[1] Ft Hays State Univ, Kansas Acad Math & Sci, 600 Pk St, Hays, KS 67601 USA
[2] Nanjing Univ, Natl Lab Solid State Microstruct, Sch Elect Sci & Engn, Nanjing 210093, Jiangsu, Peoples R China
[3] Nanjing Univ, Collaborate Innovat Ctr Adv Microstruct, Nanjing 210093, Jiangsu, Peoples R China