1. Materials and Chemistry Science and Technology Directorate, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
2. Department of Physics, Colorado School of Mines, Golden, Colorado 80401, United States
3. Applied Science and Technology Graduate Group, University of California at Berkeley, Berkeley, California 94720, United States
4. Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, California 94702, United States
5. Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, Colorado 80401, United States