semiconductors for single layer ambipolar light emitting transistors [Articolo su rivista]
Melucci, M; Favaretto, L; Zambianchi, M; Durso, M; Gazzano, M; Capelli, R; Muccini, M; Biondo, V; Toffanin, S; Troisi, S; Koopman, W; De Angelis, F; Lobello, Mg; Zanelli, A; Monari, M; Generali, G
abstract

2013 - Organic light-emitting transistors with voltage-tunable lit area and full channel illumination [Articolo su rivista]
Toffanin, S; Capelli, Raffaella; Koopman, W; Generali, G; Cavallini, S; Stefani, A; Saguatti, D; Ruani, G; Muccini, M
abstract

Organic light-emitting transistors (OLETs) are multifunctional optoelectronic devices that hold great promise for a variety of applications, including flat panel displays, integrated light sources for sensing and optical communication systems. The narrow illumination area within the device channel is considered intrinsic to the device architecture and is a severe technological drawback for all those applications where a controlled, wide and homogeneous emission area is required. Here it is shown that not only the position but also the extension of the emission area is voltage-tunable, and the entire channel of the transistor can be homogeneously illuminated. The modeling of the exciton distribution within the channel at the different bias conditions coupled to the modeling of the device emission profile highlights that excitons are spread through the entire channel width and across the bulk of the central emission layer of the p-channel/emitter/n-channel trilayer active heterostructure.

2013 - Synthesis, size-dependent optoelectronic and charge transport properties of thieno(bis)imide end-substituted molecular semiconductors [Articolo su rivista]
Durso, M; Bettini, C; Zanelli, A; Gazzano, M; Lobello, M G; De Angelis, F; Biondo, V; Gentili, D; Capelli, R; Cavallini, M; Toffanin, S; Muccini, M; Melucci, M
abstract

The synthesis of two new thieno(bis)imide (TBI, N) end functionalized oligothiophene semiconductors is reported. In particular, trimer (NT3N) and pentamer (NT5N) have been synthesized and characterized. Two different synthetic approaches for their preparation were tested and compared namely conventional Stille cross coupling and direct arylation reaction via C–H activation. Theoretical calculations, optical and electrochemical characterization allowed us to assess the role of the p-conjugation extent, i.e., of the oligomer size on the optoelectronic properties of these materials. In both TBI ended compounds, due to the strong localization of the LUMO orbital on the TBI unit, the LUMO energy is almost insensitive to the oligomer size, this being crucial for the fine-tailoring of the energy and the distribution of the frontier orbitals. Surprisingly, despite its short size and contrarily to comparable TBI-free analogues, NT3N shows electron charge transport with mobility up to lN = 104 cm2 V1 s1 , while increasing the oligomer size to NT5N promotes ambipolar behavior and electroluminescence properties with mobility up to lN = 0.14 cm2 V1 s 1 and to lP = 105 cm2 V1 s1 .

2013 - π-Core tailoring for new high performance thieno(bis)imide based n-type molecular semiconductors [Articolo su rivista]
Durso, M; Gentili, D; Bettini, C; Zanelli, A; Cavallini, M; De Angelis, F; Lobello, M G; Biondo, V; Muccini, M; Capelli, R; Melucci, M
abstract

The synthesis and characterization of two thieno(bis)imide based n-type semiconductors with electron mobilities of up to 0.3 cm2 V1 s 1 are described. The relationships between the electronic features of the p-inner core and the functional properties of the new materials are also discussed.

2012 - ORGANIC SEMICONDUCTOR MATERIAL [Brevetto]
Melucci, M; Favaretto, L; Zambianchi, M; Capelli, R; Muccini, M
abstract

A novel compound useful as organic semiconductor material, and semiconductor devices containing such organic semiconductor material are described.

