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| The double-headed arrows in the diagram show
the scattering mechanism which gives rise to the formation of
a Tamm metastable surface state. In this case the electron is
confined to a region between the bulk band gaps and the rise
of the interstitial potential near the surface. |
Very low energy (0–40 eV) electron scattering from surfaces
contains information about electron surface states, atomic positions
at surfaces and surface potentials including the barrier potential.
At higher energies information about the surface states and potentials
is mostly lost and the data is sensitive mostly to structural information
of the lateral positions of surface atomic and molecular species.
Over the last ~30 years of analysing such reflectance data in the
low energy regime, much difficulty has occurred in accounting for
all observed features and disentangling their origins to deduce
surface properties.
In particular, a feature which occurs on certain metal surfaces
of face centred cubic metal structures has been difficult to explain.
In a preliminary analysis last year it was speculated that this
extra peak could be due to scattering from the gradual rise of the
average interstitial potential on approach to the surface from the
bulk inner potential value.
To test this possibility, a calculation of the elastic electron
reflectivities was performed which included all multiple scattering
at a step potential inserted between the top atomic layer and the
next atomic layer in the crystal. This had not been included in
any calculation before.
This mechanism did produce the required experimental feature which
is due to a Tamm-type metastable surface state.
The result shows that this type of scattering mechanism is very
important in the low energy regime and should be included in the
theoretical model. With this inclusion ambiguity in interpreting
experimental data should be eliminated.
Properties of these systems are particularly important because
alkali metals adsorbed on these surfaces have the potential to be
used as quantum electronic devices which would operate at room temperature.
Marlene Read
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