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Papers by Vittorio Morandi
Applied Physics Letters, 2014
ABSTRACT We report on the epitaxial growth of Ge virtual substrates directly on Si (001) and on d... more ABSTRACT We report on the epitaxial growth of Ge virtual substrates directly on Si (001) and on different porosity porous silicon (pSi) buffers. Obtained results indicate that Ge grown on low porosity (22%) pSi buffer has a better crystalline quality compared to Ge grown on bulk Si and on higher porosity buffers. This result is attributed to the compliant nature of pSi and to its reduced Young's modulus, which leads to plastic tensile deformation of the 22% porosity buffer under the in-plane tensile stress introduced by Ge lattice. The same result is not observed for higher porosity buffers, this effect being attributed to the higher buffer fragility. A low porosity pSi layer can hence be used as buffer for the growth of Ge on Si virtual substrates with reduced dislocation content and for the growth of Ge based devices or the successive integration of III-V semiconductors on Si.
In this work we investigate the use of graphene as transducer in a novel biosensor for biomedical... more In this work we investigate the use of graphene as transducer in a novel biosensor for biomedical uses, in which electroactive membrane proteins would serve as biological recognition elements. Membrane proteins maintain their functionalities only if embedded in the cell membrane, so it is necessary to develop a system, which mimics their native environment. This study is focused on surface treatments of graphene to improve its biocompatibility and a first investigation of its interaction with liposomes, which rupture and spread to form a Supported Lipid Bilayer under specific surface conditions. The first step involved the characterization of the graphene membranes synthesized by Chemical Vapor Deposition, using several techniques to determine their morphological and structural properties. From these investigations, the CVD-synthesized graphene resulted to be mono- to few-layer. Next, the interaction of graphene with lipids (1,2-dioleoyl-sn-glicero-3-phosphocholine), in particular t...
EMC 2008 14th European Microscopy Congress 1–5 September 2008, Aachen, Germany, 2008
In the last fifteen years a significant work on the interpretation of Backscattered Electron (BSE... more In the last fifteen years a significant work on the interpretation of Backscattered Electron (BSE) and Secondary Electron (SE) compositional imaging has been performed. The starting point of the research was represented by the experimental evidence of nanometric resolution of compositional features in BSE and SE imaging at relatively high energy (20–30 keV). The interpretation of these results required a
EMC 2008 14th European Microscopy Congress 1–5 September 2008, Aachen, Germany, 2008
ABSTRACT In the last few years the STEM technique in standard SEMs has become a complementary app... more ABSTRACT In the last few years the STEM technique in standard SEMs has become a complementary approach to HAADF-STEM at high energy [1, 4], at least when high resolution is not required, as demonstrated by the availability of STEM attachments for all the commercial SEMs.
Solar Energy Materials and Solar Cells, 2015
A transparent conductive graphene film is investigated as front contact in dye-sensitized solar c... more A transparent conductive graphene film is investigated as front contact in dye-sensitized solar cells (DSSCs), as an alternative to traditional transparent conducting oxides (TCO). The film is composed of poly-crystalline few-layers graphene, covering homogeneously an area of 1 cm 2 , deposited by chemical vapour deposition (CVD) technique on larger area Cu catalyst substrate and transferred on glass. DSSC photoanode is then fabricated, according to consolidated procedure, by sequential casting of TiO 2 films through tape casting technique, followed by annealing at 500 1C, and sensitization with N719 dye. An outstanding value of photoconversion efficiency as high as 2% is recorded for the best cell, under one sun irradiation (AM 1.5 G, 100 mW cm À 2 ), which is the highest ever reported for this kind of devices using graphene as front conducting film. Compared to previous results in the literature, the application of a large area continuous graphene film, guaranteed by the CVD deposition, definitely outperforms graphene layers composed by smaller graphene platelets (at micrometer scale). Morphological and electrical characterizations of graphene are reported and the functional performances of the best cell are compared with those obtained from classical DSSC exploiting fluorine-doped tin oxide. Obtained results encourage further investigation of graphene homogeneous thin film as viable alternative to standard TCOs for application in advanced devices, requiring high temperature processing or flexible substrates, incompatible with standard TCO films.
Carbon Nanostructures, 2012
Chemical communications (Cambridge, England), Jan 10, 2015
Reduction of carbon nanohorn (CNH) aggregates with potassium naphthalenide resulted in their dism... more Reduction of carbon nanohorn (CNH) aggregates with potassium naphthalenide resulted in their dismantling and individualization. Furthermore, the reduced CNHs were functionalized via addition of electrophiles.
We investigated the adhesion of single-walled carbon nanotubes to the surface of graphene membran... more We investigated the adhesion of single-walled carbon nanotubes to the surface of graphene membranes using aberration-corrected transmission electron microscopy. We mixed nanotubes of different chiralities with a solution of dispersed graphene flakes. The spontaneous atomic match of the two lattices was directly imaged using high-resolution transmission electron microscopy, and we found evidences of a chirality dependent grafting of the tubes to the surface of the graphene membranes.
