1. Homer L. Dodge Department of Physics and Astronomy, The University of Oklahoma, 440 W. Brooks Street, Norman, Oklahoma 73019, United States
2. Department of Physics, University of North Texas, Denton, Texas 76203, United States
3. Center for Chemistry and Nanoscience, National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, United States
4. Swift Solar, Inc., San Carlos, California 94070, United States