1. a Polymer Materials Lab., Korea Institute of Science and Technology , P. O. Box 131, Cheongryang, Seoul , 130-650 , Korea
2. b Dept. of Advanced Materials Engineering , KAIST Seoul Campus , Cheongryangri-dong 207-43, Dondaemoon-ku, Seoul , 130-010 , Korea
3. c Orion Electric Co., Ltd. , Gumi, 730-030 , Kyung-Buk , Korea