Dipolar effects on the work function of an alkali-iodide overlayer (XI, X = Li, Na, K, Rb, and Cs) on tungsten surfaces

Abstract

A first-principles approach was used to investigate the effects of alkali metal iodide XI (X = Li, Na, K, Rb, and Cs) adsorption on the work functions of (100), (110), and (111) surfaces of W. For the most energetically stable structures, work functions and their corresponding electric dipole moment vectors were calculated. In agreement with available experimental measurements, it was verified that the formation of XI dipoles on the W surface causes the work function to decrease significantly. It was shown that the calculated XI dipoles are tilted with respect to the W surface for all systems. This contradicts earlier published suggestions that the surface electrostatic energy of the dipoles prevented them from being aligned along the surface and were instead normal to the surface. In our work it was shown that the orientations (tilt) and strengths of the dipole moments can be explained in terms of the internal strain caused by the alkali metal's different atomic sizes and available surface area. What matters for the decrease in the work function is the component of the dipolar moment perpendicular to the surface. For all systems, the work function reduction was shown to be directly proportional to the normal component of the electric field created by these XI dipoles

Simulation studies of secondary electron yield with electron transport from Cu (110) surfaces containing C2, N2, CO2, or NO2 adsorbates

“…In order to estimate the contribution of the NO 2 dipole in increasing the surface electron energy, the following model was used (Diaz et al, 2023): As a first approximation, the electric field due to the normal component of the dipole moment was assumed to be uniform. The energy increase of an electron corresponding to such a uniform electric field (E) is calculated by the following equation…”