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Dielectric constants of AuAg alloys
par - 13 mars 2008
This web page is devoted to the dielectric functions of AuAg alloys. The procedure used to obtain them is described in details in the reference behind. Briefly, the imaginary part of the interband dielectric function is obtained from that of the pure gold and silver bulk functions considering a linear shift with the gold content either of the interband threshold wavelength or of the interband threshold energy. The full dielectric function is then obtained using the Kramers-Krönig relation and adding the contribution of the intraband transitions.
The zip file contains both the value of the dielectric function for AuAg alloys (.dat files) and the script (.m files) we wrote using matlab to compute them. The data file names are constructed using the following rules :
- "epsilon1" and "epsilon2" correspond to the real and imaginary part of the dielectric functions.
- "inter" is added when the interband contribution only is considered.
- "xAu40" gives the gold content in percent, ie 40% of gold in the particle.
- "lambda" and "omega" refers to the way we used to compute the interband threshold. When "lambda" is appended at the end of the file name, the interband threshold wavelength is varied linearly with the gold content.
Hence "epsilon1-inter-xAu60-lambda.dat" corresponds to the real part of the interband dielectric function computed for an alloy containing 60% of gold and using a linear dependence of the interband threshold wavelength.
The wavelengths at which the dielectric functions are computed are given in a separate file "lambda.dat".
Reference :
Surface heterogeneity in Au-Ag nanoparticles probed by Hyper-Rayleigh scattering, I. Russier-Antoine, G. Bachelier, V. Sablonnière, J. Duboisset, E. Benichou, C. Jonin, F. Bertorelle, P.-F. Brevet, Phys. Rev. B , 78, 035436 (2008)
"Aqueous solutions of alloyed gold-silver nanoparticles, the diameter of which ranged between 15 and 50 nm, were prepared with varying molar fractions. The UV-Visible photoabsorption spectra for all solutions were dominated by a single Surface Plasmon Resonance, the wavelength of which was found to change linearly with the molar fraction. A model, in agreement with these findings, was then derived to compute a dielectric constant for the different alloyed gold-silver nanoparticles based on a weighted function of the pure gold and pure silver dielectric constants. Hyper Rayleigh scattering measurements where performed for these alloyed metallic nanoparticles solution to determine their quadratic hyperpolarizability. Theses values, once corrected for their size and local field factors dependencies, are found to be larger than the corresponding values for the pure gold and pure silver nanoparticles. This is attributed to the atomic surface heterogeneity of these alloyed gold-silver particles, underlining the potential of the method to investigate the surface of nanometre scale metallic particles, especially in catalysis. This atomic surface heterogeneity is assigned to the differences between the Au and Ag atoms in their interband transitions since their intraband parameters are very similar."
Epsilon AuAg - 62.3 ko Dielectric constants of AuAg alloys |
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