[1] Nanyang Technol Univ, Sch Mat Sci & Engn, Singapore 639798, Singapore
[2] Inst Mat Res & Engn, Singapore 117602, Singapore
[3] Chinese Acad Sci, Changchun Inst Appl Chem, State Key Lab Electroanalyt Chem, Changchun 130022, Jilin, Peoples R China
[4] Natl Univ Singapore, Dept Phys, Singapore 117542, Singapore
[5] Natl Univ Singapore, Dept Chem, Singapore 117542, Singapore