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
fi
rst 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
fi
rmly 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 de
fl
ection 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
fi
rst, 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
signi
fi
cant effect.
Other scan parameters may also have a signi
fi
cant effect on the image quality. Varying the
Scan
rate
,
X
and
Y offsets
,
fi
ltering, 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
fl
at 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
fi
ltering on larger
scans. Highpass
fi
ltering 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
de
fl
ection 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 Manua
l, and experiment with
parameters on a known sample.
