1. Laboratory for Energy and NanoScience (LENS), Khalifa University of Science and Technology, Masdar Campus, PO Box 54224, Abu Dhabi, UAE
2. Department of Mechanical and Materials Engineering, Khalifa University of Science and Technology, Masdar Campus, PO Box 54224, Abu Dhabi, UAE
3. Department of Physics, Khalifa University of Science and Technology, Main Campus, PO Box 127788, Abu Dhabi, UAE
4. Institute of Physics, Academia Sinica, Taipei, Taiwan, R.O.C. 11529
5. Department of Physics and Technology, UiT The Arctic University of Norway, 9010 Tromsø, Norway