In this study, we investigate the structural and chemical changes of monatomic ${\mathrm{CoO}}_2$ chains grown self-organized on the Ir(100) surface [P. Ferstl et al., Phys. Rev. Lett. 117, 046101 (2016)] and on Pt(100) under reducing and oxidizing conditions. By a combination of quantitative low-energy electron diffraction, scanning tunneling microscopy, and density functional theory we show that the cobalt oxide wires are completely reduced by ${\mathrm{H}}_2$ at temperatures above 320 K and a $3\times 1$ ordered ${\mathrm{Ir}}_2\mathrm{Co}$ or ${\mathrm{Pt}}_2\mathrm{Co}$ surface alloy is formed. Depending on temperature, the surface alloy on Ir(100) is either hydrogen covered $(T<400$ K) or clean and eventually undergoes an irreversible order-disorder transition at about 570 K. The ${\mathrm{Pt}}_2\mathrm{Co}$ surface alloy disorders with the desorption of hydrogen, whereby Co submerges into subsurface sites. Vice versa, applying stronger oxidants than ${\mathrm{O}}_2$ such as ${\mathrm{NO}}_2$ leads to the formation of ${\mathrm{CoO}}_3$ chains on Ir(100) in a $3\times 1$ superstructure. On Pt(100), such a ${\mathrm{CoO}}_3$ phase could not be prepared so far, which, however, is due to the ultrahigh vacuum conditions of our experiments. As revealed by theory, this phase will become stable in a regime of higher pressure. In general, the structures can be reversibly switched on both surfaces using the respective agents ${\mathrm{O}}_2,{\mathrm{NO}}_2$, and ${\mathrm{H}}_2$.

• Received 13 July 2017

DOI:https://doi.org/10.1103/PhysRevB.96.085407