1. Applied Physics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, United States
2. Materials and Chemical Science and Technology Directorate, National Renewable Energy Laboratory, Golden, Colorado 80401, United States
3. Department of Physics, University of South Florida, Tampa, Florida 33620, United States
4. Materials Science Centre, Indian Institute of Technology Kharagpur, Kharagpur, 721302, India
5. The Pennsylvania State University, University Park, Pennsylvania 16802, United States