GaAs光电阴极Cs,O吸附研究

Cs, O adsorption for forming GaAs photocathodes

提出了基于第一性原理的密度泛函理论框架下的广义梯度近似投影缀加波赝势法,在结构优化的基础上采用平板模型计算了GaAs(110)表面单一吸附0.5 ML Cs元素、单一吸附0.5 ML O元素及0.5 ML Cs、0.5 ML O共吸附系统的特定吸附位、吸附系统总能及吸附系统的电子结构。吸附系统总能的计算结果对比及电子结构图表明:当Cs、O元素吸附量在GaAs(110)表面达到Θ=1 ML时,它们并非各自在表面形成局域畴形态的竞争性共化学吸附,而是将在表面形成混合均匀相的协同共化学吸附。采用偶极子校正进一步计算三种吸附系统的功函数分别是4.423 e V、5.749 e V、4.377 e V,从而得出GaAs光电阴极制备过程中提高并保持光电阴极发射性能的方法及机理。

Generalized gradient approximation projector augmented wave method based on first-principle in the frame of density functional theory （DFT） were put forward. The slab model of GaAs （110） crystal plane was adapted for calculating adsorption system on basis of the optimization of bulk GaAs structure. Three types of adsorption system including specific adsorption sites, total binding energy, and adsorption electronic structure were taken fully into account with adsorbate quantity of Θ=0.5 monolayer （ML） sole Cs, Θ=0.5 ML sole O, and Θ=1.0 ML Cs, O, respectively. The comparison results of calculated total binding energy and projected maps of electron density show that when adsorbates of Cs, O reach to Θ= 1.0 ML, they don＇t form local domain of competitive chemical adsorption, while they form a compound uniformity phase of cooperative chemical adsorption. Considering electronic dipole correction in the calculation, the work function of the three adsorption systems were 4.423 eV, 5.749 eV, 4.377 eV, the method and mechanism for improving and maintaining photoemission characteristics in GaAs photocathode preparing technology were further obtained.