Role of hydroxylation for the atomic structure of a non-polar vicinal zinc oxide

From the catalytic, semiconducting, and optical properties of zinc oxide (ZnO) numerous potential applications emerge. For the physical and chemical properties of the surface, under-coordinated atoms often play an important role, necessitating systematic studies of their influence. Here we study the vicinal ZnO(10 1 \uaf 4) surface, rich in under-coordinated sites, using a combination of several experimental techniques and density functional theory calculations. We determine the atomic-scale structure and find the surface to be a stable, long-range ordered, non-polar facet of ZnO, with a high step-density and uniform termination. Contrary to an earlier suggested nano-faceting model, a bulk termination fits much better to our experimental observations. The surface is further stabilized by dissociatively adsorbed H2O on adjacent under-coordinated O- and Zn-atoms. The stabilized surface remains highly active for water dissociation through the remaining under-coordinated Zn-sites. Such a vicinal oxide surface is a prerequisite for future adsorption studies with atomically controlled local step and terrace geometry

Incidence of in-hospital cardiac arrest at general wards before and after implementation of an early warning score

Abstract Background In order to reduce the incidence of in-hospital cardiac arrest (IHCA) at general wards, medical emergency teams (MET) were implemented in the Capital Region of Denmark in 2012 as the efferent part of a track and trigger system. The National Early Warning Score (NEWS) system became the afferent part. This study aims at investigating the incidence of IHCA at general wards before and after the implementation of the NEWS system. Material and methods We included patients at least 18 years old with IHCA at general wards in our hospital in the periods of 2006 to 2011 (pre-EWS group) and 2013 to 2018 (post-EWS group). Data was obtained from a local database and the National In-Hospital Cardiac Arrest Registry (DANARREST). We calculated incidence rate ratios (IRR) for IHCA at general wards with 95% confidence interval (95% CI). Odds ratios (OR) for return of spontaneous circulation (ROSC) and 30-day survival were also calculated with 95% CI. Results A total of 444 IHCA occurred before the implementation of NEWS at general wards while 494 IHCA happened afterwards. The incidence rate of IHCA at general wards was 1.13 IHCA per 1000 admissions in the pre-EWS group (2006–2011) and 1.11 IHCA per 1000 admissions in the post-EWS group (2013–2018). The IRR between the two groups was 0.98 (95% CI [0.86;1.11], p = 0.71). The implementation did not affect the chance of ROSC with a crude OR of 1.14 (95% CI [0.88;1.47], p = 0.32) nor did it change the 30-day survival with a crude OR 1.30 (95% CI [0.96;1.75], p = 0.09). Conclusion Implementation of the EWS system at our hospital did not decrease the incidence rate of in-hospital cardiac arrest at general wards

Interaction of Water with Graphene/Ir(111) Studied by Vibrational Spectroscopy

Water in confinement exhibits altered properties in molecular arrangement, bonding, and interaction with its neighboring environment, as compared to its bulk counterpart. In this work, periodically arranged D2O nano droplets of ∼1 nm size on top of a graphene/iridium moiré superstructure were investigated by Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) under ultrahigh vacuum conditions at ∼120 K. The IR bands of D2O clusters differ significantly from those observed for bulk D2O amorphous solid water or crystalline ice phases. Blue-shifted symmetric and asymmetric stretching bands with narrower band widths and modified band intensity ratios were observed, pointing to an enhanced internal order and a reduced nearest neighbor distance. Furthermore, two IR bands of “dangling” deuterium atoms were detected originating from threefold coordinated water molecules at the surface of the clusters and at their interface to the graphene layer. The latter arose only with the transition from the water clusters to an amorphous solid water layer. We propose that upon coalescence, opposing local dipoles trigger a hydrogen bond rearrangement at the interface. Our results represent a first step toward an atomistic understanding of water in confinement

Magnetite (Fe3−O4) homoepitaxy observed by X-ray intensity growth oscillations

Processes on the Fe3−O4 (001) surface like oxidative regrowth, (partial)lifting of the subsurface cation vacancy reconstruction and theelement-specific incorporation of adatoms demonstrate the sensitiverelation of oxygen pressure, cation transport and structure in the nearsurfaceregion of Fe3−O4 influencing the performance of catalysts anddevices [1,2,3]. We exemplarily studied the homoepitaxial growth ofFe3−O4 (001) in dependence of the O2 pressure and iron flux. Xrayintensity growth oscillations proved ordered growth of Fe3−O4for all probed conditions while atomic force microscopy revealed newlyformed micrometre-sized surface structures exceeding the amount ofdeposited material [4]. Our results indicate the presence of multipleparallel processes during reactive Fe3−O4 homoepitaxy suggestingsimilar processes to occur also in other applications of Fe3−O4.[1] Nie et al., J. Am. Chem. Soc. 135, 10091 (2013), [2] Arndt, B. etal. PCCP 22, 8336 (2020), [3] Mirabella et al., Electrochimica Acta,389, 138638 (2021), [4] van der Vegt et al., Phys. Rev. Lett. 68, 3335(1992

Role of hydroxylation for the atomic structure of a non-polar vicinal zinc oxide

From the catalytic, semiconducting, and optical properties of zinc oxide (ZnO) numerouspotential applications emerge. For the physical and chemical properties of the surface, under-coordinated atoms often play an important role, necessitating systematic studies of theirinfluence. Here we study the vicinal ZnO(1014) surface, rich in under-coordinated sites, usinga combination of several experimental techniques and density functional theory calculations.We determine the atomic-scale structure and find the surface to be a stable, long-rangeordered, non-polar facet of ZnO, with a high step-density and uniform termination. Contraryto an earlier suggested nano-faceting model, a bulk termination fits much better to ourexperimental observations. The surface is further stabilized by dissociatively adsorbed H2Oon adjacent under-coordinated O- and Zn-atoms. The stabilized surface remains highly activefor water dissociation through the remaining under-coordinated Zn-sites. Such a vicinal oxidesurface is a prerequisite for future adsorption studies with atomically controlled local stepand terrace geometry

