1. Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California 90095, United States
2. California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California 90095, United States
3. Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
4. Materials Research and Education Center, Department of Mechanical Engineering, Auburn University, Auburn, Alabama 36849, United States