1. Graduate Institute of Communication Engineering, National Taiwan University 1 , Taipei 10617, Taiwan
2. Department of Electrical and Computer Engineering, University of California 2 , Los Angeles, California 90095, USA
3. Applied Mathematics and Computational Research Division, Lawrence Berkeley National Laboratory 3 , Berkeley, California 94720, USA
4. California NanoSystems Institute 4 , Los Angeles, California 90095, USA
5. Department of Electrical Engineering, National Taiwan University 5 , Taipei 10617, Taiwan