Artefacts result from the tip either becoming contaminated by material on the sample surface or from wear due to scanning. The resultant image can possess a number of tip artefacts and it is important for AFM users to recognize these artefacts.
The tip may be worn down due to excessive imaging or using excessive force. A worn tip reduces overall image quality, and may introduce odd shapes to the image.
Figure 11. An AFM image showing oddly-shaped artifatcs due to a worn tip.
Tip contamination is due to the imaging tip 'picking up' material from the sample surface. This is typically more of a problem on soft biological tissues. Tip contamination can introduce strange, sometimes repeating, shapes to an image.
Figure 12. An AFM image showing repeating blob-shaped artifacts due to tip contamination.
If the tip is damaged or picks up contamination, a tip with two or more sharp points may form. This will show on the image as a doubling of surface features.
Figure 13. A tip with a double point gives AFM images showing double images of surface features.
Debris on the surface is a good indicator of tip conditions since these are often spherical in shape - images of these, with a good tip, should therefore also be nearly spherical. Changing the scan direction should have no effect on the image artefact - to verify that these features are due to the tip, the user may physically rotate the sample relative to the tip and see if the artefacts have also rotated or not.