841 research outputs found
Adsorption of 2,2 '-dithiodipyridine as a tool for the assembly of silver nanoparticles
Silver nanostructured thin films stabilized by 2,2â-dithiodipyridine (2dtpy) were prepared. The Ag nanoparticles
were obtained by treating the complex [Ag(2dtpy)]NO3 with NaBH4 in a methanolâtoluene mixture. The films
were transferred to borosilicate glass slips by a dip-coating method and were found to consist of Ag
nanoparticles possibly linked via 2dtpy molecules. Surface-enhanced Raman scattering (SERS) studies have
offered the possibility of investigating the adsorption modes of 2dtpy at the Ag nanoparticle surfaces in the
fil
Annotated Bibliography of the Lake Charles, Mobile and Pensacola Harbor Approach Areas
Project 98 is a literature survey of the Lake Charles, Mobile and Pensacola Harbor Approach Areas sponsored by the US Hydrographic Offic
Laser heating of a sintered oxide superconductor
Raman spectroscopy, in which a laser beam serves the dual role of exciting the Raman spectrum and annealing the sample, shows promise as a means of investigating oxygen effects in the oxide superconductors. A technique is described, based on measurements of the ratios of the areas of corresponding peaks in the anti-Stokes and Stokes spectra, whereby the temperature of the illuminated region of the sample can be determined as a function of the power in the incident laser beam. It is found that, for sintered samples of bismuth 2122, a small correction must be made for the departure from thermodynamic equilibrium induced by the pumping effect of the laser beam
High-yield TiO(2) nanowire synthesis and single nanowire field-effect transistor fabrication
We report a facile method for synthesizing single-crystal rutile TiO 2 nanowires using atmospheric-pressure, chemical vapor deposition with Ti and TiO as precursors. The synthesis is found to depend critically on the predeposition of a layer of metallic Ti on the Ni catalysts layer. The omission of this step seems previously to have impeded the efficient synthesis of titania nanowires. Single-nanowire field-effect transistors showed the TiO2 nanowires to be n -type semiconductors with conductance activation energy of ???58 meV.open242
Design Principles for Plasmonic Nanoparticle Devices
For all applications of plasmonics to technology it is required to tailor the
resonance to the optical system in question. This chapter gives an
understanding of the design considerations for nanoparticles needed to tune the
resonance. First the basic concepts of plasmonics are reviewed with a focus on
the physics of nanoparticles. An introduction to the finite element method is
given with emphasis on the suitability of the method to nanoplasmonic device
simulation. The effects of nanoparticle shape on the spectral position and
lineshape of the plasmonic resonance are discussed including retardation and
surface curvature effects. The most technologically important plasmonic
materials are assessed for device applicability and the importance of
substrates in light scattering is explained. Finally the application of
plasmonic nanoparticles to photovoltaic devices is discussed.Comment: 29 pages, 15 figures, part of an edited book: "Linear and Non-Linear
Nanoplasmonics
Slow fluctuations in enhanced Raman scattering and surface roughness relaxation
We propose an explanation for the recently measured slow fluctuations and
``blinking'' in the surface enhanced Raman scattering (SERS) spectrum of single
molecules adsorbed on a silver colloidal particle. We suggest that these
fluctuations may be related to the dynamic relaxation of the surface roughness
on the nanometer scale and show that there are two classes of roughness with
qualitatively different dynamics. The predictions agree with measurements of
surface roughness relaxation. Using a theoretical model for the kinetics of
surface roughness relaxation in the presence of charges and optical electrical
fields, we predict that the high-frequency electromagnetic field increases both
the effective surface tension and the surface diffusion constant and thus
accelerates the surface smoothing kinetics and time scale of the Raman
fluctuations in manner that is linear with the laser power intensity, while the
addition of salt retards the surface relaxation kinetics and increases the time
scale of the fluctuations. These predictions are in qualitative agreement with
the Raman experiments
Photoelectric Emission from Interstellar Dust: Grain Charging and Gas Heating
We model the photoelectric emission from and charging of interstellar dust
and obtain photoelectric gas heating efficiencies as a function of grain size
and the relevant ambient conditions. Using realistic grain size distributions,
we evaluate the net gas heating rate for various interstellar environments, and
find less heating for dense regions characterized by R_V=5.5 than for diffuse
regions with R_V=3.1. We provide fitting functions which reproduce our
numerical results for photoelectric heating and recombination cooling for a
wide range of interstellar conditions. In a separate paper we will examine the
implications of these results for the thermal structure of the interstellar
medium. Finally, we investigate the potential importance of photoelectric
heating in H II regions, including the warm ionized medium. We find that
photoelectric heating could be comparable to or exceed heating due to
photoionization of H for high ratios of the radiation intensity to the gas
density. We also find that photoelectric heating by dust can account for the
observed variation of temperature with distance from the galactic midplane in
the warm ionized medium.Comment: 50 pages, including 18 figures; corrected title and abstract field
Light emission from a scanning tunneling microscope: Fully retarded calculation
The light emission rate from a scanning tunneling microscope (STM) scanning a
noble metal surface is calculated taking retardation effects into account. As
in our previous, non-retarded theory [Johansson, Monreal, and Apell, Phys. Rev.
