[1] Stanford Univ, Geballe Lab Adv Mat, Stanford, CA 94305 USA
[2] Stanford Univ, Dept Mat Sci & Engn, Stanford, CA 94305 USA
[3] Purdue Univ, Sch Elect & Comp Engn, W Lafayette, IN 47907 USA
[4] Purdue Univ, Birck Nanotechnol Ctr, W Lafayette, IN 47907 USA