Bending Elastic Moduli of the Surfactant Film and Properties of a Winsor II Microemulsion System

Abstract

The optical second harmonic (SH) response from the n-Si( 11 1) surface immersed in aqueous electrolyte solutions has been examined and is observed to be potential dependent. This potential dependence is observed for both the monohydrogen-terminated surface immersed in NH4F as well as for surfaces which are photoanodically oxidized in H2SO4. The potential dependence from the latter is screened in part by the presence of the insulating overlayer. Furthermore, a minimum is observed in the potential-dependent response which is shifted well anodic of the flatband potential. The SH observations are attributed to field effects within the space charge region of the semiconductor which are manifested in the higher order bulk SH response. Photocurrent transient analysis is utilized as a means of determining the flatband potential of these surfaces immersed in electrolyte solution. Experiments performed in UHV are discussed and compared to that observed in solution.