Liu Chang, Tobin R G
Department of Physics and Astronomy, Tufts University, Medford, Massachusetts 02155, USA.
J Chem Phys. 2008 Jun 28;128(24):244702. doi: 10.1063/1.2940336.
Measurements of surface resistivity as a function of coverage for oxygen adsorbed on sulfur-predosed Cu(100) films reveal two types of interactions between sulfur and oxygen: S-O repulsion and short-range suppression of the surface resistivity change induced by oxygen adsorption. The repulsive interaction causes oxygen atoms to first occupy adsorption sites far from the sulfur atoms, beyond second-nearest-neighbor sites, where the oxygen-induced surface resistivity is unaffected by sulfur. As a result the low-coverage variation of surface resistivity with oxygen coverage is indistinguishable from the linear dependence observed for oxygen on clean Cu(100). As the oxygen coverage increases, oxygen begins to occupy sites close to sulfur. At the nearest-neighbor sites, the resistivity change due to added oxygen is completely suppressed, and the sample resistance levels off, remaining unchanged even as oxygen continues to adsorb. This resistivity suppression may involve both a reduction of oxygen's direct effect on the resistivity and an oxygen-induced reduction in the resistivity due to the already adsorbed sulfur. With increasing sulfur precoverage both the maximum resistivity change and the oxygen coverage at which the leveling occurs decrease, because the number of sites unaffected by sulfur is reduced. Both the sulfur-oxygen repulsion and the resistivity suppression presumably arise from a through-metal coupling involving adsorbate-induced modifications of the local electronic structure.
对预吸附硫的Cu(100)薄膜上吸附的氧的表面电阻率随覆盖度的测量揭示了硫与氧之间的两种相互作用：S - O排斥以及对氧吸附引起的表面电阻率变化的短程抑制。这种排斥相互作用导致氧原子首先占据远离硫原子的吸附位点，超出次近邻位点，在这些位点上氧诱导的表面电阻率不受硫的影响。因此，表面电阻率随氧覆盖度的低覆盖度变化与在清洁的Cu(100)上观察到的氧的线性依赖关系无法区分。随着氧覆盖度的增加，氧开始占据靠近硫的位点。在最近邻位点，由于添加氧导致的电阻率变化被完全抑制，并且样品电阻趋于平稳，即使氧继续吸附也保持不变。这种电阻率抑制可能涉及氧对电阻率的直接影响的降低以及由于已经吸附的硫导致的氧诱导的电阻率降低。随着硫预覆盖度的增加，最大电阻率变化和平稳发生时的氧覆盖度都降低，因为不受硫影响的位点数量减少。硫 - 氧排斥和电阻率抑制大概都源于涉及吸附质诱导的局部电子结构修饰的穿金属耦合。
