1. Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas 78249
2. Key Lab of Materials Modification by Laser, Ion, Electron Beams, Dalian University of Technology, Dalian 116024, P. R. China
3. Electronic Materials Research Laboratory, Xi’an Jiaotong University, Shannxi, Xi’an 710049, China
4. State Key Laboratory of Electronic Thin films and Integrated Devices, University of Electronic Science & Technology of China, Chengdu, Sichuan 610054, P. R. China
5. Department of Materials Science and Engineering, University of Texas at Arlington, Arlington, Texas 76019