1. State Key Laboratory for Mechanical Behavior of Materials; Xi'an Jiaotong University; Xi'an 710049 China
2. Department of Physics; North Carolina State University; Raleigh NC 27695 USA
3. Department of Chemical Engineering; Stanford University; Stanford CA 94305 USA
4. Stanford Synchrotron Radiation Lightsource; SLAC National Accelerator Laboratory; Menlo Park CA 94025 USA