Optical absorption measurements of silica containing Si nanocrystals produced by ion implantation and thermal annealing

Optical absorption spectra from silicon-implanted silica slides are shown to contain features due to optical interference. These features, which result from the modified refractive index profile produced by the implant, can readily lead to misinterpretation of absorption spectra. To demonstrate the importance of such effects, silica samples were implanted with 80, 400, and 600 keV Si ions to fluences in the range 0.6-3.0×10¹⁷Si.cm^-2 and annealed at 1100°C for 1 h to form Si nanocrystals. Optical absorption/transmittance spectra from these samples show considerable structure that is characteristic of the particular implant conditions. This structure is shown to correlate with the transmittance of the samples as calculated from the modified refractive index profile for each implant. The lack of such structure in absorption spectra measured by photodeflection spectrometry is used to confirm this interpretation.