Vapor sensitivity of thin porous silicon layers

Spectroscopic ellipsometry has been used to study optical changes in thin porous silicon layers due to exposure to vapors from different liquids. The chan,pes in the ellipsometric parameters Psi and Delta were caused by changes in the total refractive index of the layers. The detection limit threshold for acetone vapors by the layers was 12 ppm. Using a 4-layer optical model, it was determined that capillary condensation was involved in the vapor sensitivity of the layers. Based on these findings, it was concluded that thin porous silicon layers can be used as an optical sensor material for gas sensing purposes. (C) 1997 Elsevier Science S.A.