1. Electrical and Computer Engineering Department, University of California, Santa Barbara, California 93106, USA
2. Institute for Microelectronics and Microsystems, CNR-IMM, Via Monteroni, 73100 Lecce, Italy
3. Materials Science and Engineering Department, University of Texas at Dallas, Richardson, Texas 75080, USA
4. Materials Department, University of California, Santa Barbara, California 93106, USA