elena tresso | Politecnico di Torino (original) (raw)

Papers by elena tresso

Research paper thumbnail of Nafion membranes with vertically-aligned CNTs for mixed proton and electron conduction

ABSTRACT The interest in clean energy is of increasing importance nowadays. In this regard, hydro... more ABSTRACT The interest in clean energy is of increasing importance nowadays. In this regard, hydrogen production from sun-assisted water splitting is a field of intense research in the scientific community. In the design of artificial innovative devices devoted to this task, the simultaneous transport of protons and electrons from an anode (where they are generated by water oxidation) to a cathode (where they have to recombine in order to form molecular hydrogen) is essential.Nafion, a sulfonated fluoropolymer, is of great interest because of its proven ability as a proton-conducting membrane in fuel cells, and also for its good thermal and mechanical stability. Carbon nanotubes (CNTs), rolls of graphene sheets, possess a high thermal and mechanical stability together with excellent electron conductivity. Nafion/CNTs nanocomposites with CNT amounts above the percolation threshold have been recently obtained which are capable of simultaneously conducting protons and electrons.Here we report on the fabrication of nafion/CNTs membranes in an alternative configuration, namely vertically-aligned carbon nanotubes columns embedded in a nafion matrix. Nanocomposite films of nafion embedded with an array of CNT columns were prepared by solvent casting. Films of thickness around 100 μm were obtained. They were characterized by scanning electron microscopy, electrochemical impedance spectroscopy, electronic conductivity tests, water uptake and water contact angle. Electronic and protonic conductivities were measured in ambient and wet conditions and turned out to be higher than those previously reported for nafion/CNTs nanocomposites in the conditions where such devices are expected to operate.

Research paper thumbnail of Spark plasma sintering of self-propagating high-temperature synthesized TiC0.7/TiB2 powders and detailed characterization of dense product

Ceramics International, 2009

In this work, the fabrication of bulk TiC 0.7 /TiB 2 nanostructured composites through metastable... more In this work, the fabrication of bulk TiC 0.7 /TiB 2 nanostructured composites through metastable transformation processing is investigated by taking advantages of two non-conventional powder metallurgy methods. First, the highly metastable TiC 0.7 /TiB 2 agglomerated powders are synthesized by the so-called self-propagating high-temperature synthesis (SHS), followed by rapid quenching. Then, the spark plasma sintering (SPS) method is adopted to consolidate the SHSed powders.

Research paper thumbnail of Computer Assisted Education through the WEB: the Example of FIL

The paper presents a software platform in use and under development in the Politecnico of Turin. ... more The paper presents a software platform in use and under development in the Politecnico of Turin. The name of the platform, FIL, is the acronym of Fisica In Linea (Physics On Line). FIL is designed to be a support for all students
both residential and at a distance. The guidance of the student is pursued allowing for different personalized itineraries and strategies. For this purpose we are trying to integrate FIL with the 3DE philosophy, presented in another paper of this section. FIL contains a great number of interactive objects. An actual automated tutoring is not yet implemented, but a simple feed back for the student is provided by a self-evaluation tool to which FIL is connected. All features of FIL have been developed up to this moment mainly for one specific sector of physics, i.e.
electrostatics. Work is in progress. The authors are trying to join their efforts with a good number of other universities in the world.

Research paper thumbnail of ALFA-EVALU: A Collaboration Network among Latin American and European Universities

The present paper describes the project of the network EVALU, developed in the framework of the E... more The present paper describes the project of the network EVALU, developed in the framework of the European ALFA program. The main objective of the project is the formation of a web-based, common environment joining the 13 universities in the network. The first step ...

Research paper thumbnail of An automatic evaluation system for technical education at the University level

IEEE Transactions on Education, 2002

A Web-based automatic evaluation system for students of engineering faculties is described. The s... more A Web-based automatic evaluation system for students of engineering faculties is described. The system, named Test on Line (ToL), can verify the possession of ideas, the ability to combine them into deductions, and the capability to make simple numerical calculations for otherwise practical exercises. ToL has been extensively in use for basic physics courses at the engineering faculties of the Turin Politecnico since the beginning of 1999. Consequently, the accumulated statistical data amount to approximately four thousand individual tests and show the credibility both of the method and of its results. ToL generates, for each student, a proposed mark (which can be verified by an oral colloquium on demand by the candidate) and a simple cognitive profile showing possible cognitional, logical, or practical weaknesses in the different topics of the study matter. The core of the platform consists of a database of questions, a selection algorithm, and an evaluation procedure. The instrument and the method are being refined; the major improvements under construction are listed.

