Chemistry Reference
In-Depth Information
dominant anodic reaction in fluoride-containing solutions in which the oxide dissolves
quickly. The reduction of some redox species is, however, found to compete favorably
with the oxidation of silicon, which can be used to stabilize silicon anodes against
photooxidation. For example,
and
which
can be efficiently photooxidized on
n
-Si electrode, are found to stabilize the silicon
681
electrode.
Ferricenium/ferrocene,
is capable of stabilizing
n
-Si
78
against photoanodic oxidation in EtOH solvent by efficiently capturing the holes.
and
are also found to be effective in competing for photogener-
955,960
960
ated holes on -Si and thus stabilizing the electrode. According to Loo
et al.,
non-HF aqueous solution anodic photocurrent results in the formation of a thin oxide
n
in
film. Without a reducing species, the oxide film will grow in thickness and passivate
the field buildup
in the oxide film results in a shift of the valence band relative to the redox potential
and the reduction of the redox species becomes more favorable than the oxidation of
silicon as described in Fig. 6.26. As a result, the silicon electrode is stabilized.
Participation of surface states may be important in the reactions of redox
couples.
272,553
It can result in the redox reaction to show an
i-V
curve with two one-
electron waves. Such
i-V
curves are characteristic of metallic behavior rather than one
two-electron wave as is expected at a semiconductor surface free of surface states.
Metalliclike behavior may also be due to the interaction of redox species with silicon
electrode, which may result in changes in the barrier height or cause chemical changes
to form an ohmic-like interface.
In summary, the reaction processes of redox couples are complex. Each redox
couple may have several different reaction paths, in addition to all of the possible reac-
tion schemes on the silicon electrodes without the redox couple. The kinetic behavior
of a redox couple has several general characteristics. (1) The condition of the electrode
surface is an important factor in the reaction kinetics; it differs for oxide-covered and
the surface. In the presence of a reducing species such as
