M. Salvato

M. Salvato
University of Rome Tor Vergata | UNIROMA2 · Dipartimento di Fisica

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126
Publications
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Publications

Publications (126)
Article
In the last years, epitaxial graphene (epi-Gr) demonstrated to be an excellent substrate for the synthesis of epitaxial or intercalated two dimensional (2D) materials. Among 2D materials, silicene has been for a long time a dream for the scientific community, for its importance both from fundamental and application point of view. Despite the theore...
Article
Full-text available
Nanoribbons of topological insulators (TIs) have been suggested for a variety of applications exploiting the properties of the topologically protected surface Dirac states. In these proposals it is crucial to achieve a high tunability of the Fermi energy, through the Dirac point while preserving a high mobility of the involved carriers. Tunable tra...
Article
Full-text available
Photodetector (PD) devices based on carbon nanotube/n-silicon heterojunction (NSH) have been realized, with a linear response in a large optical power range, proving competitive performances with respect to a recent nanostructure-based detector and those currently available on the market. The core of these devices is a thin semi-transparent and con...
Article
A graphene/silicon heterojunction device has been realized to overcome many different requests necessary to make it a versatile, widely used and competitive detector. The obtained photodetectors which operate at room temperature, are sensitive in the spectral region from the ultraviolet (240 nm) to the infrared (2000 nm) and they can be used in dif...
Preprint
A new fabrication process is developed for growing Bi2Se3 topological insulators in the form of nanowires/nanobelts and ultra-thin films. It consists of two consecutive procedures: first Bi2Se3 nanowires/nanobelts are deposited by standard catalyst free vapour-solid deposition on different substrates positioned inside a quartz tube. Then, the Bi2Se...
Article
We have used Bi 2 Se 3 nanoribbons, grown by catalyst-free physical vapor deposition to fabricate high quality Josephson junctions with Al superconducting electrodes. In our devices, we observe a pronounced reduction of the Josephson critical current density J c by reducing the width of the junction, which in our case corresponds to the width of th...
Preprint
We have used Bi$_2$Se$_3$ nanoribbons, grown by catalyst-free Physical Vapor Deposition to fabricate high quality Josephson junctions with Al superconducting electrodes. In our devices we observe a pronounced reduction of the Josephson critical current density $J_c$ by reducing the width of the junction, which in our case corresponds to the width o...
Article
A new fabrication process is developed for growing Bi2Se3 topological insulators in the form of nanowires/nanobelts and ultra-thin films. It consists of two consecutive procedures: first Bi2Se3 nanowires/nanobelts are deposited by standard catalyst free vapour-solid deposition on different substrates positioned inside a quartz tube. Then, the Bi2Se...
Article
Graphene (Gr) is known to be an excellent barrier preventing atoms and molecules to diffuse through it. This is due to the carbon atom arrangement in a two-dimensional (2D) honeycomb structure with a very small lattice parameter forming an electron cloud that prevents atoms and molecules crossing. Nonetheless at high annealing temperatures, interca...
Preprint
Full-text available
Highly oriented pyrolitic graphite (HOPG) is an inert substrate with a structural honeycomb lattice, well suited for the growth of two-dimensional (2D) silicene layer. It was reported that when Si atoms are deposited on HOPG surface at room temperature, they arrange in two configurations: silicene nanosheets and three dimensional clusters. In this...
Article
We investigated the response of carbon nanotube/Si photodetectors to nanosecond light pulse using two electrode configurations for photovoltaic and photoconductive operations. When operating in photovoltaic mode, the devices show a linear dependence of the photocurrent as a function of the light pulse energy with rise time of 20 ns. In photoconduct...
Article
To take advantage of the graphene appealing electronic properties, in this work we present a photodetector (PD) based on graphene/n-silicon heterojunction (GSH). In this device, graphene acts as light transmitter, counter electrode junction element and photocarrier collector. The photodetector has been provided with metal contacts allowing either p...
Article
Photodetectors (PDs) based on single-walled carbon nanotube film/silicon and graphene/silicon heterojunctions have been realized for fast applications. We investigated the response of the PDs to femtosecond pulsed laser using a three-electrode configuration for photoconductive operations. Both junction PDs exhibit rise times of some nanoseconds, de...
