Thesis-PDF - IAP/TU Wien

Figure 3.5: The left image is a topographic image of a polyurethane tube
coated with a lubricious hydrogel. Colors indicate surface height (dark blue
being low, red being high). Height range is 100 nm. The right image is a
phase image of the same area, acquired simultaneously with height information.
It displays the phase lag of the oscillating cantilever relative to the
driving force as a function of lateral position. The coating has areas with
different physical characteristics that cannot be seen in its topology. Image
adapted from [42].
cannot be fully resolved. In comparison, for biological samples often larger tip diameters
are used, because of easily perforated membranes. Tips with radii ranging
from 5 to 50 nm are commonly available.
Ambient atomic force microscopes can be enhanced for better resolution in
a variety of ways. The most common ways are the addition of a fluid cell (no
water meniscus between cantilever tip and surface), operation in UHV (no water
meniscus and clean sample surfaces) and operation at low temperatures, when
thermal motion of atoms must be reduced for very high resolution imaging. An
example for a sub-nanometer resolution as can be achieved by AFM is given in
Fig. 3.6. ([8], [43], [44], [45], [46])
3.3 Analytical Microscopy Probing
While investigation of topology was the predominant use in the early stages of
SPMs, it soon became evident that there was a much richer set of information and
possibilities to be gained from these techniques.
These new methods can roughly be divided into methods that characterize
the sample on the single atomic or molecular level, e.g. unit cell structure, atomic
species or identification of protein binding sites, and methods that characterize
the sample as a system of atoms, e.g. bulk properties or emergent properties
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