Optimization of Cs-O and Cs-NF3 adsorption on As-rich and Ga-rich GaAs(100) photocathode surfaces: An ab-initio study

Based on density functional theory, the preferred adsorption sites and ratios of Cs-O and Cs-NF₃ adsorption on GaAs(100) β₂(2 × 4) As-rich surface and β₂(4 × 2) Ga-rich surface were explored. For Cs-O adsorption, 6Cs-3O-adsorbed As-rich surface with lowest O adsorption energy and 8Cs-6O-adsorbed Ga-rich surface yield the lowest work function values. For Cs-NF₃ adsorption, 6Cs-1NF₃ configurations minimize the work function on both surfaces, excess NF₃ increase work function, whereas 8Cs-1NF₃ configuration on Ga-rich surface show the most negative NF₃ adsorption energy. Residual gases increase work function, with CO₂ adsorbing stably and H₂ having minimal effect. Notably, 6Cs-3O-adsorbed As-rich surface and 8Cs-1NF₃-adsorbed Ga-rich surface exhibit superior resistance to residual gases. Charge transfer analysis reveals that surface Ga/As charges depend on reconstruction and adsorbate ratios, Cs atoms mediate charge redistribution between adsorbates and the surface, influencing dipole moments and work function. These findings improve understanding of optimal Cs-O and Cs-NF₃ activation configurations on GaAs photocathodes.