Biomedical Engineering Reference
In-Depth Information
Chapter 7
Although AFM, via STM, had its origins in imaging of metals and semiconductors, it was
originally invented in order to be able to extend the possibilities of STM to other samples, in
particular biological samples. AFM's ability to image a wide variety of samples, coupled
with its simplicity of operation and the relatively low cost of the instruments, means that
AFM very quickly gained acceptance in an extremely wide range of fields. In this chapter
we arbitrarily divide the illustrative examples into life, physical, and nanosciences, and
industrial applications. However, AFM recognizes no such boundaries, and it is hard to
think of any field of study involving a solid surface that the technique has not been applied
to. The use of these categories can be useful, if only because AFM users have traditionally
assigned themselves to one of these areas. However, as illustrated below, the intense
interest in nanotechnology and nanosciences has further blurred the distinctions between
these areas. This is partly because by definition just about everything AFM studies is
defined on the nanoscale, since almost all AFM images have a resolution greater than
100 nm. The range of samples that have been studied by AFM is staggering. Although the
areas shown in Figure 7.1 probably cover over 90% of AFM use, AFM has also been used
in such diverse areas as art conservation [384, 385], astrobiology [386], geology [387], and
food science [388, 389], amongst others.
The variety of applications of AFM is so large that it's not possible to even mention
them all in one book. Instead we have chosen to highlight in this chapter a few applications
in each of the categories mentioned above. Mostly, these examples are chosen to illustrate
the capabilities of AFM, in particular the different modes and kinds of experiments that
can be carried out, rather than to be exhaustive lists of all the applications of AFM to any
one field. In each of the four main sections, the introductory paragraph gives an overview
of the main applications within the field, and we highlight important advantages of AFM
for the field, and more detailed reviews to guide the interested reader to comprehensive
summaries of applications within the field.
The very first applications of AFM were in surface science, and this discipline is still a
heavy user of AFM, as well as STM. The ability of AFM to image with atomic resolution
is a key advantage for the physical sciences, while the measurement of electrical, mag-
netic, or mechanical properties also extends the range of possible applications.
Fundamental applications in physical sciences include imaging of the fine structure of
metals and absorbed species on metals and semiconductors; although this is one area
where STM is still more widely applied than AFM, some studies show information from
AFM can under some circumstances exceed that available from STM. AFM imaging is
very suitable for structural studies of inorganic and organic insulators and has been widely
