1. Nanoscience Centre, University of Cambridge, Cambridge CB3 0FF, United Kingdom, ATD Team, Memory Division, Semiconductor Business, Samsung Electronics Co., Yongin City, Korea, Future Technology Research Division, Electronics and Telecommunications Research Institute (ETRI), Daejeon 305-700, Korea, BK 21 Physics Research Division, SKKU Advanced Institute of Nanotechnology (SAINT) and Center for Nanotubes and Nanostructured Composites (CNNC), Sungkyunkwan University, Suwon 440-746, Korea