Diffusion of iron in the near-surface region of magnetite (001)

The mobility of Fe in magnetite is a key ingredient towards a better understanding of its defect structure and resulting properties. For nanoparticles, which find a range of applications in medicine, spintronics, material science and catalysis, the near-surface is particularly important. Recent scanning tunnelling microscopy (STM) and low energy electron dif- fraction (LEED) studies of the ( √2× √2)R45° reconstructed (001) surface suggested a subsurface vacancy stabilisation model for this surface, later proved by surface x-ray diffraction (SXRD) [1,2]. Low energy electron microscopy (LEEM) experiments under catalytic conditions showed a regrowth process of Fe3O4-layers on (001) surfaces [3]. These results point towards an interesting interplay between cation vacancy formation and diffusion. We present the results of iron exchange at the interface between 57Fe3O4 thin-films and a Fe3O4 (001) substrate after ultra high vacuum annealing at multiple temperatures. By exploiting the scattering length variation of 57Fe and natural Fe, its interdiffusion across the film-substrate interface is characterized by neutron reflectometry at MARIA at MLZ [4]. The results on growth and diffusion are complemented by x-ray reflectometry data.[1] Bliem, R. et al. Science. 346, 1215 (2014)[2] Arndt, B. et al. Surf. Sci. 653, 76 (2016)[3] Nie, S. et al., J. Am. Chem. Soc. 135, 10091 (2013) [4] Schmidt, H. et al. Adv. Eng. Mat. 11, 446 (2009

Surface Structure of Magnetite (111) under Oxidizing and Reducing Conditions

We report on differences in the magnetite (111) surface structure when prepared under oxidizing and reducing conditions. Both preparations were done under UHV conditions at elevated temperatures, but in one case the sample was cooled down while keeping it in an oxygen atmosphere. Scanning tunneling microscopy after each of the preparations showed a different apparent morphology, which is discussed to be an electronic effect and which is reflected in the necessity of using opposite bias tunneling voltages in order to obtain good images. Surface x-ray diffraction revealed that both preparations lead to Fe vacancies, leading to local O-terminations, the relative fraction of which depending on the preparation. The preparation under reducing conditions lead to a larger fraction of Fe-termination. The geometric structure of the two different terminations was found to be identical for both treatments, even though the surface and near-surface regions exhibit small compositional differences; after the oxidizing treatment they are iron deficient. Further evidence for the dependence of iron vs oxygen fractional surface terminations on preparation conditions comes from Fourier transform infrared reflection-absorption spectroscopy, which is used to study the adsorption of formic acid. These molecules dissociate and adsorb in chelating and bidentate bridging geometries on the Fe-terminated areas and the signal of typical infrared absorption bands is stronger after the preparation under reducing conditions, which results in a higher fraction of Fe-termination. The adsorption of formic acid induced an atomic roughening of the magnetite (111) surface which we conclude from the quantitative analysis of the crystal truncation rod data. The roughening process is initiated by atomic hydrogen, which results from the dissociation of formic acid after its adsorption on the surface. Atomic hydrogen adsorbs at surface oxygen and after recombination with another H this surface hydroxyl can form H2O, which may desorb from the surface, while iron ions diffuse into interstitial sites in the bulk

Water and Atomic Hydrogen Adsorption on Magnetite (001)

We investigated structural changes of the magnetite (001) surface upon exposureto water vapor at pressures up to 10mbar as well as upon exposure to atomic hydrogenusing surface X-ray diffraction, scanning tunneling microscopy, infrared spectroscopyand X-ray photoelectron spectroscopy. Following a full structural analysis, we foundfor both adsorbates, that the surface is roughening on an atomic level, indicating signif-icant iron diffusion at the surface and in the near-surface region at room temperature.We found that this process is accompanied for both adsorbates by a lifting of thesubsurface cation vacancy reconstruction present after preparation under ultra-highvacuum conditions. In the case of water vapor, the lifting process arises in a pressurerange between 104 mbar and 103 mbar. We also observe an enhanced reactivity ofthe atomic hydrogen exposed surface with carbon species from the residual gas evenat ultra-high vacuum conditions

Adsorption of Oleic Acid on Magnetite Facets

The microscopic understanding of the atomic structure and interaction at carboxylic acid/oxide interfaces is an important step towards tailoring the mechanical properties of nanocomposite materials assembled from metal oxide nanoparticles functionalized by organic molecules. We have studied the adsorption of oleic acid (C$_{17}$H$_{33}$COOH) on the most prominent magnetite (001) and (111) crystal facets at room temperature using low energy electron diffraction, surface X-ray diffraction and infrared vibrational spectroscopy complemented with molecular dynamics simulations used to infer specific hydrogen bonding motifs between oleic acid and oleate. Our experimental and theoretical results give evidence that oleic acid adsorbs dissociatively on both facets at lower coverages. At higher coverages, the more pronounced molecular adsorption causes hydrogen bond formation between the carboxylic groups, leading to a more upright orientation of the molecules on the (111) facet in conjunction with the formation of a denser layer, as compared to the (001) facet. This is evidenced by the C=O double bond infrared line shape, in depth molecular dynamics bond angle orientation and hydrogen bond analysis, as well as X-ray reflectivity layer electron density profile determination. Such a higher density can explain the higher mechanical strength of nanocomposite materials based on magnetite nanoparticles with larger (111) facets