Phosphorus Adsorption on Fe(110): An ab Initio Comparative Study of Iron Passivation by Different Adsorbates

From corrosion protection to embrittlement and lubrication, the presence of phosphorus at iron surfaces is critical for a range of processes and applications. However, phosphorus adsorption on iron has never been studied experimentally or theoretically. Here P chemisorption on the most stable surface of iron is analyzed by means of density functional theory. The most stable adsorption geometry and coverage are identified, and the changes induced by P adsorption on the structural and electronic properties of the metal are discussed. A systematic comparison among P, S, N, and O uncovers a peculiar behavior of the P and S species: attractive adatom-adatom interactions at high coverage lead to the formation of two-dimensional overlayers that reduce the metal reactivity and work function. This effect is important in iron embrittlement and for the functionality of P- and S-containing additives included in lubricant oils.