Recent improvements in growth methodologies have decreased the grain sizes and thicknesses of polycrystalline diamond films to the nanometer range, while also increasing the film uniformity and growth rate and preserving the outstanding mechanical properties of diamond. This is rendering such films more technologically and commercially viable. Ultrananocrystalline diamond (UNCD) are the thinnest (<200 nm) and smoothest (Rq < 10 nm) diamond films available.[1] These films demonstrated self-mated friction coefficients as low as near frictionless carbon (μ < 0.007) in environments with sufficient humidity, and the corresponding wear rates could not be measured using scanning white-light interferometry. However, their response to environmental conditions (e.g. relative humidity, ambient species, velocity, and temperature) had not been systematically explored in the past. This study focused on identifying conditions that contribute to favorable tribological performance. We find low friction performance at humidity levels below 1.5% in both nitrogen and argon environments.

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