1. School of Physics, Trinity College Dublin, University of Dublin, Dublin 2, Ireland, Department of Chemistry and Engineering Physics, University of Wisconsin—Platteville, Platteville, Wisconsin 53818, Nanotechnology Center for Collaborative R&D, University of Wisconsin—Platteville, Platteville, Wisconsin 53818, and Centre for Research on Adaptive Nanostructures & Nanodevices, Trinity College Dublin, University of Dublin, Dublin 2, Ireland