Role of Surface Perfection in Chemical Force Microscopy

In this paper we investigate the effect that the quality of the gold substrate has upon the distribution of adhesion force measurements in chemical force microscopy. Gold samples have been prepared by two protocols which give either predominantly single-crystal Au(111) or polycrystalline gold films on mica. Gold-coated tips and surfaces were functionalized with self-assembled monolayers terminating in carboxylic groups, and more that 500 force-distance plots were taken. Analysis of these plots revealed a 50% narrower distribution of adhesion forces between monolayers prepared on single-crystal surfaces and monolayers prepared on polycrystalline gold, when measurements were repeated at a single point. However when measurements were taken over a 1-μm² area, the distribution of adhesion forces was similar for both samples. An explanation for this may lie in the size of the domains on the gold surface relative to the contact area of the tip.