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Poster presented at the 2021 European Conference on Silicon Carbide and Related Materials(ECSCRM).

In this paper, we address the unique nature of fully textured, high surface-to-volume 3C-SiC films, as produced by intrinsic growth anisotropy, in turn generated by the high velocity of the stacking fault growth front in two-dimensional (111) platelets. Structural interpretation of high resolution scanning electron microscopy and transmission electron microscopy data is carried out for samples grown in a hot-wall low-pressure chemical vapour deposition reactor with trichlorosilane and ethylene precursors, under suitable deposition conditions. By correlating the morphology and the X-ray diffraction analysis we also point out that twinning along (111) planes is very frequent in such materials, which changes the free-platelet configuration.

Silicon carbide detectors represent an alternative to diamond detectors for fast neutron detection in harsh environments, especially fusion plasmas. Previous studies on thin prototypes (either 10 μm or 100 μm thick) suggested that thicker active volumes might be better suited for spectroscopy measurements, due to the higher chance of retaining the neutron interaction products inside the active volume. Therefore, in this work two 250 μm SiC prototypes are tested with alpha particles following the same process conducted in the past for thinner prototypes. A stable detection is demonstrated, along an energy resolution that, if projected to DT neutrons, could become the lowest achieved so far with a SiC detector (1.3%). Some difficulties in reaching a full depletion are highlighted, as long as perspectives of a partial polarization operation of the detectors.

In this paper we report the morphology and the microstructural properties of thick [1 1 1]-oriented 3C-SiC films epitaxially grown on T-shaped Si micropillars. This compliant substrate was designed to release the stress developed in 3C-SiC grown on Si, due to the lattice mismatch and the different thermal expansion coefficients between 3C-SiC and Si. In this way it was possible to have 3C-SiC films as thick as 10 and 16 μm, with small bowing and no cracks. Our study relies on the use of an Electron Microscopy approach and elucidates the structure of the crystallographic defects across the 3C-SiC film, such as stacking faults (SFs), nano-twins and grain boundaries (GBs). After examination of the morphological and structural characteristics of the Si micropillar array, we analyzed the crystallographic properties of the thin 3C-SiC deposit on the Si micropillar sidewalls, since it may have an impact on the upper film. To assess the crystal quality of the 3C-SiC film, we quantified the SF density at the 3C-SiC surface, even estimating semi-quantitatively the depletion of SFs at much larger thickness. Hence, we analyzed the regions where 3C-SiC microcrystals grown on neighboring Si micropillars coalesce and form a continuous layer. We found that the coalescence between adjacent 3C-SiC microcrystals produces twinned regions, which terminate with the formation of GBs. We noticed that SFs may annihilate at the GBs, leading to the SF reduction across the 3C-SiC film. Finally, we observed the closure of the GBs inside the 3C-SiC film, thus improving the crystal quality of its surface. This work endorses the use of Si micropillars as compliant substrate to grow thick [1 1 1]-oriented 3C-SiC films with good crystal quality and is preliminary to the exploitation of 3C-SiC for high performing microelectronic devices.

The interfacial electrical properties of deposited oxide (SiO2) onto cubic silicon carbide (3C-SiC) were investigated after different post-oxide deposition annealing (PDA) by means of metal–oxide–semiconductor (MOS) capacitors and nanoscale capacitance mapping. The deposited oxides subjected to PDA at 450 °C in either nitrogen or forming gas showed a reduction of the interface and oxide traps, as well as an improved oxide field strength compared to the thermally grown insulating layer. Spatially resolved nanoscale capacitance mapping performed onto the oxide surface revealed that the density of the electrically active stacking faults (SFs) in 3C-SiC is diminished by appropriate PDA. The results pave the way to obtain an ideal SiO2/3C-SiC system suitable for power device applications.

