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 to a progressive monotonic redshift of the interference pattern of the photoluminescence spectrum. On the other hand, the photoluminescence intensity of the cavity peak oscillates in time. Both effects can be explained in terms of a very simple model based on the progressive change of the effective refractive index of single layers of the cavity. The change is due to the difference between the index of refraction of air and ethanol. The result suggests 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 Institute of Physics.