[1] Univ Calif Berkeley, Appl Sci & Technol Grad Grp, Berkeley, CA 94720 USA
[2] Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA
[3] Univ Twente, Fac Sci & Technol, NL-7500 AE Enschede, Netherlands
[4] US DOE, Adv Res Projects Agcy, Washington, DC 20585 USA
[5] Univ Calif Berkeley, Dept Mat Sci & Engn, Berkeley, CA 94720 USA