Evaluation of atomic force microscopy for the characterization of surface properties

The atomic force microscope (AFM) is a powerful tool for measuring surface properties with nanometer resolution. However, AFM measurements are highly dependent upon the nature of how the probe tip interacts with the sample surface, and many critical issues related to the tip-sample interaction are not well understood.; One factor that can greatly increase the total adhesion force between an AFM tip and sample is capillary condensation. The capillary adhesion force is generally regarded to obscure any chemically specific information that can be obtained from the adhesion force measurement. In this work, the magnitude of capillary adhesion force was measured on a variety of substrates as a function of relative humidity. Through comparison of the wetting properties of each substrate with the measured adhesion force, it was determined that capillary adhesion force is surface specific. In addition, a model was developed to describe the results.; In other investigations, the influence of tip-sample interaction and tip size on surface roughness measurements by AFM was studied. Intermittent and contact mode imaging were compared on both quartz and mica substrates. Utilizing several mathematical methods to calculate surface roughness from the AFM images, it was determined that intermittent mode imaging is a more reliable method for measuring surface roughness by AFM. However, limitations to the mathematical methods utilized to calculate surface roughness were found.; The influence of tip size on AFM roughness measurements was investigated by evaluating the measured roughness of quartz as a function of tip size for a variety of scan sizes (square image sizes). Transmission electron micrographs of the AFM tips were obtained to accurately determine the size of the tip. Measured surface roughness was shown to have a complex dependence upon tip size and scan size.; Another factor which can result in misleading AFM measurements is surface and (or) tip contamination. The influence of tip and sample contamination on AFM topographic and adhesion force measurements was investigated and shown to have a large effect on the measurements.