[1] Tsinghua Univ, Sch Mat Sci & Engn, State Key Lab New Ceram & Fine Proc, Beijing 100084, Peoples R China
[2] Tsinghua Univ, Ctr Nano & Micro Mech, Beijing 100084, Peoples R China
[3] Natl Ctr Nanosci & Technol, Beijing 100190, Peoples R China
[4] Tsinghua Univ, Dept Mech Engn, Beijing 100084, Peoples R China