ABSTRACT
All the AFM force-distance curves were measured at a frequency of 1 Hz and the spring constant of the cantilevers was determined using the method of Cleveland et al. [13]. The force of adhesion between nanoscale rough surfaces was calculated from pull-off force measurements made with an AFM. The experiments were performed in ambient air at a relative humidity of 45% as measured using a Fisher Scientific hygrometer. The particle on the AFM tip was brought in contact with the substrate and the adhesion force was measured from the pulloff point on the force-distance curve. No additional loading force was applied during the point of contact. The results validated previous investigations at larger roughness, where a decrease of adhesion force as a function of roughness was reported [14, 15]. Measurement of adhesion force was also performed at lower roughness than previously reported. It was experimentally determined that a root mean square (RMS) roughness value of 1.6 nm was enough to significantly decrease the force of adhesion by nearly a factor of five compared to the theoretical adhesion force between two smooth surfaces as predicted by equation (1). The magnitude of reduction in the adhesion force was additionally found to have a strong dependence on the radius of the probe (sphere or tip) contacting the surface (Fig. 1). When the adhesion force was measured with an AFM tip, whose radius was of the same order or smaller than the peak-to-peak distance or radius of the asperities, the decrease in adhesion force of a surface with roughness of 1.6 nm RMS was only 1.5 times, thus
