本文课题受国家重大科学研究计划2006CB910503;国家自然科学基金项目30370801,30770972,30500238;湖南省自然科学基金项目资助编号:06JJZ0068The National Key Scientific Program-Nanoscience and Nanotechnology2006CB910503;National Natural Science Foundation of China30370801, 30770972 and 30500238;Natural Science Foundation of Hu'nan Province06JJZ0068