[1] Tsinghua Univ, Dept Mat Sci & Engn, Beijing Natl Ctr Electron Microscopy, State Key Lab New Ceram & Fine Proc, Beijing 100084, Peoples R China
[2] PINSTECH, Nanomat Res Grp, Div Phys, Islamabad 44000, Pakistan
[3] Tsinghua Univ, Dept Mat Sci & Engn, Adv Mat Lab, Beijing 100084, Peoples R China