Mechanisms of Pd(1 1 0) surface reconstruction and oxidation: XPS, LEED and TDS study

Oxygen interaction with Pd(1 1 0) has been studied in a wide range of pressures (Po2 = 10−6–100 Pa) and temperatures (T = 400–600 K) by X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and thermal desorption spectroscopy (TDS). The amount of oxygen absorbed by Pd(1 1 0) single crystal grows to more than 100 ML when the reaction temperature and the O2 exposure are increased. Several reconstructed and oxide structures are sequentially formed on Pd(1 1 0) as the amount of adsorbed and absorbed oxygen increases. During oxygen adsorption (1 × 2) reconstruction occurs and a c(2 × 4) structure is formed on Pd(1 1 0) at θ = 0.5 ML. When the amount of absorbed oxygen increases from 0.5 to 2.0 ML, oxygen penetrates into subsurface Pd layers to the depth exceeding 15–20 Å while retaining the c(2 × 4) structure. When the amount of absorbed oxygen is between 2 and 5 ML, the surface is subjected to reconstruction with the formation of a surface oxide with θ ∼ 0.8 that has a complex LEED diffraction pattern. Further increase of the amount of absorbed oxygen beyond 5 ML leads to oxygen location in the subsurface region forming PdO clusters. They gradually grow to form an almost continuous layer composed of PdO clusters.