1. Department of Materials Sciences and Engineering; National Chiao Tung University; Hsinchu 300 Taiwan
2. Department of Biomedical Engineering and Environmental Sciences; National Tsing Hua University; Hsinchu 300 Taiwan
3. Department of Materials Sciences and Engineering; University of Pennsylvania; Philadelphia PA 19104-6272 USA
4. Material and Chemical Research Laboratories; Industrial Technology Research Institute; 195, Sec. 4, Chung Hsing Rd. Chutung Hsinchu Taiwan 31040 R.O.C.