1. Department of NanoEngineering; University of California, San Diego; 9500 Gilman Drive La Jolla CA 92093 USA
2. Department of Bioengineering; University of California, San Diego; 9500 Gilman Drive La Jolla CA 92093 USA
3. Center for Memory and Recording Research; University of California, San Diego; 9500 Gilman Drive La Jolla CA 92093 USA