1. Contribution from the School of Materials Science and Engineering, Tianjin University, Tianjin 300072, P. R. China, PRRC-Asia, Motorola (China) Electronics Ltd., No. 10, 4th Avenue, TEDA, Tianjin 300457, P. R. China, and Department of Applied Sciences, University of Quebec, Saguenay, PQ, Canada G7H 2B1