321034 research outputs found
Sort by
Tailored Supramolecular Additives to Control the Crystallization Process and Morphology of
No full textPerovskite films feature unique optoelectronic properties, rendering them promising for electronic devices. The properties depend on the morphology on a broad range of length scales from nanometers to millimeters, influenced by a variety of factors. However, controlling the morphology is challenging. A tailored supramolecular additive, N, N’-bis(2-aminoethyl) terephthalamide is developed to control the intermediate and perovskite crystallization of methyl ammonium lead iodide (MAPbI3) and enhance the thermal and moisture stability in the final film. Reversible coordinative interactions of the carbonyl groups with Pb2+ ions via Lewis acid-base adduct and subsequent ion–ion interactions of the peripheral ammonium groups with the perovskite grain boundaries are combined which is stabilized by a strong hydrogen bonding pattern formed between the amide moieties of the additive molecules. Adding low amounts of this additive to the precursor solution significantly decelerates the structure formation and systematically reduces the crystallite size. Slower growth of the intermediate phases and the incorporation of the additive to the grain boundary is observed with multiple time-resolved techniques. Evidence for the formation of single-molecule interlayers between the MAPbI3 crystals and the presence of directed supramolecular interaction between additive molecules is shown. Transferability of this approach to other perovskites is anticipated, paving the way to improved processing control and stability
Revealing solidification behaviour and phase transformations in FeCoNiMo and FeCoNi alloys by using high-speed video and in situ X-ray diffraction
No full textA combination of time-resolved synchrotron X-ray diffraction (XRD), high-speed video and electromagnetic levitation (EML) enabled revealing the solidification path and phase transformations in FeCoNiMo and FeCoNi alloys during heating and cooling. High-speed XRD provided direct evidence for nucleation of metastable δ-ferrite in undercooled liquid state and its quick transformation to γ-austenite. Addition of Mo clearly favours nucleation of -ferrite in FeCoNiMo melts undercooled by T of about 100 K and more. In contrast, primary crystallisation of any of and γ phases appears to be possible in FeCoNi melts at all levels of undercooling. Neither Ni nor Mo exhibit any notable effect on the growth behaviour of and phases, which remains close to the one in the FeCo base alloy. Alloying with Mo has a strong impact on the microstructure and solid state transformations in the FeCoNiMo samples such as grain refinement at T < 200 K, incomplete transformation of -austenite to -ferrite, and formation of martensite at T ≥ 330 K
Evidence of quadratic time dependence of the kinetics in a continuous order-disorder transition
No full textKinetics of order-disorder transitions including melting in low-dimensional systems is theoretically predicted to be heterogeneous that start by nucleation in defect sites at lower than homogeneous bulk-melting temperature requiring substantially lower energy barrier. We probed kinetics of such transition in thin multilayered films using x-ray scattering and in situ atomic force microscopy (AFM) studies. X-ray results show linear increase with time in in-plane separation of ordered domains while in situ AFM measurements show a linear increase in height of disordered domains with time. The structure factor of the diffraction peak reduces linearly with square of time as the material disorder
Enhanced perpendicular magnetic anisotropy through thermal phase transformation in Co/Pd/Ta multilayers
No full textMagnetic multilayers with high uniaxial anisotropy make them suitable for application in spintronic devices needing thermal stability. This investigation demonstrates that annealing at 300 °C can effectively introduce phase transformation of a paramagnetic cobalt oxide (CoO) thin film sandwiched between Pd and Ta layers into a ferromagnetic cobalt (Co) thin film. Reduced multilayers show a large recovery in magnetic moment, enhanced coercivity, and strong perpendicular magnetic anisotropy (PMA). In-plane hysteresis measurements reveal a stronger anisotropic field, highlighting the presence of considerable PMA. Surface roughness rises during annealing, while interface roughness decreases, indicating improved interface quality as confirmed by reflectivity. The rise in electron density implies a shift from CoO to Co which further confirms the reduction. Depth-selective standing wave hard x-ray photoelectron spectroscopy (HAXPES) analysis also confirms the reduction that takes place during thermal annealing and demonstrates the occurrence of the oxide-to-metallic phase transformation. The Co concentrations are significantly greater in bulk regions than in interface locations, showing that the reduction is dominated through bulk Co in the multilayer structure under an effective phase transformation during thermal-induced reduction
New Amber Fossils Indicate That Larvae of Dermestidae Had Longer Defensive Structures in the Past
No full textRepresentatives of Dermestidae (skin, larder, and carpet beetles) play a crucial role as decomposers in global ecosystems, facilitating the recycling of animal and plant biomass to sustain nutrient cycling. Despite their widespread ecological presence and functional importance, the fossil record of their larval stages has remained sparse, with previous documentation limited to occasional discoveries. This study significantly expands the larval fossil record by identifying 36 amber-preserved specimens from the Cretaceous, Eocene, and Miocene time slices, obtained from deposits distributed globally. By challenging the historical view of larval fossil rarity, we reveal morphological changes in defensive setae over geological time, demonstrating that Cretaceous and later fossil larvae possess significantly longer absolute and relative setal lengths compared to their extant counterparts. These findings, bolstered by quantitative comparisons of setal and body dimensions across fossil and extant representatives, indicate evolutionary adaptations in defensive structures dating back at least 100 million years. Our results offer new insights into the paleobiology of the group Dermestidae, highlighting how the morphology of larvae potentially reflects historical ecological pressures and resources availability. This study emphasizes the importance of integrating fossil evidence with comparative morphology to elucidate the evolutionary trajectories and functional roles of larvae in ancient terrestrial ecosystems
