[Liu, Qian; Tian, Ye] Natl Ctr Nanosci & Technol, CAS Key Lab Nanosyst & Hierarch Fabricat, CAS Ctr Excellence Nanosci, 11 Beiyitiao, Beijing 100190, Peoples R China.
[Tian, Ye] Hunan City Univ, Sch Commun & Elect Engn, Yiyang 413000, Peoples R China.
[Pan, Lida] Vanderbilt Univ, Dept Phys & Astron, Nashville, TN 37235 USA.
[Pan, Lida] Chinese Acad Sci, Inst Phys, Beijing 100190, Peoples R China.
[Tian, Ye] Univ Ghent, IMEC, Dept Informat Technol, Photon Res Grp, B-9000 Ghent, Belgium.