An in operando study of chemical expansion and oxygen surface exchange rates in epitaxial GdBaCo2O5.5 electrodes in a solid-state electrochemical cell by time-resolved X-ray diffraction

This report explores the fundamental characteristics of epitaxial thin films of a mixed ionic electronic conducting GdBaCoO (GBCO) material with a layered perovskite structure, relevant for use as an active electrode for the oxygen reduction and evolution reactions in electrochemical devices. Time-resolved X-ray diffraction in combination with voltage step chrono-amperometric measurements in a solid state electrochemical cell provides a deeper insight into the chemical expansion mechanism in the GBCO electrode. The chemical expansion coefficient along the c-axis, α, shows a negative value upon the compound oxidation contrary to standard perovskite materials with disordered oxygen vacancies. Chemical expansion also shows a remarkable asymmetry from α = -0.037 to -0.014 at δ 0, respectively. This change in chemical expansion is an indication of a different mechanism of the structural changes associated with the variable Co cation oxidation state from Co → Co → Co. Since redox reactions are dominated by oxygen surface exchange between the GBCO electrode and gas atmosphere, monitoring the time response of the structural changes allows for direct determination of oxygen reduction and evolution reaction kinetics. The reaction kinetics are progressively slowed down upon reduction in the δ 0 region, in agreement with the structural changes and the electronic carrier delocalization when crossing δ = 0. This work validates the time-resolved XRD technique for fast and reversible measurements of electrode activity in a wide range of oxygen non-stoichiometry in a solid-state electrochemical cell operating under realistic working conditions

Tunable Molecular Electrodes for Bistable Polarization Screening

The polar discontinuity at any ferroelectric surface creates a depolarizing field that must be screened for the polarization to be stable. In capacitors, screening is done by the electrodes, while in bare ferroelectric surfaces it is typically accomplished by atmospheric adsorbates. Although chemisorbed species can have even better screening efficiency than conventional electrodes, they are subject to unpredictable environmental fluctuations and, moreover, dominant charged species favor one polarity over the opposite. This paper proposes a new screening concept, namely surface functionalization with resonance-hybrid molecules, which combines the predictability and bipolarity of conventional electrodes with the screening efficiency of adsorbates. Thin films of barium titanate (BaTiO) coated with resonant para-aminobenzoic acid (pABA) display increased coercivity for both signs of ferroelectric polarization irrespective of the molecular layer thickness, thanks to the ability of these molecules to swap between different electronic configurations and adapt their surface charge density to the screening needs of the ferroelectric underneath. Because electron delocalization is only in the vertical direction, unlike conventional metals, chemical electrodes allow writing localized domains of different polarity underneath the same electrode. In addition, hybrid capacitors composed of graphene/pABA/ferroelectric have been made with enhanced coercivity compared to pure graphene-electode capacitors

Role of pO2 and film microstructure on the memristive properties of La2NiO4+δ/LaNiO3−δ bilayers

Altres ajuts: ICN2 is funded by the CERCA programme/Generalitat de Catalunya.LaNiO/LaNiO bilayers deposited at varying pO conditions resulted in remarkable differences in film microstructure and cell parameters, directly affecting the electrical behaviour of Pt/LaNiO/LaNiO/Pt devices. The devices deposited at low pO showed the largest memristance. We propose this is due to the formation of a p-type Schottky contact between LaNiO and LaNiO, where the extent of its carrier depletion width can be modulated by the electric-field induced drift of interstitial oxygen ions acting as mobile acceptor dopants in LaNiO

Antisite Defects and Chemical Expansion in Low-damping, High-magnetization Yttrium Iron Garnet Films

Yttrium iron garnet is widely investigated for its suitability in applications ranging from magneto-optical and microwave devices to magnonics. However, in the few-nanometer thickness range, epitaxial films exhibit a strong variability in magnetic behavior that hinders their implementation in technological devices. Here, direct visualization and spectroscopy of the atomic structure of a nominally stoichiometric thin film, exhibiting a small damping factor of 3.0 ⋅ 10, reveals the occurrence of Y-excess octahedral antisite defects. The two-magnon strength is very small, Γ≈10 Oe, indicating a very low occurrence of scattering centers. Notably, the saturation magnetization, 4πM=2.10 (±0.01) kOe, is higher than the bulk value, in consistency with the suppression of magnetic moment in the minority octahedral sublattice by the observed antisite defects. Analysis of elemental concentration profiles across the substrate-film interface suggests that the Y-excess is originated from unbalanced cationic interdiffusion during the early growth stages

