1. Department of Physics and School
of Engineering, Brown University, Providence,
Rhode Island 02912, United States
2. Environmental and Molecular
Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
3. Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico
87545, United States
4. Department
of Electrical and
Computer Engineering, University of California, San Diego, California 92093, United States