[1] Tsinghua Univ, Key Lab Adv Mat Proc Technol, Minist Educ, Beijing 100084, Peoples R China
[2] Tsinghua Univ, Dept Mech Engn, Beijing 100084, Peoples R China
[3] Peking Univ, Dept Adv Mat & Nanotechnol, Coll Engn, Beijing 100871, Peoples R China
[4] Tsinghua Univ, Ctr Nano & Micro Mech, Beijing 100084, Peoples R China