© ICSPI Corp. 2007-2021
nGauge AFM User Manual 2.0
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7.3.3.
False Engage
A false engage can occur when there is electrostatic build-up on the surface of the sample or
AFM tip. The forces affect the automatic approach: the controller thinks that the tip has reached
the setpoint when it has not.
Proper approach. Steep snap-in to the
setpoint.
False engage. Gradual decrease to the
setpoint.
If you encounter a false engage, first click on
Disengage
, then click
Approach
to re-attempt the
approach.
If you encounter another false engage after re-approaching, try the following procedures:
Scan another site
: Click on
Disengage
, then click and hold on
Retract
, and if possible, move
the sample and to scan another site, then approach again. Often, a single area may be charged.
Increasing cantilever drive amplitude:
Click on
Disengage
and go to the
Sweep
page.
Increase the
Cantilever Drive Amplitude
so that the maximum of the amplitude peak is as high
as possible, depending on the type of chip. The recommended maximum cantilever drive
amplitude is 3 V for aluminum tips and 2 V for diamond tips.
Decreasing the setpoint:
Click on
Disengage
and decrease the
Setpoint
. By default, the
setpoint is set to half of the cantilever drive amplitude. For example, if the cantilever drive
amplitude is 3 V, the setpoint is set to 1.5 V (i.e., 50%). Decreasing the setpoint to 1.2 V (60%)
or 1 V (67%).
Increase relative humidity:
increasing the local relative humidity can help reduce surface
charging.
If you still encounter a false engage, proceed to 7.3.4 Discharging a sample.
7.3.4.
Discharging a sample or tip
The most effective way to discharge the sample is to place the sample on top of a piece of
metal (“substrate”) and to make an electrical connection from the thumb nut of the nGauge
system to the substrate. This electrical connection will ground the sample and prevent surface
charging.
It is recommended to use a thin wire (AWG 26-30) so that the wire does not cause the sample
to move around during scanning.
