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| Paper IPM / P / 9562 |
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| Abstract: | |||||||
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Cu@Cu2O core-shell nanoparticles on a-C :H thin films are
prepared by co-deposition of RF-sputtering and RF-PECVD. Samples
with different copper concentrations are grown. The copper content
of films increases with reduction in initial pressure and rises
with increasing RF power. When the Cu/C ratio reaches 0.5, the
surface plasmon resonance (SPR) peak that is a signature of the
formation of Cu nanoparticles appears in visible spectra of these
films. X-ray photoelectron spectroscopy (XPS) characterization
indicates that the surface of the copper nanoparticles oxidizes
when they are exposed to air. The results are indicative that the
shell of the nanoparticle is mainly the Cu2O phase that is
stabilized with CuO covering a thin layer on the Cu2O shell.
Using Mie theory for the SPR peak in visible spectra, the size of
the copper cores and copper oxide shell, the dielectric constant
of shells and the plasma frequency are estimated. The Mie theory
estimation indicates that the SPR peak is damped by decreasing the
size of copper cores. The SPR peak appears in visible spectra for
a copper core with a diameter larger than 2 nm. This empirical
result confirms the reported calculation result. The shift in the
energy of the SPR peak follows the shift in the plasma frequency
with respect to the reported value for copper bulk. The dielectric
constant of the combined Cu2O shells and the CuO cover layer
is larger than the reported value for Cu2O nanoparticles and
increases with increasing CuO/Cu2O ratio.
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