Determination of molecular orientational distribution using surface second-harmonic generation analyzed by five-layer model and maximum-entropy method

Abstract

A novel analytical method to determine molecular orientational distribution functions (ODFs) at interfaces has been developed to apply to polymer film possessing second-harmonic generation (SHG) active side chains with C-infinity v symmetry. This method treats SHG in five layers, i.e., air, an upper SHG-active layer, an SHG-inactive polymer bulk, a lower SHG-active layer and a substrate (five-layer model). We first obtain tentative ODFs of the side chains at two SHG-active layers by the assumption of two undetermined multipliers in the maximum-entropy method. These ODFs give the order parameters of the side chains and in turn the dielectric constants of the SHG-active layers. Achieving the best fit of the theoretical SHG intensity to the experimental results obtained in four different geometries, we succeeded in obtaining unbiased ODFs together with the dielectric constants of the SHG-active layers. (C) 1998 American Institute of Physics. [S0021-8979(98)03620-2].