1. Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
2. Department of Materials Science and Engineering, Pennsylvania State University, University Park, PA 16802, USA.
3. Sandia National Laboratories, Mail Stop 1411, Albuquerque, NM 87185, USA.
4. Department of Electrical and Computer Engineering, Texas A&M University, College Station, TX 77843, USA.
5. Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
6. Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB3 OFS, UK.