Nanowire fabrication methods can be classified either as 'top down', involving photo- or electron-beam lithography, or 'bottom up', involving the synthesis of nanowires from molecular precursors. Lithographically patterned nanowire electrodeposition (LPNE) combines attributes of photolithography with the versatility of bottom-up electrochemical synthesis. Photolithography defines the position of a sacrificial nickel nanoband electrode, which is recessed into a horizontal trench. This trench acts as a 'nanoform' to define the thickness of an incipient nanowire during its electrodeposition. The electrodeposition duration determines the width of the nanowire. Removal of the photoresist and nickel exposes a polycrystalline nanowire--composed of gold, platinum or palladium--characterized by thickness and width that can be independently controlled down to 18 and 40 nm, respectively. Metal nanowires prepared by LPNE may have applications in chemical sensing and optical signal processing, and as interconnects in nanoelectronic devices.
A number of heterogeneous reactions of atmospheric importance occur in thin water films on surfaces in the earth's boundary layer. It is therefore important to understand the interaction of water with various materials, both those used to study heterogeneous chemistry in laboratory systems, as well as those found in the atmosphere. We report here studies at 22 C to characterize the interaction of water with such materials as a function of relative humidity from 0-100%. The surfaces studied include borosilicate glass, both untreated and after cleaning by three different methods (water, hydrogen peroxide and an argon plasma discharge), quartz, FEP Teflon film, a self assembled monolayer of n-octyltrichlorosilane (C8 SAM) on glass, halocarbon wax coatings prepared by two different methods, and several different types of Teflon coatings on solid substrates. Four types of measurements covering the range from the macroscopic level to the molecular scale were made: (1) contact angle measurements of water droplets on these surfaces to obtain macroscopic scale data on the water-surface interaction, (2) atomic force microscopy measurements to provide micron to sub-micron level data on the surface topography, (3) transmission FTIR of the surfaces in the presence of increasing water vapor concentrations to probe the interaction with the surface at a molecular level, and (4) X-ray photoelectron spectroscopy measurements of the elemental surface composition of the glass and quartz samples. Both borosilicate glass and the halocarbon wax coatings adsorbed significantly more water than the FEP Teflon film, which can be explained by a combination of the chemical nature of the surfaces and their physical topography. The C8 SAM, which is both hydrophobic and has a low surface roughness, takes up little water. The implications for the formation of thin water films on various surfaces in contact with the atmosphere, including building materials, soil, and vegetation, are discussed.
We report on the electrochemical growth of micro/nanowire devices using e-beam-patterned electrolyte channels, potentially enabling the controlled fabrication of individually addressable arrays. The concept of growing single wires and small arrays using this technique is demonstrated by single and double wires of Pd and polypyrrole with 500-nm and 1-μm widths up to 7-μm lengths and 200-nm thicknesses. The use of Pd wires as hydrogen sensors and polypyrrole wires as pH sensors is demonstrated.
Electrochemical cells based on a V2O5 composite cathode, aluminum anode, and AlCl3 + 1-ethyl-3-methylimidazolium chloride ionic liquid electrolyte were prepared and characterized to ascertain the role of V2O5. The V2O5 was found to be electrochemically inactive in a potential window of 5 mV to 1.5 V vs. Al/Al3+. The electrochemical behavior of the cells was found to be independent of the V2O5 and depend entirely on the stainless steel used as a current collector, thus showing stainless steel and V2O5 to be of limited use in this electrolyte.
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