This project is in the general area of analytical and surface chemistry and in the subfield of thin film materials. Although thin films comprise an extremely interesting and important class of materials, techniques for chemical analysis which are specific to thin films are currently inadequate. In this research activity, Professor Bohn and his students will build on their progress under NSF grant CHE-8508722 to extend the use of nonclassical excitation phenomena for optical spectroscopy in thin films at size scales from 5 angstroms to 5 micrometers. This will be accomplished by pursuing two separate research thrusts. In one, gallium arsenide and aluminum-substituted gallium arsenide heterostructures will be used as dielectric optical waveguides to perform frequency modulated cross section measurements at photon energies just below the III-V bandgap. The absorption measurements require the long pathlengths available only in optical waveguides, because the cross sections of the impurity related transitions in the sub-bandgap energy region of high purity III-V semiconductors is extremely weak. In the second thrust, structure-function relationships in molecular monolayers will be examined at dielectric surfaces. A portion of this effort will use surface plasmon mediated optical second harmonic generation and high precision reflectivity measurements to follow the dynamics of monolayer formation. Additionally, the capability for examining Raman scattering from molecular monolayers on dielectric surfaces that is resident in Professor Bohn's laboratory will be used to probe the relationship between adsorbate molecular structure and film architecture on the supermolecular level. This research impacts broadly on the technologically important area of III-V semiconductor devices. These studies are expected to yield new techniques for the characterization of trace impurities that determine the behavior of high purity semiconductors. Additionally, this work should lead to an enhanced understanding of the interfacial structure of these materials and to insights into the dynamics of formation of these multi-layered molecular structures which are of prime importance to the electronics industry.
