1. Department
of Physics, Applied Physics and Astronomy, Binghamton University, Binghamton, New York 13902, United States
2. Department
of Materials Science and Engineering, Cornell University, Ithaca, New York 14853-1501, United States
3. School
of Applied and Engineering Physics, Cornell University, Ithaca, New York 14853, United States
4. Materials
Science and Engineering, Binghamton University, Binghamton, New York 13902, United States
5. Department
of Physics and Materials Research Institute, Pennsylvania State University, University Park, Pennsylvania, 16802, United States
6. Department
of Physics, University of Illinois at Urbana−Champaign, Urbana, Illinois 61801, United States
7. Advanced
Light Source, Lawrence Berkeley National Laboratory, Berkeley, California, United States
8. Materials
Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States
9. Kavli Institute at Cornell for Nanoscale Science, Ithaca, New York 14853, United States