1. a Institute of Physics, Ukr. Academ. Sci. , prospekt Nauki, 46 Kiev-22, 252650, Ukraine
2. b Institute of Surface Chemistry, Ukr. Academ. Sci. , prospekt Nauki, 31, Kiev-22, 252022, Ukraine
3. c Anyang Recearch Laboratories , Gold Star Co. , Anyang-Shi, Kyunghi-Po , 430-080 , Korea