4,592 research outputs found
Synthesis of hollow gold nanoparticles and rings using silver templates
Gold nanoshells have gained attention recently due to their versatile optical properties. In particular, their spectrally selective extinction has been exploited for experimental medical applications, functional coatings and contrast enhancement for analytical techniques. Here we discuss nanoshells and the formation of gold nanorings by the galvanic replacement of Ag nanosphere template particles. Hollow Au/Ag nanoshells can be converted to nanorings upon addition of excess HAuCl4. Nanorings present a distinct particle geometry, with optical properties exhibiting characteristics of both nanorods and nanoshells. © 2008 IEEE
Coherent acoustic vibration of metal nanoshells
Using time-resolved pump-probe spectroscopy we have performed the first
investigation of the vibrational modes of gold nanoshells. The fundamental
isotropic mode launched by a femtosecond pump pulse manifests itself in a
pronounced time-domain modulation of the differential transmission probed at
the frequency of nanoshell surface plasmon resonance. The modulation amplitude
is significantly stronger and the period is longer than in a gold nanoparticle
of the same overall size, in agreement with theoretical calculations. This
distinct acoustical signature of nanoshells provides a new and efficient method
for identifying these versatile nanostructures and for studying their
mechanical and structural properties.Comment: 5 pages, 3 figure
Electronic structure and optical properties of metallic nanoshells
The electronic structure and optical properties of metallic nanoshells are
investigated using a jellium model and the Time Dependent Local Density
Approximation (TDLDA). An efficient numerical implementation enables
applications to nanoshells of realistic size with up to a million electrons. We
demonstrate how a frequency dependent background polarizability of the jellium
shell can be included in the TDLDA formalism. The energies of the plasmon
resonances are calculated for nanoshells of different sizes and with different
dielectric cores, dielectric embedding media, and dielectric shell backgrounds.
The plasmon energies are found to be in good agreement with the results from
classical Mie scattering theory using a Drude dielectric function. A comparison
with experimental data shows excellent agreement between theory and the
measured frequency dependent absorption spectra
Gain assisted harmonic generation in near-zero permittivity metamaterials made of plasmonic nanoshells
We investigate enhanced harmonic generation processes in gain-assisted,
near-zero permittivity metamaterials composed of spherical plasmonic
nanoshells. We report the presence of narrow-band features in transmission,
reflection and absorption induced by the presence of an active material inside
the core of the nanoshells. The damping-compensation mechanism used to achieve
the near-zero effective permittivity condition also induces a significant
increase in field localization and strength and, consequently, enhancement of
linear absorption. When only metal nonlinearities are considered, second and
third harmonic generation efficiencies obtained by probing the structure in the
vicinity of the near-zero permittivity condition approach values as high as for
irradiance value as low as . These results clearly demonstrate that a
relatively straightforward path now exists to the development of exotic and
extreme nonlinear optical phenomena in the KW/cm2 rang
Modification Method for Preparation Gold Nanoshells
Nanoshells are a novel class of optically tunable nanoparticlesthat consist of a dielectric core surrounded by a thin gold shell. Nanoshells are fabricated the silica cores were made by reducing tetraethylorthosilicate ,the gold colloid adsorbs onto the aminated surface and the gold shell was then grown by reacting sodium tetra chloroaurate (gold salt) with the gold –seeded aminated particles in the presence of formaldehyde . The absorbance characteristics of nanoshell were monitored using UV-Vis spectrophotometer ( at 528 nm ) and the average size of the silica core nanoparticles were then the determined by scanning prope microscopy ( 349 nm ).But size of gold nanoparticles (25 nm), Fourier transform infra-red spectroscopy (FTIR) SiO2--Au particles peak 1098, 80 cm?1 can be assigned to Si–O–Si bond and peak 947 cm?1 can be attributed to Si–OH bond and for functionalized silica particles peaks at 3215 cm?1 is assigned to NH bond. The present method, the combination of citrate and borohydride method, gives much better results and it works at room temperature. The presence of gold coating was confirmed by FTIR spectroscopy. Keywards: Gold nanoshells ,Silicon dioxide nanoparticles , Nanoparticles
Spectroscopic properties of a two-level atom interacting with a complex spherical nanoshell
Frequency shifts, radiative decay rates, the Ohmic loss contribution to the
nonradiative decay rates, fluorescence yields, and photobleaching of a
two-level atom radiating anywhere inside or outside a complex spherical
nanoshell, i.e. a stratified sphere consisting of alternating silica and gold
concentric spherical shells, are studied. The changes in the spectroscopic
properties of an atom interacting with complex nanoshells are significantly
enhanced, often more than two orders of magnitude, compared to the same atom
interacting with a homogeneous dielectric sphere. The detected fluorescence
intensity can be enhanced by 5 or more orders of magnitude. The changes
strongly depend on the nanoshell parameters and the atom position. When an atom
approaches a metal shell, decay rates are strongly enhanced yet fluorescence
exhibits a well-known quenching. Rather contra-intuitively, the Ohmic loss
contribution to the nonradiative decay rates for an atomic dipole within the
silica core of larger nanoshells may be decreasing when the silica core - inner
gold shell interface is approached. The quasistatic result that the radial
frequency shift in a close proximity of a spherical shell interface is
approximately twice as large as the tangential frequency shift appears to apply
also for complex nanoshells. Significantly modified spectroscopic properties
(see computer program (pending publication of this manuscript) freely available
at http://www.wave-scattering.com) can be observed in a broad band comprising
all (nonresonant) optical and near-infrared wavelengths.Comment: 20 pages plus 63 references and 11 figures, plain LaTex, for more
information see http://www.wave-scattering.com (color of D sphere in figures
2-6 altered, minor typos corrected.
Spectroscopy of vibrational modes in metal nanoshells
We study the spectrum of vibrational modes in metal nanoparticles with a
dielectric core. Vibrational modes are excited by the rapid heating of the
particle lattice that takes place after laser excitation, and can be monitored
by means of pump-probe spectroscopy as coherent oscillations of transient
optical spectra. In nanoshells, the presence of two metal surfaces results in a
substantially different energy spectrum of acoustic vibrations than for solid
particles. We calculated the energy spectrum as well as the damping of
nanoshell vibrational modes. The oscillator strength of fundamental breathing
mode is larger than that in solid nanoparticles. At the same time, in very thin
nanoshells, the fundamental mode is overdamped due to instantaneous energy
transfer to the surrounding medium
- …