Macromolecular Chemistry and Physics, 2015
ABSTRACT Graphene–epoxy flexible capacitors are obtained by graphene–polymer transfer and bonding... more ABSTRACT Graphene–epoxy flexible capacitors are obtained by graphene–polymer transfer and bonding via UV-cured epoxy adhesive. Ceramic fillers are dispersed into the epoxy resin with the aim of enhancing the capacitive behavior of the final device. Parallel plate capacitors in which epoxy resin is filled with ceramic nanoparticles demonstrate superior performance, up to two orders of magnitude better than unfilled samples. Zirconia, showing the highest dielectric constant, fails to give a stable output in the whole frequency range, as some competing phenomena occur and reduce the overall polarization of the system. Boehmite appears to be a better choice and gives reasonable performances, better than gibbsite.
Sensors and Actuators a-Physical, 2006
The focus of this study is on the adsorption properties of nanocrystalline materials and SnO 2 ha... more The focus of this study is on the adsorption properties of nanocrystalline materials and SnO 2 has been chosen as the appropriate example. Nanocrystalline SnO 2 , in fact, has many practical applications for gas sensors but is virtually absent from the current physico-chemical literature on nanomaterials. The purpose of this study is a deeper understanding of its gas-absorbing properties in order to better exploit its gas-sensor applications. Therefore model structures consisting on small SnO 2 grains have been considered and the adsorbed system is generated by depositing a CO molecule above a tin, or oxygen, atom on the grain surface. The calculations illustrate the structural properties of grains, their binding and adsorption energies and their conductance and are based on semi-empirical Hartree-Fock and scattering theories. It has been found that the molecule is stably bonded to the grain without penetration or intermixing and adsorption is not dissociative. These are also properties of adsorption on the surfaces of bulk samples. However the analysis of the adsorbed system indicates that stable adsorption derives from the molecule being integrated into the grain structure. Furthermore adsorption depends on the grain shape, on the adsorption site and on the orientation of the molecule. These dependencies do not exist in the bulk, though the values of the adsorption energy may be similar in the two cases. In agreement with known properties of structures of finite size, the conductance changes with the grain structure. A relevant result is that the dependence of this quantity on the grain size and shape is the same as the one of the binding and of the adsorption energies.
Applied Physics Letters, 2014
ABSTRACT We report on the epitaxial growth of Ge virtual substrates directly on Si (001) and on d... more ABSTRACT We report on the epitaxial growth of Ge virtual substrates directly on Si (001) and on different porosity porous silicon (pSi) buffers. Obtained results indicate that Ge grown on low porosity (22%) pSi buffer has a better crystalline quality compared to Ge grown on bulk Si and on higher porosity buffers. This result is attributed to the compliant nature of pSi and to its reduced Young's modulus, which leads to plastic tensile deformation of the 22% porosity buffer under the in-plane tensile stress introduced by Ge lattice. The same result is not observed for higher porosity buffers, this effect being attributed to the higher buffer fragility. A low porosity pSi layer can hence be used as buffer for the growth of Ge on Si virtual substrates with reduced dislocation content and for the growth of Ge based devices or the successive integration of III-V semiconductors on Si.
In this work we investigate the use of graphene as transducer in a novel biosensor for biomedical... more In this work we investigate the use of graphene as transducer in a novel biosensor for biomedical uses, in which electroactive membrane proteins would serve as biological recognition elements. Membrane proteins maintain their functionalities only if embedded in the cell membrane, so it is necessary to develop a system, which mimics their native environment. This study is focused on surface treatments of graphene to improve its biocompatibility and a first investigation of its interaction with liposomes, which rupture and spread to form a Supported Lipid Bilayer under specific surface conditions. The first step involved the characterization of the graphene membranes synthesized by Chemical Vapor Deposition, using several techniques to determine their morphological and structural properties. From these investigations, the CVD-synthesized graphene resulted to be mono- to few-layer. Next, the interaction of graphene with lipids (1,2-dioleoyl-sn-glicero-3-phosphocholine), in particular t...
EMC 2008 14th European Microscopy Congress 1–5 September 2008, Aachen, Germany, 2008
In the last fifteen years a significant work on the interpretation of Backscattered Electron (BSE... more In the last fifteen years a significant work on the interpretation of Backscattered Electron (BSE) and Secondary Electron (SE) compositional imaging has been performed. The starting point of the research was represented by the experimental evidence of nanometric resolution of compositional features in BSE and SE imaging at relatively high energy (20–30 keV). The interpretation of these results required a
EMC 2008 14th European Microscopy Congress 1–5 September 2008, Aachen, Germany, 2008
ABSTRACT In the last few years the STEM technique in standard SEMs has become a complementary app... more ABSTRACT In the last few years the STEM technique in standard SEMs has become a complementary approach to HAADF-STEM at high energy [1, 4], at least when high resolution is not required, as demonstrated by the availability of STEM attachments for all the commercial SEMs.
