Paper SS2-TuA12
Examination of Force Interactions on Surfaces with Atomic Resolution Using Noncontact Atomic Force Microscopy

Tuesday, October 21, 2008, 5:20 pm, Room 209

Interaction forces on the atomic scale govern the underlying physics of many fields of nanotechnology research, such as, catalysis, thin film growth, device fabrication, and tribology. Therefore, we present a method of atomic force microscopy which allows for the generation of 3D force maps of sample surfaces with atomic scale resolution. A homebuilt tuning fork based noncontact atomic force microscope (NC-AFM) facilitates the measurement of tip position and frequency shift that can be translated into force. Until recently, acquisition of surface forces on the atomic scale has been restricted to low resolution maps of single point force curves or 2D atomic resolution (xz) maps. The main difficulty in producing 3D force maps has been minimizing the drift of the instrument over the long acquisition times associated with 3D data collection. To address this issue, our low temperature ultrahigh vacuum NC-AFM was built with a high degree of thermal and mechanical stability. This stability has been demonstrated by our first 3D measurements on highly oriented pyrolytic graphite (HOPG). We chose HOPG as a test material in order to investigate the atomic scale origins of its qualities as a solid lubricant. Data was collected spanning several unit cells laterally and vertically from the attractive region to where no force interactions could be measured. A fine data mesh shows pN forces with less than 7 pm lateral and 1-2 pm vertical resolution. From this 3D data set, cuts along any plane can be plotted in 2D. Cuts in a plane parallel to the sample surface show atomic resolution. Cuts along the surface normal visualize how the atomic attractive force fields extend into vacuum. Now that this technique has been demonstrated it may serve for the further study of chemical force interactions. It is our intention to apply this technique to simple metal oxide surfaces to determine the chemical force interactions between the scanning probe tip and specific surface sites.