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18 Structure in Solids
FIGURE LJG Elements of a scanning
tunneling microscope.
number of dangling bonds, and thus to lower the surface energy, some atoms migrate
and attach to three previously dangling bonds. These atoms are called adatoms. Surface
atoms that do not bond to adatoms are called rest atoms (R). The rearrangement is
referred to as a reconstruction of the surface.
The silicon (111) surface was first investigated by electron diffraction. But the results
were not conclusive. Only STM studies revealed unambiguously how the surface atoms
were rearranged. On the reconstructed (111) surface, one finds unit cells of 7 X 7 inte-
rior lattice units in size. See figure 1.17.
Top View 7 x 7
Side View 7 x 7
FIGURE 1.17 How a (Ill) surface of a pure silicon crystal is reconstructed.
