1. Department of Civil and Environmental Engineering, University of California, Los Angeles, CA 90095, USA.
2. Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, CA 90095, USA.
3. Department of Mechanical Engineering, Virginia Tech, Blacksburg, VA 24061, USA.
4. Department of Electrical and Computer Engineering, University of California, San Diego, CA 92093, USA.
5. Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843, USA.
6. California NanoSystems Institute, University of California, Los Angeles, CA 90095, USA.