1. Department of Electronics Engineering, Catholic University of Daegu, Hayang 38430, Korea (Republic of)
2. Department of Electrical and Computer Engineering, MC 0407, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0407, USA, and Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 15588, Korea (Republic of) , E-mail: