Molecular beam epitaxial growth of III-V semiconductor ... - KOBRA

4.3 Atomic Force Microscopy
and knowing the stiness of the cantilever. The probe is placed on the end of a
cantilever (which one can think of as a spring). The amount of force between the
probe and sample is dependent on the spring constant stiness of the cantilever
and the distance between the probe and the sample surface. This force can be
described using Hooke's Law described in Eq. 4.1.
F = −kz (4.1)
Where F is the force, k is the stiness of the lever, and z is the distance
the lever is bent. However, the dominant interactions at short probe-sample
distances in the AFM are Van der Waals (VdW) interactions. The AFM consists
of a cantilever with a sharp tip (probe) at its end that is used to scan the specimen
surface. The cantilever is typically silicon or silicon nitride with a tip radius of
curvature on the order of nanometers. When the tip is brought into proximity
of a sample surface, forces between the tip and the sample lead to a deection of
the cantilever according to Hooke's law.
Figure 4.5: Scheme of an atomic force microscope and the force-distance curve characteristic
of the interaction between the tip and sample [71].
The motion of the probe across the surface is controlled using feedback loop
and piezoelectronic scanner as it is shown in Fig. 4.5. If the electronic feedback
is on, as the tip is raster-scanned across the surface, the piezo will adjust the
tip sample separation so that a constant deection is maintained so the force
is the same as its setpoint value. This operation is known as constant force
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