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Figure 3.6: Highly ordered and freshly cleaved pyrolytic graphite at atomic
resolution imaged with an AFM in UHV. Image adapted from [8].
characteristic for a collection of atoms like electrostatic, magnetic, tribological,
and viscoelastic properties.
A selection of the most widely used techniques is given beneath.
3.3.1 Single Atom and Molecule Information
- Position of single atoms and single molecules (e.g. pyrolytic graphite in Fig.
3.6)
- Chemical identification of individual surface atoms. The onset of chemical
bonding between the approaching tip and surface atoms gives rise to shortrange
forces that depend sensitively on the chemical identity of the atoms
involved. These can be measured by sensitive AFM. (Tin (Sn), Silicon (Si),
Lead (Pb) as detected by AFM can be seen in Fig. 3.7, [47])
- Molecular recognition studies using AFM open the possibility to detect
specific ligand–receptor interaction forces and to observe molecular recognition
of a single ligand–receptor pair. The approach is to bind either ligand
or receptor to the AFM tip when its counterpart should be found on the
investigated surface. In a force–distance cycle (as graphed by a force curve,
see below), the tip is approached towards the surface and, if the counterpart
is present, a receptor–ligand complex is formed because of the specific ligand
receptor recognition. Upon retraction an increased force (unbinding force)
must be exerted in order to break the ligand–receptor connection (e.g. antibody
binding and recognition in [48]). Such experiments allow for estimation
of affinity, rate constants, energies ([49]) and structural data of the binding
pocket ([48], [50], [51], [52], [53], [54]). There have also been attempts to
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