Notes:
We thank T.L. Vu, A.V. Shneidman, L. Mishchenko, A.W. Rodriguez, B.D. Hatton, M. Aizenberg, and F. Spaepen for helpful discussions, and T.S. Wong for surface tension measurements. This work was supported by the AFOSR Award No. FA9550-09-1-0669-DOD35CAP. I.B.B. acknowledges support from the Natural Sciences and Engineering Research Council of Canada through the PGS-D program. M.K. acknowl- edges support from the Alexander von Humboldt Foundation. Electron microscopy was performed at Harvard's Center for Nanoscale Systems.