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To describe adhesion between bodies of known arbitrary shape and known elastic properties, contact mechanics models require knowledge or assumptions of a minimum of two parameters, the strength of the adhesive interaction (characterized by the intrinsic work of adhesion W) and the length scale of the interaction (described by the range of adhesion z). One parameter can easily be measured if the other is estimated or assumed, but experimental techniques for determining both simultaneously are lacking. Here, we demonstrate a novel technique-called the Snap-in/pull-off Numerical Adhesion Parameter method-for experimentally determining both parameters simultaneously using adhesion measurements performed with an atomic force microscope probe whose geometry has been characterized. The method applies to materials that approach the rigid limit (high elastic moduli). The technique is explained and validated analytically for simple shapes (flat punch, paraboloid, and right cone), and trends in results are compared against prior literature. This approach allows calculation of the adhesion parameters to enable prediction of adhesion behavior, including for advanced technology applications. [ABSTRACT FROM AUTHOR]

The effect of atomic-scale roughness on adhesion between carbon-based materials is examined by both simulations and experimental techniques. Nanoscale asperities composed of either diamond-like carbon or ultrananocrystalline diamond are brought into contact and then separated from diamond surfaces using both molecular dynamics simulations and in situ transmission electron microscope (TEM)-based nanoindentation. Both techniques allow for characterization of the roughness of the sharp nanoasperities immediately before and after contact down to the subnanometer scale. The root mean square roughness for the simulated tips spanned 0.03 nm (atomic corrugation) to 0.12 nm; for the experimental tips, the range was 0.18-1.58 nm. Over the tested range of roughness, the measured work of adhesion was found to decrease by more than an order of magnitude as the roughness increased. The dependence of adhesion upon roughness was accurately described using a simple analytical model. This combination of simulation and experimental methodologies allows for an exploration of an unprecedented range of tip sizes and length scales for roughness, while also verifying consistency of the results between the techniques. Collectively, these results demonstrate the high sensitivity of adhesion to interfacial roughness down to the atomic limit. Furthermore, they indicate that care must be taken when attempting to extract work of adhesion values from experimental measurements of adhesion forces. [ABSTRACT FROM AUTHOR]