Asymmetric Electrostatic Dodecapole: Compact Bandpass Filter with Low Aberrations for Momentum Microscopy

Imaging energy filters in photoelectron microscopes and momentum microscopes employ spherical fields with deflection angles of 90{\deg}, 180{\deg} and even 2 x 180{\deg}. These instruments are optimized for high energy resolution, yet they come along with image aberrations when they are operated in high transmission mode with medium energy resolution. Here we present a new approach for bandpass-filtered imaging in real or reciprocal space, using an asymmetric electrostatic dodecapole. This multipole enables energy-dispersive beam deflection and correction of image aberrations up to the 3rd order. Owing to a deflection angle of only 4{\deg}, the total beam displacement in the filter is just ~10 mm. Hence, the entire instrument is compact and just requires a straight vacuum tube. The multipole is framed by transfer lenses in the entrance and exit branch. Two sets of 16 entrance and exit apertures with different sizes on piezomotor-driven holders allow selecting the desired resolution. The combination of apertures and dodecapole acts as a bandpass pre-selector in a high-energy time-of-flight momentum microscope at the hard X-ray beamline P22 at PETRA-III (DESY, Hamburg). At pass energies between 400 and 600 eV it transmits electrons with kinetic energies in the range of 20-40 eV and thus effectively eliminates unwanted intensity from higher-energy electrons in the ToF analyzer. At low pass energies, the instrument allows energy-filtered imaging without subsequent ToF analysis. In a laboratory experiment the 4{\deg} prototype reached < 500 meV resolution, which is sufficient for fast survey studies in the X-ray range.Comment: 16 pages, 6 figures, 26 reference

Valence-transition-induced changes of the electronic structure in EuPd2_2Si2_2

We present results of hard X-ray angle-resolved photoemission spectroscopy and photoemission diffraction measurements performed on high-quality single crystals of the valence transition compound EuPd$_2$Si$_2$ for temperatures 25~K $\leq$ T $\leq$ 300~K. At low temperatures we observe a Eu $4f$ valence $v=2.5$, % occupation number $n=6.5$, which decreases to $v=2.1$ for temperatures above the valence transition around $T_V \approx 160$~K. The experimental valence numbers resulting from an evaluation of the Eu(III)/Eu(II) $3d$ core levels, are used for calculating band structures using density functional theory. The valence transition significantly changes the band structure as determined by angle-resolved photoemission spectroscopy. In particular, the Eu $5d$ valence bands are shifted to lower binding energies with increasing Eu $4f$ occupancy. To a lesser extent, bands derived from the Si $3p$ and Pd $4d$ orbitals are also affected. This observation suggests a partial charge transfer between Eu and Pd/Si sites. Comparison with {\it ab-initio} theory shows a good agreement with experiment, in particular concerning the unequal band shift with increasing Eu $4f$ occupancy

Multi-Mode Front Lens for Momentum Microscopy: Part II Experiments

We have experimentally demonstrated different operating modes for the front lenses of the momentum microscopes described in Part I. Measurements at energies from vacuum UV at a high-harmonic generation (HHG)-based source to the soft and hard X-ray range at a synchrotron facility validated the results of theoretical ray-tracing calculations. The key element is a ring electrode concentric with the extractor electrode, which can tailor the field in the gap. First, the gap-lens-assisted extractor mode reduces the field strength at the sample while mitigating image aberrations. This mode gave good results in all spectral ranges. Secondly, by compensating the field at the sample surface with a negative voltage at the ring electrode we can operate in zero-field mode, which is beneficial for operando experiments. Finally, higher negative voltages establish the repeller mode, which removes all slow electrons below a certain kinetic energy to eliminate the primary contribution to the space-charge interaction in pump-probe experiments. The switch from extractor to repeller mode is associated with a reduction in the k-field-of-view (10-20 % at hard-X-ray energies, increasing to ~50% at low energies). Real-space imaging also benefits from the new lens modes as confirmed by ToF-XPEEM imaging with 650 nm resolution.Comment: 22 pages, 9 figures, 56 reference

Suppression of the vacuum space-charge effect in fs-photoemission by a retarding electrostatic front lens