This letter reports on initial investigation results on the material quality and device suitability of a homo-epitaxial 3C-SiC growth process. Atomic force microscopy surface investigations revealed root-mean square surface roughness levels of 163.21 nm, which was shown to be caused by pits (35 μm width and 450 nm depth) with a density of 1.09 × 105 cm−2 which had formed during material growth. On wider scan areas, the formation of these were seen to be caused by step bunching, revealing the need for further epitaxial process improvement. X-ray diffraction showed good average crystalline qualities with a full width of half-maximum of 160 arcseconds for the 3C-SiC (002) being lower than for the 3C-on-Si material (210 arcseconds). The analysis of C–V curves then revealed similar interface-trapped charge levels for freestanding 3C-SiC, 3C-SiC on Si and 4H-SiC, with forming gas post-deposition annealed freestanding 3C-SiC devices showing D IT levels of 3.3 × 1011 cm−2 eV−1 at E C−E T = 0.2 eV. The homo-epitaxially grown 3C-SiC material’s suitability for MOS applications could also be confirmed by leakage current measurements.

Cubic silicon carbide (3C-SiC) is an emerging material for high power and new generation devices, but the development of high quality 3C-SiC layer still represents a scientific and technological challenge especially when grown on a Si substrate. In the present lecture, we discuss the use of a buffer layer between the epitaxial layer and the substrate in order to reduce the defectiveness and improve the overall quality of the SiC epi-film. In particular, we find that the morphology and the quality of the epi-film depends on the carbonization temperature and the concentration of Ge in close proximity of the Si1-xGex/SiC interface. Ge segregation at the interface influences the film quality, and in particular a [Ge]>12% in close proximity to the interface leads to the formation of poly-crystalls, while close to 10% induces a mirror like morphology. Moreover, by finely tuning the Ge concentration and carbonization temperature, crystal quality higher than that observed for SiC grown on bare silicon is achieved., 15 pages, 6 figures

Silicon Carbide (SiC) is a relatively new entry in the world of solid-state detectors. Although SiC response to neutrons is more complex than the one obtained with diamonds, the measured energy resolution (FWHM/ E d 4 % ) makes SiC an interesting alternative to diamond and silicon detectors for fast neutrons. The results obtained from the measurements of the response of a 100 μ m thick SiC detector to neutrons in the energy range between 3 and 20 MeV at the n_TOF spallation source at CERN are presented in this paper. By selecting the neutron energy by means of the time of flight, the detector response to quasi-mono-energetic neutrons was measured. The main neutron-induced nuclear reactions were identified in the measured pulse height spectrum. Detection efficiency as a function of neutron energy was measured and interpreted based on available neutron cross section and by making use of Monte Carlo simulations.

Photoelectrochemical water splitting is a promising method to produce H 2 by making use of solar energy. In this paper we report on a photocathode made by p-type crystalline Si covered with an n-type 3C-SiC polycrystalline film, acting as protective layer and transparent emitter. The photoelectrodes exhibit a saturated photocurrent above 30 mA cm −2 . No decay is observed after 9 h under constant current stress at 1 kW m −2 with AM1.5G spectrum illumination. Improvement of the photocurrent value is achieved by covering the 3C-SiC emitter with Au or Pt nanoparticles. Under suitable metal nanoparticles deposition conditions, compared to the samples without nanoparticles, two major effects are observed: first the onset potential is considerably reduced, and second, higher saturated photocurrent is found, up to 38 mA cm −2 , i.e. with a 27% increase. Optical and micro-structural studies on the nanoparticles provide insights on the origin of the observed effects.

We report on the growth of bulk 3C-SiC by sublimation on epitaxial seeding layers (3C-SiC/Si) from chemical vapor deposition. We have reached a materials thickness of 0.85 mm and an area of 10.5 cm2 which can be enlarged further. The high crystalline quality is characterized by the absence of secondary polytype inclusions and the absence double position grain boundaries.

4H-SiC defects evolution after thermal processes has been evaluated. Different annealing temperatures have been used to decrease the defect density of epitaxial layer (as stacking faults) and recover the damage occurred after ion implantation. The propagation of defects has been detected by Photoluminescence tool and monitored during the thermal processes. The results show that implants do not affect the surface roughness and how a preliminary annealing process, before ion implantation step, can be useful in order to reduce the SFs density. It shown the effect of tuned thermal process. A kind of defect, generated by implant and subsequent annealing, can be removed by an appropriate thermal budget, while others can increase. A fine tuning of thermal process parameters, temperature and timing, is useful to recover the crystallographic quality of the epilayer and increase the yield of the power device.

