低折射率钨表面钠覆盖层的表面电子结构和场发射电流
Surface Electronic Structures and Field Emission Currents at Sodium Overlayers on Low-Index Tungsten Surfaces
摘要：
计算了具有重要技术意义的W表面的场致发射和表面光场致发射的发射电流的总能量分布（TEDs）以及覆盖层引起的表面电子结构的变化。将全势线性缀加平面波方法推广到场发射和光场发射的研究中，得到的场发射和光场发射谱线解释了在亚单层和单层Na覆盖下，W（100）和W（110）表面场发射和光场发射谱线峰值的移动. 3s Na态与干净W（100）中强Swanson峰的dz 2-类表面态对和低于费米能的干净W（111）中的表面共振的杂化使这些W态移动约-1.2 eV和-1.0 eV，从而稳定这些态，在W（100）/Na c（2 × 2）和W（111）/Na（1 × 1）的场致发射和光场致发射中分别产生新的强峰。Na层内相互作用的影响进行了讨论，并示出移动强的S-和P-样峰的W（110）的表面态密度低于和高于费米能量分别降低能量与增加Na覆盖，与实验一致。
英文摘要：
The total energy distributions (TEDs) of the emission currents in field emission and surface photofield emission and the overlayer-induced modifications in the surface electronic structures from the technologically important W surfaces with the commensurate W(100)/Na c(2x2), W(110)/Na (2x2) and W(111)/Na (1x1) overlayers are calculated. The TEDs obtained by our recent numerical method that extends the full-potential linear augmented plane wave method for the electronic structures to the study of field and photofield emission are used to interpret the shifts of the peaks in the experimental TEDs in field emission and photofield emission from the W(100) and W(110) surfaces at sub-monolayer and monolayer Na coverage. Hybridization of the 3s Na states with the pairs of dz2-like surface states of the strong Swanson hump in clean W(100) and surface resonances in clean W(111) below the Fermi energy shifts these W states by about -1.2 eV and -1.0 eV, thus stabilizing these states, to yield new strong peaks in the TEDs in field emission and photofield emission from W(100)/Na c(2x2) and W(111)/Na (1x1) respectively. The effect of Na intralayer interactions are discussed and are shown to shift the strong s- and p-like peaks in the surface density of states of W(110) below and above the Fermi energy respectively to lower energy with increased Na coverage, in agreement with experiments.
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