2012 - Organic Light Emitting Field Effect Ambipolar Transistor with Distributed Light Emission [Brevetto]
Capelli, R; Toffanin, S; Generali, G; Muccini, M
abstract

n organic ambipolar light emitting field effect transistor having an architecture with layers stacked one over the other, adapted to generate a diffused illumination is described. The transistor has a gate electrode, a dielectric layer superposed to the gate electrode, an ambipolar channel superposed to the dielectric layer having a P-type semiconductor layer whose energy band is determined by its highest occupied molecular orbital HOMO-SCp and lowest unoccupied molecular orbital LUMO-SCp, a N-type semiconductor layer whose energy band is determined by its highest occupied molecular orbital HOMO-SCn and lowest unoccupied molecular orbital LUMO-SCn and a light emitting layer adapted to allow recombination of charge carriers of opposite sign, interposed between the P-type semiconductor layer and the N-type semiconductor layer, whose energy band is determined by its highest occupied molecular orbital HOMO-R and lowest unoccupied molecular orbital LUMO-R, respectively; a source electrode adapted to inject charges of a first type and a drain electrode adapted to inject charges of a second type, said source electrode and drain electrode being in contract with a same layer of said P-type or N-type semiconductor layers, the other of said semiconductor layers being in contact with the dielectric layer.

2012 - Organic semiconductor material [Brevetto]
Melucci, M; Favaretto, L; Zambianchi, M; Capelli, R; Muccini, M
abstract

The present invention relates to novel compounds useful as organic semiconductor materials, and semiconductor devices containing said organic semiconductor materials.

2012 - THIENO[2,3-C]PYRROLE-DIONE DERIVATIVES AND THEIR USE FOR ORGANIC SEMICONDUCTORS [Brevetto]
Zambianchi, M; Favaretto, L; Melucci, Ma; Muccini, M; Capelli, R
abstract

Compounds of formulae (I) and (II) useful as organic semiconductor materials, and semiconductor devices containing such organic semiconductor materials are described.

2011 - Correlation among Morphology, Crystallinity, and Charge Mobility in OFETs Made of Quaterthiophene Alkyl Derivatives on a Transparent Substrate Platform [Articolo su rivista]
Generali, G; Dinelli, F; Capelli, R; Toffanin, S; di Maria, F; Gazzano, M; Barbarella, G; Muccini, M
abstract

2011 - ELECTROLUMINESCENT ORGANIC DOUBLE GATE TRANSISTOR [Brevetto]
Muccini, M; Capelli, R
abstract

An organic electroluminescent transistor is described. The organic electroluminescent transistor has a first and a second dielectric layer, a first and a second control electrode and an assembly having a source electrode, a drain electrode and an ambipolar channel. The ambipolar channel has a first layer of semiconductor material, a second layer of semiconductor material and a layer of emissive material arranged between the first layer of semiconductor material and the second layer of semiconductor material. The source electrode and the drain electrode are both in contact with only one of the two layers of semiconductor material.

2011 - ELECTROLUMINESCENT ORGANIC TRANSISTOR [Brevetto]
Muccini, M; Capelli, R; Toffanin, S
abstract

he present invention relates to a field effect electroluminescent ambipolar organic transistor (1) in which there are two couples of control electrodes (15-18), a layer of ambipolar organic semiconductor (10) in direct contact with the source (11) and the drain (12) electrode and two separate dielectric layers (13, 14), and wherein said dielectric layers (13, 14) are each arranged between the ambipolar organic semiconductor layer (10) and a couple of control electrodes (15-18).

2011 - Electroluminescent Organic Double Gate Transistor [Brevetto]
Muccini, M; Capelli, R
abstract

Electroluminescent organic transistor (1) in which there is a semiconductor heterostructure (12) constituted by a plurality of layers of semiconductor materials of p-type and n-type (15, 15', 15", 15"'), which act, respectively, for the conduction of holes and electrons within said heterostructure (12), and at least two layers of emitting materials (16, 16', 16") each of which is interposed between, and in direct contact with, one of said layers of p-type semiconductor material and one of said layers of n-type semiconductor material (15, 15', 15", 15"').

