1. Advanced Materials Research
Institute, University of New Orleans, New
Orleans, Louisiana 70148,
United States
2. Department
of Physics and Astronomy, The University of Toledo, 2801 Bancroft Street, Toledo, Ohio 43606,
United States
3. National Renewable Energy Laboratory, Golden, Colorado 80401,
United States
4. Department
of Physics, Colorado School of Mines, Golden,
Colorado
80401,
United States
5. Nanostructures
Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan