[1] Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA
[2] Stanford Univ, Dept Phys, Stanford, CA 94305 USA
[3] Stanford Univ, Dept Mol & Cellular Physiol, Stanford, CA 94305 USA
[4] Stanford Univ, Dept Appl Phys, Stanford, CA 94305 USA
[5] Univ Calif Berkeley, Dept Chem, Berkeley, CA 94720 USA
[6] Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley, CA 94720 USA
[7] Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA
[8] Kavli Energy NanoSci Inst, Berkeley, CA 94720 USA