AFM University Introduction to Atomic Force Microscopy by Paul West

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6.1 Probe Artifacts
6.1.1 Features on a Surface Appear Too Large
6.1.2 Features in an Image Appear Too Small
6.1.3 Strangely Shaped Objects
6.1.4 Repeating Strange Patterns in an Image
6.2 Scanner Artifacts
6.2.1 Probe / Sample Angle
6.2.2 X-Y Calibration / Linearity
6.2.3 Z Calibration / Linearity
6.2.4 Background Bow / Tilt
6.2.5 Z Edge Overshoot
6.2.6 Scanner Drift
6.2.7 X-Y Angle Measurements
6.2.8 Z Angle Measurements
6.3 Image Processing
6.3.1 Leveling
6.3.2 Low Pass Filter
6.3.3 Matrix Filter / Smoothing
6.3.4 Fourier Filtering
6.3.5 Image Looks Too Good
6.4 Vibrations
6.4.1 Floor Vibrations
6.4.2 Acoustic Vibrations
6.5 Other Sources
6.5.1 Surface Contamination
6.5.2 Electronics
6.5.3 Vacuum Leaks
6.5.4 PID Settings / Scan Rate
6.5.5 Laser Interference Patterns
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Chapter 6
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6.3.1 Leveling
As mentioned in Section 6.2.4, most images have some tilt and bow that is introduced to the images by the scanner or stage configuration. There are a number of background subtraction options that are possible. The two most common types are:
  • Line by line leveling - 0 to 4(th) order
  • Plane Leveling - 0 to 4(th) order
Also, software typically allows you to exclude areas from the leveling. When an area is excluded, it is not used for the calculation of the background in the image.
FIGURE 6-21 A-C: AFM images of a 1.6 x 1.6 micron area of nanospheres on a surface. A: The original image measured by the AFM before any image processing. Tilt is easily recognized in the image as the right side of the image appears darker than the left side of the image. B: The AFM image shown in "A" after a line-by-line leveling of the image with a first order backgroundcorrection. The dark band in the image is caused by the image processing and is not a real structure. C: Particles are excluded from the background subtraction process to derive this image.
6.3.2 Low Pass Filter
A low pass filter is often used to "smooth" data before it displays. Such filters can cause steps in images to appear distorted.

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