AFM University Introduction to Atomic Force Microscopy by Paul West

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« Foreward
« Chapter 1
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 « Chapter 3
 
3.1 Sample Preparation
3.2 Probe Alignment
3.3 Probe Approach
3.4 Optimizing Scan Conditions
3.5. Scan Image / Zoom
3.6 AFM Scanning Suggestions
 « Chapter 4
 « Chapter 5
 « Chapter 6
 « Chapter 7
« Appendix A
« Appendix B
« Appendix C
« Appendix D
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Chapter 3
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This chapter assumes that contact mode is being used for scanning. If a vibrating mode is being used, Section 3.2 will change to include measuring the resonant curve of the cantilever.

3.1 Sample Preparation
Sample preparation for an AFM is reasonably simple. There are a few basic rules that must be followed to adequately prepare a sample for AFM scanning. The rules are:
  • Sample must be adhered to the surface: If the sample has material adhered to the surface, the material must be rigidly mounted to the surface. If the material is not rigidly adhered two problems can occur. First, the probe can push the material to the edge of the scan range. When this occurs, the image appears as though there is nothing on the surface and only the substrate is observed. Second, the probe can pick up material from the surface because the material has a greater affinity for the probe than the surface. In this case the images often have streaks in them. The streaks are created by material moving on and off the probe, i.e.: the probe geometry is changed by the material from the surface.
  • Sample must be clean: AFM imaging requires that the probe move directly across the sample’s surface topography. If the surface is dirty with a thick contamination layer, the probe needs to penetrate through the contamination layer to reach the surface. The contamination layer then causes severe distortion in the image( see Section 6.5.1).
  • Sample dimensions must be realistic: The AFM can image a large variety of samples; however, there are a few constraints. Features on the sample's surface must be smaller than the dynamic range of the Z ceramic. Typically this is less than 10 microns. If the features on the surface are larger than 10 microns, then the Z piezo will not be able to move the probe over the features. Second, the probe must be able to directly access the features. As an example, if the sample has a 10 nm diameter hole, and the probe is 40 nm in diameter, the probe will not reach into the hole.
  • Sample must be rigidly mounted in the AFM stage: When the sample is fastened into the AFM stage, it must be mounted rigidly. If the sample is not mounted rigidly, it can vibrate. Vibrations substantially reduced the resolution of the microscope and often make it impossible to see small surface features.

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