[1] Sichuan Univ, Inst Atom & Mol Phys, Chengdu 610065, Sichuan, Peoples R China
[2] Univ Arkansas, Phys Dept, Fayetteville, AR 72701 USA
[3] Univ Arkansas, Inst Nanosci & Engn, Fayetteville, AR 72701 USA
[4] Nanjing Univ, Natl Lab Solid State Microstruct, Coll Engn & Appl Sci, Nanjing 210093, Jiangsu, Peoples R China
[5] Nanjing Univ, Collaborat Innovat Ctr Adv Microstruct, Nanjing 210093, Jiangsu, Peoples R China
[6] Fudan Univ, Dept Phys, Key Lab Computat Phys Sci, State Key Lab Surface Phys,Minist Educ, Shanghai 200433, Peoples R China
[7] Univ Arkansas, Microelect Photon Program, Fayetteville, AR 72701 USA
[8] LIST, Mat Res & Technol Dept, 5 Ave Hauts Fourneaux, L-4362 Esch Sur Alzette, Luxembourg