Self-Assembly of Synthetic and Biological Polymeric Systems of ...

2.5.- Atomic force microscopy (AFM)
An atomic force microscope (AFM) is part of a large family of instruments termed as scanning
probe microscopes (SPM). The common factor in all SPM techniques is the use of a very sharp
tip probe, which is scanned across a surface of interest. The interactions between the probe
and the surface are able to produce a high resolution image of the sample (potentially up to
the sub-nanometre scale) depending on the technique and sharpness of the probe tip. For
AFM, the probe usually interacts directly with the surface probing the repulsive and attractive
forces which exist between the probe and the sample surface to produce a high resolution
three-dimensional topographic image of the latter. The great versatility of AFM makes possible
measurements in air or fluid environments rather than in high vacuum, which allows the
imaging of polymeric and biological samples in their native states. In addition, it is highly
adaptable, with tip probes being able to be chemically functionalised to allow quantitative
measurement of interactions between many different types of materials (38).
Figure 2.12. Typical AFM setup. A tip probe is mounted at the apex of a flexible cantilever,
made of Si or Si3N4. The cantilever itself or the sample surface is mounted on a piezo-crystal,
which allows the position of the probe to be shifted respect to the surface. The deflection of
the cantilever is monitored by changes in the path of a laser light beam deflected from the
upper side end of the cantilever recorded by a photodetector (38).
An AFM instrument consists of a sharp tip probe mounted near the end of a cantilever arm,
which is able to make a full scanning across the entire sample surface. By means of monitoring
the arm’s deflection originated by the topographic features present on the sample surface, a
three dimensional picture can be built up at high resolution. In Figure 2.12 the basic setup of a
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