1. Department of Materials Science, Faculty of Pure and Applied Sciences, and Tsukuba Research Center for Energy Materials Science (TREMS), University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
2. Leibniz Institute of Photonic Technology, Albert-Einstein Str. 9, 07745 Jena, Germany
3. Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Helmholtzweg 4, D-07743 Jena, Germany
4. Research Center for Applied Sciences, Academia Sinica, 128 Sec. 2, Academia Road, Nankang
District, Taipei 11529, Taiwan
5. Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan
6. Faculty of Physics and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Lotharstraβe 1, Duisburg D-47048, Germany