There has been significant interest in a variety of nanowire (NW) systems for various sensing
applications. We had developed highly sensitive dielectric core/metal sheath nanowires composites
which serve as surface-enhanced Raman scattering (SERS) substrates. Previously, our composites
were fabricated using e-beam deposition, which has the problem of incomplete coverage. Here we
report an electroless (EL) plating approach to cover the NWs with a silver sheath, producing the
core/metal NW structures for the SERS measurements. In comparison with the common silver
deposition via e-beam evaporation, electroless coating can result in the full metal coverage on NWs.
Therefore, this approach provides a way to fully cover nanostructures with Ag, including NWs arrays,
regardless of the orientations and shapes of the nanostructures. SERS measurements on EL produced
Ag/NWs composites show stronger signals than those produced by e-beam evaporation. Electric field
calculations suggest that the strong SERS signal is due to plasmonic coupling of neighboring closely
spaced islands.
Novel ternary nanostructures (ZnO-Ga2O3 nanobrushes, SnO2-Ga2O3 heterostructures and Sn-doped Ga2O3 nanowires)
are excellent materials for gas sensing applications due to their large surface areas and structural defects. Also, these
nanostructures consist of different materials with different degrees of crystallinity and defect densities thus broadening
their gas sensing capabilities. Gas sensing devices, developed in our laboratory based on room temperature capacitance
measurements, were first fabricated by standard photolithography and lift-off techniques to pattern platinum (Pt) pads
and interdigitated fingers acting as conducting paths. The nanostructures, which were characterized by electron
backscatter diffraction (EBSD), transmission electron microscopy (TEM), and photoluminescence (PL), were then
incorporated by the catalyst-assisted growth directly onto the devices. The most efficient devices were those with high
yield of nanostructures and with low-resistivity of the Pt pads. To achieve that, different catalysts (nickel, Ni; copper,
Cu, and gold, Au) were used for different nanostructures. For example, the best catalyst for the device fabrication of Sn-doped
Ga2O3 nanowires was Ni whereas for nanostructures with high Sn content Cu was the best catalyst. Challenges
and successes of device fabrication for capacitance-based gas sensing devices are discussed in this work together with
some sensing results for such analytes as acetone, acetic acid, isopropanol, dichoropentane, nitrotolouene and
nitromethane.
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