1. Department of Electrical Engineering, University of California, Los Angeles, California 90095,
United States
2. Center for
High Technology Materials
and Electrical and Computer Engineering Department, University of New Mexico, Albuquerque, New Mexico 87106, United
States
3. Graduate Institute
of Photonics
and Optoelectronics and Department of Electrical Engineering, National Taiwan University, Taipei 10617, Taiwan
4. California
Nano-Systems Institute, University of California, Los Angeles, California 90095,
United States