[1] Tsinghua Univ, Minist Educ, Key Lab Atom & Mol Nanosci, Dept Chem, Beijing 100084, Peoples R China
[2] Tsinghua Univ, Dept Mat Sci & Engn, Beijing 100084, Peoples R China
[3] Tsinghua Univ, Tsinghua Foxonn Nanotechnol Lab, Beijing 100084, Peoples R China