Effect of Cs and CsI on the low-index surfaces of W

The adsorption of material adlayers has been used to tailor and change the properties of transition metal surfaces. Here, we investigate the effects of Cs and CsI adsorbates on the low-index surfaces of W. Using density functional theory (DFT), the formation energies, potential energies, and density of states were calculated for all surfaces. The adsorption of Cs resulted in a work function decrease of more than 1.90 eV for all surfaces with the following trend ΔΦ₁₁₁ < ΔΦ₁₀₀ < ΔΦ₁₁₀. The decrease is due to an interplay between the bond strength (formation energy) and the z-component of the surface dipole layer formed as a result of the Cs adsorbate. The adsorption of CsI also resulted in a decrease in the work function but did not reveal the same relationship with the formation energy. The disagreement is due to the competition between the surface dipole layer components demonstrating the importance of the dipole orientation. These findings were used to increase the electron field emission (tunneling current) of W emitter arrays.