Scanning force microscopy experiments probing micromechanical properties on polymer surfaces using harmonically modulated friction techniques I. Principles of operation

Abstract

AbstractApplying a high‐frequency lateral vibration between the sample surface and the tip of a scanning force microscope (SFM), a harmonically modulated lateral (friction) force image can be obtained using lock‐in techniques. The principles of operation are explained, in particular the dramatic decrease of image artefacts generally caused by topography cross‐talk and laser beam interference. Flat interfaces between the two immiscible polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), are prepared on a sodium chloride single crystal from the melt. These samples are used to evaluate the appropriate model for the tip‐sample interaction geometry. The relationship between frictional and normal force does not follow Amonton's law. This shows that a single‐asperity interaction between the tip and sample surface can be considered. Using the new technique, local measurements of shear strength and Young's modulus can be performed.