1. School of Materials Science and Engineering University of New South Wales Sydney NSW 2052 Australia
2. Department of Physics College of Science University of Bahrain P.O. Box 32038, Sakhir Campus, Zallaq Kingdom of Bahrain
3. Computer, Electrical and Mathematical Sciences and Engineering Physical Sciences and Engineering Division King Abdullah University of Science and Technology Thuwal 23955‐6900 Saudi Arabia
4. Department of Materials Science and Engineering City University of Hong Kong Tat Chee Avenue Kowloon Hong Kong SAR China