The progress of laser technology has brought extensive applications of nonlinear optical (NLO) spectroscopy to analytical fields. Especially, optical second harmonic generation (SHG), which is one of the most popular NLO phenomena, has been successfully applied to the study of interfaces (surfaces). Several fine reviews on surface SHG spectroscopies have appeared recently. The present article will concentrate on some new applications of SHG: second harmonic microscopy (SHM) for microstructural characterization, SHG interferometry for the determination of absolute molecular orientation, surface analysis of microstructures, and some molecular interactions at the interfaces.
Poly(methyl methacrylate) (PMMA) thin films incorporating amphiphilic dyes, ruthenium tris(2,2-bipyridine)-type complexes, were prepared by water casting. Films fabricated in this manner are peculiar with their well lined-up molecular orientations at the surface and thus are highly nonlinear effective. Unfortunately, like most other nonlinear materials, the surface orders of the dye molecules tend to collapse once exposed to heat. This work presents our recent studies on heat-induced molecular reorientation by probing SHG and fluorescence spectra. It shows that, in the course of heating between 20 °C and 80°C, the secondary glass transition of PMMA molecules is responsible for both the randomization of the surface alignments of the Ru complex molecules and the migration of these molecules into the body of the PMMA layer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.