Thesis-PDF - IAP/TU Wien

Figure 3.11: The cantilever deflection (bending). For a hard surface it
amounts to the same effect if either the cantilever is pushed against the
surface or a surface feature pushes against the cantilever. This fact can
be used in order to calibrate the reading from the photodiode measuring
cantilever bending.
Figure 3.12: Force extension profile of a single titin molecule. The titin
protein is folded in several subunits that unfold in sequential order when the
protein is stretched. Each unfolding event is recorded as a sharp drop of the
pulling force that acts on the cantilever. Image adapted from [8].
titin molecule is show in Fig. 3.12. The periodic sawtooth-like pattern reflects
domain unfolding in the peptide chain consistent with its modular construction
and can be explained as a stepwise increase of the molecule’s length upon each
unfolding event. ([70])
3.4 AFM Manipulation Techniques
Besides information collection the AFM can be used to manipulate matter on the
small scale. Although this can be a time consuming process, only having one
cantilever to do the work, the sample can be altered in a very precise way. The
techniques can be classified into three categories, adding matter to, rearranging or
removing matter from the substrate. Some of the methods, of course, may overlap
in those categories as more effects apply at the same time.
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