[Liu, Jinping; Fan, Hong Jin] Nanyang Technol Univ, Div Phys & Appl Phys, Sch Phys & Math Sci, Singapore 637371, Singapore.
[Liu, Jinping; Jiang, Jian] Cent China Normal Univ, Dept Phys, Inst Nanosci & Nanotechnol, Wuhan 430079, Peoples R China.
[Bosman, Michel] ASTAR, Inst Mat Res & Engn, Singapore 117602, Singapore.
[Fan, Hong Jin] Nanyang Technol Univ ERI N, Energy Res Inst, Singapore 637553, Singapore.
[Fan, Hong Jin] Nanyang Technol Univ, Div Phys & Appl Phys, Sch Phys & Math Sci, 21 Nanyang Link, Singapore 637371, Singapore.