βC-SiC/SiO2 core-shell nanowires studied by TEM and SEM-CL

SiC nanostructures have attracted attention for potential applications in nanoelectronic devices, nanoelectromechanical systems and biochemical sensors. Here we report on the growth of SiC nanowires on Si (100) and (111) substrates by a carbothermal method, and their structural and optical properties studied by TEM, micro-Raman and SEM- CL spectroscopy. The reaction between carbon monoxide and the silicon substrate, catalysed by nichel nitrate, yielded a dense forest of vertically aligned wires. HRTEM, elemental mapping by energy-filtering, and Z contrast studies evidence a core-shell structure, with a SiC crystalline core (≤ 50 nm) coated by amorphous silicon oxide. The core has a 3C structure with some stacking faults and rotational twins mainly on (111) planes perpendicular to the growth axis. Ni catalyst particles are observed at the tip of the NWs, suggesting a VLS growth mechanism. Raman studies reveal some modes of the SiO2 shell, and a main peak due to the LO phonon mode of the β-SiC, from which an estimate of the NW strain state can be obtained. CL spectra show a broad emission band, with a main blue component at about 470 nm and a shoulder at about 536 nm. The latter is related to near-band-gap transitions in the β-SiC core. The blue emission was studied as a function of the NW diameter and by performing HF etching and electron beam irradiation. As a result, it is possible to exclude a quantum confinement induced blue-shift of the core emission, and to ascribe it to transitions in the SiO2 oxide shell.vedi abstract ingles