Research paper thumbnail of Verifying the learning process in physics

European Journal of Physics, 2001

The paper describes an automated evaluation system for the learning of general Physics. The syste... more The paper describes an automated evaluation system for the learning of general Physics. The system whose name is Test on Line (ToL) is based on a questions bank from which an appropriate software generates individual multi-issue questionnaires to be submitted through the web. ToL has been extensively experimented during three years and is presently in use for basic Physics courses at the Engineering Faculties of the Turin Politecnico. The results of the experimentation and use are presented and discussed. Cumulating data allows for an optimization of the internal partitions of the questions bank and of the selection criteria for the generation of the questionnaires. The instrument proved to be useful and reliable and could become the core of an agreed common standard for physics education at university level.

Research paper thumbnail of Effect of defects on electrical properties of 4H-SiC Schottky diodes

Materials Science and Engineering: C, 2008

Typical power switching devices such as diodes, thyristors, and transistors are based on a monocr... more Typical power switching devices such as diodes, thyristors, and transistors are based on a monocrystalline silicon semiconductor or silicon carbide. Silicon is less expensive, more widely used, and a more versatile processing material than silicon carbide. The silicon carbide (SiC) has ...

Research paper thumbnail of Correlation between gap density of states and recombination processes in high electronic quality aC:H

Journal of Non-crystalline Solids, 1998

. The investigation on electronic density of states DOS and photoluminescence processes in a-C:H ... more . The investigation on electronic density of states DOS and photoluminescence processes in a-C:H films has attracted, in the last years, interest, due to the foreseen technological application of carbon based materials. In this paper we present a new model for electronic DOS of a-C:H having sp 2 fraction less than a percolation threshold. This model is able to explain the optical absorption coefficient for photon energies in the range 0.7 to 3.5 eV. Moreover, with this model we correlate, as it happens in a-Si:H, the photoluminescence quantum efficiency and the density of states close to the Fermi energy. Such states, however, can have either diamagnetic or paramagnetic nature so that some of them can be detected by electron spin resonance and others by optical transitions. q

Research paper thumbnail of Characterization of silicon–YBCO buffered multilayers grown by sputtering

Applied Surface Science, 2004

In recent years, the scientific community has considered with interest the possibility to integra... more In recent years, the scientific community has considered with interest the possibility to integrate YBCO-based devices with silicon-based electronics. In fact, the proved YBCO radiation hardness makes this integration appealing from the point of view of space and telecommunication applications. In this paper we report on the influence of buffered substrate properties on the superconducting performances of YBCO films. In this framework we here consider the Si/CeO 2 /YBCO multilayer. The nonsatisfying quality of the YBCO film in this multilayer is attributed to an unavoidable interlayer of SiO 2 between Si and CeO 2 . On the other hand, we prove, by means of quantitative magneto-optical analysis, the excellent properties of the bi-layer CeO 2 / YBCO on YSZ substrate. Thus, these measurements indicate YSZ as the best candidate to be deposited between Si and CeO 2 for optimal YBCO performances on silicon. #

Research paper thumbnail of Light induced defects in amorphous silicon-carbon alloys aSiC:H

Optical Materials, 1996

Silicon-carbon alloys were prepared using a UHV PECVD system by the mixture of CH 4 + Sill 4 with... more Silicon-carbon alloys were prepared using a UHV PECVD system by the mixture of CH 4 + Sill 4 with and without hydrogen dilution. The CH 4 fraction in the plasma was varied between 40 and 95%. The energy gap of our samples varies between 1.8 and 2.5 eV. The effect of degradation induced by light exposure for several hours was studied using Photothermal Deflexion Spectroscopy (PDS). The experimental data are consistent with a bond breaking model, by conversion of tail weak bonds into dangling bonds. The data show more stability in the optoelectronic properties of diluted samples.

