NT-MDT Solver Next - Contact Error Mode; Brief Description of the Mode

Solver NEXT SPM. Instruction Manual
76
How to Improve Image Quality
ATTENTION! Too tight mechanical contact between the probe and the
sample may cause damage to the conductive coating of the probe.
If necessary, you can try the following recommendations:
● Adjust the SetPoint parameter (it controls pressure applied to the sample by the probe);
● Adjust the bias voltage applied between the probe and the sample (Bias Voltage
parameter). Note that excessive voltage may cause local oxidization of the surface;
● Replace the probe (with different elasticity or another type of conductive coating).
7.1.4. Contact Error Mode
7.1.4.1. Brief Description of the Mode
When scanning, the value of the cantilever deflection varies following the surface
topography of the sample. The feedback loop tries to preserve the given level of the
cantilever deflection (Set Point) by maintaining the DFL signal level, which is linked with
the deflection. However the feedback loop cannot compensate for variations of the DFL
signal instantaneously as it has some inertia (characterized by a time delay).
During scanning, the current value of the DFL signal (which is linked with the cantilever
deflection) is the error signal of the feedback loop and it contains additional information on
surface topography. This signal can be used for a more detailed reproduction of the
topography. The mode that allows imaging of surface topography by the Constant Force
Mode simultaneously with measurements of the error signal (the
DFL signal, in our case) is
called the Contact Error Mode.
The Contact Error Mode can be considered as an intermediate mode between the Constant
Force Mode and the Constant Height Mode. This is possible providing that the speed of
error signal data processing (the feedback gain factor, in our case) is optimized so that the
feedback loop is able to trace smooth topography variations while not been able to
recognize sharp features. Then, scanning of smooth surfaces, with smooth and extended
features, is performed with the piezo-scanner of almost constant length. As a result, the
final image will have higher contrast for sharp features and lower contrast for smooth and
large ones. This can be useful for identification of small features on the background of
large and relatively smooth variations of surface.