Article
Large nanostructures of silicene have been successfully grown on graphene covered 6H-SiC (0001) substrates. The graphene played an important role to obtain honeycomb structures of silicon in sp2 configuration and acting as an ideal template for 2D materials. The scanning tunneling microscopy (STM) images showed nanosheets of silicene with a very sm...
Article
Highly oriented pyrolitic graphite (HOPG) is an inert substrate with a structural honeycomb lattice, well suited for the growth of two-dimensional (2D) silicene layer. It was reported that when Si atoms are deposited on HOPG surface at room temperature, they arrange in two configurations: silicene nanosheets and three dimensional clusters. In this...
Article
Single-walled carbon nanotube (SWCNT) ultrathin films were deposited on n-doped Si substrates provided with three electrodes for photoconductive measurements. Without illumination, the devices show good rectifier properties and holes mobility in the range 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xli...
Article
The fascinating properties of two dimensional (2D) crystals have gained increasing interest for many applications. The synthesis of a 2D silicon structure, namely silicene, is attracting great interest for possible development of next generation electronic devices. The main difficulty in working with silicene remains its strong tendency to oxidatio...
Article
A systematic study of the optical response of photodetectors based on carbon nanotube/Si heterojunctions is performed by measuring the responsivity, the detectivity and the time response of the devices with different contact configurations. The sensors are obtained by dry transferring single-walled carbon nanotube films on the surface of n-doped Si...
Article
Single Walled Carbon Nanotube/n-Si (SWCNT/n-Si) hetero-junctions have been obtained by depositing SWCNT ultra-thin films on the surface of an n-Si substrate by dry transfer method. The as obtained junctions are photo sensitive in the measured wavelength range (300 nm-1000 nm) and show zero bias responsivity and detectivity values of the order of 1...
Article
Superconducting NbN nanonetworks with a very small number of interconnected nanowires, with diameter of the order of 4 nm, are fabricated combining a bottom-up (use of porous silicon nanotemplates) with a top-down technique (high-resolution electron beam lithography). The method is easy to control and allows to fabricate, on a robust support, devic...
Article
Superconducting strips coated with boron were engineered with a view to subnuclear particle detection. Combining the characteristics of boron as a generator of α-particles (as a consequence of neutron absorption) and the ability of superconducting strips to act as resistive switches, it is shown that fabricated Nb–boron and NbN–boron strips represe...
Article
Bulk heterojunction films made of polychiral single-walled carbon nanotubes (SWCNTs) form efficient heterojunction solar cells with n-type crystalline silicon (n-Si), due to their superior electronic, optical, and electrical properties. The films are multi-functional, since their hierarchical surface morphology provides a biomimetical anti-reflecti...
Article
Superconducting thin films of the noncentrosymmetric superconductor Nb 0.18 Re 0.82 were successfully deposited by UHV sputtering technique. X-ray diffraction analysis indicated that the films are polycrystalline, with a preferential (nn0) orientation and the lattice parameter in agreement with the expected single α-Mn cubic phase. A detailed elect...
Article
Full-text available
A neutron detection concept is presented that is based on superconductive niobium nitride (NbN) strips coated by a boron (B) layer. The working principle is well described by a hot spot mechanism: upon the occurrence of the nuclear reactions n + ¹⁰B → α + ⁷Li + 2.8 MeV, the energy released by the secondary particles into the strip induces a superco...
Article
The transport properties of CaCuO2/SrTiO3 single interfaces are studied by resistance versus temperature measurements in external magnetic fields. The superconducting anisotropy where and are the superconducting coherence lengths parallel and perpendicular to the interface, respectively, shows values higher than that previously obtained for CaCuO2/...
Article
Full-text available
A new neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction 10B+n $\rightarrow$ $\alpha$+ 7Li , with $\alpha$ and Li ions generating a hot spot on the current-biased Nb strip which in turn induces a superconducting...
Article
Superconducting niobium (Nb) has been successfully obtained by sputter deposition on carbon nanotube fibers. The transport properties of the niobium coating the fibers are compared to those of niobium thin films deposited on oxidized Si substrates during the same deposition run. For niobium films with thicknesses above 300 nm, the niobium coating t...
