1. Key Laboratory of Polar Materials and Devices; Ministry of Education; East China Normal University; Shanghai 200062 China
2. Nanostructures Research Laboratory; Japan Fine Ceramics Center; Nagoya 456-8587 Japan
3. Department of Materials Science and Engineering; National Chiao Tung University; Hsinchu 30010 Taiwan, ROC
4. Advanced Light Source; Lawrence Berkeley National Laboratory; Berkeley CA 94720 USA
5. National Laboratory for Infrared Physics; Chinese Academy of Sciences; Shanghai 200083 China
6. Institute of Engineering Innovation; the University of Tokyo; Tokyo 113-8656 Japan