A graphitic phase is very unreactive toward hydrogenation and represents a deactivated surface. In the present study, the inactive form of carbon formed from methane decomposition on single-crystal Ru catalysts has been characterized using scanning tunneling microscopy (STM) and high-resolution electron energy loss spectroscopy (HREELS). The results show that the carbonaceous species formed on Ru surfaces at temperatures exceeding 800 K is graphitic. On a Ru(0001) surface, a graphitic species initially forms discrete clusters with dimensions 10-15 Angstrom in diameter and 2-3 Angstrom in apparent height. Only at temperatures exceeding 1300 K is the hexagonal superstructure of continuous graphite monolayers observed. In contrast, the carbonaceous species from methane decomposition at 800 K nucleates to form large three-dimensional particles of graphite on Ru(11 (2) over bar 0).