Bipolar "table with legs" resistive switching in epitaxial perovskite heterostructures

We report the experimental investigation of bipolar resistive switching with "table with legs" shaped hysteresis switching loops in epitaxial perovskite GdBaCo O /LaNiO bilayers deposited by pulsed laser deposition. The possibility of varying the resistivity of GdBaCo O by changing its oxygen content allowed engineering this perovskite heterostructure with controlled interfaces creating two symmetric junctions. It has been proved that the resistance state of the device can be reproducibly varied by both continuous voltage sweeps and by electrical pulses. The symmetric devices show slightly non-symmetric resistance profiles, which can be explained by a valence change resistive switching model, and presented promising multilevel properties required for novel memories and neuromorphic computing

Control of lateral composition distribution in graded films of soluble solid systems A1-xBx by partitioned dual-beam pulsed laser deposition

Altres ajuts: AGAUR agency (project 2017SGR)Lateral compositionally-graded thin films are powerful media for the observation of phase boundaries aswell as for high-throughputmaterials exploration.We herein propose amethod to prepare epitaxial lateral compositionally-graded films using a dual-beampulsed laser deposition (PLD)method with two targets separated by a partition. Tuning the ambient pressure and the partition-substrate gap makes it possible to control of the gradient length of the deposits at the small sizes (≤ 10 mm) suitable for commercial oxide single crystal substrates. A simple Monte Carlo simulation qualitatively reproduced the characteristic features of the lateral thickness distribution. To demonstrate this method, we prepared (1-x)PbTiO-xPbZrO and (1-x)LaMnOLaSrMnO films with lateral composition gradient widths of 10 and 1 mm, respectively, with the partitioned dual PLD

Atrofia de múltiples sistemas. Reportes de caso

La Atrofia de Múl6ples Sistemas (AMS) es una enfermedad neurodegenera6va de carácter esporádico que hace parte de las α-sinucleinopajas, cursa con síntomas piramidales y autonómicos en diversas combinaciones. Se presenta entre la quinta y sexta década de la vida y 6ene una esperanza de vida desde el inicio de los síntomas de entre 6 a 10 años (rango 2-18 años)1. Desde el punto de vista neuropatológico, lo más sobresaliente, es la presencia de pérdidas neuronales y gliosis en los ganglios basales, sustancia nigra, locus coeruleus, oliva inferior, núcleos pón6cos, células de Purkinje del cerebelo, núcleos autonómicos del tallo cerebral y médula espinal. Una caracterís6ca asociada, es la presencia de inclusiones citoplasmá6cas en las células gliales (ICG), que se 6ñen mediante inmunohistoquímica con an6cuerpos an6ubiqui6na, tau y α-sinucleína2. Se dis6nguen dos 6pos principales dependiendo del área afectada y los síntomas: el 6po cerebeloso y el 6po parkinsoniano. A con6nuación presentamos el reporte de dos casos diagnos6cado en el Centro de memoria y cognición Intellectus – HUSI, uno correspondiente a la variante parkinsoniana y otro a la variante cerebelosa

Direct Visualization of Anti-Ferroelectric Switching Dynamics via Electrocaloric Imaging