Research paper thumbnail of Intrinsic pinning and current percolation signatures in E-J characteristics of Si/YSZ/CeO 2 /YBCO layouts

European Physical Journal B, 2005

In the context of superconducting electronics integrated with traditional silicon-based electroni... more In the context of superconducting electronics integrated with traditional silicon-based electronics we grew Si/YSZ/CeO2/YBa2Cu3O7-x architectures by means of the scalable magnetron sputtering growth technique. In this paper we report on structural, surface and electrical transport characterization of typical multilayers. We focus on the electrical transport characterization in the temperature range 18–30 K of c-axis YBa2Cu3O7-x films grown on top of several (001) oriented buffered substrates. The electric field vs. current density (E-J) curves exhibit step-like behaviour in correspondence to the transition between the non-dissipative and the flux-flow regimes. This trend is accompanied by the signature of linearly correlated pinning. On the other hand, in the flux-flow regime clear signatures of weak-link behaviour and current percolation are exhibited. In this complex framework possible future applications are discussed.

Research paper thumbnail of Observation of negative capacitance in aSiC:H/aSi:H UV photodetectors

Solid-state Electronics, 2006

UV photosensors based on a-Si:H/a-SiC:H were deposited by ultra high vacuum plasma enhanced chemi... more UV photosensors based on a-Si:H/a-SiC:H were deposited by ultra high vacuum plasma enhanced chemical vapour deposition system (UHV-PECVD) over a large area (10 cm · 10 cm) in p-i-n configuration.

Research paper thumbnail of Structural and optoelectronic properties of doped microcrystalline silicon carbide films

Semiconductor Science and Technology, 1994

Undoped and phosphorus-doped microcrystalline silicon carbide ( mu c-SiC:H) films were deposited ... more Undoped and phosphorus-doped microcrystalline silicon carbide ( mu c-SiC:H) films were deposited by plasma-enhanced chemical vapour deposition (PECVD) with high hydrogen dilution and high RF power density. The doped films obtained have a bandgap up to 2.0 eV and electrical dark conductivity up to 17 S cm-1. The thermoelectric power (TEP) measurements and the behaviour of the conductivity and Hall

Research paper thumbnail of Influence of hydrogen on the evolution of structural properties of amorphous silicon carbide

Journal of Non-crystalline Solids, 1991

Device-quality films of a-SiC:H deposited by glow-discharge and reactive sputtering have been sub... more Device-quality films of a-SiC:H deposited by glow-discharge and reactive sputtering have been subjected to annealing treatments in the range 200-800°C in order to study the influence of hydrogen on the evolution of their structural properties. IR, density, optical and electrical measurements contribute to identify the different phase transitions of the network.

Research paper thumbnail of Modelling and analysis of aSiC:H p–i–n photodetectors: Effect of hydrogen dilution on dynamic model

Solid-state Electronics, 2007

The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in ... more The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in amorphous silicon and its compounds are the object of intense research works. By starting on the concept that such p-i-n structures can be compared to p + -n and n-n + junctions in series, and by referring to Shockley's model in one modified diode, we propose an equivalent electrical circuit in dynamic state of the considered structure resulting from a series association of Shockley's model. A simulation study by PSPICE of the equivalent electrical circuit so obtained is in good agreement with the experimental results, and physical interpretations connected to this model are discussed.

Research paper thumbnail of Publications of Emanuele Centurioni

Research paper thumbnail of Investigation on electronic density of states in a-SixC1-x: H films

Applied Surface Science, 1993

Films of a-Si xC 1- x: H with different carbon contents were deposited by an ultrahigh vacuum pla... more Films of a-Si xC 1- x: H with different carbon contents were deposited by an ultrahigh vacuum plasma enhanced chemical vapour desposition system and characterized by means of the following experimental techniques: photothermal deflection spectroscopy, constant photocurrent method, optical modulation spectroscopy and electron spin resonance. The results include data on optical gap, Urbach tail energy, thermal activation energy of dark conductivity, density and distribution of defects and quantum efficiency-mobility-lifetime product. Comparison of the data obtained with the different techniques is presented and discussed.

