1. 1) M.Fujii, Y.Yamada, T.Imamura, and H.Honda : 18 th Biennial Conference on Carbon, p.405, 1987.
2. 2) JPN Patent, 64-9288, 1989.
3. 3) D.Tateishi, K.Esumi, and H.Honda : Carbon, 29, 1296 (1991).
4. 4) R.Warren, C.H.Anderson, and M.Carlsson : J. Mater. Sei., 13,178 (1978).
5. 5) M.S.Dresselhaus and G.Dresselhaus : Adv. Phys., 30,139 (1981).