Hypothesis: Surface effects arising from roughness and deformation can negatively affect the results of AFM contact experiments. Using the non-contact portion of an AFM deflection curve is therefore desirable for estimating the Hamaker constant, A, of a solid material. A previously validated non-contact quasi-dynamic method for estimating A is revisited, in which the cantilever tip is now always represented by an "effective sphere". In addition to simplifying this previous method, accurate estimates of A can still be obtained even though precise knowledge of the nanoscale geometric features of the cantilever tip are no longer required.
Experiments: The tip's "effective" radius of curvature, Reff, is determined from a "calibration" step, in which the tip's deflection at first contact with the surface is measured for a substrate with a known Hamaker constant. After Reff is known for a given tip, estimates of A for other surfaces of interest are then determined.
Findings: An experimental study was conducted to validate the new method and the obtained results are in good agreement with predictions from the Lifshitz approximation, when available. Since Reff accounts for all geometric uncertainties of the tip through a single fitted parameter, no visual fitting of the tip shape was required.
Keywords: Atomic force microscope; Cantilever geometry; Hamaker constant estimation; Sphere-plate; van der Waals force.
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