2011 - Electroluminescent Organic Transistor [Brevetto]
Capelli, R; Muccini, M
abstract

Electroluminescent organic transistor (1) in which there is a semiconductor heterostructure (12) constituted by a plurality of layers of semiconductor materials of p-type and n-type (15, 15', 15", 15"'), which act, respectively, for the conduction of holes and electrons within said heterostructure (12), and at least two layers of emitting materials (16, 16', 16") each of which is interposed between, and in direct contact with, one of said layers of p-type semiconductor material and one of said layers of n-type semiconductor material (15, 15', 15", 15"').

2011 - Influence of the substrate platform on the opto-electronic properties of multi-layer organic light emitting field-effect transistors [Articolo su rivista]
Generali, G; Dinelli, F; Capelli, R; Toffanin, S; Muccini, M
abstract

2011 - Integration of silk protein in organic and light-emitting transistors [Articolo su rivista]
Capelli, R; Amsden, Jj; Generali, G; Toffanin, S; Benfenati, V; Muccini, M; Kaplan, Dl; Omenetto, Fg; Zamboni, R
abstract

2011 - Organic Semiconductor Material [Brevetto]
Melucci, M; Favaretto, L; Zambianche, M; Capelli, R; Muccini, M
abstract

Novel compounds useful as organic semiconductor material are described. Semiconductor devices containing said organic semiconductor material are also described.

2011 - Photoswitchable OFETs controlled by optical bistability in the dielectric layer [Relazione in Atti di Convegno]
Sworakowski, J.; Lutsyk, P.; Janus, K.; Generali, G.; Capelli, R.; Muccini, M.; Kochalska, A.; Nespurek, S.
abstract

Interest in electronic properties of organic materials has been stimulated by emerging prospects of their application in electronics and photonics [1-4]. Among potential applications, one may envisage use of organic materials as active elements of molecular switches. According to a general definition, a switch is a mechanical, electrical, electronic, or optical device for opening or closing a circuit, or for diverting energy or charge from one part of a circuit to another. In this context, photochromic materials have been extensively studied. © 2011 IEEE.

2011 - Photoswitching of an n-Type Organic Field Effect Transistor by a Reversible Photochromic Reaction in the Dielectric Film [Articolo su rivista]
Lutsyk, P; Janus, K; Sworakowski, J; Generali, G; Capelli, R; Muccini, M
abstract

2011 - Platform Comprising an Organic Field Effect Transistor for Biological and Medical Applications [Brevetto]
Capelli, R; Toffanin, S; Benfenati, V; Muccini, M; Zamboni, R; Generali, G
abstract

2011 - Thienopyrrolyl dione end-capped oligothiophene ambipolar semiconductors for thin film- and light emitting transistors [Articolo su rivista]
Melucci, M; Zambianchi, M; Favaretto, L; Gazzano, M; Zanelli, A; Monari, M; Capelli, R; Troisi, S; Toffanin, S; Muccini, M
abstract

2010 - A silk platform that enables electrophysiology and targeted drug delivery in brain astroglial cells [Articolo su rivista]
Benfenati, V; Toffanin, S; Capelli, R; Camassa, Lma; Ferroni, S; Kaplan, Dl; Omenetto, Fg; Muccini, M; Zamboni, R
abstract

2010 - Ambipolar field-effect transistor based on a,x-dihexylquaterthiophene and a,x -diperfluoroquaterthiophene vertical heterojunction [Articolo su rivista]
Generali, G; Capelli, R; Toffanin, S; Facchetti, A; Muccini, M
abstract

2010 - Molecular Host-Guest Energy-Transfer System with an Ultralow Amplified Spontaneous Emission Threshold Employing an Ambipolar Semiconducting Host Matrix [Articolo su rivista]
Toffanin, S; Capelli, R; Hwu, Ty; Wong, Kt; Plotzing, T; Forst, M; Muccini, M
abstract

2010 - Organic light-emitting transistors with an efficiency that outperforms the equivalent light-emitting diodes [Articolo su rivista]
Capelli, R; Toffanin, S; Generali, G; Usta, H; Facchetti, A; Muccini, M
abstract

2009 - Luminescent Ethynyl-Pyrene Liquid Crystals and Gels for Optoelectronic Devices [Articolo su rivista]
Diring, S; Camerel, F; Donnio, B; Dintzer, T; Toffanin, S; Capelli, R; Muccini, M; Ziessel, R
abstract

