The atomic structures of the oxygen chemisorbed TiC(111) surface exhibiting both 1 × 1 and √3 × √3 R30° structures have been studied using impact collision He+ ion scattering spectroscopy (ICISS). At the TiC(111)1 × 1-O surface, oxygen atoms are in two states on the three-fold hollow site which is characterized by the absence of carbon beneath it in the second layer. The two states arise from the difference in the position of the oxygen atom: one located 1.0 Å above the topmost Ti layer and the other 0.8 Å above it. The latter disappears at the TiC(111)√3 × √3 R30°-O surface which is obtained after heating of the TiC(111)1 × 1-O surface at about 1000°C.
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