Contact Area Correction for Random Surface Roughness on Nanoadhesion
Seung H. Yang, Huan Zhang, Stephen M. Hsu
Atomic force microscopes (AFM) have been used to measure adhesion at nanoscale between two surfaces. Colloidal probes are often utilized for such measurements because they provide much lower contact pressures and controlled contact geometry, facilitating data analysis. We measured adhesion between glass spheres and silicon (100) surface using colloidal probes of different radii under controlled atmosphere (relative humidity of <3%, 25 1 ). Results showed that the adhesion forces do not correlate with the radii of the spheres as suggested by elastic contact mechanics theories. Surface roughness and random surface features were found to change the real area of contact. We evaluate various methods and models in an attempt to correct for the surface random roughness features on the measured adhesive forces. We use surface roughness parameters, Rumpf and Rabinovich models, load bearing area model, and a new multiscale contact model. Most models do not provide adequate correction for the roughness features. The contact areas estimated from a new multiscale contact model was able to correct for most of the surface roughness features. However, this model is limited to spherical asperity shapes and therefore cannot account for sharp surface ridges or surfaces with sharp irregular features.
adhesion, AFM, bearing area correction, colloidal probes, multiscale contact model, random surface features, real area of contact, roughness