1. Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA
2. Department of Applied Physics and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California 94305, USA
3. School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, USA
4. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
5. Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA