1. Department of Physics and Astronomy, University of Wyoming, Laramie, Wyoming 82071, USA
2. Department of Electrical and Computer Engineering, University of Wyoming, Laramie, Wyoming 82071, USA
3. Material Sciences Center, National Renewable Energy Laboratory, Golden, Colorado 82071, USA
4. Materials Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA