Following our development of a model for the operation of extreme-pressure model lubricant additives, we are now exploring the behavior of model systems in ultrahigh vacuum. We are mimicking the reactively formed layer using thin, unreactive halide films starting with KCl. We have demosntrated that a single monolayer of this film is responsible for friction reduction and we have initiated a theoretical collaboration with Mike Weinert of the Physics Department to understand the mechanical properties of these films. We are now systematically exploring the effect of changing the nature of the substrate and the film on the tribological properties. As part of this work, we have shown that a film of FeCl2 has a similar coefficient of friction to the reactively formed film during lubrication. Finally, we are using atomic force microscopy to measure the frictional properties of thin halide films using well-defined, single-asperity contacts in consultation with Professor Roland Bennewitz of McGill University in Canada to provide a full, molecular-level understanding of solid-solid friction. We are collaboratig with Dr. Ali Erdemir and Professor Rod Carpick of the Univerity of Pennsylvania to understand the frictional behavior of "superlow" frictional materials, which have friction coefficients of ~10-3.