Numerical Investigation of Topography's Role During Conductive Atomic Force Microscope mapping of Organic Semiconductors

In recent years, conductive atomic force microscopy (C-AFM) has been an indispensable tool for probing the nanoscale electrical properties of organic semiconductor films. It is currently unclear, however, the extent to which local topography impacts the probe-sample contact area, and in turn the measured C-AFM current levels. In this study, we numerically model the adhesive contact between C-AFM probes and organic semiconductor films with experimentally determined film topographies. The adhesive interactions are represented by the Lennard-Jones potential and the surface deformations are coupled by using half-space Green’s functions discretized on the surface. We find that classical contact models do not accurately represent the probe-sample contact area. Topography is shown to impact the local contact area in cases when the local root mean squared roughness is greater than a few nanometers. For organic semiconductor films with a local root mean squared roughness under 5 nm, contact area variations from the planar case are less than 10%, indicating that for such samples, topography will have a minimal influence on C-AFM current.