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Fig. 1.12 Scheme of
recording the tunnel
current: the constant tip-
sample distance (a),
constant current value (b)
possibilities of the method looking at the images of the platinum surface with
observed vacancies (Fig.
1.13
) or annealed decanethiol films on a golden substrate.
The method of scanning tunneling microscopy allows obtaining unique information
about the processes occurring on a solid surface. In particular, the diffusion of
atoms and molecules on surfaces has been studied and new stages of catalytic
processes identified. At the same time the capabilities of tunneling microscopy are
much broader than just the study of the structural characteristics of surface phe-
nomena. This technique is being successfully utilized to navigate the surface of
individual atoms and molecules and to create on this basis complex atomic and
molecular structures.
Let an atom be adsorbed on the surface of a crystal, with the needle tip of the
tunneling microscope being close by. In the field of the tip, a force arises which
attracts the atom to the tip. The normal and the tangential components of this force
with respect to the surface will vary depending on the relative position of the atom
and the needle (Fig.
1.14
). Therefore, if the needle tip moves along the surface, the
atom starts to move along the surface in “jumps,” from one energetic minimum of
the crystal surface to another one. This effect was used in 1990 by Eigler and
Schweitzer of the IBM research center in San Jose (California). They dragged
adsorbed xenon atoms along the surface of a single nickel-35 crystal so that they
formed on the surface the three letters IBM (Fig.
1.14
). Since then a variety of
structures (the Brandenburg Gate, a cattle coral, triangles, etc.) have been crafted on
solid surfaces with the help of the tunneling microscope in different laboratories. In
1991 Eigler, Lutz, and Rudge also proposed a surface construction of a bistable
element in which switching was achieved by transferring a xenon atom on the
surface of a nickel monocrystal from one steady state to another. Unfortunately,
practically usable nanoelements of this type have not been developed so far.