Search for the jet-induced diffusion wake in the quark-gluon plasma via measurements of jet-track correlations in photon-jet events in Pb+Pb collisions at = 5.02 TeV with the ATLAS detector
No full textThis paper presents a measurement of jet-track correlations in photon-jet events, using 1.72 nb of Pb+Pb data at = 5.02 TeV recorded with the ATLAS detector at the LHC. Events with energetic photon-jet pairs are selected, where the photon and jet are approximately back-to-back in azimuth. The angular correlation between jets and charged-particle tracks with transverse momentum () in the range 0.5-2.0 GeV in the hemisphere opposite to the jet, , is measured as a function of their relative pseudorapidity difference, . In central Pb+Pb collisions, these correlations are predicted to be sensitive to the diffusion wake in the quark-gluon plasma resulting from the lost energy of high- partons traversing the plasma, with a characteristic modification as a function of . The correlations are examined with different selections on the jet-to-photon ratio to select events with different degrees of energy loss. No diffusion wake signal is observed within the current sensitivity and upper limits at 95% confidence level on the diffusion wake amplitude are reported
Search for magnetic monopole pair production in ultraperipheral Pb+Pb collisions at TeV with the ATLAS detector at the LHC
No full textThis Letter presents a search for highly ionizing magnetic monopoles in 262b of ultraperipheral Pb+Pb collision data at TeV collected by the ATLAS detector at the LHC. A new methodology that exploits the properties of clusters of hits reconstructed in the innermost silicon detector layers is introduced to study highly ionizing particles in heavy-ion data. No significant excess above the background, which is estimated using a data-driven technique, is observed. Using a nonperturbative semiclassical model, upper limits at 95% confidence level are set on the cross-section for pair production of monopoles with a single Dirac magnetic charge in the mass range of 20-150 GeV. The search significantly improves on the previous cross-section limits for production of low-mass monopoles in ultraperipheral Pb+Pb collisions
Estimation of backgrounds from jets misidentified as -leptons using the Universal Fake Factor method with the ATLAS detector
No full textProcesses with -leptons in the final state are important for Standard Model measurements and searches for physics beyond the Standard Model. The ATLAS experiment at the Large Hadron Collider observes -leptons produced in proton-proton collisions only through their decay products. Data analyses involving hadronically decaying -leptons face challenges due to backgrounds from jets misidentified as -leptons. These fake -leptons are not modelled reliably by Monte Carlo simulations. Data-driven methods such as the fake-factor method allow such 'fake' backgrounds to be predicted by measuring transfer factors, known as fake factors, in data from control regions. This paper describes a new technique for determining the fake factors, the Universal Fake Factor method. It evaluates the fake factors for any signal region by using fake factors from samples enriched in different sources of fake -leptons (light-quark, gluon, -quark, and pile-up jets). Each fake factor is calculated as a linear combination of fake factors measured in these different enriched samples. For the full Run 2 data set, the systematic uncertainty of the calculated fake factors ranges from 15% to 35% depending on the -lepton's transverse momentum and charged-particle decay multiplicity
Search for a light charged Higgs boson in decays, with , in collisions at with the ATLAS detector
No full textA search for a light charged Higgs boson produced in decays of the top quark, with , is presented. This search targets the production of top-quark pairs , with (), resulting in a lepton-plus-jets final state characterised by an isolated electron or muon and at least four jets. The search exploits b-quark and c-quark identification techniques as well as multivariate methods to suppress the dominant background. The data analysed correspond to of collisions at recorded with the ATLAS detector at the LHC between 2015 and 2018. Observed (expected) 95% confidence-level upper limits on the branching fraction , assuming , are set between 0.066% (0.077%) and 3.6% (2.3%) for a charged Higgs boson with a mass between 60 and 168 GeV
A 250 Hz fast shutter with flexible sampling schemes for low-dose XPCS experiments at beamline P10 at PETRA III
No full textLow-dose X-ray photon correlation spectroscopy experiments on biological samples can be used to investigate the structure formation and underlying dynamics during phase separation, denaturation, and gelation. However, the use of intensive X-ray beams as an investigative tool is limited due to the susceptibility of biological samples to radiation-induced changes. XPCS in particular requires recording a series of high-frame-rate images to capture fast dynamics. In such cases, a fast X-ray shutter system is required to minimize beam damage to the samples by allowing a flexible delay between two images. Here we show how a fast (250 Hz) X-ray shutter system, built by the University of Siegen in close collaboration with DESY, improves low-dose XPCS capabilities at the P10 beamline at PETRA III. We found that by employing this shutter system in a logarithmic sampling scheme, the absorbed X-ray dose on the samples could be significantly decreased