1. Department of Physics, West Chester University, West Chester, Pennsylvania 19383, USA
2. Division of Materials and Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
3. Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409, USA
4. Center for Nanomaterials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
5. Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan
6. Department of Physics, Lehigh University, Bethlehem, Pennsylvania 18015, USA