[1] Chinese Acad Sci, Key Lab Mat Phys, Hefei 230031, Peoples R China
[2] Chinese Acad Sci, Anhui Key Lab Nanomat & Nanostruct, Inst Solid State Phys, Hefei 230031, Peoples R China
[3] Natl Inst Mat Sci, Nanoscale Mat Ctr, Tsukuba, Ibaraki 3050044, Japan
[4] Natl Inst Mat Sci, Adv Elect Mat Ctr, Tsukuba, Ibaraki 3050044, Japan
[5] Natl Inst Mat Sci, World Premier Int Ctr Mat Nanoarchitecton, Tsukuba, Ibaraki 3050044, Japan