1. Department of Materials Science and Engineering and California NanoSystems Institute University of California Los Angeles Los Angeles CA 90095 USA
2. Department of Physics Marmara University 34722 Ziverbey Istanbul Turkey
3. Division of Materials Science and Engineering Hanyang University Seoul 04763 Republic of Korea
4. SKKU Advanced Institute of Nanotechnology (SAINT) and Department of Nanoengineering Sungkyunkwan University Suwon 16419 Republic of Korea