Research paper thumbnail of Influence of film thickness on optical and electrical properties of hydrogenated amorphous silicon

Thin Solid Films, 1987

The optical and electrical properties of hydrogenated amorphous silicon (a-Si:H) films produced b... more The optical and electrical properties of hydrogenated amorphous silicon (a-Si:H) films produced by magnetron sputtering (SP) and glow discharge (GD) were studied as a function of the film thickness (50-300 nm). A strong dependence on the thickness was observed in the maximum values of the absorption coefficient and in the energy gap Eg (obtained from (~E) 1/2 vs. E plots) for both series. For the SP films the refractive index n(2) increased with thickness, whereas for GD films e2,,a ~ and its corresponding energy decreased with increasing thickness. The resistivity values are within the range of typical values for a-Si:H, but no effect of thickness was observed, because of non-uniformity of the films and band bending at the substrate interface.

Research paper thumbnail of Compositional and structural properties of hydrogenated amorphous silicon-carbon films prepared by ultra-high-vacuum plasma-enhanced chemical vapour deposition with different carbon sources

Philosophical Magazine A-physics of Condensed Matter Structure Defects and Mechanical Properties, 1995

ABSTRACT

Research paper thumbnail of Correlation between gap density of states and recombination processes in high electronic quality aC:H

Journal of Non-crystalline Solids, 1998

. The investigation on electronic density of states DOS and photoluminescence processes in a-C:H ... more . The investigation on electronic density of states DOS and photoluminescence processes in a-C:H films has attracted, in the last years, interest, due to the foreseen technological application of carbon based materials. In this paper we present a new model for electronic DOS of a-C:H having sp 2 fraction less than a percolation threshold. This model is able to explain the optical absorption coefficient for photon energies in the range 0.7 to 3.5 eV. Moreover, with this model we correlate, as it happens in a-Si:H, the photoluminescence quantum efficiency and the density of states close to the Fermi energy. Such states, however, can have either diamagnetic or paramagnetic nature so that some of them can be detected by electron spin resonance and others by optical transitions. q

Research paper thumbnail of Nafion membranes with vertically-aligned CNTs for mixed proton and electron conduction

ABSTRACT The interest in clean energy is of increasing importance nowadays. In this regard, hydro... more ABSTRACT The interest in clean energy is of increasing importance nowadays. In this regard, hydrogen production from sun-assisted water splitting is a field of intense research in the scientific community. In the design of artificial innovative devices devoted to this task, the simultaneous transport of protons and electrons from an anode (where they are generated by water oxidation) to a cathode (where they have to recombine in order to form molecular hydrogen) is essential.Nafion, a sulfonated fluoropolymer, is of great interest because of its proven ability as a proton-conducting membrane in fuel cells, and also for its good thermal and mechanical stability. Carbon nanotubes (CNTs), rolls of graphene sheets, possess a high thermal and mechanical stability together with excellent electron conductivity. Nafion/CNTs nanocomposites with CNT amounts above the percolation threshold have been recently obtained which are capable of simultaneously conducting protons and electrons.Here we report on the fabrication of nafion/CNTs membranes in an alternative configuration, namely vertically-aligned carbon nanotubes columns embedded in a nafion matrix. Nanocomposite films of nafion embedded with an array of CNT columns were prepared by solvent casting. Films of thickness around 100 μm were obtained. They were characterized by scanning electron microscopy, electrochemical impedance spectroscopy, electronic conductivity tests, water uptake and water contact angle. Electronic and protonic conductivities were measured in ambient and wet conditions and turned out to be higher than those previously reported for nafion/CNTs nanocomposites in the conditions where such devices are expected to operate.

Research paper thumbnail of Spark plasma sintering of self-propagating high-temperature synthesized TiC0.7/TiB2 powders and detailed characterization of dense product

Ceramics International, 2009

In this work, the fabrication of bulk TiC 0.7 /TiB 2 nanostructured composites through metastable... more In this work, the fabrication of bulk TiC 0.7 /TiB 2 nanostructured composites through metastable transformation processing is investigated by taking advantages of two non-conventional powder metallurgy methods. First, the highly metastable TiC 0.7 /TiB 2 agglomerated powders are synthesized by the so-called self-propagating high-temperature synthesis (SHS), followed by rapid quenching. Then, the spark plasma sintering (SPS) method is adopted to consolidate the SHSed powders.

Research paper thumbnail of Computer Assisted Education through the WEB: the Example of FIL

The paper presents a software platform in use and under development in the Politecnico of Turin. ... more The paper presents a software platform in use and under development in the Politecnico of Turin. The name of the platform, FIL, is the acronym of Fisica In Linea (Physics On Line). FIL is designed to be a support for all students
both residential and at a distance. The guidance of the student is pursued allowing for different personalized itineraries and strategies. For this purpose we are trying to integrate FIL with the 3DE philosophy, presented in another paper of this section. FIL contains a great number of interactive objects. An actual automated tutoring is not yet implemented, but a simple feed back for the student is provided by a self-evaluation tool to which FIL is connected. All features of FIL have been developed up to this moment mainly for one specific sector of physics, i.e.
electrostatics. Work is in progress. The authors are trying to join their efforts with a good number of other universities in the world.

Research paper thumbnail of ALFA-EVALU: A Collaboration Network among Latin American and European Universities

The present paper describes the project of the network EVALU, developed in the framework of the E... more The present paper describes the project of the network EVALU, developed in the framework of the European ALFA program. The main objective of the project is the formation of a web-based, common environment joining the 13 universities in the network. The first step ...

Research paper thumbnail of An automatic evaluation system for technical education at the University level

IEEE Transactions on Education, 2002

A Web-based automatic evaluation system for students of engineering faculties is described. The s... more A Web-based automatic evaluation system for students of engineering faculties is described. The system, named Test on Line (ToL), can verify the possession of ideas, the ability to combine them into deductions, and the capability to make simple numerical calculations for otherwise practical exercises. ToL has been extensively in use for basic physics courses at the engineering faculties of the Turin Politecnico since the beginning of 1999. Consequently, the accumulated statistical data amount to approximately four thousand individual tests and show the credibility both of the method and of its results. ToL generates, for each student, a proposed mark (which can be verified by an oral colloquium on demand by the candidate) and a simple cognitive profile showing possible cognitional, logical, or practical weaknesses in the different topics of the study matter. The core of the platform consists of a database of questions, a selection algorithm, and an evaluation procedure. The instrument and the method are being refined; the major improvements under construction are listed.

Research paper thumbnail of Verifying the learning process in physics

European Journal of Physics, 2001

The paper describes an automated evaluation system for the learning of general Physics. The syste... more The paper describes an automated evaluation system for the learning of general Physics. The system whose name is Test on Line (ToL) is based on a questions bank from which an appropriate software generates individual multi-issue questionnaires to be submitted through the web. ToL has been extensively experimented during three years and is presently in use for basic Physics courses at the Engineering Faculties of the Turin Politecnico. The results of the experimentation and use are presented and discussed. Cumulating data allows for an optimization of the internal partitions of the questions bank and of the selection criteria for the generation of the questionnaires. The instrument proved to be useful and reliable and could become the core of an agreed common standard for physics education at university level.

Research paper thumbnail of Effect of defects on electrical properties of 4H-SiC Schottky diodes

Materials Science and Engineering: C, 2008

Typical power switching devices such as diodes, thyristors, and transistors are based on a monocr... more Typical power switching devices such as diodes, thyristors, and transistors are based on a monocrystalline silicon semiconductor or silicon carbide. Silicon is less expensive, more widely used, and a more versatile processing material than silicon carbide. The silicon carbide (SiC) has ...

