Limitations on accurate shape determination using amplitude modulation atomic force microscopy

The limitations of amplitude modulation atomic force microscopy to accurately measure the shape or form of features are investigated. The control feedback loop and the dynamics of the cantilever limit the response time of the atomic force microscope. Simply subtracting appropriately scaled amplitude (error) signal from the topography data significantly improves the accuracy of the data and can correct for the slow response time of the feedback loop. Two mechanisms were found to induce topographic errors independent of scan speed. The first is the change in tip/surface interaction at a step edge observed by comparison with results from a 'virtual' sample. The second is due to friction between the probe and sample but only for a specifically oriented step edge determined by the direction of oscillation of the cantilever.