1. Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, USA
2. Department of Physics, Xi'an Jiaotong University, Xi'an 710049, China
3. Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
4. Canadian Light Source, Inc., 44 Innovation Boulevard, Saskatoon, Saskatchewan S7N 2V3, Canada