1. Laser Micro/Nano-Fabrication Laboratory; School of Mechanical Engineering; Beijing Institute of Technology; Beijing 100081 China
2. Laboratory of Organic Nanophotonics and Key Laboratory of Photochemical Convention and Functional Materials; Technical Institute of Physics and Chemistry; Chinese Academy of Sciences; Beijing 100190 China
3. Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials; Key Laboratory of Cluster Science; Ministry of Education; School of Chemistry; Beijing Institute of Technology; Beijing 100081 China
4. Department of Electrical Engineering; University of Nebraska-Lincoln; Lincoln NE 68588-0511 USA