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An uncorrected amplitude image has a useful vertical range only across the transition between free oscillation and strongly suppressed oscillation. If the free motion is a few tens of nanometres peak-to-peak, its one-sided amplitude is half that excursion. The relevant vertical height range is therefore of the order of the oscillation excursion, only tens of nanometres, rather than micrometres. It is not a sharp universal limit equal to the quoted peak-to-peak value: the chosen mean gap, contact law and usable sensitivity determine the actual range. A sufficiently high feature can quench the motion or produce destructive contact; a sufficiently deep depression leaves the probe oscillating freely with essentially no height sensitivity. This argument limits height tracking, not the lateral width of a feature. Lateral resolution instead depends on AFM tip convolution, sampling and the probe-surface interaction.

The repeated, similarly oriented rounded triangular outlines in panel (a) are characteristic of AFM tip convolution: a narrow raised object can image the shape of a blunt or contaminated AFM probe, rather than reveal its own lateral shape. A finite tip radius broadens lateral dimensions. Replace or clean the AFM probe, check it on an independently characterized sharp-feature standard, and repeat at low load; agreement after a tip change is stronger evidence than a visually pleasing image. Image processing cannot uniquely recover unmeasured sidewalls or prove that every particle with a similar outline is an artefact.

Panel (b) contains horizontal streaks associated with steep features. The natural instrumental diagnosis is AFM feedback artefact: the height controller does not track a rapid change faithfully, or rings after it. Reduce the scan speed and adjust proportional/integral gains below the oscillation threshold. Compare trace and retrace and rotate the fast-scan direction: a streak following the scan rather than the specimen is instrumental. Loose contamination can also produce scan-line streaks, so clean or change the AFM probe if tuning does not remove them. Tip-shape broadening in (a), and scan-direction tracking/streaking in (b), are the principal diagnoses; the images alone do not uniquely establish every underlying cause.

The spatial height and shape of a surface. In atomic force microscopy, apparent lateral shape also depends on AFM tip convolution and the controller response.