1. Nomadics, Inc., 1024 South Innovation Way, Stillwater, Oklahoma 74074, Department of Materials Chemistry, Chemical Center, University of Lund, S-22100, Lund, Sweden, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, and National Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, P.O. Box 912, Beijing 100083, China