Biomedical Engineering Reference
In-Depth Information
Fig. 7.1. Application areas where AFM is most commonly used.
applied [372, 390-392]. Such fundamental studies of pure surfaces which require atomic
or near-atomic resolution are often carried out at low temperatures, in vacuum or both.
These types of experiments are outside of the scope of most commercial AFM instruments.
Structural studies of molecules have mostly focussed on high-resolution imaging of
assemblies of molecules packed into crystals [390], because resolution is generally higher
when the molecules are arranged in such highly-ordered structures. However, one of the
strong points of AFM is that unlike, for example X-ray diffraction, single molecules can
also be studied, and the ability to crystallize the sample is not a prerequisite for AFM
imaging. Molecular interactions are commonly studied by AFM, both directly by chemical
force microscopy [142] and by studying the topography of the complexes they form [393],
and this sort of study is greatly aided by the ability to image in different environments,
enabling the study of interactions
in situ
.
The ability of AFM to directly study the sliding of materials over each other (i.e. lateral
force microscopy) means the technique is very useful in fundamental work on friction and
wear, which is of vital importance in materials science [189, 394, 395]. In fact, AFM is a
particularly useful technique in materials science, and other popular applications include the
topographic, tribological, roughness, and adhesion/fouling characterization of a wide variety
of technologically useful materials [395-397]. Mechanical characterization of materials is
also an area where AFM can contribute to their study, especially when studying materials
that are heterogeneous on the nanoscale [158, 398-400]. For biomaterials, the modification
of the materials by proteins, cells or other biological materials is ideally suited to analysis by
AFM due to its ability to image both soft and hard materials [398, 401].
7.1.1 Roughness measurements of high-performance materials
Surface roughness is an extremely important parameter for many material surfaces.
Surface roughness can affect adhesion to other materials, optical and electronic properties,
surface energy, bioadhesion and other properties [402-405]. Surface roughness is easy to
