Influence of submonolayer sodium adsorption on the photoemission of the Cu(111)/water ice surface.
Influence of submonolayer sodium adsorption on the photoemission of the Cu(111)/water ice surface.
复制标题
亚单层钠吸附对 Cu(111)/水冰表面光电子发射的影响。
作者：
T. Vondráḱ;J. Plane;S. Meech
在表面-真空界面上观察到了沉积在Cu（111）上的冰膜在钠原子存在和不存在的情况下的光电发射随厚度的变化。对于单独的吸附物和低于4 eV的光子能量，来自Cu（111）衬底的双光子光电发射占主导地位。Cu（111）光电子能谱受到低覆盖度Na的干扰，其强度被几个单层冰强烈衰减。对于低密度的非晶冰膜，观察到强的充电效应。对于退火产生致密的非晶相或结晶相的冰膜，不存在这种效应。仅沉积0.02单层Na导致光电发射阈值急剧降低至2.3+/-0.2 eV。因此，光电子是由可见光辐射在单光子过程中产生的，其横截面超过10（-18）cm（2）。光电发射的初始状态被确定为亚稳态表面俘获电子，其以10+/-2 kJ mol（-1）的活化能热衰变。量子计算支持这个模型，并表明，钠原子是容纳在第一层的冰表面。
Photoemission from an ice film deposited on Cu(111) as a function of thickness has been observed in the presence and absence of sodium atoms at the surface-vacuum interface. For either adsorbate alone and photon energies below 4 eV, two-photon photoemission from the Cu(111) substrate dominates. The Cu(111) photoelectron spectrum is perturbed by low coverages of Na, and its intensity is strongly attenuated by a few monolayers of ice. For a low density amorphous ice film, strong charging effects are observed. For ice films annealed to yield either the dense amorphous or crystalline phase, this effect is absent. Deposition of only 0.02 monolayer of Na leads to a dramatic decrease in the threshold for photoemission to 2.3+/-0.2 eV. Thus, photoelectrons are generated by visible radiation in a one-photon process with a cross section that exceeds 10(-18) cm(2). The initial state for the photoemission is identified as a metastable surface trapped electron, which decays thermally with an activation energy of 10+/-2 kJ mol(-1). Quantum calculations are described which support this model and show that the Na atom is accommodated in the first layer of the ice surface.