An updated overview of recent results on Heavy-Ion induced reactions of interest for neutrinoless double beta decay is reported in the framework of the NUMEN project. The NUMEN idea is to study heavy-ion induced Double Charge Exchange (DCE) reactions with the aim to get information on the nuclear matrix elements for neutrinoless double beta (0νββ) decay. Moreover, to infer the neutrino average masses from the possible measurement of the half- life of 0νββ decay, the knowledge of the nuclear matrix elements is a crucial aspect. Uma visão geral atualizada dos resultados recentes sobre reações induzidas por íons pesados ​​de interesse para o decaimento beta duplo sem neutrinos é relatada na estrutura do projeto NUMEN. A ideia do NUMEN é estudar reações de Double Charge Exchange (DCE) induzidas por íons pesados ​​com o objetivo de obter informações sobre os elementos da matriz nuclear para o decaimento beta duplo sem neutrinos (0νββ). Além disso, para inferir as massas médias dos neutrinos a partir da possível medição da meia-vida do decaimento 0νββ, o conhecimento dos elementos da matriz nuclear é um aspecto crucial. 1308 012002

This paper is a report on Ohmic contacts on n-type and p-type type cubic silicon carbide (3C-SiC) layers grown on silicon substrates. In particular, the morphological, electrical and structural properties of annealed Ni and Ti/Al/Ni contacts has been studied employing several characterization techniques. Ni films annealed at 950 degrees C form Ohmic contacts on moderately n-type doped 3C-SiC (N-D similar to 1 x 10(17) cm(-3)), with a specific contact resistance of 3.7 x 10(-3) Omega cm(2). The main phase formed upon annealing in this contact was nickel silicide (Ni2Si), with randomly dispersed carbon in the reacted layer. In the case of a p-type 3C-SiC with a high doping level (N-A similar to 5 x 10(19) cm(-3)), Ti/Al/Ni contacts were preferable to Ni ones, as they gave much lower values of the specific contact resistance (1.8 x 10(-5 )Omega cm(2)). Here, an Al3Ni2 layer was formed in the uppermost part of the contact, while TiC was detected at the interface. For this system, a temperature dependent electrical characterization allowed to establish that the thermionic field emission rules the current transport at the interface. All these results can be useful for the further development of a device technology based on the 3C-SiC polytype.

In spite of its great promises for energy efficient power conversion, the electronic quality of cubic silicon carbide (3C-SiC) on silicon is currently limited by the presence of a variety of extended defects in the heteroepitaxial material. However, the specific role of the different defects on the electronic transport is still under debate. In this work, a macro- and nano-scale characterization of Schottky contacts on 3C-SiC/Si was carried out, to elucidate the impact of the anti-phase-boundaries (APBs) and stacking-faults (SFs) on the forward and reverse current-voltage characteristics of these devices. Current mapping of 3C-SiC by conductive atomic force microscopy (CAFM) directly showed the role of APBs as the main defects responsible of the reverse bias leakage, while both APBs and SFs were shown to work as preferential current paths under forward polarization. Distinct differences between these two kinds of defects were also confirmed by electronic transport simulations of a front-to-back contacted SF and APB. These experimental and simulation results provide a picture of the role played by different types of extended defects on the electrical transport in vertical or quasi-vertical devices based on 3C-SiC/Si, and can serve as a guide for improving material quality by defects engineering., Comment: 20 pages, 7 figures

A study of the response of three Δ E-E telescopes to fragments produced in nuclear interactions at 40 AMeV is presented. All the employed telescopes feature silicon carbide (SiC) detectors for at least one detection stage. Two identification methods have been used and their performance discussed: the Δ E-E technique and the Pulse Shape Analysis technique (for identification of nuclear fragments stopped in a single SiC layer). Identification capabilities similar to those obtained with the best available silicon detectors have been found for the SiC detector prototypes studied in this work.

