The oxidation of hydrogen-terminated porous silicon surfaces
produced by electrochemical etching has been
studied using transmission FTIR spectroscopy. The surface is
passivated to oxidation by surface hydrogen
below about 523 K. Above this temperature as hydrogen depletion
occurs by H2 evolution, Si surface dangling
bond sites, capable of O2 dissociation, are involved in
initiating the first stage of oxidation. Two
reactions
are observed. The first, O insertion into Si−Si back-bonds,
leads to −O
y
SiH
x
surface species which exhibit
frequency shifts to the blue compared to parent
SiH
x
stretching modes. In addition,
Si−O−Si modes are
also observed to form. The second reaction involves oxygen atom
insertion into Si−H bonds to produce
isolated Si−OH surface species.
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