Monitoring penetration of ethanol in a porous silicon microcavity by photoluminescence interferometry

A photoluminescent porous silicon microcavity is exposed to saturated vapor of ethanol. The ethanol substitutes the air inside the pores giving rise t o a progressive monotonic redshift of the interference pattern of the photo luminescence spectrum. On the other hand, the photoluminescence intensity o f the cavity peak oscillates in time. Both effects can be explained in term s of a very simple model based on the progressive change of the effective r efractive index of single layers of the cavity. The change is due to the di fference between the index of refraction of air and ethanol. The result sug gests that a porous silicon microcavity can be a tool to study the dynamics of gas penetration into porous silicon since it allows a monitoring of the depth reached by the ethanol at any given time. (C) 2001 American Institut e of Physics.