Investigation of Strain and Wetting in Porous Silicon and Feasibility of an Optical Sensor for Chemical Monitoring

Abstract

In this paper an experimental study of wetting phenomena in porous silicon by Raman scattering is reported and the feasibility of an optical sensor for chemical monitoring is addressed. First, a systematic study of strain effects in 'as formed porous silicon layers' of different porosity and thickness is described. Samples of greater thickness (20 µm) and higher porosity (70%) have been individuated as the best candidates for the observation of wetting phenomena. Then, an experimental investigation of wetting phenomena in PS layers by Raman scattering is reported. The experimental results prove a reversible blue-shift of PS Raman speak of wetted porous silicon layers by isopropanol or ethanol with respect to unperturbed layers. We ascribe the shift to a compressive stress due to the increased lattice mismatch between the porous silicon layer and the bulk silicon substrate in wetting conditions. Finally, the feasibility of an optical sensor for chemical monitoring, using an approach based on porous silicon wetting and Raman scattering measurements is discussed. We conclude that being the measured shift of Raman peak very small, this mechanism could be not useful 'as a transducer' for sensing application i.e. to monitor vapors and liquids in an environment.