Dull or Dirty Tip
features in the image all have the same shape
In order to image a fine feature, the imaging surface of the tip must have a smaller radius of curvature than the feature. If not, then the sample will reverse image the tip, meaning the worn shape of the tip or debris on the tip will be imaged rather than the sample's surface features. Reverse imaging effects are sometimes used to an advantage when determining the shape and radius of a tip's imaging surface. Tip shape standards and software are available to characterize tips.
Double or Multiple Tips
features appear in doubles or multiples
A tip with two or more imaging surfaces contacting the surface at the same time creates double or multiple images of features on a surface.
Contamination from Sample Surface
loss of image resolution, skipping or streaking of image
Imaging surface by AFM is heavily dependent on having clean probes. Usually we want the probe to interact minimally with the sample. Similarly, if the sample is not clean, loose debris creates poor resolution and streaking. Sometimes the debris can be swept out of the image after a few scans to restore image clarity. Often however, the debris will stick to the probe and the probe must be changed or cleaned.
sinusoidal pattern ranging from 1.5-2.5μm
When using coherent lasers in an AFM, any light that reflects from surfaces may add or subtract from the laser signal bouncing off of the surface. This interference is dependent of the phase of the reflecting light. Thus, the phase will vary depending on the distance between the laser and the reflecting surface. In practical use, AFM samples may be reflective. If the laser spot spills off of the cantilever, light will reflect off of the surface and interfere with the signal laser. As the scanner moves closer and further away from the sample during a scan, the phase will change and a sinusoidal pattern will appear in the image. This effect most often occurs in contact mode and can be reduced by changing the angle between the head and the sample, by adjusting the laser alignment so less light reflects off the sample surface, or by using a non-coherent light source. The effects of laser/surface interference patterns are readily apparent in force curves on highly reflective surfaces.
features are imaged with "tails"
The tip will not trace down the back side of features in non-contact mode if the feedback parameters are not adjusted properly. To adjust, lower setpoint voltage, increase gain, and slow scan rate.
Rings during High Frequency Operation
rings appear around raised features
When operating at high frequencies in non-contact mode rings may appear around raised features of the sample. Decreasing the drive frequency will eliminate this artifact.
2nd Order Bow
At large sizes the bow in the scanner becomes visible. It may be removed by performing a 2nd order Planefit in X and Y.
3rd Order Bow
At large scan sizes the bow in the scanner may take on an S-shaped appearance. It may be removed by performing a 3rd order Planefit in X and Y.