K. Ashidaa, K. Kanamorib, K. Watanabea
a Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan
b Department of Chemistry, Faculty of Science, Toyama University, Gofuku 3190, Toyama 930, Japan
Graphite is the primary candidate for the first wall of magnetically confined fusion devices. For this purpose, it is important to know the surface properties of graphite to understand the plasma-surface interaction as well as vacuum properties of graphite. From this viewpoint, we examined the binding states of carbon atoms, inherent hydrogen content, and crystallinity of the surfaces of isotropic graphites prepared by several Japanese companies as well as anisotropic ones with x-ray photoelectron (XPS), secondary ion mass (SIMS), and Raman (RS) spectroscopies. Although no measurable difference in the binding state of carbon atoms was detected among the isotropic and anisotropic graphites with XPS, RS revealed that their crystallite sizes differed from each other. Namely, the crystallite sized of the isotropic were in the range from 100 to 300 Å, whereas those of the anisotropic graphites were more than 〜 1000Å. In addition, nongraphitized carbon which was not observed for the anisotropic graphites was present in the surface layers of the isotropic ones. SIMS revealed that the inherenthydrogen contents in the isotropic graphites were larger than those in the anisotropic ones. The results indicate that the larger hydrogen contents in the isotropic graphites are due to the presence of nongraphitized carbon which acts as the trapping site of hydrogen atoms.