Reaction of Quasi-Compounds on Metal Surfaces

Abstract〈−2 1 1〉

When Cu atoms are vaporized on a (2 × 1)(–AgO–)/Ag(110) surface, the quasi-compound (–AgO–) strings react with Cu atoms and a new quasi-compound (–CuO–) string grows in the 〈1–10〉 direction on the Ag(110) surface; the (2 × 1)(–AgO–)/Ag(110) surface changes to (1 × 2)(Cu–O–)/Ag(110). This newly formed (–CuO–) string on the Ag(110) surface undergoes reversible reaction described by (–CuO–) string ⇌ (Cu₂)₃ + O₂ at moderate temperatures. When a (–AgO–)/Ag(110) surface is exposed to CO₂, a hybrid surface with (–AgO–) and Ag–CO₃ is formed. The Cu atoms vaporized on this hybrid [(–AgO–) + Ag–CO₃]/Ag(110) surface undergo selective reaction with the (–AgO–) strings. However, the reverse selective reaction of Cu atoms occurs by the sweep of the hybrid surface with a W-tip of STM contaminated with Cu atoms. That is, Cu atoms on a W-tip react selectively with AgCO₃ dots, and a [(–AgO–) + (–CuO–)] hybrid surface is formed by painting using a Cu/W-tip, which is named as “atom painting.” The quasi-compound may be formed on the surface by reaction via a precursor state, although it is difficult to detect. The presence of precursor states is well proved by the dissociation of alcohol molecules on the 7 × 7-Si(111) surface, that is, the dissociation probability of alcohol molecule in a half unit cell depends on the local conformation of the sites, which strongly suggests the dissociation via a precursor state.