1. Department of Engineering and System Science; National Tsing Hua University; Hsinchu 300 Taiwan R. O. China
2. Nano-Science and Technology Program; Taiwan International Graduate Program; Academia Sinica; Taipei 115 Taiwan R. O. China
3. National Tsing Hua University; Hsinchu 300 Taiwan R. O. China
4. Department of Physics; National Taiwan University; No. 1, Sec. 4, Roosevelt Road Taipei 106 Taiwan R. O. China
5. Center for Emerging Material and Advanced Devices; National Taiwan University; No. 1, Sec. 4, Roosevelt Road Taipei 106 Taiwan R. O. China
6. Department of Chemistry; National Taiwan University; No. 1, Sec. 4, Roosevelt Road Taipei 106 Taiwan R. O. China
7. Geballe Laboratory for Advanced Materials; Stanford University; Stanford CA 94305 USA
8. Department of Materials Science and Engineering; Drexel University; Philadelphia PA 19104 USA