1. Department of Chemical Engineering, National Tsing Hua University, Hsinchu 30013, Taiwan
2. Department of Materials and Optoelectronic Science, Center for Nanoscience and Nanotechnology, National Sun Yat-sen University, Kaohsiung 80424, Taiwan
3. Institut Charles Sadron, Centre National de la Recherche Scientifique, 23, Rue du Loess, B.P. 84047, 67034 Strasbourg, France