SCANNING-TUNNELING-MICROSCOPY STUDIES OF NIOBIUM CARBIDE(100) AND CARBIDE(110) SURFACES

Scanning tunneling microscopy (STM) studies were conducted on the surf aces of NbC0.75(100) and NbC0.865(110) single crystals after in situ c leaning treatments of sputtering and annealing cycles. STM images show atom-resolved structures of both surfaces. On NbC0.75(100), localized areas of a square (1 x 1) structure were observed, together with regi ons of hexagonal structure, indicative of a coexisting surface phase, possibly that of Nb4C3-x. On the NbC0.865(110) surface, a ridge-and-va lley grating structure consisting of both (4 x 1) and (5 x 1) geometri es was observed over large areas. The nanometer-scale faceting phenome non may be common to the (110) surfaces of most transition-metal carbi des.