1,132 research outputs found
Prediction of huge X-ray Faraday rotation at the Gd N_4,5 threshold
X-ray absorption spectra in a wide energy range around the 4d-4f excitation
threshold of Gd were recorded by total electron yield from in-plane magnetized
Gd metal films. Matching the experimental spectra to tabulated absorption data
reveals unprecedented short light absorption lengths down to 3 nm. The
associated real parts of the refractive index for circularly polarized light
propagating parallel or antiparallel to the Gd magnetization, determined
through the Kramers-Kronig transformation, correspond to a magneto-optical
Faraday rotation of 0.7 degrees per atomic layer. This finding shall allow the
study of magnetic structure and magnetization dynamics of lanthanide elements
in nanosize systems and dilute alloys.Comment: 4 pages, 2 figures, final version resubmitted to Phys. Rev. B, Brief
Reports. Minor change
Enhanced electron-phonon coupling in graphene with periodically distorted lattice
Electron-phonon coupling directly determines the stability of cooperative
order in solids, including superconductivity, charge and spin density waves.
Therefore, the ability to enhance or reduce electron-phonon coupling by optical
driving may open up new possibilities to steer materials' functionalities,
potentially at high speeds. Here we explore the response of bilayer graphene to
dynamical modulation of the lattice, achieved by driving optically-active
in-plane bond stretching vibrations with femtosecond mid-infrared pulses. The
driven state is studied by two different ultrafast spectroscopic techniques.
Firstly, TeraHertz time-domain spectroscopy reveals that the Drude scattering
rate decreases upon driving. Secondly, the relaxation rate of hot
quasi-particles, as measured by time- and angle-resolved photoemission
spectroscopy, increases. These two independent observations are quantitatively
consistent with one another and can be explained by a transient three-fold
enhancement of the electron-phonon coupling constant. The findings reported
here provide useful perspective for related experiments, which reported the
enhancement of superconductivity in alkali-doped fullerites when a similar
phonon mode was driven.Comment: 12 pages, 4 figure
LEED Holography applied to a complex superstructure: a direct view of the adatom cluster on SiC(111)-(3x3)
For the example of the SiC(111)-(3x3) reconstruction we show that a
holographic interpretation of discrete Low Energy Electron Diffraction (LEED)
spot intensities arising from ordered, large unit cell superstructures can give
direct access to the local geometry of a cluster around an elevated atom,
provided there is only one such prominent atom per surface unit cell. By
comparing the holographic images obtained from experimental and calculated data
we illuminate validity, current limits and possible shortcomings of the method.
In particular, we show that periodic vacancies such as cornerholes may inhibit
the correct detection of the atomic positions. By contrast, the extra
diffraction intensity due to slight substrate reconstructions, as for example
buckling, seems to have negligible influence on the images. Due to the spatial
information depth of the method the stacking of the cluster can be imaged down
to the fourth layer. Finally, it is demonstrated how this structural knowledge
of the adcluster geometry can be used to guide the dynamical intensity analysis
subsequent to the holographic reconstruction and necessary to retrieve the full
unit cell structure.Comment: 11 pages RevTex, 6 figures, Phys. Rev. B in pres
Band structure engineering of epitaxial graphene on SiC by molecular doping
Epitaxial graphene on SiC(0001) suffers from strong intrinsic n-type doping.
We demonstrate that the excess negative charge can be fully compensated by
non-covalently functionalizing graphene with the strong electron acceptor
tetrafluorotetracyanoquinodimethane (F4-TCNQ). Charge neutrality can be reached
in monolayer graphene as shown in electron dispersion spectra from angular
resolved photoemission spectroscopy (ARPES). In bilayer graphene the band gap
that originates from the SiC/graphene interface dipole increases with
increasing F4-TCNQ deposition and, as a consequence of the molecular doping,
the Fermi level is shifted into the band gap. The reduction of the charge
carrier density upon molecular deposition is quantified using electronic Fermi
surfaces and Raman spectroscopy. The structural and electronic characteristics
of the graphene/F4-TCNQ charge transfer complex are investigated by X-ray
photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy
(UPS). The doping effect on graphene is preserved in air and is temperature
resistant up to 200\degree C. Furthermore, graphene non-covalent
functionalization with F4-TCNQ can be implemented not only via evaporation in
ultra-high vacuum but also by wet chemistry
Theoretical study of O adlayers on Ru(0001)
Recent experiments performed at high pressures indicate that ruthenium can
support unusually high concentrations of oxygen at the surface. To investigate
the structure and stability of high coverage oxygen structures, we performed
density functional theory calculations, within the generalized gradient
approximation, for O adlayers on Ru(0001) from low coverage up to a full
monolayer. We achieve quantitative agreement with previous low energy electron
diffraction intensity analyses for the (2x2) and (2x1) phases and predict that
an O adlayer with a (1x1) periodicity and coverage of 1 monolayer can form on
Ru(0001), where the O adatoms occupy hcp-hollow sites.Comment: RevTeX, 6 pages, 4 figure
Analysis of the question–answer service of the Emma Children’s Hospital information centre
The information centre of the Emma Children’s Hospital AMC (EKZ AMC) is a specialised information centre where paediatric patients and persons involved with the patient can ask questions about all aspects of disease and its social implications. The aim of the study was to evaluate the question–answer service of this information centre in order to determine the role of a specialised information centre in an academic children’s hospital, identify the appropriate resources for the service and potential positive effects. For this purpose, a case management system was developed in MS ACCESS. The characteristics of the requester and the question, the time it took to answer questions, the information sources used and the extent to which we were able to answer the questions were registered. The costs of the service were determined. We analysed all questions that were asked in the year 2007. Fourteen hundred thirty-four questions were asked. Most questions were asked by parents (23.3%), healthcare workers (other than nurses; 16.5%) and nurses (15.3%). The scope of the most frequently asked questions include disease (20.2%) and treatment (13.0%). Information on paper was the main information source used. Most questions could be solved within 15 min. Twelve percent to 28% of total working hours are used for the question–answer service. Total costs including staff salary are rather large. In conclusions, taking over the task of providing additional medical information and by providing readily available, good quality information that healthcare professionals can use to inform their patients will lead to less time investment of these more expensive staff members. A specialised information service can anticipate on the information need of parents and persons involved with the paediatric patient. It improves information by providing with relatively simple resources that has the potential to improve patient and parent satisfaction, coping and medical results. A specialised information centre is therefore a valuable and affordable asset to an academic children’s hospital
Technology Development to Explore the Relationship Between Oral Health and the Oral Microbial Community
The human oral cavity contains a complex microbial community that, until recently, has not been well characterized. Studies using molecular tools have begun to enumerate and quantify the species residing in various niches of the oral cavity; yet, virtually every study has revealed additional new species, and little is known about the structural dynamics of the oral microbial community or how it changes with disease. Current estimates of bacterial diversity in the oral cavity range up to 700 species, although in any single individual this number is much lower. Oral microbes are responsible for common chronic diseases and are suggested to be sentinels of systemic human diseases. Microarrays are now being used to study oral microbiota in a systematic and robust manner. Although this technology is still relatively young, improvements have been made in all aspects of the technology, including advances that provide better discrimination between perfect-match hybridizations from non-specific (and closely-related) hybridizations. This review addresses a core technology using gel-based microarrays and the initial integration of this technology into a single device needed for system-wide studies of complex microbial community structure and for the development of oral diagnostic devices
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