[1] Univ Calif Los Angeles, Dept Mat Sci & Engn, Los Angeles, CA 90095 USA
[2] Peking Univ, Minist Educ, Key Lab Polymer Chem & Phys, Dept Mat Sci & Engn,Coll Engn, Beijing 100871, Peoples R China
[3] Univ Calif Los Angeles, Calif NanoSyst Inst, Los Angeles, CA 90095 USA
[4] Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA 94720 USA