1. Department of Materials Science and Engineering; Massachusetts Institute of Technology; Cambridge MA 02139 USA
2. Department of Electrical Engineering and Computer Science; Massachusetts Institute of Technology; Cambridge MA 02139 USA
3. IBM Almaden Research Center; 650 Harry Road San Jose CA 95120 USA
4. Department of Materials Science and Engineering; Korea Advanced Institute of Science and Technology (KAIST); 291 Daehak-ro, Yuseong-gu Daejeon 305-701 Republic of Korea