1. School of Engineering, University of California Santa Cruz, 1156 High Street, Santa Cruz, California 95064, USA
2. Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
3. New Memory Technology Lab, Semiconductor R&D Center, Samsung Electronics, Milpitas, California 95053, USA
4. Department of Electrical and Computer Engineering, Brigham Young University, 459 Clyde Building, Provo, Utah 84602, USA