B 42, 9210 (1990)], the STM tip is modeled by a sphere, and the dielectric
properties of tip and sample are described by experimentally measured
dielectric functions. The calculations are based on exact diffraction theory
through the vector equivalent of the Kirchoff integral. The present results are
qualitatively similar to those of the non-retarded calculations. The light
emission spectra have pronounced resonance peaks due to the formation of a
tip-induced plasmon mode localized to the cavity between the tip and the
sample. At a quantitative level, the effects of retardation are rather small as
long as the sample material is Au or Cu, and the tip consists of W or Ir.
However, for Ag samples, in which the resistive losses are smaller, the
inclusion of retardation effects in the calculation leads to larger changes:
the resonance energy decreases by 0.2-0.3 eV, and the resonance broadens. These
changes improve the agreement with experiment. For a Ag sample and an Ir tip,
the quantum efficiency is 10 emitted photons in the visible
frequency range per tunneling electron. A study of the energy dissipation into
the tip and sample shows that in total about 1 % of the electrons undergo
inelastic processes while tunneling.Comment: 16 pages, 10 figures (1 ps, 9 tex, automatically included); To appear
in Phys. Rev. B (15 October 1998
Surfactant-Free Synthesis of Bi_(2)Te_(3)-Te Micro-Nano Heterostructure with Enhanced Thermoelectric Figure of Merit
An ideal thermoelectric material would be a semiconductor with high electrical conductivity and relatively low thermal conductivity: an âelectron crystal, phonon glassâ. Introducing nanoscale heterostructures into the bulk TE matrix is one way of achieving this intuitively anomalous
electron/phonon transport behavior. The heterostructured interfaces are expected to play a significant role in phonon scattering to reduce thermal conductivity and in the energy-dependent scattering of electrical carriers to improve the Seebeck coefficient. A nanoparticle building block assembly approach is plausible to fabricate three-dimensional heterostructured materials on a bulk commercial scale. However, a key problem in applying this strategy is the possible negative impact on TE performance of organic residue from the nanoparticle capping ligands. Herein, we report a wet chemical, surfactant-free, low-temperature, and easily up-scalable strategy for the synthesis of
nanoscale heterophase Bi_(2)Te_(3)-Te via a galvanic replacement reaction. The micro-nano heterostructured material is fabricated bottom-up, by mixing the heterophase with commercial Bi_(2)Te_3. This unique structure shows an enhanced zT value of ~0.4 at room temperature. This heterostructure has one of the highest figures of merit among bismuth telluride systems yet achieved by a wet chemical bottom-up assembly. In addition, it shows a 40% enhancement of the figure of merit over our lab-made material without nanoscale heterostructures. This enhancement is mainly due to the decrease in the thermal conductivity while maintaining the power factor. Overall, this cost-efficient and room temperature synthesis methodology provides the potential for further improvement and large-scale thermoelectric applications
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