1. Nanofabrication LaboratoryCAS Laboratory for Nanosystems and Hierarchical FabricationCAS Center for Excellence in NanoscienceNational Center for Nanoscience and Technology Beijing 100190 P. R. China
2. Center of Materials Science and Optoelectronics EngineeringUniversity of Chinese Academy of Sciences Beijing 100039 P. R. China
3. Department of PhysicsUniversity of the Punjab Quaid‐e‐Azam Campus Lahore 54000 Pakistan
4. School of Information EngineeringLingnan Normal University Zhanjiang 524048 Guangdong P. R. China