1. Department of Electrical and Computer Engineering, George Washington University, Washington, District of Columbia 20052, United States
2. Department of Mechanical and Aerospace Engineering, George Washington University, Washington, District of Columbia 20052, United States
3. Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, California 92093, United States
4. Materials Science and Engineering Program, University of California San Diego, La Jolla, California 92093, United States