1. Division of Physics and Applied Physics; School of Physical and Mathematical Sciences; Nanyang Technological University; Singapore 637371 Singapore
2. College of Aerospace Engineering; Chongqing University; Chongqing 400044 P. R. China
3. Key Laboratory for Ultrafine Materials of Ministry of Education; School of Materials Sciences and Engineering; East China University of Science and Technology; 130 Meilong Road Shanghai 200237 P. R. China
4. Heterogeneous Catalysis; Institute of Chemical Engineering and Sciences; A*star, 1 Pesek Road Jurong Island 627833 Singapore
5. Energy Research Institute @NTU (ERI@N); Nanyang Technological University; Singapore 639798 Singapore