1. School of Advanced Materials Engineering and Research Center of Advanced Materials Development, Chonbuk National University, Jeonju 561-756, South Korea
2. School of Semiconductor and Chemical Engineering, Semiconductor Physics Research Center, Chonbuk National University, Jeonju 561-756, South Korea
3. Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611
4. Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611