We have previously discovered a novel, facile approach to encapsulate ZnO nanorods within thiol complexes. This
approach results in a thiol uptake of 30-40% and a 400-500 nm thick thiol-Zn-thiol complex encapsulation layer
surrounding ZnO nanorods. By controlling experimental parameters, it is possible to control the thiol deposition,
enabling less uptake, which results in a surface monolayer instead of encapsulation. Through this approach, thiol
modification of other metal oxide materials, namely TiO2, Al2O3, and MgO, has been attempted. FTIR analysis indicates
that thiol adsorption occurs only on ZnO; chemisorption of thiols on other nanoparticles is not evident. Ultrahigh
vacuum single crystal adsorption studies demonstrate that ZnO(0001) is also more susceptible to thiol monolayer
formation, as evidenced by lack of methanethiol adsorption on TiO2(110) and MgO(0001). These results indicate that the
facile thiol modification approach opens a new avenue for surface modification of multi-component metal oxide
materials by enabling selective thiol modification of ZnO. This work has potential applicability for creating multiple
ligand-functionalized materials, which could be useful for the design of novel multiplexing sensors and photovoltaics.
The wide band gap and unique photoluminescence (PL) spectrum of nanocrystalline zinc oxide (nano-ZnO) make it
useful for a variety of photonics and sensor applications. Toward the goal of modifying the electronic structure and
optical properties of nano-ZnO, nanorods were functionalized with electron withdrawing organosilanes, 1H,1H,2H,2H-perfluorodecyltriethoxysilane
(PFDS) and pentafluorophenyltriethoxysilane (PFS), and a partially conjugated
heterobifunctional molecule, p-maleimidophenyl isothiocyanate (PMPI). Fourier transform infrared (FTIR) spectroscopy
and x-ray photoelectron spectroscopy (XPS) confirmed the presence of the modifiers on the nano-ZnO surface and
verified covalent attachment. PL spectroscopy was performed to evaluate the influence of the modifiers on the nano-ZnO
inherent optical behavior. An increase in the nano-ZnO near-band edge emission (UV) was evident for the organosilane
modifiers, despite their differing electronic structures, while the defect emission (visible) remained unchanged.
However, surface modification with the non-silane modifier PMPI resulted in unaltered UV and visible emission
intensity. The varying influence of the modifiers may be due to the absence of a silane group in the PMPI, allowing for
more efficient electron transport to the modifier. The influence of size/shape of the nanocrystalline ZnO was also
examined by reacting spherical nanoparticles with PFDS. Preliminary results indicate that PFDS modification of the
nanospheres resulted in similar PL behavior as the nanorods; although, the inherent PL of the spheres differs from the
nanorods. These studies will elucidate the role of modifier structure on surface-modified nano-ZnO optical behavior, so
that optical tailoring of the nano-ZnO inherent PL can be realized.
The wide band gap and unique photoluminescence (PL) spectrum of nanocrystalline zinc oxide (nano-ZnO) make it
attractive for a variety of photonics and sensor applications. Toward the goal of modifying the electronic structure and
optical properties of nano-ZnO, the adsorption of 3-mercaptopropyltriethoxysilane (MPTES) has been investigated.
Nano-ZnO rods having widths of 10-20 nm and lengths of 100-300 nm were functionalized by ultrasonicating them in a
hot ethanol/water solution and adding MPTES. FTIR and X-ray photoelectron spectroscopy (XPS) of the modified nano-
ZnO confirm silane functionalization. The presence of hydroxyl groups prior to functionalization suggests that
adsorption to ZnO occurs primarily via a condensation reaction and the formation of Zn-O-Si bonds. Comparison has
been made to 3-mercaptopropyltrimethoxysilane (MPTMS) adsorbed in ultrahigh vacuum onto sputter-cleaned single
crystal ZnO(0001) in which MPTMS vapor is leaked into the vacuum chamber. In this case, bonding occurs via the thiol
groups, as indicated by angle-resolved XPS studies. Similar experiments in which sputter-cleaned ZnO(0001) is dosed
with dodecanethiol (DDT) confirm adsorption via S-Zn bond formation. Photoluminescence measurements of MPTES-functionalized
nano-ZnO show an increase in intensity of the UV emission peak and a decrease in the visible peak
relative to the unfunctionalized particles. The reduction of the visible emission peak is believed to be due to passivation
of surface defects.
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