[1
]Department of Electrical Engineering, Stanford University, Stanford, California 94305,
USA
[2
]Geballe Laboratory for Advanced Materials, Department of Applied Physics, Stanford
University, 476 Lomita Mall, Stanford, California 94305, USA
[3
]Department of Inorganic Materials Science, Faculty of Science and Technology and MESA+
Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE Enschede,
The Netherlands
[4
]Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory,
2575 Sand Hill Road, Menlo Park, California 94025, USA