In this work we present the response of a new large volume 4H Silicon Carbide (SiC) detector to 14 MeV neutrons. The device has an active thickness of 100 μ m (obtained by epitaxial growing) and an active area of 25 mm2. Tests were conducted at the ENEA-Frascati Neutron Generator facility by using 14.1 MeV neutrons. The SiC detector performance was compared to that of Single-Crystal Diamond (SCD) detectors. The SiC response function was successfully measured and revealed a very complex structure due to the presence in the detector of both Silicon and Carbon atoms. Nevertheless, the flexibility in the SiC manufacturing and the new achievements in terms of relatively large areas (up 1x1 cm2) and a wide range of thicknesses makes them an interesting alternative to diamond detectors in environments where limited space and high neutron fluxes are an issue, i.e. modern neutron cameras or in-vessel tokamak measurements for the new generation fusion machines such as ITER. The absence of instabilities during neutron irradiation and the capability to withstand high neutron fluences and to follow the neutron yield suggest a straightforward use of these detectors as a neutron diagnostics.

In this paper the defects generated by ion implantation in 4H-SiC DIMOSFET (Double Implanted MOSFETs), and their evolution after annealing process, have been studied in detail. The point defects generated by the source or body implantation process have been detected by micro-photoluminescence (µPL) and the effect of these defects on the electrical characteristics of the DIMOSFET has been studied. The role of the annealing process has been carefully investigated by using different temperatures. It appears fundamental for the restoring of the crystal damage. The effect of the ion implantation dose has been investigated as well. By reducing the source ion implanted dose a large decrease of point defects has been detected and a considerable improvement of the electrical characteristic of the DIMOSFET has been observed.

3C-SiC devices are hampered by a high crystal defect density due to the hetero-epitaxial growth of these films, which results in the presence of stacking faults (SF). In this paper high growth rate CVD processes have been used to try to reduce the SF density in 3C-SiC films. In a first step a high growth rate (30 µm/h) has been used to grow 50 µm thick 3C-SiC layer on (100) Si. Then the silicon substrate was removed via etching and a further 3C-SiC growth was performed with a higher growth rate (90 µm/h) at a higher temperature (1600 °C) to obtain a final thickness of 150 µm. The SF presence and density were evaluated by TEM analysis performed on as-grown samples and SEM analysis on KOH etched samples with various thicknesses. A decrease of SF density was observed with an increase of 3C-SiC film thickness, with the best results (500/cm) obtained for the thickest sample. The 3C-SiC film quality and orientation was evaluated by XRD are correlated with film thickness and SF density.

The dielectric breakdown (BD) of thermal oxide (SiO2) grown on cubic silicon carbide (3C-SiC) was investigated comparing the electrical behavior of macroscopic metal–oxidesemiconductor (MOS) capacitors with nanoscale current and capacitance mapping using conductive atomic force (C-AFM) and scanning capacitance microscopy (SCM). Spatially resolved statistics of the oxide BD events by C-AFM revealed that the extrinsic premature BD is correlated to the presence of peculiar extended defects, the anti-phase boundaries (APBs), in the 3C-SiC layer. SCM analyses showed a larger carrier density at the stacking faults (SFs) the 3C-SiC, that can be explained by a locally enhanced density of states in the conduction band. On the other hand, a local increase of minority carriers concentration was deduced for APBs, indicating that they behave as conducting defects having also the possibility to trap positive charges. The results were explained with the local electric field enhancement in correspondence of positively charged defects.

In the last decades Silicon Carbide (SiC) received special attentions, in particular as semiconductor material, because is considered as alternative to Silicon for the future high-power, low consumption, radiation-hard microelectronics devices. This ambitious goal is particularly interesting also for the physics of the detectors. In this work are discussed some of the recent results obtained by SiCILIA collaboration, a joint research activity between INFN and IMM institutions to increase the level of technological development in the field of SiC detectors.

International audience; NUMEN aims at accessing experimentally driven information on Nuclear Matrix Elements (NME) involved in the half-life of the neutrinoless double beta decay (0νββ), by high-accuracy measurements of the cross sections of Heavy Ion (HI) induced Double Charge Exchange (DCE) reactions. First evidence about the possibility to get quantitative information about NME from experiments is found for the (^18O,^18Ne) and (^20Ne,^20O) reactions. Moreover, to infer the neutrino average masses from the possible measurement of the half-life of 0νββ decay, the knowledge of the NME is a crucial aspect. The key tools for this project are the high resolution Superconducting Cyclotron beams and the MAGNEX magnetic spectrometer at INFN Laboratori Nazionali del Sud in Catania (Italy). The measured cross sections are extremely low, limiting the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. A major upgrade of the LNS facility is foreseen in order to increase the experimental yield of at least two orders of magnitude, thus making feasible a systematic study of all the cases of interest.

