1. Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720, USA
2. NaMLab gGmbH, Noethnitzer Str. 64, D-01187 Dresden, Germany
3. School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA
4. Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5. Chair of Nanoelectronic Materials, TU Dresden, D-01062 Dresden, Germany