Research paper thumbnail of Correlation between gap density of states and recombination processes in high electronic quality aC:H

Journal of Non-crystalline Solids, 1998

. The investigation on electronic density of states DOS and photoluminescence processes in a-C:H ... more . The investigation on electronic density of states DOS and photoluminescence processes in a-C:H films has attracted, in the last years, interest, due to the foreseen technological application of carbon based materials. In this paper we present a new model for electronic DOS of a-C:H having sp 2 fraction less than a percolation threshold. This model is able to explain the optical absorption coefficient for photon energies in the range 0.7 to 3.5 eV. Moreover, with this model we correlate, as it happens in a-Si:H, the photoluminescence quantum efficiency and the density of states close to the Fermi energy. Such states, however, can have either diamagnetic or paramagnetic nature so that some of them can be detected by electron spin resonance and others by optical transitions. q

Research paper thumbnail of Characterization of silicon–YBCO buffered multilayers grown by sputtering

Applied Surface Science, 2004

In recent years, the scientific community has considered with interest the possibility to integra... more In recent years, the scientific community has considered with interest the possibility to integrate YBCO-based devices with silicon-based electronics. In fact, the proved YBCO radiation hardness makes this integration appealing from the point of view of space and telecommunication applications. In this paper we report on the influence of buffered substrate properties on the superconducting performances of YBCO films. In this framework we here consider the Si/CeO 2 /YBCO multilayer. The nonsatisfying quality of the YBCO film in this multilayer is attributed to an unavoidable interlayer of SiO 2 between Si and CeO 2 . On the other hand, we prove, by means of quantitative magneto-optical analysis, the excellent properties of the bi-layer CeO 2 / YBCO on YSZ substrate. Thus, these measurements indicate YSZ as the best candidate to be deposited between Si and CeO 2 for optimal YBCO performances on silicon. #

Research paper thumbnail of Light induced defects in amorphous silicon-carbon alloys aSiC:H

Optical Materials, 1996

Silicon-carbon alloys were prepared using a UHV PECVD system by the mixture of CH 4 + Sill 4 with... more Silicon-carbon alloys were prepared using a UHV PECVD system by the mixture of CH 4 + Sill 4 with and without hydrogen dilution. The CH 4 fraction in the plasma was varied between 40 and 95%. The energy gap of our samples varies between 1.8 and 2.5 eV. The effect of degradation induced by light exposure for several hours was studied using Photothermal Deflexion Spectroscopy (PDS). The experimental data are consistent with a bond breaking model, by conversion of tail weak bonds into dangling bonds. The data show more stability in the optoelectronic properties of diluted samples.

Research paper thumbnail of Intrinsic pinning and current percolation signatures in E-J characteristics of Si/YSZ/CeO 2 /YBCO layouts

European Physical Journal B, 2005

In the context of superconducting electronics integrated with traditional silicon-based electroni... more In the context of superconducting electronics integrated with traditional silicon-based electronics we grew Si/YSZ/CeO2/YBa2Cu3O7-x architectures by means of the scalable magnetron sputtering growth technique. In this paper we report on structural, surface and electrical transport characterization of typical multilayers. We focus on the electrical transport characterization in the temperature range 18–30 K of c-axis YBa2Cu3O7-x films grown on top of several (001) oriented buffered substrates. The electric field vs. current density (E-J) curves exhibit step-like behaviour in correspondence to the transition between the non-dissipative and the flux-flow regimes. This trend is accompanied by the signature of linearly correlated pinning. On the other hand, in the flux-flow regime clear signatures of weak-link behaviour and current percolation are exhibited. In this complex framework possible future applications are discussed.

Research paper thumbnail of Observation of negative capacitance in aSiC:H/aSi:H UV photodetectors

Solid-state Electronics, 2006

UV photosensors based on a-Si:H/a-SiC:H were deposited by ultra high vacuum plasma enhanced chemi... more UV photosensors based on a-Si:H/a-SiC:H were deposited by ultra high vacuum plasma enhanced chemical vapour deposition system (UHV-PECVD) over a large area (10 cm · 10 cm) in p-i-n configuration.

