Selenium Chemisorption Makes Iron Surfaces Slippery

In the effort to reduce the energy consumption due to friction, finding new effective lubricants is of primary importance. Here we suggest selenium as a possible element for a highly effective lubricant on iron/iron interfaces by means of density functional theory. The adsorption properties of Se on the most stable iron surface are studied and the metal–adsorbate interaction is characterized. The adsorption reveals that selenium behaves similarly to sulfur and phosphorus, two key elements for high-pressure, anti-wear lubricant additives. The tribological properties of the Fe–Se/Se–Fe interface and the electronic modifications induced by the additive are then investigated and compared with Fe–P/P–Fe and Fe–S/S–Fe interfaces. The charge rearrangement at the interface and the density of states reveal the formation of strong covalent interactions inside the adsorbed layer of selenium atoms that weaken the metal–metal interaction. The calculated work of adhesion and ideal interfacial shear strength show that, with respect to P and S, Se possesses superior lubricating properties.