Abstract
Underβstoichiometric thin silica layers SiO~x~ with different stoichiometric degree 1 β€ x β€ 2, were prepared by thermal evaporation of silicon monoxide in vacuum and in ambient oxygen atmosphere of various pressure onto crystalline silicon substrates. The chemical composition has been determined by Fourier transform infrared spectroscopy (FTIR). A special formula is derived to correlate the stoichiometric degree x with the wavenumber of the main TO stretching mode (SiβOβSi) in silica, finally to determine the actual composition values x of the layers. Cathodoluminescence (CL) of these layers shows the development of typical amorphous SiO~2~ luminescence bands at the composition threshold x > 1.5 and then onwards to x = 2. These luminescence bands were observed at 4.3, 2.7, 2.15, and 1.9 eV. The greenβyellow luminescence (2.15 eV) is strongly increasing with the annealing temperature up to 1300 Β°C and is assigned to phase separation of SiO~x~ into Si and SiO~2~ and formation of hexamer silicon rings in the understoichiometric silica network. Finally we observe Si nanoclusters by means of transmission elecβ tron microscopy (TEM) micrographs. (Β© 2006 WILEYβVCH Verlag GmbH & Co. KGaA, Weinheim)