Research paper thumbnail of Structural and optoelectronic properties of doped microcrystalline silicon carbide films

Semiconductor Science and Technology, 1994

Undoped and phosphorus-doped microcrystalline silicon carbide ( mu c-SiC:H) films were deposited ... more Undoped and phosphorus-doped microcrystalline silicon carbide ( mu c-SiC:H) films were deposited by plasma-enhanced chemical vapour deposition (PECVD) with high hydrogen dilution and high RF power density. The doped films obtained have a bandgap up to 2.0 eV and electrical dark conductivity up to 17 S cm-1. The thermoelectric power (TEP) measurements and the behaviour of the conductivity and Hall

Research paper thumbnail of Influence of hydrogen on the evolution of structural properties of amorphous silicon carbide

Journal of Non-crystalline Solids, 1991

Device-quality films of a-SiC:H deposited by glow-discharge and reactive sputtering have been sub... more Device-quality films of a-SiC:H deposited by glow-discharge and reactive sputtering have been subjected to annealing treatments in the range 200-800°C in order to study the influence of hydrogen on the evolution of their structural properties. IR, density, optical and electrical measurements contribute to identify the different phase transitions of the network.

Research paper thumbnail of Modelling and analysis of aSiC:H p–i–n photodetectors: Effect of hydrogen dilution on dynamic model

Solid-state Electronics, 2007

The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in ... more The p-i-n structure of photodetectors and solar cells in amorphous materials and particularly in amorphous silicon and its compounds are the object of intense research works. By starting on the concept that such p-i-n structures can be compared to p + -n and n-n + junctions in series, and by referring to Shockley's model in one modified diode, we propose an equivalent electrical circuit in dynamic state of the considered structure resulting from a series association of Shockley's model. A simulation study by PSPICE of the equivalent electrical circuit so obtained is in good agreement with the experimental results, and physical interpretations connected to this model are discussed.

Research paper thumbnail of Publications of Emanuele Centurioni

Research paper thumbnail of Investigation on electronic density of states in a-SixC1-x: H films

Applied Surface Science, 1993

Films of a-Si xC 1- x: H with different carbon contents were deposited by an ultrahigh vacuum pla... more Films of a-Si xC 1- x: H with different carbon contents were deposited by an ultrahigh vacuum plasma enhanced chemical vapour desposition system and characterized by means of the following experimental techniques: photothermal deflection spectroscopy, constant photocurrent method, optical modulation spectroscopy and electron spin resonance. The results include data on optical gap, Urbach tail energy, thermal activation energy of dark conductivity, density and distribution of defects and quantum efficiency-mobility-lifetime product. Comparison of the data obtained with the different techniques is presented and discussed.

Research paper thumbnail of Influence of film thickness on optical and electrical properties of hydrogenated amorphous silicon

Thin Solid Films, 1987

The optical and electrical properties of hydrogenated amorphous silicon (a-Si:H) films produced b... more The optical and electrical properties of hydrogenated amorphous silicon (a-Si:H) films produced by magnetron sputtering (SP) and glow discharge (GD) were studied as a function of the film thickness (50-300 nm). A strong dependence on the thickness was observed in the maximum values of the absorption coefficient and in the energy gap Eg (obtained from (~E) 1/2 vs. E plots) for both series. For the SP films the refractive index n(2) increased with thickness, whereas for GD films e2,,a ~ and its corresponding energy decreased with increasing thickness. The resistivity values are within the range of typical values for a-Si:H, but no effect of thickness was observed, because of non-uniformity of the films and band bending at the substrate interface.

Research paper thumbnail of Compositional and structural properties of hydrogenated amorphous silicon-carbon films prepared by ultra-high-vacuum plasma-enhanced chemical vapour deposition with different carbon sources

Philosophical Magazine A-physics of Condensed Matter Structure Defects and Mechanical Properties, 1995

ABSTRACT

Research paper thumbnail of Correlation between gap density of states and recombination processes in high electronic quality aC:H

Journal of Non-crystalline Solids, 1998

. The investigation on electronic density of states DOS and photoluminescence processes in a-C:H ... more . The investigation on electronic density of states DOS and photoluminescence processes in a-C:H films has attracted, in the last years, interest, due to the foreseen technological application of carbon based materials. In this paper we present a new model for electronic DOS of a-C:H having sp 2 fraction less than a percolation threshold. This model is able to explain the optical absorption coefficient for photon energies in the range 0.7 to 3.5 eV. Moreover, with this model we correlate, as it happens in a-Si:H, the photoluminescence quantum efficiency and the density of states close to the Fermi energy. Such states, however, can have either diamagnetic or paramagnetic nature so that some of them can be detected by electron spin resonance and others by optical transitions. q