Redox Properties
of Mixed Methyl/Vinylferrocenyl Monolayers
on Si(111) Surfaces
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Abstract
We
report the redox properties of Si(111) surfaces functionalized
with a mixed monolayer of vinylferrocenyl and methyl moieties that
have been characterized using spectroscopic, electrical, and electrochemical
techniques. The silicon was functionalized using reaction conditions
analogous to those of hydrosilylation, but instead of a H-terminated
Si surface, a chlorine-terminated Si precursor surface was used to
produce the linked vinyl-modified functional group. The functionalized
surfaces were characterized by time-resolved photoconductivity decay,
X-ray photoelectron spectroscopy, electrochemical measurements, and
photoelectrochemical measurements. The functionalized Si surface was
well passivated, exhibited high surface coverage and few remaining
reactive Si atop sites, had a very low surface recombination velocity,
and displayed little initial surface oxidation. The surface was stable
toward atmospheric and electrochemical oxidation. The surface coverage
of vinylferrocene (or fluorostyrene) was controllably varied from
0 up to 30% of a monolayer. Interfacial charge transfer to the attached
ferrocene group was relatively rapid, and a photovoltage of 0.4 V
was generated upon illumination of functionalized n-type silicon surfaces
in CH<sub>3</sub>CN