Chemistry Reference
In-Depth Information
surface. The area not covered by the bubbles is etched by about 50-100 nm after
polarization for about 50 h. The dissolution at this negative potential implies that the
absorption of hydrogen results in an increased reactivity of the silicon.
Formation of an amorphous silicon hydride surface layer can also occur during
anodic photoetching of
n
-Si. For example, surface Si-H bonds corresponding to about
40 monolayers of hydrogen on an
n
-Si have been observed to form at a photocurrent
of in 0.5mM
Thus, the silicon surface is fully covered by an oxide film at anodic potentials
higher than
whereas it is fully covered by hydrogen at potentials more negative than
From the OCP to the surface coverage of hydrogen gradually decreases as
the coverage of hydroxyl increases. Also, whereas at potentials near the OCP and
below the hydrogen or oxide layer is on the order of a monolayer, the hydride layer at
cathodic potentials and the oxide layer at
the OC
P.
is thicker than one monolayer. Figure 6.7
