SURFACE OXIDE LAYERS OF SI AND GE NANOCRYSTALS

Surface oxide layers formed on gas-evaporated Si and Ge microcrystals as small as 100Å were investigated by means of infrared spectroscopy, high-resolution electron microscopy and X-ray photoemission spectroscopy. It is shown that 20Å-thick native oxide layers in the form of SiOx with x=∼1.2 are first formed on the surfaces of Si microcrystals. When the microcrystals are annealed in air at 400°C, the composition x increases up to 2, but the oxide thickness remains almost the same. The evolution of the oxide occurs in the first 15min of annealing and saturates afterwards. This implies that stable oxide layers (SiO2) can successfully be obtained by annealing at relatively low temperatures. Results obtained for Ge microcrystals are qualitatively the same and indicate that stable oxide coatings can be obtained by annealing at 300°C for 30min. © 1990.