International audience; The article describes the main achievements of the NUMEN project together with an updated and detailed overview of the related R&D activities and theoretical developments. NUMEN proposes an innovative technique to access the nuclear matrix elements entering the expression of the lifetime of the double beta decay by cross section measurements of heavy-ion induced Double Charge Exchange (DCE) reactions. Despite the fact that the two processes, namely neutrinoless double beta decay and DCE reactions, are triggered by the weak and strong interaction respectively, important analogies are suggested. The basic point is the coincidence of the initial and final state many-body wave functions in the two types of processes and the formal similarity of the transition operators. First experimental results obtained at the INFN-LNS laboratory for the$^{40}$Ca($^{18}$O,$^{18}$Ne)$^{40}$Ar reaction at 270MeV give an encouraging indication on the capability of the proposed technique to access relevant quantitative information. The main experimental tools for this project are the K800 Superconducting Cyclotron and MAGNEX spectrometer. The former is used for the acceleration of the required high resolution and low emittance heavy-ion beams and the latter is the large acceptance magnetic spectrometer for the detection of the ejectiles. The use of the high-order trajectory reconstruction technique, implemented in MAGNEX, allows to reach the experimental resolution and sensitivity required for the accurate measurement of the DCE cross sections at forward angles. However, the tiny values of such cross sections and the resolution requirements demand beam intensities much larger than those manageable with the present facility. The on-going upgrade of the INFN-LNS facilities in this perspective is part of the NUMEN project and will be discussed in the article.

Silicon carbide is a very promising material for next generation nuclear physics experiments at high beam luminosity. Such activities require devices able to sustain high fluxes of particles (up to 1014 ions/cm2) in order to determine the cross sections of very rare nuclear phenomena. One of these activities is the NUMEN project, which aims, through the double charge exchange reactions, to impact in the determination of nuclear matrix elements entering in the expression of half-life of the neutrino-less double beta decay. Due to the very low cross sections, these features can just be explored at fluences which exceed by far those tolerated in state of the art solid state detectors, typically used in this kind of experiments. The SiC technology offers today an ideal response to such challenges, giving the opportunity to cope the excellent properties of silicon detectors with the radiation hardness, thermal stability and visible blindness of SiC material.

We present a stochastic simulation method designed to study at an atomic resolution the growth kinetics of compounds characterized by the sp3-type bonding symmetry. Formalization and implementation details are discussed for the particular case of the 3C-SiC material. A key feature of our numerical tool is the ability to simulate the evolution of both point-like and extended defects, whereas atom kinetics depend critically on process-related parameters. In particular, the simulations can describe the surface state of the crystal and the generation/evolution of defects as a function of the initial substrate condition and the calibration of the simulation parameters. We demonstrate that quantitative predictions of the microstructural evolution of the studied systems can be readily compared with the structural characterization of actual processed samples.

In this review the effect of the growth process on the formation of defects in the hetero-epitaxial 3C-SiC film and the possible path for defects reduction has been reported. In our analysis of the experimental data we started from the realization of the carbonization layer, the defects at the interface and in the silicon substrate, to the growth of thin and even very thick layers. The discussion has been focalized on the growth on planar blanket Si substrates without the presence of structures or specific buffer layers. Both Chemical Vapour Deposition (CVD) and Sublimation Epitaxy (SE) processes have been reported and studied in detail.