2009 - Silk Transistor Devices [Brevetto]
Omenetto, F; Kaplan, D; Amsden, J; Capelli, R; Toffanin, S; Benfenati, V; Muccini, M; Zamboni, R
abstract

The invention relates to ecosustainable and biocompatible, low cost, ambient friendly electronic and optoelectronic devices, such as transistors and light-emitting transistors, made with silk fibroin or blended with other biopolymers, methods for fabrication and methods of using the silk-based electronics and optoelectronics. The silk-based electronics and optoelectronics can be implanted in vivo and in vitro for biomedical applications, such as for drug discovery or drug screening assays and devices. The silk-based devices may be used in the food industry and embedded in packaging for tracking and sensing, for security purposes or exploited as disposable not harmful for the environment efficient general electronic and optoelectronic devices.

2009 - Very low amplified spontaneous emission threshold from a molecular host-guest energy-transfer system and electroluminescence from lightemitting diode structure [Relazione in Atti di Convegno]
Toffanin, S.; Capelli, R.; Generali, G.; Hwu, T. -Y.; Wong, K. -T.; Zamboni, R.; Muccini, M.
abstract

We report on the characteristics of a host-guest lasing system obtained by co-evaporation of an oligo(9,9-diarylfluorene) derivative named T3 with the red-emitter 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran dye (DCM). We demonstrate that the ambipolar semiconductor T3 can be implemented as active matrix in the realization of a host-guest system in which an efficient energy transfer takes place from T3 matrix to the lasing DCM molecules. We performed a spectroscopic study on the system by systematically varying the DCM concentration in the T3 matrix. Measurements of steady-state photoluminescence (PL), PL quantum yield (PLQY) and amplified spontaneous emission (ASE) threshold are used to optimize the acceptor concentration at which the ASE from DCM molecules takes place with the lowest threshold. Organic light-emitting diodes (OLEDs) implementing the DCM:T3 host-guest system as recombination layer are fabricated for verifying the optical properties of the optimised blend in real working devices. Indeed, the very low ASE threshold of T3:DCM makes the investigated blend an appealing system for use as active layer in lasing devices. In particular, the ambipolar charge transport properties of the T3 matrix and its field-effect characteristics make the host-guest system presented here an ideal candidate for the realization of electrically-pumped organic lasers. © 2009 SPIE.

2008 - A bridge between two important problems in optics and electrostatics [Articolo su rivista]
Capelli, R; Pozzi, G
abstract

It is shown how the same physically appealing method can be applied to find analytic solutions for two difficult and apparently unrelated problems in optics and electrostatics. They are: (i) the diffraction of a plane wave at a perfectly conducting thin half-plane and (ii) the electrostatic field associated with a parallel array of stripes held at opposite potentials and lying in a half-plane. In the latter case, the solution of the problem is essential in order to calculate the electron optical phase shift experienced by the electron beam in electron microscopy experiments, where the model mimics an array of reverse biased p–n junctions. This paper is intended, in particular, for the undergraduate student who has completed his programme of calculus and electromagnetism, but it can also be of interest to the general physicist.

2008 - Correlation between dielectric/organic interface properties and key electrical parameters in PPV-based OFETs [Articolo su rivista]
Todescato, F; Capelli, R; Dinelli, F; Murgia, M; Camaioni, N; Yang, M; Bozio, R; Muccini, M
abstract

2008 - Investigation of the Optoelectronic Properties of Organic Light-Emitting Transistors Based on an Intrinsically Ambipolar Material [Articolo su rivista]
Capelli, R; Dinelli, F; Toffanin, S; Todescato, F; Murgia, M; Muccini, M; Facchetti, A; Marks, Tj
abstract

2008 - Molecular Packing Effects on the Optical Spectra and Triplet Dynamics in Oligofluorene Films [Articolo su rivista]
Cabanillas-Gonzalez, J; Sciascia, C; Lanzani, G; Toffanin, S; Capelli, R; Ramon, Mc; Muccini, M; Gierschner, J; Hwu, Ty; Wong, Kt
abstract

