1. Key Laboratory of Materials Modification by Laser, Ion, and Electron Beams (Ministry of Education), School of Physics, Dalian University of Technology, Dalian 116024, China
2. Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Konkoly-Thege Miklós str. 29-33, H-1121 Budapest, Hungary
3. Evatec AG, CH-9477 Trübbach, Switzerland
4. Key Laboratory of Materials Modification by Laser, Ion, and Electron Beams (Ministry of Education), School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024, China
5. Institute for Electrical Engineering, Ruhr-University Bochum, 44801 Bochum, Germany
6. Department of Physics, West Virginia University, Morgantown, West Virginia 26506-6315, USA