The NUMEN project aims at accessing experimentally driven information on Nuclear Matrix Elements (NME) involved in the half-life of the neutrinoless double beta decay (0νββ), by high-accuracy measurements of Heavy Ion (HI) induced Double Charge Exchange (DCE) reaction cross sections. In particular, the (18O,18Ne) and (20Ne,20O) reactions are used as tools for β+β+ and β−β− decays, respectively. In the experiments, performed at INFN - Laboratory Nazionali del Sud (LNS) in Catania, the beams are accelerated by the Superconducting Cyclotron (CS) and the reaction ejectiles are detected the MAGNEX magnetic spectrometer. The measured cross sections are challengingly low (a few nb), being the total reaction cross section much larger (a few b), thus a high sensitivity and a large rejection capability are demanded to the experimental set-up. This limits the present exploration to few selected isotopes of interest in the context of typically low-yield experimental runs. A major upgrade of the LNS facility is foreseen in order to increase the experimental yield of at least two orders of magnitude, still keeping the high sensitivity of the present set-up, making it feasible a systematic study of all the cases of interest. Frontiers technologies are going to be developed, to this purpose, for the accelerator and the detection systems. In parallel, advanced theoretical models are being developed in order to extract the nuclear structure information from the measured cross sections.

In this work an extended study of the carbonization process of the silicon surface and of a low temperature transition layer in the temperature rump on the 3C-SiC epitaxial growth has been reported. It has been observed that increasing the C/H 2 ratio the voids density decreases, the thickness of the carbonization layer and the density increase and the morphology improves. The low temperature transition layer, grown during the ramp between the carbonization step and the real growth process, produce a further reduction of the voids at the 3C-SiC/Si interface and a considerable reduction of the stress of the 3C-SiC film. This stress reduction is related to a large change of the film morphology. No effect of the interface silicon layer on the stress is observed. This study has shown the complex connection between the first steps of the 3C-SiC growth process and the properties of the film in term of stress and superficial morphology. The residual stress has important implications with regard to the processing (wafer bow) and quality of the epitaxy. Residual stress also changes the mechanical response and/or the resonant frequency of the thin-film structure and may degrade the performance in MEMS-based devices. Therefore, a better understanding of the stress relaxation mechanism could improve the performances of 3C-SiC devices and sensor technologies.

In this paper, we use three-dimensional kinetic Monte Carlo simulations on superlattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on hexagonal 6H-SiC step-bunched substrates with miscuts towards the and directions. We find that the preferential 3C conversion observed on misoriented substrates could be due to a different step-to-island interaction which enhances island stability and expansion in this specific direction. For this reason 3-4 degrees off step-bunched 6H substrates with miscut towards the direction should be the best choice for the stable and reproducible hetero-polytypical growth of high quality cubic epitaxial films. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

During the heteroepitaxial growth of a thin film on a thick substrate, important stresses arise in the grown material and may influence the physical properties of the film. The residual stresses result in a bending of the substrate/film system. In this work the evaluation of the wafer curvature and the residual stress along different crystallographic directions of the wafer was proposed. Performed by an interferometric optical profilometer, optical microscope and X-ray diffraction analysis, the curvature of the wafer along the [110] and [1−10] wafer directions was observed for hetero-epitaxial Cubic Silicon Carbide (3C-SiC) on Si (001) films. As a consequence of the stress generated during hetero-epitaxy, due to the difference in thermal expansion coefficient and lattice mismatch between the two materials, an asymmetric wafer curvature was observed.

$\mathrm{G}{\mathrm{e}}_{2}\mathrm{S}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{e}}_{5}$ polycrystalline films either in the trigonal stable phase or in the metastable rock-salt structure have been irradiated with 150 keV ${\mathrm{Ar}}^{+}$ ions. The effects of disorder are studied by electrical, optical, and structural measurements and density functional theory (DFT) simulations. In the metastable structure, the main effect of ion irradiation is a progressive amorphization, with an optical threshold at a fluence of $3\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$. For the trigonal structure, a metal-insulator transition and a crystalline transition to rock-salt structure occur prior to amorphization, which requires a fluence of $8\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$. The bonds of Te atoms close to the van der Waals gaps, present in the trigonal phase and identified by Raman spectroscopy, change as a function of the disorder induced by the irradiation. Comparison with DFT simulations shows that ion irradiation leads to the gradual filling of the van der Waals gaps with displaced Ge and Sb lattice atoms, giving rise first to a metal-insulator transition $(9%$ of displaced atoms) correlated to the modification of the Te bonds and then induces a structural transition to the metastable rock-salt phase $(15%$ of displaced atoms). The data presented here not only show the possibility to tune the degree of order, and therefore the electrical properties and the structure of phase change materials by ion irradiation, but also underline the importance of the van der Waals gaps in determining the transport mechanisms and the stability of the crystalline structure.

