Metal clusters in plasma polymer matrices. Part III. Optical properties and redox behaviour of Cu clusters
2000
Using
an inert gas evaporation technique in combination with a simultaneous plasma polymerisation, copper
clusters with mean diameters between 2.9 to 5.4 nm have been prepared within plasma polymer matrices
from hexamethyldisiloxane (HMDSO) monomer. UV-visible spectroscopy of Cu clusters embedded in a plasma polymer
film revealed a red shift and a damping of the surface plasmon frequency and resonance, respectively, with
increasing thickness and changing nature of copper oxide layers surrounding the clusters. Experimental transmission
UV-visible spectra were compared with simulations using the Maxwell–Garnett theory, which is extended to
coated spheres. Owing to larger differences in the dielectric constant CuO layers lead to a stronger
red shift than Cu2O coatings. The formation and the reduction of the two copper oxide species during
successive treatments of Cu clusters with oxygen, hydrogen and carbon monoxide was observed by in situ
diffuse reflectance measurements at a wavelength
of λ=600 nm and
a temperature of 250°C.
The redox reactions with O2, CO, H2 are reversible.
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