Recognizing Probe Artifacts

Two common tip artifacts are sometimes observed in life science AFM imaging.

Double Tip

The the so-called "double tip" occurs when the probe tip has more than one point in contact with the sample. This most often occurs when the tip breaks and leaves a jagged point. The image shown in Figure 1 is a typical example, where you can see that each DNA strand is doubled, like a shadow. The effect is usually fairly obvious, but one way to diagnose it for certain is to change the scan angle, which changes the directionality of the "shadow." The only solution is normally to replace the probe. Sometimes double tips are caused by contamination rather than breakage, in which case sometimes the contamination disappears on its own or the probe can be cleaned (see Removing Organic Contamination).

Figure 1: Image with double tip artifact

Tip Sidewall Image

A second tip artifact occurs on very tall samples or samples where the slope of the features is greater than the slope of the tip. This causes the tip sidewall to interact with the sample instead of the tip apex. The typical appearance is that of an almost linear ramp-like artifact around the feature, as shown in Figure 2.

Figure 2: Image with tip sidewall artifact

Cleaning and Modifying Probes

Information on cleaning and functionalizing probes can be found in Bruker Application Note #44: "Choosing AFM Probes for Biological Applications." Note that some of the newer probes are not discussed in this publication. It is available from the Library section of the Bruker website.

Information on attaching microspheres to AFM probes can be found in Support Note #226: "Attaching Particles to AFM Cantilevers." Support Notes are available on request from Bruker's Customer Care Center.

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