Optics11 CHIARO NANOINDENTER, Руководство пользователя, Страница: 25 / 65

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Also the stepsizes, which are set by default to 10 µm (large) and 1 µm (small), can be defined in that
‘Advanced’ tab (Figure 19). During find surface , the point of contact is determined by monitoring
the bending of the cantilever while performing this routine. The automatic procedure starts after
clicking ‘Find Surf’ in the main software window. The stepping of the motorized Z-stage can be
confirmed by the ‘beeping’ sound, which is the sound of the motor moving. In case the find -surface
routine is aborted and the message ‘surface not found’ is displayed, the ‘Find - surface’ function can
be restarted. When using very soft cantilevers (<0.4N/m) you might need to disable the ‘Sensitive
mode’ if the surface is “found” too early (Figur e 19). After finding the surface the tip should now be
in focus, together with the sample surface. It is recommended to raise the tip a few micrometers
away from the sample surface (in Z direction) to avoid a damage of the tip while moving the sample
in XY direction.
Please note that a wrong cantilever stiffness – sample stiffness combination can cause the
find-surface routine to fail. Always verify the state of the cantilever by looking at the
interferometer screen during finding the surface (see Chapter 7.1).
3.4 Modes of operation
The Piuma Nanoindenter is able to operate in three different modes:
•
Piezo displacement control: D-mode
•
Load or Force control:
P-mode
•
Indentation depth control:
I-mode
All three modes of operation are monitoring piezo movement, load (cantilever bending) and
indentation depth. The modes are differing in their controlling parameters and in their operational
loop with the sample, as shown in the following table (Table 2). It is very important to understand
that the piezo displacement is not the same as indentation depth, since a part of the probe
displacement is converted into cantilever bending and material deformation. This means that the
indentation depth is the difference between the piezo displacement and the cantilever bending
minus the approach. In all operational modes the electronic working principle of the piezo, which
regulates the probe displacement, is always in closed loop with the strain gauge, which
permanently measures the absolute extension of the piezo.
D-mode P-mode I-mode
Control Probe movement Load Indentation depth
Controlled
parameter Piezo
displacement
Cantilever
bending
Piezo displacement-
cantilever bending
Electronic circuit closed loop closed loop closed loop
Sample circuit open loop closed loop closed loop
Table 2: Comparison of the three modes of operation