Si K-edge X-ray absorption fine structure studies of porous silicon

X-ray absorption fine structure (XAFS) spectra of porous Si prepared by the anodization of a Si wafer in aqueous HF solution have been obtained with synchrotron radiation. The Si K-edge near-edge X-ray absorption fine structure and extended X-ray absorption fine structures clearly show that porous silicon samples that have been exposed to the ambient environment (untreated) have an oxide layer, while the "clean" (treated) porous Si sample regenerated by HF treatment shows some degradation in its crystallinity. Noticeable differences in the XAFS between porous Si and crystalline Si are noted. The results and implications of this observation and the chemistry leading to the formation of surface oxygen compound are discussed.