[1] Sun Yat Sen Univ, Sch Phys & Engn, State Key Lab Optoelect Mat & Technol, Guangzhou 510275, Guangdong, Peoples R China
[2] Sun Yat Sen Univ, Sch Phys & Engn, Guangdong Prov Key Lab Low Carbon Chem & Energy C, Guangzhou 510275, Guangdong, Peoples R China
[3] Gen Motors Res & Dev Ctr, Warren, MI 48090 USA