Simulations of the effect of an oxide on contact area measurement using conductive atomic force microscopy

Rimei Chen¹, Sai Bharadwaj Vishnubhotla², Tevis D. B. Jacobs², Ashlie Martini²

¹Mechanical Engineering, University of California-Merced, Merced, CA

²Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA

ABSTRACT: Nanoscale contact area in conductive atomic force microscopy can be determined by analyzing current flow using electronic constriction theories. However, it is recognized that native oxides on the conductive tip will reduce current flow, thus degrading the accuracy of the measurement. Unfortunately, the error in contact area due to the presence of an oxide is typically unknown. Here, we address this using molecular dynamics simulations of an oxide-coated platinum tip and crystalline platinum substrate, where both the contact size and conductance can be inferred from the positions of atoms in the interface. We develop a method to calculate conductance based on the distance between atoms in platinum channels across the contact that incorporates both direct metallic conduction and tunneling conduction. Then, we compare the contact area calculated using classical constriction theories to that obtained using the known positions of atoms in the contact. The difference between them - which reflects the error of the contact area measurement - increases with increasing oxide thickness. Finally, we fit the data to an error function which can be used to estimate the accuracy of contact area measurements due to an oxide on the surface of a conductive platinum tip.