1,000 research outputs found
Sub-nanometer free electrons with topological charge
The holographic mask technique is used to create freely moving electrons with
quantized angular momentum. With electron optical elements they can be focused
to vortices with diameters below the nanometer range. The understanding of
these vortex beams is important for many applications. Here we present a theory
of focused free electron vortices. The agreement with experimental data is
excellent. As an immediate application, fundamental experimental parameters
like spherical aberration and partial coherence are determined.Comment: 4 pages, 5 figure
First principles theory of chiral dichroism in electron microscopy applied to 3d ferromagnets
Recently it was demonstrated (Schattschneider et al., Nature 441 (2006),
486), that an analogue of the X-ray magnetic circular dichroism (XMCD)
experiment can be performed with the transmission electron microscope (TEM).
The new phenomenon has been named energy-loss magnetic chiral dichroism (EMCD).
In this work we present a detailed ab initio study of the chiral dichroism in
the Fe, Co and Ni transition elements. We discuss the methods used for the
simulations together with the validity and accuracy of the treatment, which
can, in principle, apply to any given crystalline specimen. The dependence of
the dichroic signal on the sample thickness, accuracy of the detector position
and the size of convergence and collection angles is calculated.Comment: 9 pages, 6 figures, submitted to Physical Review
Site-specific ionisation edge fine-structure of Rutile in the electron microscope
Combined Bloch-wave and density functional theory simulations are performed to investigate the effects of different channelling conditions on the fine-structure of electron energy-loss spectra. The simulated spectra compare well with experiments. Furthermore, we demonstrate that using this technique, the site-specific investigation of atomic orbitals is possible. This opens new possibilities for chemical analyses
Site Specific Ab-initio Calculations of the Oxygen 1s Ionisation Edge in Vanadium Pentoxide
Ab-Initio Simulation of the Oxygen 1s Ionisation Near Edge Structure in Vanadium Pentoxide
A novel vortex generator and mode converter for electrons
A mode converter for electron vortex beams is described. Numerical
simulations, confirmed by experiment, show that the converter transforms a
vortex beam with topological charge into beams closely resembling
Hermite-Gaussian HG and HG modes. The converter can be used as a
mode discriminator or filter for electron vortex beams. Combining the converter
with a phase plate turns a plane wave into modes with topological charge . This combination serves as a generator of electron vortex beams of high
brilliance
Theory and applications of free-electron vortex states
Both classical and quantum waves can form vortices: with helical phase fronts
and azimuthal current densities. These features determine the intrinsic orbital
angular momentum carried by localized vortex states. In the past 25 years,
optical vortex beams have become an inherent part of modern optics, with many
remarkable achievements and applications. In the past decade, it has been
realized and demonstrated that such vortex beams or wavepackets can also appear
in free electron waves, in particular, in electron microscopy. Interest in
free-electron vortex states quickly spread over different areas of physics:
from basic aspects of quantum mechanics, via applications for fine probing of
matter (including individual atoms), to high-energy particle collision and
radiation processes. Here we provide a comprehensive review of theoretical and
experimental studies in this emerging field of research. We describe the main
properties of electron vortex states, experimental achievements and possible
applications within transmission electron microscopy, as well as the possible
role of vortex electrons in relativistic and high-energy processes. We aim to
provide a balanced description including a pedagogical introduction, solid
theoretical basis, and a wide range of practical details. Special attention is
paid to translate theoretical insights into suggestions for future experiments,
in electron microscopy and beyond, in any situation where free electrons occur.Comment: 87 pages, 34 figure
Experimental application of sum rules for electron energy loss magnetic chiral dichroism
We present a derivation of the orbital and spin sum rules for magnetic
circular dichroic spectra measured by electron energy loss spectroscopy in a
transmission electron microscope. These sum rules are obtained from the
differential cross section calculated for symmetric positions in the
diffraction pattern. Orbital and spin magnetic moments are expressed explicitly
in terms of experimental spectra and dynamical diffraction coefficients. We
estimate the ratio of spin to orbital magnetic moments and discuss first
experimental results for the Fe L_{2,3} edge.Comment: 11 pages, 2 figure
Long term stability and infectivity of herpesviruses in water
For viruses to utilize environmental vectors (hard surfaces, soil, water) for
transmission, physical and chemical stability is a prerequisite. There are
many factors including pH, salinity, temperature, and turbidity that are known
to contribute to the ability of viruses to persist in water. Equine
herpesvirus type-1 (EHV-1) is a pathogenic alphaherpesvirus associated with
domestic horses and wild equids. EHV-1 and recombinants of EHV-1 and EHV-9 are
able to cause infections in non-equid animal species, particularly in captive
settings. Many of the captive non-equid mammals are not naturally sympatric
with equids and do not share enclosures, however, in many cases water sources
may overlap. Similarly, in the wild, equids encounter many species at
waterholes in times of seasonal drought. Therefore, we hypothesized that EHV-1
is stable in water and that water may act as a vector for EHV-1. In order to
establish the conditions promoting or hindering EHV-1 longevity, infectivity
and genomic stability in water; we exposed EHV-1 to varied water environments
(pH, salinity, temperature, and turbidity) in controlled experiments over 21
days. The presence and infectivity of the virus was confirmed by both qPCR and
cell culture experiments. Our results show that EHV-1 remains stable and
infectious under many conditions in water for up to three weeks
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