Thesis-PDF - IAP/TU Wien

Figure 5.5: The feedback control of the cantilever during a scan is not
always fast enough to follow topographic changes of the sample - although
retraction (when the cantilever encounters a upwards slope in sample topography)
usually closely follows sample topography, lowering of the cantilever
to follow a downwards slope is sometimes too slow. In the above figure the
cantilever traces a sample hillock moving from left to right (the z-axis corresponds
to sample height) (1). In comparison with the retrace image (2),
scanning from right to left, it can be seen that in both cases the lowering of
the cantilever having passed the peak of the hillock happens too slowly and
therefore produces image artifacts. These artifacts can be removed through
combination of both traces, where each point is calculated as the minimum
height of each trace (3 - the curve limiting the hatched area). The artifact
slopes due to the slow feedback loop during the scan can be removed and
the obtained image more closely matches the true sample topography.
slide (coverslip) on top of specimen and glass support, sealing the edges to protect
against specimen drying and general manipulation.
For observation of the condition of the alga as well as for checking the quality
of specimen preparation the optical confocal microscope was additionally used
in phase contrast mode and dark field illumination mode. Higher magnification
objectives were used with oil.
5.3.2 Preparation for AFM imaging in air
The best results were obtained by imaging of dried dead cells. One of the problems
to overcome was the bursting of the cells due to evaporation of the surrounding
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