52 research outputs found
Optical properties of metal nanoparticles with arbitrary shapes
We have studied the optical properties of metallic nanoparticles with
arbitrary shape. We performed theoretical calculations of the absorption,
extinction and scattering efficiencies, which can be directly compared with
experiments, using the Discrete Dipole Approximation (DDA). In this work, the
main features in the optical spectra have been investigated depending of the
geometry and size of the nanoparticles. The origin of the optical spectra are
discussed in terms of the size, shape and material properties of each
nanoparticle, showing that a nanoparticle can be distinguish by its optical
signature.Comment: 19 pages + 8 figure
Circular dichroism simulated spectra of chiral gold nanoclusters: A dipole approximation
Circular dichroism (CD) spectra of chiral bare and thiol-passivated gold
nanoclusters have been calculated within the dipole approximation. The
calculated CD spectra show features that allow us to distinguish between
clusters with different indexes of chirality. The main factor responsible of
the differences in the CD lineshapes is the distribution of interatomic
distances that characterize the chiral cluster geometry. These results provide
theoretical support for the quantification of chirality and its measurement,
using the CD lineshapes of chiral metal nanoclusters.Comment: 3 pages + 4 figure
The role of geometry on dispersive forces
The role of geometry on dispersive forces is investigated by calculating the
energy between different spheroidal particles and planar surfaces, both with
arbitrary dielectric properties. The energy is obtained in the non-retarded
limit using a spectral representation formalism and calculating the interaction
between the surface plasmons of the two macroscopic bodies. The energy is a
power-law function of the separation of the bodies, where the exponent value
depends on the geometrical parameters of the system, like the separation
distance between bodies, and the aspect ratio among minor and major axes of the
spheroid.Comment: Presneted at QFEXT05, Barcelona 2005. Submitted to J. Phys.
Controlled Anisotropic Deformation of Ag Nanoparticles by Si Ion Irradiation
The shape and alignment of silver nanoparticles embedded in a glass matrix is
controlled using silicon ion irradiation. Symmetric silver nanoparticles are
transformed into anisotropic particles whose larger axis is along the ion beam.
Upon irradiation, the surface plasmon resonance of symmetric particles splits
into two resonances whose separation depends on the fluence of the ion
irradiation. Simulations of the optical absorbance show that the anisotropy is
caused by the deformation and alignment of the nanoparticles, and that both
properties are controlled with the irradiation fluence.Comment: Submitted to Phys. Rev. Lett. (October 14, 2005
Excitons in twisted AA' hexagonal boron nitride bilayers
The twisted hexagonal boron nitride (hBN) bilayer has demonstrated
exceptional properties, particularly the existence of electronic flat bands
without needing a magic angle, suggesting strong excitonic effects. Therefore,
a systematic approach is presented to study the excitonic properties of twisted
AA' hBN using the Bethe-Salpeter equation based on single-particle
tight-binding wave functions. These are provided by a one-particle Hamiltonian
that is parameterized to describe the main features of {\it ab initio}
calculations. The Bethe-Salpeter equation is then solved in the so-called
excitonic transition representation, which significantly reduces the problem
dimensionality by exploiting the system's symmetries. Consequently, the
excitonic energies and the excitonic wave functions are obtained from the
direct diagonalization of the effective two-particle Hamiltonian of the
Bethe-Salpeter equation. We have studied rotation angles as low as
. The model allows the study of commensurate and incommensurate
moir\'e patterns at much lower computational cost than the {\it ab initio}
version of the Bethe-Salpeter equation. Here, using the model and effective
screening of the Keldysh type, we could obtain the absorption spectra and
characterize the excitonic properties of twisted hBN bilayers for different
rotation angles, demonstrating how this property affects the excitonic energies
and localizations of their wavefunctions.Comment: 32 pages, 16 figure
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