Synthesis and oxidation of luminescent silicon nanocrystals from silicon tetrachloride byvery high frequency nonthermal plasma

Abstract

Silicon nanocrystals have recently attracted significant attention for applications inelectronics, optoelectronics, and biological imaging due to their size-dependent optical andelectronic properties. Here a method for synthesizing luminescent silicon nanocrystals fromsilicon tetrachloride with a nonthermal plasma is described. Silicon nanocrystals with meandiameters of 3–15 nm are synthesized and have a narrow size distribution with thestandard deviation being less than 20% of the mean size. Control over crystallinity isachieved for plasma pressures of 1–12 Torr and hydrogen gas concentrations of5–70% through adjustment of the plasma power. The size of nanocrystals, andresulting optical properties, is mainly dependent on the gas residence time in theplasma region. Additionally the surface of the nanocrystals is covered by bothhydrogen and chlorine. Oxidation of the nanocrystals, which is found to follow theCabrera–Mott mechanism under ambient conditions, is significantly faster than hydrogenterminated silicon due to partial termination of the nanocrystal surface by chlorine.