1. Department of Applied Plasma Engineering, Chonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju 561-756, South Korea
2. Plasma Technology Research Center, National Fusion Research Institute, 814-2 Ohsikdo-dong, Gunsan 573-540, South Korea
3. Mass Spectrometry and Advanced Instrument Group, Korea Basic Science Institute, Ochang Center, Chungbuk 28119, South Korea