1 research outputs found
Plasmon Spectroscopy and Chemical Structure of Small Bimetallic Cu<sub>(1ā<i>x</i>)</sub>Ag<sub><i>x</i></sub> Clusters
The
optical properties of small CuāAg bimetallic clusters
have been experimentally and theoretically investigated in relation
to their chemical structure analyzed by high resolution transmission
electron microscopy (HRTEM). Cu <sub>(1ā<i>x</i>)</sub>Ag<sub><i>x</i></sub> clusters of about 5 nm in diameter
are produced in a laser vaporization source with a well-defined stoichiometry
(<i>x</i> = 0, 25, 50, 75, and 100%) and dispersed in an
alumina matrix. Absorption spectra are dominated by a broad and strong
surface plasmon resonance whose shape and location are dependent on
both cluster composition and sample aging. Detailed modeling and systematic
calculations of the optical response of pure and oxidized mixed clusters
of various chemical structures have been carried out in the framework
of classical and semiquantal formalisms. Optical and HRTEM measurements
combined with theoretical predictions lead to the conclusion that
these bimetallic clusters are not alloyed at the atomic scale but
rather present a segregation of chemical phases. Most likely, they
adopt a Cu@Ag coreāshell configuration. Moreover, the nanoparticle
oxidation process is consistent with the formation of a copper oxide
layer by dragging out inner copper atoms to the cluster surface