1. State Key Laboratory of Physical Chemistry of Solid Surfaces College of Chemistry and Chemical Engineering and Pen-Tung Sah Institute of Micro-Nano Science and Technology Xiamen University 361005 Xiamen, Fujian P. R. China
2. Department of Physics Faculty of Science University of Tabuk P.O. Box 741 Tabuk Saudi Arabia
3. Department of Physics Lancaster University Lancaster LA1 4YB United Kingdom