We employ time-dependent photoluminescence (PL) and steady-state PL excitation (PLE) measurements to study the size-dependent optical properties of ultrasmall silicon carbide (SiC) nanoparticles (NPs). We find that the nature of the optical transition transforms from solid-state indirect gap to molecular-like as the diameter of spherical SiC NPs is reduced from 4–6 to 1–3 nm with a smooth transition in between. We deduce the radiative lifetimes of SiC NPs that are well supported by ab initio time-dependent density functional theory calculations on realistically large SiC NPs with realistic surface terminations, including the solvation effects.

Carbon diffusion in a SiO 2 /Si system was investigated. The source was provided by chemical vapor deposition of a hydrogenated amorphous carbon layer onto the oxide at low temperature. From layers with low oxygen content, no carbon outdiffusion was detected up to 1190 • C. If the O content was high, the diffusion would start suddenly at 1140 • C, and carbon accumulation would be found on the Si side of the SiO 2 /Si interface in the form of SiC precipitates. These results are interpreted by assuming oxygen-assisted dissociation of carbon atoms from the carbon layer in form of CO molecules, fast CO diffusion through SiO 2 and an exothermic reaction of CO with Si. No carbon segregation was found in SiO 2 . Consequences of carbon island formation during SiC oxidation are pointed out.

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A new, simple method is described resulting in the growth of cubic SiC on Si. Thermally oxidized Si(100) wafers annealed in a CO-containing atmosphere at 1190°C for several hours show epitaxial 3C-SiC grains, formed at the SiO2/normalSi interface, growing into the silicon crystal. After 3 h the SiC grains have a diameter of 25-50 nm and a width of ∼20 normalnm. They contain very few visible defects, and no void between the grain and the Si matrix can be observed. After 20 h, the size of the epitaxial SiC grains doubles, but the density of grains remains about the same. At 900°C no SiC grain formation is observed. © 2002 The Electrochemical Society. All rights reserved.