2008 - OLET architectures for electrically-pumped organic lases [Relazione in Atti di Convegno]
Zamboni, R.; Capelli, R.; Toffanin, S.; Murgia, M.; Forst, M.; Muccini, M.
abstract

Organic light emitting transistors (OLET) have been recently demonstrated as innovative architectures combining into an integrated optoelectronic device multi-functional properties namely, the driving ability of a transistor device with the conversion of electrical current into efficient light emission via electronic relaxation of organic semiconductors. State of the art materials, achievement and performances will be presented and discussed in view of possible OLET architectures exploitation as electrically pumped organic nanolasers. © 2008 SPIE.

2008 - Oligofluorene derivative in a host-guest system with a red-emitter: Molecular packing effect on the host bimolecular recombination and guest ASE threshold reduction [Relazione in Atti di Convegno]
Cabanillas-Gonzalez, J.; Toffanin, S.; Capelli, R.; Wong, K. -T.; Muccini, M.
abstract

The dynamics of triplet recombination in fluorene trimers have been studied using steady state photoinduced absorption (PA) spectroscopy. We investigated two type of oligomeric films, deposited by different techniques: thermal evaporation and spincoating. The different molecular arrangement in both films is manifested in a red-shift of the absorption, PL and T1-Tn triplet PA spectra of the sublimated film relative to the spincoated one. Triplet recombination dynamics follow a dispersive bimolecular recombination model away from the trap filling regime. Moreover we report on the characteristics of a host-guest lasing system obtained by co-evaporation of the most promising oligofluorene derivative (T3) with the red-emitter 4-(dicyanomethylene)-2-methyl-6-(p- dimethylaminostyryl)-4H-pyran dye (DCM). The blend satisfies the necessary condition for an efficient FÖrster energy transfer to take place from T3 matrix to DCM molecules.

2007 - Influence of the dielectric and of the active layer doping on the FET mobility in PPV-based devices [Relazione in Atti di Convegno]
Todescato, F.; Capelli, R.; Dinelli, F.; Murgia, M.; Camaioni, N.; Yang, M.; Muccini, M.
abstract

We report on the influence of the dielectric/organic interface properties on the electrical characteristics of field-effect transistors based on Poly-phenylenevinylene derivatives. We observe a direct influence of the dielectric surface on the field-effect mobility as well as on the charge injection at the source electrode, despite the fact that we used a top contact transistor structure. We find that the presence of traps at the dielectric surface, decreases the hole mobility and increases the threshold voltages. By treating the silicon dioxide dielectric surface with gas phase molecules such as octadecyltrichlorosilane (OTS) and hexamethyldisilazane (HMDS) the hole mobility improves and the threshold voltage slightly increases. The effects of a dielectric polymer layer spin coated onto silicon dioxide substrates before deposition of the semiconductor polymer can be related to the density of the oxydryl groups (-OH), which are the most efficient traps for the charges flowing in the device. We use different polymer species such as polyvinylalchol (PVA), polymethylmetacrilate (PMMA) and a cyclotene derivative (B-staged bisbenzocyclobutene or BCB). The elimination of the -OH groups and of other traps, produces the same effect observed with HMDS coupled to a more pronounced enhancement of the threshold voltage, with the exception of PMMA. The electrical characteristics obtained with HMDS and PMMA polymer dielectrics are the highest reported to date for PPV-based field-effect transistors. We confirm that the purification of the active material is crucial to enhance the device performances and to achieve a better device to device reproducibility. We also investigated the effect of the dispersion of a phosphorescent dye into the active polymeric material. The electrical characteristics of OFETs with HMDS or PMMA dielectric with and without dye doping are compared.