Article
We report on the characterization of electroformed copper. Different copper films have been deposited, on a brass rod, paying attention to modify only one parameter of the galvanic bath for each specimen (acidity, temperature, density of current, etc.). The samples obtained have been analyzed by residual resistivity ratio (RRR) to evaluated the ele...
Article
Full-text available
Measurements performed on superconductive networks shaped in the form of planar graphs display anomalously large currents when specific branches are biased. The temperature dependencies of these currents evidence that their origin is due to Cooper pair hopping through the Josephson junctions connecting the superconductive islands of the array. The...
Article
The superconducting properties of (CaCuO2)n/(SrTiO3)m artificial superlattices have been investigated via transport measurements under the application of external magnetic fields. The coherence lengths in the plane of the substrate and in the direction perpendicular to it (ξab and ξc, respectively) have been measured while varying m, the thickness...
Article
Full-text available
We report the occurrence of superconductivity, with maximum Tc=40 K, in superlattices (SLs) based on two insulating oxides, namely CaCuO2 and SrTiO3. In these (CaCuO2)n/(SrTiO3)m SLs, the CuO2 planes belong only to CaCuO2 block, which is an antiferromagnetic insulator. Superconductivity, confined within a few unit cells at the CaCuO2/SrTiO3 interfa...
Article
Full-text available
We investigate the transport properties of granular nickel electrodeposited on carbon nanotube fibers by measuring the electrical resistance and the current voltage characteristics as a function of the temperature. The bare fiber is governed by a three-dimensional variable range hopping transport mechanism, however, a semiconducting to metallic tra...
Article
Full-text available
We report on experiments conducted on single-walled carbon nanotube bundles aligned in chains and connected through a natural contact barrier. The dependence upon the temperature of the transport properties is investigated for samples having different characteristics. Starting from two bundles separated by one barrier deposited over four-contact pr...
Article
MgB2 thin films were grown in-situ at INFM- University of Naples by a magnetron sputtering technique in a UHV system (10-7 Pa) equipped with 3 focused 2′′ magnetron sources (a stoichiometric MgB2 and metallic Mg and B targets by Superconducting Components Inc.). The substrates (sapphire or MgO) were placed "on axis" at 7 cm from the target surface...
Article
We report on the preparation and the structural characterization of both YBa2Cu3O7-δ/La0.7Ca0.3MnO3 and La0.7Ca0.3MnO3/YBa2Cu3O7-δ bilayers grown onto (100) SrTiO3 substrates. The samples have been realized by sequential dc sputtering processes in high oxygen pressure starting from stoichiometric targets. The X-ray diffractograms and ϕ-scan reveal...
Article
High temperature superconducting multilayers have been obtained depositing Bi2Sr2CuO6+δ(2201) and ACuO2 layers, where A is Ca or Sr, by Molecular Beam Epitaxy (MBE) on MgO and SrTiO3 substrates. The samples, formed by a sequence of 2201/ACuO2 bilayers, have different thickness of ACuO2 layers while the thickness of the 2201 layers is kept constant....
Article
Full-text available
We investigate the effect of potassium (K) doping on the transport properties of aligned single-walled carbon nanotube fibers. The temperature dependence of the electrical resistance, the current-voltage characteristics, and the magnetoresistance vs external magnetic field of the fibers consistently show that doping enhances the metallic character...
Article
Full-text available
We compare, over wide temperature ranges, the transport properties of single-wall carbon nanotubes arranged in the form of aligned arrays or in the form of fibres. The experimental data show that both the forms of aggregates present a crossover in the transport mechanism from three-dimensional hopping of the electrons between localized states at hi...
Article
Full-text available
We present an innovative approach for interconnections based on aligning nanosized nickel particles along single-walled carbon nanotubes bundles. The nanotubes are first deposited to connect normal gold contacts or niobium nitride superconducting pads and a successive step in fabrication, based on an electrochemical method, enables us to “coat” the...
