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A tip-change artefact occurs when the effective apex changes during scanning, for example through material pickup, loss of an attached particle or damage. In tapping-mode atomic force microscopy, a sudden change can introduce a false height offset between parts of the image, even on a continuous terrace.

The change alters the probe–surface interaction or the effective point at which the chosen amplitude setpoint is reached. The controller moves the vertical scanner to recover that setpoint, recording a spurious step or a change in line baseline. The sign is not fixed: different apex changes can move the apparent surface up or down.

The amplitude channel usually shows a transient deviation as the interaction changes; with stable feedback it returns toward its setpoint. It therefore need not retain the same persistent offset as the recorded height. A change in probe resonance or free amplitude can also change the operating condition. If the apex geometry has changed, widths and shapes can change too, or duplicated structures can appear as a double-tip artefact. A baseline correction cannot recover these lost geometric data.

Flattening removes fitted components of the image whether they are instrumental or real. A true specimen slope, broad dome or slow height variation can be erased if it resembles the chosen background. Strong features can bias a fit and create false depressions, streaks or halos; an overly flexible polynomial can fit away scientifically useful topography.

Line-by-line correction can destroy real differences between terraces, especially when no common flat region spans the lines. Height statistics, roughness and feature depths then depend on masking and fit order. Report those choices and compare profiles before and after processing.

Flattening does not restore structures inaccessible to the tip, undo a double-tip artefact, remove finite-tip broadening, reconstruct a saturated signal or recover data lost to unstable feedback. It also does not calibrate the scanner. These limitations are important when a superficially smoother image is mistaken for a more accurate measurement.

An attached particle changes the effective tip shape, potentially creating a second contact apex. The image can then show duplicated or broadened copies of surface features, shifted edge positions and altered apparent roughness: a double-tip artefact or more general AFM tip-convolution artefact. Detachment can produce a sudden line-to-line change in that image kernel, so a region may abruptly recover a sharper profile. A change that follows the probe state or scan history should not be interpreted as a real reconstruction of the semiconductor surface.