1. Department of Mechanical Engineering, University of California, Riverside, 900 University Ave., Riverside, California 92521, USA
2. Department of Physics, University of California, Riverside, 900 University Ave., Riverside, California 92521, USA
3. Department of Physics, University of California, San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA
4. Materials Science and Engineering, University of California, Riverside, 900 University Ave., Riverside, California 92521, USA