Shanghai Institute of Applied Physics,Chinese Academy of Sciences,PO Box 800-204,Shanghai 201800;
Department of Information Material Science and Englneering,Guilin University of Electronic Technology,Guilin 541004;
College of Physics and Information Technology,Guangxi Normal University,Guilin 541004;
Surface Laboratory and Department of Physics Fudan University,Shanghai 200433;
Shanghai Institute of Applied Physics,Chinese Academy of Sciences,PO Box 800-204,Shanghai 201800;