Article
Full-text available
We report the occurrence of superconductivity, with maximum Tc = 40 K, in superlattices (SLs) based on two insulating oxides, namely CaCuO2 and SrTiO3. In these (CaCuO2)n/(SrTiO3)m SLs, the CuO2 planes belong only to CaCuO2 block, which is an antiferromagnetic insulator. Superconductivity, confined within few unit cells at the CaCuO2/SrTiO3 interfa...
Article
Full-text available
Heterostructures engineering by advanced layer by layer deposition techniques has been recently exploited to synthesize novel high transition temperature (Tc) superconductors based on insulating and metallic (non-superconducting) cuprates. However, in those heterostructures, at least one of the constituents can individually develop superconductivit...
Article
Full-text available
We investigate the effects of magnetic and electric fields on electron wavefunction interactions in single walled carbon nanotube bundles. The magnetoresistance measurements performed at 4.2K and the dependence of the data upon the electric field, obtained by varying the bias current through the samples, reveal good agreement with weak localization...
Article
We report on oscillations of a Josephson-junction system revealing a close analogy with fundamental effects known in laser physics. The experiments are performed on series arrays of junctions whose IV curves show evidence of a mode in which all the junctions oscillate in synchronism on resonances appearing, in zero external magnetic field, at multi...
Article
Full-text available
We report on experiments conducted on single walled carbon nanotube bundles aligned in chains and connected through a natural contact barrier. The dependence upon the temperature of the transport properties is investigated for samples having different characteristics. Starting from two bundles separated by one barrier deposited over four contact pr...
Article
Full-text available
We investigate experimentally the transport properties of single-walled carbon nanotube bundles as a function of temperature and applied current over broad intervals of these variables. The analysis is performed on arrays of nanotube bundles whose axes are aligned along the direction of the externally supplied bias current. The data are found consi...
Article
Transport properties of single and multiwalled carbon nanotubes, with the tube axes aligned along the bias current direction, have been studied as a function of the temperature and applied current. The experimental data are consistent with a model of charge transport governed by tunnel between potential barriers created at the connection between th...
Article
Full-text available
Series arrays of Josephson junctions show evidence of a mode in which all the junctions oscillate in synchronism on voltage resonances appearing, in zero external magnetic field, at multiples of the fundamental Fiske step spacing. The measurements show that the current amplitude of the resonances increases linearly as their voltages are summed. Inv...
Article
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We have integrated on oxidized silicon wafers superconductive films and Josephson junctions along with sol-gel optical channel waveguides. The fabrication process is carried out in two steps that result to be solid and noninvasive. It is demonstrated that 660 nm light, coupled from an optical fiber into the channel sol-gel waveguide, can be directe...
Article
Copper thin films have been deposited on Si substrates by molecular beam epitaxy (MBE) at different deposition rates varying from 1 up to 22Å/s. X-ray reflectivity and θ–2θ measurements have shown that the surface roughness correlation length, the structural disorder and the grain dimensions are strongly affected by the deposition rate. Comparing t...
Article
NbN superconductor and wide band gap AlN thin films were deposited using sputtering at room temperature. Study of the nitride interfaces are forerunner to the growth Josephson junctions that are considered able to work in the terahertz frequency. We find that to be compatible with lithography technology and to have a high critical transition temper...
Article
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We have investigated the dissipative behaviour of MgB2 textured thin films at different perpendicular magnetic fields H and bias currents J, to study activation energy dependencies U(J) and U(H). For J < J*, where J* is a magnetic-field–dependent crossover current, activation energies are weakly current dependent, U(J) ≈ const, while, for J > J*, U...
Article
Full-text available
Pinning properties of Nb/CuMn multilayers with regular array of antidots have been studied at different temperatures in perpendicular magnetic field. The presence of antidots causes a sudden increase (jump) of the critical current at the liquid-helium lambda point (T = 2.18 K). The jump value is a function of magnetic field and sample anisotropy. T...
Article
The growth of scandium, titanium and zirconium diborides thin films by pulsed laser ablation technique on different substrates has been studied. In situ reflection high energy electron diffraction and ex situ X-ray diffraction analyses indicate that the films are strongly c-axis oriented on all the substrates and also epitaxial, apart from Si(111),...
