1. Department of Materials Science and Engineering, University of California, Berkeley, California 94720-1760, USA
2. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
3. Advanced Evaluation and Technology Development Department Technology Division, Sumco Corporation, 1-52 Kubara, Yamashiro-cho, Imari-shi, Saga 849-4256, Japan
4. Applied Science and Technology, University of California, Berkeley, California 94720-1760, USA
5. Department of Physics, City University of Hong Kong, 83 Tat Chee Ave., Kowloon, Hong Kong SAR, China