1. Department of Safety Engineering, Incheon National University (INU), 119 Academy-ro, Yeonsu-gu, Incheon 22012, Republic of Korea
2. Energy Materials and Surface Sciences Unit (EMSSU), Okinawa Institute of Science and Technology Graduate University (OIST), 1919-1 Tancha, Onna-son, Okinawa 904-0495, Japan