2006 - Ambipolar light-emitting field-effect transistors based on molecular thin films [Relazione in Atti di Convegno]
Capelli, R.; Dinelli, F.; Loi, M. A.; Murgia, M.; Muccini, M.
abstract

Organic light-emitting field-effect transistors are a new class of electrooptical devices that could provide a novel architecture to address open questions concerning fundamental optoelectronic phenomena in organic semiconductors, and can be potentially used as key components in optical communication systems, advanced display technology, solid-state lighting and organic lasers. The realisation of Organic Light-Emitting Transistors (OLETs) with high quantum efficiency and fast switching time is crucial for the development of highly integrated organic optoelectronic systems. Organic molecular materials having intrinsically ambipolar transport and high charge mobility values are restricted in number and show poor light-emission efficiency. Here, we describe the device operation principles of OLETs and report on the approach of combining p-type and n-type molecular materials in a layered structure to achieve ambipolar transport and light emission. Imaging of the individual layers and a correlation between active layer structure and device electrical performances is achieved by means of the Laser Scanning Confocal Microscopy.

2006 - Ambipolar organic light-emitting transistors employing heterojunctions of n-type and p-type materials as the active layer [Articolo su rivista]
Capelli, R; Dinelli, F; LOI M., A; Murgia, M; Zamboni, R; Muccini, M
abstract

2006 - High-Mobility Ambipolar Transport in Organic Light-Emitting Transistors [Articolo su rivista]
Dinelli, F; Capelli, R; Loi, Ma; Murgia, M; Muccini, M; Facchetti, A; Marks, Tj
abstract

2004 - Tetracene-based organic light-emitting transistors: optoelectronic properties and electron injection mechanism [Relazione in Atti di Convegno]
Santato, ; C, ; Capelli, R; R, ; Loi, ; Ma, ; Et, Al
abstract

2003 - "Modeling of the photophysical properties of a-sexithiophene thin films" [Articolo su rivista]
Capelli, R; C. TALIANI AND M., Muccini
abstract

2003 - A potential J aggregate molecular system: Crystal packing and optical properties of 4,4′-bis(2,3,4,5,6-pentafluorostyryl)stilbene [Articolo su rivista]
Capelli, R; LOI M., A; Taliani, C; HANSEN H., B; Murgia, M; Ruani, G; Muccini, M; LOVENICH P., W; FEAST W., J
abstract

2002 - Ab initio calculation of electron energy loss spectra of clean and 1ML Fe-covered Ni(111) [Articolo su rivista]
Capelli, R; Monachesi, P; Del Sole, R; Gazzadi, Gc
abstract

2002 - Calculation of optical properties within the local density approximation to density functional theory: application to palladium [Articolo su rivista]
Monachesi, P; Capelli, R; Del Sole, R
abstract

2002 - Structural transition in Fe ultrathin epitaxial films grown on Ni(111) [Articolo su rivista]
Gazzadi, Gc; Bruno, F; Capelli, R; Pasquali, Luca; Nannarone, Stefano
abstract

A structural study of Fe ultrathin epitaxial films, grown at room temperature on Ni(111), has been performed in the 1.5-18 ML coverage range by angle-scanned photoelectron diffraction. Both backscattering and forward-scattering energy regimes have been employed, in order to enhance the structural sensitivity at lower and higher film thicknesses, respectively. Modeling of the experimental data has been performed with multiple scattering calculations. We found indications that Fe atoms in the first layer occupy fcc hollow sites and stack with a pseudomorphic fcc structure up to 2 ML. Concerning the growth mode at these early stages, data suggest that a good substrate wetting and a sharp Fe/Ni interface take place. Between 3 and 6 ML, transition to a bcc(110) phase develops. By quantitative R-factor analysis, we found that Nishiyama-Wassermann (NW) in-plane orientation of the bcc(110) cell (<001>(bcc)parallel to<110>(fcc)) is favored over the Kurdjumov-Sachs (<1 (1) over bar1>(bcc)parallel to<1 (1) over bar0>(fcc)) orientation. The best-fit vertical interlayer distance between bcc(110) planes is d(NW)=2.11 Angstrom (+3.9% expansion) at 6 ML and relaxes to d(NW)=2.05 Angstrom (+1.0%) at 18 ML, in agreement with the angular shift observed for the forward-focusing features. In the same coverage range, the angle between bcc(110) surface basis vectors changes from 67.7degrees to 69.0degrees, corresponding to -1.7% and -1.0% contractions of the surface cell area, respectively.

2001 - Interface magnetometry in a (Fe-6A/Ni-24A)(10) multilayer [Articolo su rivista]
Capelli, R; D'Addato, Sergio; Gazzadi, Gc; Pasquali, Luca; Verucchi, R; Nannarone, Stefano; Dudzik, E; Mirone, A; Sacchi, M.
abstract

The interplay between atomic geometry and magnetic properties of Fe atoms at the Fe-Ni(1 1 1) interface was studied. To this end dichroic optical absorption and reflectivity (both in energy and theta -2 theta angular scan mode) were carried out in the L-2,L-3 edge region of Fe in (Fe-6 (Angstrom)/Ni-24 (Angstrom)(1 1 1))(10) multilayer while the atomic geometry of the Fe site at the interface was studied for 1 atomic layer of Fe on Ni(1 1 1) by photo-electron diffraction tin angular scan mode and back-scattering regime). The Fe atom was found to be chemisorbed in an fee hollow site and to stack pseudomorphically to Ni(1 1 1). Its magnetic moment was found to be in the range 2.9 +/- 0.9-1.93 +/- 0.6 mu (B). Possibility of surface anisotropy is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.

2000 - A model for the interpretation of holographic and Lorentz images of tilted reverse-biased p-n junctions in a finite specimen [Articolo su rivista]
Beleggia, M; Capelli, R; Pozzi, G
abstract

2000 - A model for the interpretation of holographic and Lorentz images of tilted reverse-biased p-n junctions in a finite specimen [Relazione in Atti di Convegno]
Beleggia, M.; Capelli, R.; Pozzi, G.
abstract

An analytical model for the electric field associated with a periodic array of alternating p- and n-doped stripes lying in a half-plane, tilted with respect to the specimen edges and thus better representing the actual experimental set-up is presented. With respect to a previous treatment, relative to the case of stripes perpendicular to the edge, a more physical derivation is outlined, and the calculated phase shift is used to interpret the main features of holography and Lorentz microscopy images, allowing a quantitative assessment of the influence of the specimen edge on them.

2000 - Growth of Fe ultrathin films on Ni(111): structure and electronic properties [Articolo su rivista]
D'Addato, Sergio; Pasquali, Luca; Gazzadi, Gc; Verucchi, R; Capelli, R; Nannarone, Stefano
abstract

We investigated the evolution during film growth of the electronic properties of Fe/Ni(111) ultrathin films with electron energy loss spectroscopy from the valence band and from the Fe L-2,L-3 ionization edges, relating them with structural modifications monitored with low energy electron diffraction. At ca. 4 monolayers of Fe a fee to bce phase transition was observed with the major changes in the electronic structure occurring in the 3d band region. (C) 2000 Elsevier Science B.V. All rights reserved.

2000 - Structural analysis of epitaxial Fe films on Ni(001) [Articolo su rivista]
Gazzadi, Gc; Luches, P; D'Addato, Sergio; Marassi, L; Capelli, R; Pasquali, Luca; Valeri, Sergio; Nannarone, Stefano
abstract

The atomic geometry and growth mechanism of Fe films (0.5-20 monolayers (ML)) epitaxially grown on Ni(001) have been investigated by a multitechnique approach with the twofold aim of assessing the reliability of quick structural techniques (primary-beam diffraction modulated electron emission (PDMEE), secondary electron imaging (SEI)), suitable for on-line monitoring of film growth, and studying the structural evolution of the Fe/Ni system. To this end, samples were analysed by PDMEE and SEI together with synchrotron radiation photoelectron diffraction (PD), and extended x-ray absorption fine structure (EXAFS). Results show the effectiveness of the approach by quick techniques. In the early stage of growth, Fe arranges in a strained fcc(001) structure. Transition to the bce phase occurs through nucleation of bcc(110) domains with the bce < 111 > //fcc < 110 > orientation. Quantitative analysis based on PD and EXAFS data is also presented. (C) 2000 Elsevier Science B.V. All rights reserved.