1. Department of Electrical Engineering; University of California at Los Angeles; CA 90095 USA
2. National Nanotechnology Research Center; King Abdulaziz City for Science and Technology; Riyadh 11442 Saudi Arabia
3. Laboratory for Terahertz and Terascale Electronics; University of California at Riverside; CA 92521 USA
4. Department of Materials Science and Engineering; University of California at Los Angeles; CA 90095 USA
5. California NanoSystems Institute; University of California at Los Angeles; CA 90095 USA
6. Laboratory for Electron and X-ray Instrumentation; University of California at Irvine; CA 92697 USA