1. Contribution from the Department of Physics and Astronomy and the Center for Materials Research and Analysis, University of Nebraska, Lincoln, Nebraska 68588-0111, the Center for Advanced Microstructures and Devices, Louisiana State University, 6980 Jefferson Highway, Baton Rouge, Louisiana 70806, the Department of Chemistry, 536 Hamilton Hall, University of Nebraska, Lincoln Nebraska 68588-0304, and the Institute of Physics of National Academy of Sciences of Ukraine, Prospect Nauki 46, Kiev 03028, Ukraine