Thin walled, carbon tubular structures (see Figure and also cover) with varying inner diameters in the form of nozzles, straight tubes, tube‐on‐cones, and funnels have been synthesized by in‐situ control of gallium‐carbon wetting behavior using gas phase chemistry. In addition, carbon tubular structures with large internal diameters have been coalesced during growth to create Y‐junctions suitable for micro/nano‐fluidic applications.
In this paper, we report a synthesis strategy for a new class of hollow, curved carbon morphologies, 'carbon microtubes' (CMTs), with absolute control over their conical angles and internal diameters. Our synthesis methodology employs nitrogen or oxygen dosing to change the wetting behaviour of gallium metal with the growing carbon walls to tune the conical angles. Increasing N(2) concentrations in the gas phase during growth increases the conical angles of CMTs from +25° to about -20°. A methodology using the timing of oxygen or nitrogen dosing during CMT growth is shown to tune the internal diameters anywhere from a few nanometres to a few microns. The walls of the carbon microtubes are characterized using transmission electron microscopy (TEM) and Raman spectroscopy and are found to consist of aligned graphite nanocrystals (2-5 nm in size). Furthermore, dark field images of CMTs showed that the graphite nanocrystals are aligned with their c-axes perpendicular to the wall surface and that the crystals themselves are oriented with respect to the wall surface depending upon the conical angle of the CMT.
We report the synthesis and characterization of a new electrode material consisting of nanocrystalline graphite ͑NCG͒ deposited onto Pt via microwave plasma chemical vapor deposition. This material exhibits stable and quasi-reversible electrochemistry for a uniquely wide range of model compounds including Fe͑CN͒ 6 4− , Ru͑NH 3 ͒ 6 2+ , and selected catechols and quinones. Raman spectroscopy and electron nanodiffraction were used to confirm the presence of nanocrystals of graphite and support the hypothesis that NCG exhibits electrochemical activity similar to that of edge planes of crystalline graphite. The as-synthesized NCG material did not require any electrochemical pretreatment; however, occasionally, a one-time anodic oxidation did improve the kinetics for the catechol-and quinone-related electron transfer reactions. The electrochemical response of the electrodes was stable even after one year of storage time. The electrodes yielded clearly resolvable peaks in the voltammograms for the analytes at concentration levels similar to those in extracellular neural fluids and suggest that the electrode material may be useful for in vivo biological applications.
We report the bulk synthesis of hydrogenated, amorphous Si x N y and Si x O y nanowires using pools of molten gallium as the solvent medium and microwave plasma consisting of silane in nitrogen and silane in oxygen respectively. High densities of multiple nanowires nucleated and grew from molten gallium pools. The resulting nanowires were tens of nanometers in diameter and tens of microns long. Electron energy loss spectroscopy (EELS) and Fourier transform infra-red (FTIR) spectroscopy showed that the silicon nitride nanowires are hydrogenated amorphous silicon nitride (a-Si x N y H). The results of energy dispersive X-ray spectroscopy (EDS) yielded N : Si and O : Si ratios less than the stoichiometric composition of silicon nitride (Si 3 N 4) and silica (SiO 2). Studies on the chemical stability and refractive index (RI) measurements demonstrate a-Si x N y H nanowires are potential candidates for use as etching masks in nanoscale lithography, and as high index materials in optical coatings.
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