1. a Nanotechnology Research Institute (NRI), National Institute of Advanced Industrial Science and Technology (AIST) , Ikeda, Osaka, Japan
2. b Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University , Suita, Osaka, Japan
3. c Institut de Physique et Chimie des Matériaux de Strasbourg, Groupe des Matériaux Organiques , Strasbourg Cedex 2, France