Offline Operation
48
Scanning Probe Microscope Training Notebook
Rev. F
Flatten
Flatten may be used to remove image artifacts due to vertical (Z) scanner drift, image bow, skips,
and anything else that may have resulted in a vertical offset between scan lines.
Flattening modifies the image on a
line-by-line
basis. It consists of removing the vertical offset
between scan lines in the fast scan direction (X at 0° scan angle) by calculating a least-squares fit
polynomial for a scan line, and subtracting the polynomial fit from the original scan line.
•
This has the affect of making the average Z value of each scan line equal to 0V out of
the +/- 220V z-range.
Flattening can be performed by applying a 0th, 1st, 2nd, or 3rd order polynomial fit to each scan
line.
Figure 18.3a
Schematic Showing the Effects of Flattening Order on Two Scan Lines in X Acquired at Different
Locations in Y in the Image
Flattening is a powerful filter which you may or may not use often. However, it is important to
understand how flattening can effect subsequent measurements.
First order (1) flatten removed the Z
offset between scan lines, and the
tilt in each scan line.
Second order (2) flatten removes the
Z offset between scan lines, and the
tilt and bow (arch shaped) in each
scan line.
Third order (3) flatten removes the Z
offset between scan lines, and the tilt
and bow (S-shaped) in each scan line.
Zero order (0) flatten removes the
Z offset between each scan line by
subtracting the average Z value
from every point in the scan line.
