K and S coadsorption on Ni(100) surfaces

In this contribution we report a study of K and S coadsorption on Ni(100) surfaces by means of Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS) and WF (work-function) measurements in UHV. Adsorption of elemental S on clean Ni(100) increases the binding energy, and the maximum coverage of the subsequently deposited K. The presence of the S underlayer maintains the ionicity of K adatoms close to the ionic state up to the completion of the first layer, at Phi (K) = 0.67 ML. The latter coverage is, thus, greater than the estimated 0.38 ML of K on clean Ni(100). The K overlayer on S-covered Ni(100) weakens the S-Ni bond, and forms a compound with S. The presence of S on Ni(100) lowers the WF minimum, Phi (min), of K on Ni(100) to a value of similar to1 eV, which is attributed to K-S compound formation. Deposited S atoms on K-covered Ni(100) are submerged under me K layer up to 0.5 ML and subsequently they are adsorbed on top of the K layer.