1. Department of Electrical Engineering, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, Texas 75080, USA
2. Texas Instruments Inc., Richardson, Texas 75243, USA
3. Department of Physics, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, Texas 75080, USA
4. Department of Materials Science and Engineering, The University of Texas at Dallas, 800 W. Campbell Rd., Richardson, Texas 75080, USA