We thank Prof. A. Sidorenko and Dr. M. Aizenberg for discussions and Drs. Ashley Taylor and Mughees Kahn for substrate fabrication. This work was supported by the AFOSR under Award FA9550 – 09-1 – 0669-DOD35CAP and by the DOE under award DE-SC0005247. The work was performed in part at the Center for Nanoscale Systems (CNS), a member of the National Nanotechnology Infrastructure Network (NNIN), which is supported by the NSF under award ECS-0335765. L. D. Z. thanks the Department of Defense (DoD) for support through the National Defense Science & Engineering Graduate Fellowship (NDSEG) Program, as well as the National Science Foundation (NSF) for support through the Graduate Research Fellowship Program (GRFP).