This work focuses on the photo-catalytic activity of TiO2 nanoparticles produced by an alternative, industrially compatible and environmentally friendly technique such as laser ablation in liquids. Amorphous and highly hydroxylated TiO2 nanoparticles were synthesized by using the first harmonic of a Nd:Yag laser. Despite their amorphous phase, the nanoparticles showed a photocatalytic activity comparable to that of crystalline TiO2 in the degradation of Methylene Blue dye. This unexpected high rate is discussed taking into account the amount of hydroxyl groups and the presence of amorphous phase. Furthermore, a possible mechanism to achieve this high activity is pointed out.

Micro- and nano-electromechanical systems (MEMS and NEMS) fabricated in 3 C-SiC are receiving particular attention thanks to the material physical properties: its wide band gap (2.3 eV), its ability to operate at high temperatures, its mechanical strength and its inertness to the exposure in corrosive environments. However, high residual stress (which is normally generated during the hetero-epitaxial growth process) makes the use of 3 C-SiC in Si-based MEMS fabrication techniques very limited leading to a failure of micro-machined/sensor structures. In this paper, micro-Raman characterizations and finite-element modeling (FEM) of microstructures realized on poly and single-crystal (100) 3 C-SiC/Si films are performed. Transverse optical (TO) Raman mode analysis reveals the stress relaxation on the free standing structure (796.5 cm−1) respect to the stressed unreleased region (795.7 cm−1). Also, microstructures as cantilever, bridge and planar rotating probe show an intense stress field located around the undercut region. Here, the TO Raman mode undergoes an intense shift, up to 2 cm−1, ascribed to the modification of the Raman stress tensor. Indeed, the generalized axial regime, described by diagonal components of the Raman stress tensor, cannot be applied in this region. Raman maps analysis and FEM simulations show the ‘activation’ of the shear stress, i.e. non-diagonal components of the stress tensor. The stress-Raman modes shift correlation, in the case of fully non-diagonal stress tensors, has been investigated. The aim of future works will be to minimize the stress field generation and the defects density within the epitaxial layer. Copyright © 2012 John Wiley & Sons, Ltd.

Arc discharge is commonly used for the synthesis of carbon nanotubes (CNTs), even though not much is known concerning the process itself and the role of the discharge parameters on the formation of different kinds of nanostructures. We have investigated the formation and the morphology of the C deposit on the cathode, after arc discharge between two graphite electrodes immersed in liquid nitrogen. The deposit consists of disordered carbon structures at the bottom and on the external part of the deposit, forming like a bowl that contains randomly oriented CNTs, aggregated in several pillars in the internal part and on top. We have found that the applied voltage not only influences the macroscopic structure of the C deposit, but also the structural properties of the individual CNTs.

SiC is a candidate material for microelectromechanical and nanoelectromechanical systems, but the high residual stress created during the film grow limits the development of the material for these applications. To understand the stress relaxation mechanism in hetero-epitaxial 3C-SiC films, different micromachined free-standing structures have been realized. In this paper, assisted by finite-element method (FEM), a micromachined planar rotating probe was developed for residual stress analysis to split the stress into the following two components: 1) the gradient residual stress (σ1) related to the film defects and 2) the uniform stress (σ0) related to the substrate. Transmission electron microscopy characterization studies about the defect formation and the defect evolution as a function of thickness on 3C-SiC on the Si substrate revealed the problems due to the incorrect linear stress approximation in a heteroepitaxial thin film. With FEM, an exponential approximation of the stress relationship was studied, yielding a better fit with the experimental data. This paper shows that the new approximation of the total residual stress function reduces the actual disagreement between experimental and simulation data.

Neutrinoless double beta decay (0v\b{eta}\b{eta}) is considered the best potential resource to access the absolute neutrino mass scale. Moreover, if observed, it will signal that neutrinos are their own anti-particles (Majorana particles). Presently, this physics case is one of the most important research "beyond Standard Model" and might guide the way towards a Grand Unified Theory of fundamental interactions. Since the 0v\b{eta}\b{eta} decay process involves nuclei, its analysis necessarily implies nuclear structure issues. In the NURE project, supported by a Starting Grant of the European Research Council (ERC), nuclear reactions of double charge-exchange (DCE) are used as a tool to extract information on the 0v\b{eta}\b{eta} Nuclear Matrix Elements. In DCE reactions and \b{eta}\b{eta} decay indeed the initial and final nuclear states are the same and the transition operators have similar structure. Thus the measurement of the DCE absolute cross-sections can give crucial information on \b{eta}\b{eta} matrix elements. In a wider view, the NUMEN international collaboration plans a major upgrade of the INFN-LNS facilities in the next years in order to increase the experimental production of nuclei of at least two orders of magnitude, thus making feasible a systematic study of all the cases of interest as candidates for 0v\b{eta}\b{eta}.

Growth of 3C-SiC on (100) Si has been performed via chemical vapor deposition under two pressure regimes (low and atmospheric pressure) in the early stage of growth. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) have been conducted to study the initial stage of growth while X-ray diffractometry (XRD) and TEM have been used to analyze thicker films and to detect and quantify defects, resulting in a comprehensive and detailed investigation of 3C-SiC structural defects. We have found out that the secondary nucleation of 3C-SiC island growth leads to a higher defect generation rate and, at the same time, to a more effective defect elimination rate. Hillocks found on the surface of thin samples grown under reduced pressure conditions are more pronounced as they seem to be a consequence of twins created in the early stage of growth. Finally, a different initial nucleation density (in the two pressure regimes considered) does not strongly influence stacking fault and microtwin density when growth of thick 3C-SiC films is performed. A very strong influence is indeed observed when 3C-SiC thickness is limited to hundreds of nanometers.

The low temperature evolution of point defects induced in SiC by ion irradiation was investigated by deep level transient spectroscopy. The defects were introduced by irradiation with a 7.0 MeV beam of C+ ions at a fluence of 6 × 109 cm− 2. Annealing was then performed in the temperature range of 330–400 K in order to study the change in point defect structure with temperature. The low temperature annealing performed was observed to induce a change in the produced defects. The deep levels related to the Sx (EC − 0.6 eV) and S2 defects (EC − 0.7 eV) recovered with annealing while, simultaneously, a new level, S1 (EC − 0.4 eV), was formed. The activation energy of the S1 defect is 0.94 eV, while the annealing of both the Sx and S2 levels occurred with activation energy of 0.65 eV.

The effects of the crystal quality and surface morphology on the electrical properties of MOS capacitors have been studied in devices manufactured on 3C-SiC epitaxial layers grown on silicon (1 0 0) substrate. The interface state density, which represents one of the most important parameters, has been determined through capacitance measurements. A cross-correlation between high resolution X-ray diffraction, AFM analysis and electrical conductance measurements has allowed to determine the relationship between the crystalline quality and the interface state density. A decrease of the interface state density down to about 1011 cm-2 eV-1 was observed with improving the crystalline quality.

The excellent physical and chemical properties and the radiation hardness of silicon carbide (SiC) render this material particularly suitable for the realization of radiation detectors. In this paper we describe the main properties of SiC and the processes needed to realize good performance detectors. To this purpose, we made SiC Schottky diodes that were electrical characterized by using different techniques. In order to test the radiation hardness, the diodes were irradiated with different ion beams and the analysis of the electrical measurements allowed to identify the defects responsible of the device degradation. These detectors have been used to monitor the multi-MeV ions of the plasma emitted by irradiation of various targets with 300-ps laser at high intensity (1016 W/cm2). These measurements highlighted that the use of SiC detectors enhances the sensitivity to ions detection due to the cutting of the visible and soft ultraviolet radiation emitted from plasma. The small rise time and the proportio...

The effects of ion irradiation defects on the carrier concentration of 6H-SiC epitaxial layer were studied by current–voltage (I–V), capacitance.-voltage (C–V) measurements, thermally stimulated capacitance and deep level transient spectroscopy. The defects were produced by irradiation with 10 MeV C+ at a fluence of 1011 ions/cm2 and subsequent thermal annealings were carried out in the temperature range 500–1700 K under N2 flux.