The performance of time-resolved photoemission experiments at fs-pulsed photon sources is ultimately limited by the e–e Coulomb interaction, downgrading energy and momentum resolution. Here, we present an approach to effectively suppress space-charge artifacts in momentum microscopes and photoemission microscopes. A retarding electrostatic field generated by a special objective lens repels slow electrons, retaining the k-image of the fast photoelectrons. The suppression of space-charge effects scales with the ratio of the photoelectron velocities of fast and slow electrons. Fields in the range from −20 to −1100 V/mm for Ekin = 100 eV to 4 keV direct secondaries and pump-induced slow electrons back to the sample surface. Ray tracing simulations reveal that this happens within the first 40 to 3 μm above the sample surface for Ekin = 100 eV to 4 keV. An optimized front-lens design allows switching between the conventional accelerating and the new retarding mode. Time-resolved experiments at Ekin = 107 eV using fs extreme ultraviolet probe pulses from the free-electron laser FLASH reveal that the width of the Fermi edge increases by just 30 meV at an incident pump fluence of 22 mJ/cm2 (retarding field −21 V/mm). For an accelerating field of +2 kV/mm and a pump fluence of only 5 mJ/cm2, it increases by 0.5 eV (pump wavelength 1030 nm). At the given conditions, the suppression mode permits increasing the slow-electron yield by three to four orders of magnitude. The feasibility of the method at high energies is demonstrated without a pump beam at Ekin = 3830 eV using hard x rays from the storage ring PETRA III. The approach opens up a previously inaccessible regime of pump fluences for photoemission experiments

Pulseless disease

The article discusses a rare form of large vessel vasculitis – Takayasu arteritis, based on the literature data; the questions of epidemiological, the sequence of diagnostic procedures and treatment tactics are reflectedВ статье рассмотрена редкая форма васкулита крупных артерий - Артериит Такаясу, на основании литературных данных отражены вопросы эпидемиологии, последовательность проведения диагностических процедур и тактики лечени

Epidemiology of bloodstream infections in the burn icu

The study included data on 80 adult patients hospitalized in the ICU of the Yekaterinburg Burn Center in 2018 - 2019, who underwent at least one bacteriological blood test. In a small observational study, bloodstream infection did not lead to an increase in mortality, but is an important factor in increasing the incidence (length of hospitalization and ICU). In 70,5% of cases, the source of bloodstream infections are P. aeruginosa and S. aureus. The duration of standing of the CVC is one of the most important criteria for the development of bloodstream infectionsВ исследование включены данные о 80 взрослых пациентах, госпитализированных в ОРИТ ожогового центра Екатеринбурга в 2018 – 2019 гг, которым было сделано по крайней мере одно бактериологическое исследование крови. В небольшом обсервационном исследовании инфекция кровотока не привела к увеличению летальности, но является важным фактором увеличивающем заболеваемость (длительность госпитализации в стационаре и ОРИТ). В 70,5% случаев источником инфекций кровотока являются P. aeruginosa и S. aureus. Длительность стояния ЦВК один из важнейших критериев, обуславливающих развитие инфекций кровотока

Emitter-site specificity of hard x-ray photoelectron Kikuchi-diffraction

High-resolution full-field imaging of (k$_x$, k$_y$) photoelectron distributions (k-resolution 0.03 Å$^{−1}$, angular resolution 0.03° at 6.7 keV) in a large field of view (up to 16 Å$^{−1}$ dia.) allows to observe fine details in Kikuchi-type diffractograms. Alongside with the element specificity via core-level spectra, this method opens a new avenue to structural analysis using hard x-ray photoelectron diffraction (hXPD). Here we present a theoretical study of the emitter-site specificity by simulating hXPD patterns for arbitrary positions of emitter atoms in the unit cell. Using the Bloch wave approach to photoelectron diffraction from lattice planes, the diffraction patterns from a number of positions in the unit cell can be obtained simultaneously exploiting the reciprocity theorem. Simulations for dopant atoms and dopant multimers (dimers, trimers, clusters) in the Si lattice at various positions in the unit cell reveal a strong site-sensitivity in terms of dramatic changes in the diffraction patterns with emitter-atom position. The results are compared with measurements for Si hyperdoped with Te