* Corresponding authors

^a Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
E-mail: slee@umd.edu
Fax: +1 301 314 9121
Tel: +1 301 405 7906

^b Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742, USA
E-mail: rubloff@umd.edu
Tel: +1 301 405 3011

^c Institute for Systems Research, University of Maryland, College Park, Maryland 20742, USA

^d Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742, USA

^e Graduate School of Nanoscience and Technology (WCU), Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea