38 research outputs found
Coupled surface polaritons and the Casimir force
The Casimir force between metallic plates made of realistic materials is
evaluated for distances in the nanometer range. A spectrum over real
frequencies is introduced and shows narrow peaks due to surface resonances
(plasmon polaritons or phonon polaritons) that are coupled across the vacuum
gap. We demonstrate that the Casimir force originates from the attraction
(repulsion) due to the corresponding symmetric (antisymmetric) eigenmodes,
respectively. This picture is used to derive a simple analytical estimate of
the Casimir force at short distances. We recover the result known for Drude
metals without absorption and compute the correction for weakly absorbing
materials.Comment: revised version submitted to Phys. Rev. A, 06 November 200
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
Spatio-temporal dynamics of quantum-well excitons
We investigate the lateral transport of excitons in ZnSe quantum wells by
using time-resolved micro-photoluminescence enhanced by the introduction of a
solid immersion lens. The spatial and temporal resolutions are 200 nm and 5 ps,
respectively. Strong deviation from classical diffusion is observed up to 400
ps. This feature is attributed to the hot-exciton effects, consistent with
previous experiments under cw excitation. The coupled transport-relaxation
process of hot excitons is modelled by Monte Carlo simulation. We prove that
two basic assumptions typically accepted in photoluminescence investigations on
excitonic transport, namely (i) the classical diffusion model as well as (ii)
the equivalence between the temporal and spatial evolution of the exciton
population and of the measured photoluminescence, are not valid for
low-temperature experiments.Comment: 8 pages, 6 figure
The design and fabrication of one-dimensional random surfaces with specified scattering properties
We describe methods for designing and fabricating one-dimensional random surfaces that scatter light uniformly within a specified range of scattering angles, and produce no scattering outside this range. These methods are tested by means of computer simulations. Preliminary experimental results are presented. (C) 1999 American Institute of Physics. [S1063-7834(99)04305-1]
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The design and fabrication of one-dimensional random surfaces with specified scattering properties
We describe methods for designing and fabricating one-dimensional random surfaces that scatter light uniformly within a specified range of scattering angles, and produce no scattering outside this range. These methods are tested by means of computer simulations. Preliminary experimental results are presented. (C) 1999 American Institute of Physics. [S1063-7834(99)04305-1]