1. Department of Physics, Oakland University, Rochester, Michigan 48309, USA
2. Department of Applied Physics, Northwestern Polytechnical University, Xi’an 710129, People’s Republic of China
3. Department of Applied Physics and COMP Centre of Excellence, Aalto University School of Science, P.O. Box 11000, FI-00076 Aalto, Finland
4. Department of Physics, University of Swaziland, Private Bag 4, Kwaluseni, Swaziland
5. Department of Physics and Astronomy, Wayne State University, Detroit, Michigan 48201, USA
6. Department of Physics, Brown University, P.O. Box 1843, Providence, Rhode Island 02912, USA
7. Laboratório Associado de Sensores e Materiais, Instituto Nacional de Pesquisas Espaciais, 12227-010 São José dos Campos, SP, Brazil