Papers by Author: Francesca Rossi

Abstract: We report on the synthesis of SiC nanowires (NWs) using iron as catalyst. The NWs were grown on silicon substrate by vapour-liquid-solid (VLS) mechanism with propane and silane as precursors, both 3% diluted in hydrogen, and hydrogen as carrier gas. The growth temperature was 1250°C, to reach the eutectic values of the Si-Fe alloy and to permit the VLS mechanism. The as-grown SiC nanowires were characterized by scanning and transmission electron microscopy. The nanowires are from 30 to 100 nm in diameter and several μm in length, with <111> growth direction.

Abstract: Cubic silicon carbide - silicon dioxide core-shell nanowires have been synthesized in a thermal CVD system from carbon monoxide on silicon substrate. Using a non-ionic surfactant during the coating process of the substrate by the catalyst, the uniformity of the catalytic layer was improved, resulting in a more uniform nanowires growth. It is demonstrated that the core diameter is strongly correlated with the precursor concentration.

Abstract: In this work we report the enhancement of the 3C-SiC band edge luminescence induced by the SiO2 shell in SiC/SiO2 core/shell nanowires (NWs) system. We demonstrate that the shell enhances the SiC near band edge luminescence and we argue the formation of a type-I quantum well between the SiC core and the SiO2 shell, with the consequent injection of carriers from the larger band-gap shell to the narrower band-gap core.

Abstract: β-SiC/SiO₂ core-shell NWs have been synthesized on patterned silicon wafers in a CVD system, using carbon oxide as single precursor and nickel nitrate as catalytic element, in nitrogen or argon atmosphere at 1100°C. The coaxial structure and the crystallinity of the NW core are examined by (scanning) transmission electron microscopy. The patterning of the substrate allows to grow NWs in selected areas only, as imaged by SEM. Cathodoluminescence (CL) panchromatic images of the same areas point out that the light emitted under electron excitation is localized only in the area covered with NWs. The room-temperature CL spectrum has three different components peaked at 2.45 eV, related to the 3C-SiC near-band-edge emission, and at 2.75 and 3.75 eV, that are induced by the triplet and singlet states of oxygen-deficiency centers ODC(II) in silicon dioxide shell.

Abstract: Cubic silicon carbide nanowires (-SiC or 3C-SiC NW) have been grown by Vapour Phase Epitaxy on (001) silicon substrates patterned by conventional photolithography and on Micro Electro Mechanical Systems (MEMS, e.g. cantilevers, springs, bridges) fabricated on (001) Silicon On Insulator (SOI) wafers. The NW morphology was investigated by scanning electron microscopy, showing that the nanowires grew selectively where a nickel thin layer was previously deposited, thanks to its catalytic action. High resolution transmission electron microscopy studies showed that the NWs are predominantly 3C polytype with <111> growth axis and stacking defects on (111) planes.

Abstract: To assess deformation issues in SiC/Si, different pre-growth procedures were investigated, involving the addition of SiH4 to C3H8 during the temperature ramps used for the carbonization. 3C-SiC layers were deposited on (001) and (111) Si substrates by VPE. The mechanical deformation of the wafer was measured by makyoh, obtaining 2D maps of the entire wafers. For the same pre-growth procedures, the substrate curvature depends strongly on the orientation of the substrate, (001) or (111), being generally lower for (111) substrates. The deformation results were compared with XRD and Raman spectroscopy. Plastic deformation of the substrate was evidenced by XRD, while the presence of tensile stress is suggested by Raman analysis.

Abstract: -SiC and -SiC/SiO2 core-shell nanowires (NWs) grown on silicon substrates by three different processes, based on the use of i) carbon monoxide, ii) silane with propane and iii) carbon tetrachloride precursors, are analysed by structural and optical techniques. Spectroscopic cathodoluminescence studies show a luminescence enhancement in core-shell structures, ascribed to an effective role of the shell as both carrier injecting barrier and passivation layer. In NWs grown using CCl4 precursor, a peculiar luminescence with dominant red component at about 2 eV has been detected and ascribed to point defects related to an unintentional oxygen incorporation.

Abstract: 3C-SiC films were grown on Si by VPE using CBr4 as the carbon source, at temperatures ranging between 1100 to 1250°C. XRD, TEM, AFM, and SEM results indicate that the epitaxy proceeds as a 3D growth of uncoalesced islands at low temperature, whereas a continuous layer with hillocks on top is obtained above 1200°C. The shape and faceting of the islands are analyzed by AFM, showing (311) preferred facets.

Abstract: A comparative study of the morphology of 3C-SiC films prepared with different C:Si ratios is presented. The silane precursor controls the growth rate at all values of C:Si ratio but combined of observations using Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) indicates that the C:Si ratio is critical in determining the grain size and at values of C:Si close to 1 texturing and faceting become evident. Makyoh Topography reveals various surface defects, a slight mesoscale roughness and bending of the epiwafers.