Chemistry Reference
In-Depth Information
tions generated by mechanical polishing can increase the reaction rate by the hole injec-
tion mechanism. According to Morrison
et al
.,
986
dislocations can behave like micro-
electrodes (~2nm) for hole injection and the holes are conducted along the dislocation
lines, where tunneling to the valence band becomes possible.
Figure 6.24 shows the
i-V
curves of
p-
and
n
-type silicon in 0.1 M KCl solution
containing 2mM methylviogen (1,1
'
-dimethy1-4,4
'
-bipyridinium)
cathodic
i-V
curve has two reduction maxima indicating a metalliclike behavior. The
first peak is ascribed to the reduction of
The
and the second to the reduction
of to The peak value depends on the potential scanning rate and rotation of
the electrode indicating that the reactions are diffusion limited. The two-step reduction
proceeds via the conduction band. Figure 6.24 also shows that the reduction on
to
-Si is
under an accumulation condition whereas on
p-
Si it is under a depletion condition.
Kooij
et
n
.
629,969
investigated the cathodic reaction of a number of one-electron oxi-
dizing agents such as and on
p-
Si in 1M
The agents with redox potentials considerably more positive than the flatband
potential of the electrode
629
al
tend to inject holes into the valence band as
shown in Table 6.4.
The rate of injection is high for those agents with redox potentials
much more positive than the valence band edge, such as and The rate of injec-
tion is weak for the redox couples with potentials close or negative of the valence band
edge. For which has a redox potential similar to hole injection does not
occur due to the adsorption of to form surface states which interact only with con-
duction band electrons. The hole injection is strong for
but very weak for
