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

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

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

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

Ballistic Electron Emission Microscopy on CoSi2{}_2/Si(111) interfaces: band structure induced atomic-scale resolution and role of localized surface states

Applying a Keldysh Green`s function method it is shown that hot electrons injected from a STM-tip into a CoSi${}_2$/Si(111) system form a highly focused beam due to the silicide band structure. This explains the atomic resolution obtained in recent Ballistic Electron Emission Microscopy (BEEM) experiments. Localized surface states in the $(2 \times 1)$-reconstruction are found to be responsible for the also reported anticorrugation of the BEEM current. These results clearly demonstrate the importance of bulk and surface band structure effects for a detailed understanding of BEEM data.Comment: 5 pages, RevTex, 4 postscript figures, http://www.icmm.csic.es/Pandres/pedro.ht