AFM University Introduction to Atomic Force Microscopy by Paul West

« Cover
« Foreward
« Chapter 1
 « Chapter 2
 « Chapter 3
 « Chapter 4
 « Chapter 5
 « Chapter 6
 
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
 « Chapter 7
« Appendix A
« Appendix B
« Appendix C
« Appendix D
About
Downloads
Home


Chapter 6
next » index « back

FIGURE 6-11 This graph shows the relationship between an actual Z height and a measured Z height in an atomic force microscope. Often only one calibration point is measured as shown by the grey circle, and the Z ceramic is assumed to be linear, as shown by the blue line. However, as is often the case, the ceramic is nonlinear, as shown by the red line. In such cases incorrect Z heights are measured with the microscope unless the feature being measured is close to the calibration measurement.
6.2.4 Background Bow / Tilt
The piezoelectric scanners that move the probe in an atomic force microscope typically move the probe in a curved motion over the surface. The curved motion results in a "Bow" in the AFM image. Also, a large planar background or "Tilt" can be observed if the probe/sample angle is not perpendicular.
Often the images measured by the AFM include a background "Bow" and a background "Tilt" that are larger than the features of interest. In such cases the background must be subtracted from the image. This is often called "leveling" or "flattening" the image.
FIGURE 6-12 An AFM piezoelectric scanner is often supported at the top by a mechanical assembly. Thus the motion of the probe is nonlinear in the Z axis as it is scanned across a surface. The motion can be spherical or even parabolic depending on the type of piezoelectric scanner.

next » « back
  116