Instruction manual

Calibration, Maintenance, Troubleshooting and Warranty
Contact AFM Troubleshooting
Rev. B MultiMode SPM Instruction Manual 317
vertical drift is indicative of optical path drift, while a horizontal drift is due to a mechanical change
in tip-to-sample separation.
Use the following as first steps in correcting drift:
•Verify that the sample, tip and stage are all stabilized. There should be no free
movement between any of these components
• Recheck that the cantilever is firmly seated in its place and that there are no dirt particles
wedged beneath it. Check that everything is tight and secure. Once this is checked, there
may still be some drift. Using the Tip Up and Tip Down command can bring the sample
back into range. (This may have to be done due to any number of factors).
• Check for thermal stability. The SPM should not be located directly in the path of
heating or air conditioning ducts; also, avoid locating the SPM near large windows
which trap solar heat. Thermally caused drift due to thermal expansion of SPM
components is the most common cause of mechanical drift. The MultiMode tends to
heat up and drift when used with the acoustic isolation hood because it traps heat
produced by electronics in the base and head.
15.11.10 Poor image quality
If the tip is engaged with the vertical deflection reading a stable, near-setpoint value and the Z
center position is not overly sensitive to small changes in Setpoint, then laser alignment is probably
good and the tip is scanning the sample. If image quality is poor with distorted shapes and low
contrast, try adjusting the gains first, then optimize the scan direction to take advantage of the best
tip shape to improve image quality. Vary the Scan angle parameter in the Scan Controls panel and
see if this will help clean up the image. There is some variation in the shape of tip from substrate-to-
substrate and the tip shape can affect the engagement process. (For example, a blunt tip may tend to
engage falsely.) Therefore, changing the angle at which the tip scans some surfaces may have a
significant effect.
Other scan parameters may also have a significant effect on the image quality. Varying the Scan
rate, X and Y offsets, filtering, feedback gains and ranges all may improve the image (or make it
worse!). Once engaged, adjust parameters in the Scan controls panel to improve the image quality.
In general, the Scan rate should be lower for large scans and for samples having tall features. The
Scan rate can be increased on flat samples.
The offsets and zoom commands should be used to locate good clean regions on the sample.
Filtering can improve atomic-scale images, but it is usually better to go without filtering on larger
scans. Highpass filtering will distort the height information in all but atomic scans. For height data,
the Integral and Proportional gains should be high but not high enough to cause oscillations. For
deflection data, the feedback gains should all be low (close to zero). LookAhead gain should only
be used for samples with regular features oriented along the slow axis. Please review the
descriptions of all the parameters in the Command Reference Manual, and experiment with
parameters on a known sample.