Solar Energy Materials and Solar Cells, 2015
A transparent conductive graphene film is investigated as front contact in dye-sensitized solar c... more A transparent conductive graphene film is investigated as front contact in dye-sensitized solar cells (DSSCs), as an alternative to traditional transparent conducting oxides (TCO). The film is composed of poly-crystalline few-layers graphene, covering homogeneously an area of 1 cm 2 , deposited by chemical vapour deposition (CVD) technique on larger area Cu catalyst substrate and transferred on glass. DSSC photoanode is then fabricated, according to consolidated procedure, by sequential casting of TiO 2 films through tape casting technique, followed by annealing at 500 1C, and sensitization with N719 dye. An outstanding value of photoconversion efficiency as high as 2% is recorded for the best cell, under one sun irradiation (AM 1.5 G, 100 mW cm À 2 ), which is the highest ever reported for this kind of devices using graphene as front conducting film. Compared to previous results in the literature, the application of a large area continuous graphene film, guaranteed by the CVD deposition, definitely outperforms graphene layers composed by smaller graphene platelets (at micrometer scale). Morphological and electrical characterizations of graphene are reported and the functional performances of the best cell are compared with those obtained from classical DSSC exploiting fluorine-doped tin oxide. Obtained results encourage further investigation of graphene homogeneous thin film as viable alternative to standard TCOs for application in advanced devices, requiring high temperature processing or flexible substrates, incompatible with standard TCO films.
Carbon Nanostructures, 2012
Chemical communications (Cambridge, England), Jan 10, 2015
Reduction of carbon nanohorn (CNH) aggregates with potassium naphthalenide resulted in their dism... more Reduction of carbon nanohorn (CNH) aggregates with potassium naphthalenide resulted in their dismantling and individualization. Furthermore, the reduced CNHs were functionalized via addition of electrophiles.
We investigated the adhesion of single-walled carbon nanotubes to the surface of graphene membran... more We investigated the adhesion of single-walled carbon nanotubes to the surface of graphene membranes using aberration-corrected transmission electron microscopy. We mixed nanotubes of different chiralities with a solution of dispersed graphene flakes. The spontaneous atomic match of the two lattices was directly imaged using high-resolution transmission electron microscopy, and we found evidences of a chirality dependent grafting of the tubes to the surface of the graphene membranes.
Macromolecular Chemistry and Physics, 2015
ABSTRACT Graphene–epoxy flexible capacitors are obtained by graphene–polymer transfer and bonding... more ABSTRACT Graphene–epoxy flexible capacitors are obtained by graphene–polymer transfer and bonding via UV-cured epoxy adhesive. Ceramic fillers are dispersed into the epoxy resin with the aim of enhancing the capacitive behavior of the final device. Parallel plate capacitors in which epoxy resin is filled with ceramic nanoparticles demonstrate superior performance, up to two orders of magnitude better than unfilled samples. Zirconia, showing the highest dielectric constant, fails to give a stable output in the whole frequency range, as some competing phenomena occur and reduce the overall polarization of the system. Boehmite appears to be a better choice and gives reasonable performances, better than gibbsite.
Sensors and Actuators a-Physical, 2006
The focus of this study is on the adsorption properties of nanocrystalline materials and SnO 2 ha... more The focus of this study is on the adsorption properties of nanocrystalline materials and SnO 2 has been chosen as the appropriate example. Nanocrystalline SnO 2 , in fact, has many practical applications for gas sensors but is virtually absent from the current physico-chemical literature on nanomaterials. The purpose of this study is a deeper understanding of its gas-absorbing properties in order to better exploit its gas-sensor applications. Therefore model structures consisting on small SnO 2 grains have been considered and the adsorbed system is generated by depositing a CO molecule above a tin, or oxygen, atom on the grain surface. The calculations illustrate the structural properties of grains, their binding and adsorption energies and their conductance and are based on semi-empirical Hartree-Fock and scattering theories. It has been found that the molecule is stably bonded to the grain without penetration or intermixing and adsorption is not dissociative. These are also properties of adsorption on the surfaces of bulk samples. However the analysis of the adsorbed system indicates that stable adsorption derives from the molecule being integrated into the grain structure. Furthermore adsorption depends on the grain shape, on the adsorption site and on the orientation of the molecule. These dependencies do not exist in the bulk, though the values of the adsorption energy may be similar in the two cases. In agreement with known properties of structures of finite size, the conductance changes with the grain structure. A relevant result is that the dependence of this quantity on the grain size and shape is the same as the one of the binding and of the adsorption energies.