Time-resolved sensing of organic vapors in low modulating porous silicon dielectric mirrors

Time-resolved vapor diffusion into low modulating porous silicon dielectric mirrors has uncovered salient information about the spatial concentration distribution of the vapor within the porous matrix. Results indicate that relatively high concentrations of vapor result in instantaneous capillary condensation in the pores and yield a uniform concentration distribution. Results are modeled for both a concentration gradient and uniform filling of the porous matrix and compared to the experimental observations. Experiments with acetone, butanone, and pentanone have shown a linear dependence of the capillary condensation saturation time on the molecular weight of the organic solvents. An indicator of a concentration gradient within the matrix has been identified in the form of the full width at half maximum of the first-order reflectivity peak. (C) 2001 American Institute of Physics.