1. Department of Materials Science and Engineering and the Materials Science Center, Cornell University, Ithaca, New York 14853, Eastman Kodak Company, B-82, Rochester, New York 14650, Department of Materials Science and Engineering, SUNYStony Brook, Stony Brook, New York 11794, and School of Applied and Engineering Physics and the Materials Science Center, Cornell University, Ithaca, New York 14853