1. a Department of Organic and Polymeric Materials , Tokyo Institute of Technology , O-okayama, Meguro-ku, Tokyo , 152 , Japan
2. b Opto-Electronics Research Laboratory, Semiconductor Research Center, Matsushita Electric Industry Co., Ltd. , 3-1-1 Yagumonakamachi, Moriguchi-shi, Osaka , 570
3. c Electronic Imaging & Devices Research Lab., Fuji Xerox Co., Ltd. , 2274 Hongo, Ebina-shi, Kanagawa , 243-04