1. College of Chemistry and Materials Science Sichuan Normal University Chengdu 610066 P. R. China
2. Nanomaterials Research Institute National Institute of Advanced Industrial Science and Technology (AIST) Ikeda Osaka 563-8577 Japan
3. Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS) CNRS-Université de Strasbourg (UMR 7504) 67034 Strasbourg France