Chemistry Reference
In-Depth Information
The energy level, and energy level, can be related to the redox energy
level, by a quantity called the reorientation energy which is
determined by the relaxation process involved in the regrouping and reorientation of
the solvation shell after electron transfer between the oxidized and reduced states. The
value of can be experimentally determined and is on the order of 0.5 to 1 eV.
44,876
The
individual energy states are distributed over a certain energy range and can be described
by the density of occupied states and empty states Assuming a Gaussian type
of distribution and a harmonic oscillation for the solvation shell,
and
can be
described by
where
are normalizing factors. Figure 1.4 schematically illustrates the
energy levels of the reduced and oxidized species and their distribution functions.
and
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1.2.4. Energy Levels at Semiconductor/Electrolyte Interface
For a semiconductor/electrolyte interface, the equilibrium condition requires the
Fermi levels of the semiconductor and solution to be equal. To achieve equilibrium,
electrons cross the interface, which changes the charge distribution and the potential in
the interface region until
The band structure at equilibrium for the interface region is illustrated in Fig. 1.5.
The band bending is the potential drop in the space charge layer. The potential drop
on the solution side is measured by the Helmholtz potential. and are the
conduction band edge and the valence band edge at the surface, respectively. is the
measured potential. Normally, the band edge positions at the surface are equal for
p-
and
n
-type materials because the same Helmholtz potential is expected for the two
