Thermodynamics and Optical Response of Palladium-Gold Nanoparticles
2016
Alloyed nanoparticles of palladium (Pd) and gold (Au) are promising candidates
for hydrogen sensing in e.g., cars powered by fuel cells. Specifically, the plasmonic
response of Pd-Au nanoparticles changes upon absorption of hydrogen, enabling
quantitative measurement of the hydrogen partial pressure. The optical properties
of alloyed nanoparticles are not only dependent on the concentration of the
respective element, but also on the atomic ordering. This thesis presents atomistic
simulations as well as first-principles calculations on Pd-Au nanoparticles, where the
former aim at elucidating the thermodynamics, and the latter were conducted to
investigate the optical properties of representative particles. A novel algorithm for
determination of optical nanoparticle shapes, based on Monte Carlo simulations, is
also presented. The atomistic simulations show that Au tends to segregate to the
surface of the nanoparticle, especially at corner and edge sites, while the subsurface
layer exhibits a Pd excess. The first-principles calculations, specifically density
functional theory (DFT) and time-dependent density functional theory (TDDFT),
show that the electronic oscillations occur almost exclusively on the surface of the
particles, while the interior atoms play an important role in screening of the optical
response. The calculations do not, however, reveal any distinct plasmonic peak in
the optical absorption spectra.
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