1. Chemical Engineering Program, Department of Nanoengineering, University of California, San Diego, La Jolla, California 92093, United States
2. National Renewable Energy Laboratory, Golden, Colorado 80401, United States
3. Materials Science and Engineering Program, University of Colorado, Boulder, Colorado 80309, United States
4. Renewable and Sustainable Energy Institute, University of Colorado, Boulder, Colorado 80309, United States
5. Department of Physics, University of Colorado, Boulder, Colorado 80309, United States