1. Key Laboratory for Micro–Nano Physics and Technology of Hunan ProvinceState Key Laboratory of Chemo/Biosensing and Chemometrics and College of Materials Science and EngineeringHunan University Changsha Hunan 410012 China
2. Beijing Key Laboratory of Optoelectronic Functional Material & Micro–Nano DevicesDepartment of PhysicsRenmin University of China Beijing 100872 China
3. School of Physics and ElectronicsHunan University Changsha Hunan 410012 China