1. Department of Physics and Laboratory for Surface Studies, University of Wisconsin—Milwaukee, Milwaukee, Wisconsin 53211, United States
2. Department of Mechanical Engineering and Laboratory for Surface Studies, University of Wisconsin—Milwaukee, Milwaukee, Wisconsin 53211, United States
3. Synchrotron Radiation Center, Stoughton, Wisconsin 53589, United States
4. Department of Mechanical Engineering and the Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712, United States