Initial stages of degradation of superconductor surfaces: ${\mathrm{O}}_2$, ${\mathrm{H}}_2$O, ${\mathrm{CO}}_2$, and CO chemisorption on ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Sr}}_{\mathrm{x}}$${\mathrm{CuO}}_4$

The initial stages of degradation of high-$T_c$ superconductor surfaces by interaction with atmospheric gases have been studied using ultraviolet photoelectron spectroscopy. ${\mathrm{O}}_2$ has little effect, while ${\mathrm{H}}_2$O adsorbs dissociatively with an initial sticking coefficient $S_0$∼1, and form a surface hydroxide. ${\mathrm{CO}}_2$ adsorbs forming a carbonatelike surface species with an initial sticking coefficient of ∼0.3. CO is observed to result in similar adsorbed surface species with a much lower sticking coefficient of ∼3×${10}^{\mathrm{-}4}$.