1. Division of Biomedical Engineering, School of Engineering, University of Glasgow, Glasgow G12 8LT, U.K.
2. Institute for Optoelectronics and Microsystems (ISOM), Universidad Politécnica de Madrid, José Gutiérrez Abascal 2, 28006 Madrid, Spain
3. Graduate School of Organic Materials Science, Yamagata University, Yonezawa 992-8510, Japan
4. Department of Materials Physics, Nagoya University, Nagoya 464-8603, Japan