1. State Key Laboratory of Silicon MaterialsSchool of Materials Science and EngineeringZhejiang University Hangzhou 310027 P. R. China
2. Department of Physics and AstronomyUniversity of California Irvine CA 92697 USA
3. College of Information Science and Electronic EngineeringZhejiang University Hangzhou 310027 China
4. Key Laboratory for Biomedical Engineering of Ministry of EducationCollege of Biomedical Engineering and Instrument ScienceZhejiang University Hangzhou 310027 China