1. CAS Center for Excellence in NanoscienceBeijing Institute of Nanoenergy and NanosystemsChinese Academy of Sciences Beijing 100083 P. R. China
2. School of Nanoscience and TechnologyUniversity of Chinese Academy of Sciences Beijing 100049 P. R. China
3. Center on Nanoenergy ResearchSchool of Physical Science and TechnologyGuangxi University Nanning 530004 P. R. China
4. Department of Oral and Maxillofacial SurgeryPeking University School and Hospital of Stomatology Beijing 100081 P. R. China
5. School of PhysicsUniversity of Electronic Science and Technology of China Chengdu 610054 P. R. China
6. School of Materials Science and EngineeringGeorgia Institute of Technology Atlanta GA 30332‐0245 USA