The large electrocaloric coupling in PbZrO allows using high-speed infrared imaging for visualizing anti-ferroelectric switching dynamics via the associated temperature change. It is found that in ceramic samples of homogeneous temperature and thickness, switching is fast due to the generation of multiple nucleation sites, with devices responding in the millisecond range. By introducing gradients of thickness, however, it is possible to change the dynamics to propagation limited, whereby a single-phase boundary sweeps across the sample like a cold front, at a speed of ≈20 cm s. Additionally, introducing thermostatic temperature differences between two sides of the sample enables the simultaneous generation of a negative electrocaloric effect on one side and a positive one on the other, yielding a Janus-like electrocaloric response.The authors acknowledge financial support to ICN2, which is funded by the CERCA programme/Generalitat de Catalunya and by the Severo Ochoa programme of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant No. SEV-2017-0706). The authors also acknowledge the support of Plan Nacional (MINECO, Grant Nos. MAT2016-77100-C2-1-P and BES-2016-077392), as well as the Agencia Estatal de Investigacion (Grant No. PID2019-108573GB-C21). R.F. and E.D. thank the Luxembourg National Research Fund (FNR) for funding part of this research through the projects CAMELHEAT/C17/MS/11703691/Defay. This work was also supported in part by the Spanish Ministry of Science, Innovation and Universities under the HIPERCELLS project (RTI2018-098392-B-I00), the Regional Government of the Generalitat de Catalunya under Grant Nos. 2017 SGR 1384 and 2017 SGR 00579. This work was also supported by the National Science Centre, Poland, within the Project No. 2016/21/B/ST3/02242

Carbon incorporation in MOCVD of MoS2 thin films grown from an organosulfide precursor

Altres ajuts: CERCA Programme/Generalitat de CatalunyaWith the rise of two-dimensional (2D) transition-metal dichalcogenide (TMD) semiconductors and their prospective use in commercial (opto)electronic applications, it has become key to develop scalable and reliable TMD synthesis methods with well-monitored and controlled levels of impurities. While metal-organic chemical vapor deposition (MOCVD) has emerged as the method of choice for large-scale TMD fabrication, carbon (C) incorporation arising during MOCVD growth of TMDs has been a persistent concern-especially in instances where organic chalcogen precursors are desired as a less hazardous alternative to more toxic chalcogen hydrides. However, the underlying mechanisms of such unintentional C incorporation and the effects on film growth and properties are still elusive. Here, we report on the role of C-containing side products of organosulfur precursor pyrolysis in MoS2 thin films grown from molybdenum hexacarbonyl Mo(CO)6 and diethyl sulfide (CH3CH2)2S (DES). By combining in situ gas-phase monitoring with ex situ microscopy and spectroscopy analyses, we systematically investigate the effect of temperature and Mo(CO)6/DES/H2 gas mixture ratios on film morphology, chemical composition, and stoichiometry. Aiming at high-quality TMD growth that typically requires elevated growth temperatures and high DES/Mo(CO)6 precursor ratios, we observed that temperatures above DES pyrolysis onset (â 600 °C) and excessive DES flow result in the formation of nanographitic carbon, competing with MoS2 growth. We found that by introducing H2 gas to the process, DES pyrolysis is significantly hindered, which reduces carbon incorporation. The C content in the MoS2 films is shown to quench the MoS2 photoluminescence and influence the trion-To-exciton ratio via charge transfer. This finding is fundamental for understanding process-induced C impurity doping in MOCVD-grown 2D semiconductors and might have important implications for the functionality and performance of (opto)electronic devices

Delayed surgery and health related quality of life in patients with proximal femoral fracture

This study aimed to establish factors associated with delayed surgery in patients with proximal femoral fracture and to assess patients’ health-related quality of life (HRQoL) after surgery including all-cause 6-months mortality. This was a single-center, observational, prospective cohort study that included patients with a proximal femur fracture. We described patients’ HRQoL measured by EuroQoL (EQ-5D-5L and EQ-VAS) questionnaire and perioperative complications (including mortality) 6 months after surgery. We included 163 patients with a mean age of 80.5 years, the majority were women and 76.1% reported falling from their own height. The mean time between hospital admission and surgery was 8.3 days (SD 4.9 days) and the mean hospital stay was 13.5 days (SD 10.4 days). After adjustment, the principal factor associated with delayed surgery was adjournment in surgery authorization (3.7 days). EQ-5D-5L index values and the VAS score at 1 month after surgery were 0.489 and 61.1, at 3 months were 0.613 and 65.8, and at 6 months 0.662 and 66.7 respectively. Mortality at 6 months of follow-up was 11% (18 patients). In conclusion, administrative authorization was the strongest associated factor with delayed time from hospital admission to surgery. HRQoL of patients with a proximal femoral fracture improved 6 months after surgery. Trial registration: NCT04217642.</p