Article
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We have investigated the influence of thickness on the pinning properties of granular sputtered Nb films in a parallel magnetic field. The presence of a crossover in the pinning mechanisms at some critical thickness dc was established. Below dc the pinning is due to individual vortices. Above dc the commensurability between the vortex period and th...
Conference Paper
A new deposition technology has been developed, based on a cathodic arc system working under UHV conditions to produce metallic thin films. The trchnique presents several advantages compared to standard sputtering, mainly: ionized state of the evaporated material, absence of gases to sustain the discharge, higher energy of atoms reaching the substr...
Article
Full-text available
Resistivity vs. temperature measurements on La0.7Ca0.3MnO3/YBa2Cu3O7-delta /La0.7Ca0.3MnO3 (LCMO/YBCO/LCMO) trilayers with different YBCO thickness, were performed in external magnetic field H up to 8 T. By evaluating the activation energy U from the slope of the resistivity Arrhenius plot, a strong depression of U has been observed when decreasing...
Article
The transport properties of superconductor/weak ferromagnet Nb/Pd86Ni14 sputtered bilayers have been studied. The critical thickness needed for superconductivity to develop is determined from the dependence of the transition temperature Tc on dNb.
Article
Full-text available
The proximity effect between a superconductor (S) and a weak ferromagnet (F) in sputtered Nb/Pd0.86Ni0.14 bilayers has been studied. The dependence of the critical temperature on the S- and F-layer thicknesses can be interpreted in the framework of recent theoretical models and yields reasonable numbers for the exchange energy of the ferromagnet an...
Article
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The angular dependence of the upper critical field, Hc(Θ), for Nb∕Pd multilayers with different geometrical symmetries (i.e., with an even or an odd number of bilayers, Nbil) and thickness of Nb and Pd layers of the order of superconducting coherence length were investigated (the angle Θ is here defined from the plane parallel to the sample surface...
Article
Full-text available
The effect of oxygen annealing on the structural and transport properties of La0.7Ca0.3MnO3 thin films deposited on SrTiO3 substrates has been investigated by x-ray diffraction analysis and resistive measurements. The as-grown films are fully tensile strained on the substrates and show a depressed metal-insulator transition temperature Tp = 131 K....
Conference Paper
Electrical transport properties of LCMO/YBCO/LCMO trilayers have been studied by resistivity versus temperature measurements in external magnetic fields up to 8 Tesla. The samples were characterized by similar LCMO thickness and different YBCO thickness. The experimental results show resistive transitions which reflect different properties of the s...
Article
We report on the preparation and the structural characterization of both YBa 2 Cu 3 O 7-δ / La 0.7 Ca 0.3 MnO 3 and La 0.7 Ca 0.3 MnO 3 / YBa 2 Cu 3 O 7-δ bilayers grown onto (100) SrTiO3 substrates. The samples have been realized by sequential dc sputtering processes in high oxygen pressure starting from stoichiometric targets. The X-ray diffracto...
Conference Paper
Full-text available
The angular dependence of the upper critical magnetic field, H c2(θ), for Nb/Pd proximity coupled multilayered nanostructures with a thickness of Nb and Pd layers of the order of the superconducting coherence length were investigated. We show that the deviation of the experimental data from the theory is temperature dependent. The performed precise...
Article
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We have investigated, in the framework of the proximity effect theory, the interface transparency between Nb and Cu in the case of high quality Nb/Cu trilayers fabricated by molecular beam epitaxy (MBE) and sputtering deposition techniques. The obtained values do not seem to be strongly influenced by the fabrication methods but more by the intrinsi...
Article
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The influence of the finite dimensions of superconducting metallic multilayers on H-T phase diagram is studied. It is established that the geometrical symmetry of the samples determines crucially the Hc2||(T)H_{c2\vert \vert}(T) dependencies. For samples where the symmetry plane is in the middle of the superconducting layer the Hc2||H_{c2\vert \v...
Article
Transport properties of superconducting polycrystalline GdSr2RuCu2O8 have been studied by resistivity versus temperature measurements in external magnetic fields up to 8 T. The analysis of the experimental data shows that an activated pinning mechanism is present with low values of the pinning energy and that an irreversibility line (IL) can be ide...