5 research outputs found
Redox Properties of Mixed Methyl/Vinylferrocenyl Monolayers on Si(111) Surfaces
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_(3)CN
Assembly, characterization, and electrochemical properties of immobilized metal bipyridyl complexes on silicon(111) surface
Silicon(111) surfaces have been functionalized with mixed monolayers consisting of submonolayer coverages of immobilized 4-vinyl-2,2′-bipyridyl (1, vbpy) moieties, with the remaining atop sites of the silicon surface passivated by methyl groups. As the immobilized bipyridyl ligands bind transition metal ions, metal complexes can be assembled on the silicon surface. X-ray photoelectron spectroscopy (XPS) demonstrates that bipyridyl complexes of [Cp*Rh], [Cp*Ir], and [Ru(acac)2] were formed on the surface (Cp* is pentamethylcyclopentadienyl, acac is acetylacetonate). For the surface prepared with Ir, X-ray absorption spectroscopy at the Ir LIII edge showed an edge energy as well as post-edge features that were essentially identical with those observed on a powder sample of [Cp*Ir(bpy)Cl]Cl (bpy is 2,2′-bipyridyl). Charge-carrier lifetime measurements confirmed that the silicon surfaces retain their highly favorable photoelectronic properties upon assembly of the metal complexes. Electrochemical data for surfaces prepared on highly doped, n-type Si(111) electrodes showed that the assembled molecular complexes were redox active. However the stability of the molecular complexes on the surfaces was limited to several cycles of voltammetry
Molecular proton-reduction catalysis at silicon semiconductor surfaces
Driving catalysis at semiconductor:liq. junctions with light enables the efficient conversion and storage of solar energy in chem.
fuels. Hydrogen evolution from water is one possible path to fuel, as there are known heterogeneous and homogeneous
catalysts for proton redn. Homogeneous catalysts show the greatest promise for clarifying both (1) key mechanistic aspects of
the hydrogen-evolution reaction at the surface and (2) energetic considerations of the semiconductor band structure. Along this
line, we are studying a family of rhodium complexes as model catalysts for hydrogen evolution at semiconductor:liq. junctions.
Both diffusional and silicon surface-attached systems have been developed, and will be compared. This approach has yielded
new information concerning the ambiguities of homogeneous vs. Heterogeneous catalysis, as well as the possible catalytic
mechanism(s) of the surface-attached species
Redox Properties of Mixed Methyl/Vinylferrocenyl Monolayers on Si(111) Surfaces
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