Measurement of the strength and range of adhesion using atomic force microscopy

Adhesion of nanoscale contacts is important in many applications, including microelectromechanical systems, fibrillar adhesives, and atomic force microscopy (AFM). Here, we quantify the properties of the adhesive traction-separation relation between ultrananocrystalline diamond (UNCD) AFM tips and polymethyl methacrylate (PMMA) surfaces using a novel AFM-based method that combines pull-off force measurements and characterization of the 3D geometry of the AFM tip. Three AFM tips with different nanoscale geometries were characterized and used to perform pull-off force measurements. Using the pull-off force data, the measured 3D tip geometries, and an assumed form of the traction-separation relation, specifically the Dugdale or 3-9 Lennard-Jones relations, the range, strength, and work of adhesion of the UNCD-PMMA contact were determined. The assumptions in the analyses were validated via finite element modeling. Both forms of the traction-separation laws result in a work of adhesion of approximately 50 mJ/m2 and the peak adhesive stress in the Lennard Jones relation is found to be about 50% higher than that obtained for the Dugdale law.