Chemistry Reference
In-Depth Information
0.1M KBr as electrolyte.
373
The anodic current observed above 0.6V is due to the
solvent oxidation through hole capture from the valence band:
It has been found that for various organic solvents—acetone methanol, 2-
methoxyethanol, 2-ethoxyethanol, 1-propanol, 2-propanol, 2-methyl-1-propanol, pro-
pylene carbonate, ethylmethylketone,
-methylformamide, and tetrahydrofuran—
appreciable photocurrents are only observed in acetone and methanol.
675
Higher pho-
tocurrent is observed in acetone than in methanol. But the open-circuit voltage is
independent of the redox couples in methanol and is higher than in acetone, in which
the open-circuit potential depends on the redox couple. In the case of methanol solu-
tion a rise in barrier height occurs due to the chemisorption of methanol. In general,
N
the open-circuit photopotentials of silicon electrodes in solvents such as acetonitrile are
not very high which is close to the the-
oretical value, have been found in methanol. According to Lewis
crucial factor in achieving high open-circuit voltage is the initial photoelectrochemical
oxide formation which passivates the surface recombination sites. On the other hand,
according to Chazaviel
et
However,
276,569
,
276,569
the
et
al.
,
686
it is the formation of bonds that is respon-
sible for the improved stability and low density of surface states in organic solvents.
The electrode behavior of silicon in nonaqueous solvents strongly depends on
the presence of water. The presence of a very small amount of water will cause the
formation of silicon oxide at anodic potentials and cause reduction of water at large
cathodic potentials.
372,373
The presence of a thin oxide layer due either to native oxide
or to water presence affects the electrode behavior by acting as a physical barrier
and source of interface states. It has been found that with 10 ppm water in organic
electrolytes the silicon surface is oxidized slowly via formation of oxide islands which
grow to 0.6 nm thick and cover about 60% of the surface after 1 week of immersion.
934
al.
