1. Hewlett Packard Labs, Hewlett Packard Enterprise, Palo Alto, California 94304, United States
2. Department
of Electrical and Computer Engineering, University of Massachusetts, Amherst, Massachusetts 01003, United States
3. Department of Materials Science and Engineering, Seoul National University of Science and Technology, Seoul 139-743, Republic of Korea
4. Department of Materials
Science and Engineering and Inter-University Semiconductor Research
Center, College of Engineering, Seoul National University, Seoul 151-744, Republic of Korea