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Revealing the positive role of porosity within polymeric additively manufactured lattices via X ray computed tomography
No full textThe mechanical properties of lattice geometries are known to be significantly influenced by a variety of manufacturing defects. This study investigates the influence of porosity on the mechanical behaviour of strut based body centred cubic BCC lattice structures produced with powder bed fusion with laser beam PBF LB P using PA2200 nylon powder. The study combines advanced techniques, including in situ laboratory X ray computed tomography XCT , synchrotron XCT to visualise pores and roughness in high resolution at a single cell level and image based finite element analysis FEA . The findings show that failure in thin walled AM lattices is governed by the combined effects of porosity morphology, location, surface roughness, and cross section reduction. The presence of internal porosity is found to attenuate both the amplitude of elastic modulus fluctuations and the severity of stress concentrations induced by surface irregularitie
Advanced IR polarimetry to study morphology and structure of ultrathin films
Full text linkWe demonstrate an infrared IR polarimetric approach for the detailed analysis of structural and morphological interface properties via the inspection of bands related to a pair of vibrations with perpendicular transition dipole moments. Performing polarization dependent IR spectroscopy and supplementary X ray photoelectron spectroscopy XPS measurements, freshly prepared H Si 111 surfaces as well as their long term degradation in dry air environment and after exposure to humid air are investigated. Vibrational bands related to Si H bending and Si H stretching modes are discussed in conjunction with analytical optical simulations, elucidating the status of passivation and influence of varying domain sizes and oscillator densities. Notably, the vibration related to a strong out of plane directed transition dipole moment is extremely sensitive to the morphology and structure of the surface, whereas the in plane directed band serves as a sensitive sensor for the overall status of the functionalization or passivation. Studies limited to only one of these bands may result in misleading conclusions on the passivation status, the pathway of degradation or structural properties. The analytic concept is also applied for the interpretation of vibrational bands of a methyl monolayer on Si 111 . IR polarimetry is performed in a single reflection geometry which, compared to often used ATR geometries, is not restricted to specifically designed IR transparent substrates and also gives higher flexibility to potential adaptions to measurement chambers and cells. Our approach offers advanced possibilities for analysis in the field of interface science and contributes to a deeper understanding of interface properties. It is relevant for applications relying on specific interface properties, such as sensing, catalysis, photovoltaics, and electronic
Optical, Structural, and Charge Transport Properties of Individual Ti3C2T x MXene Flakes via Micro Ellipsometry and Beyond
Full text linkMXenes have attracted significant attention in recent years due to their remarkable properties for electrochemical and optoelectronic applications. While the physical properties of MXene thin films, consisting of stacked delaminated flakes, have been extensively studied, the intrinsic MXene properties can only be derived from individual flakes. Indeed, flake interconnectivity, intercalated species, and film morphology introduce extrinsic factors that affect charge transport and optical properties. In this work, we quantitatively characterize the intrinsic optical, structural, and transport properties of micrometer sized Ti3C2Tx MXene flakes by employing our non invasive, advanced spectroscopic micro ellipsometry SME technique in the visible near infrared spectral range. SME exploits back focal plane imaging in a reflection microscopy geometry to simultaneously capture the spectral and incidence angle dependent optical response of individual flakes with up to diffraction limited lateral resolution. Through a comprehensive multi flake analysis, encompassing flakes from mono to 32 layers, we reveal thickness dependent variations in the complex refractive index and charge transport properties of ultrathin flakes, where resistivity increases as the number of Ti3C2Tx layers NoLs decreases. Flake thicknesses, non uniformities, and NoLs, determined via SME with sub nm precision, closely match nanoscale observations from atomic force microscopy AFM and scanning transmission electron microscopy STEM . Additionally, charge transport properties derived from SME agree with four probe measurements performed on single flake devices. Unveiling the intrinsic optical, structural, and charge transport properties of Ti3C2Tx MXene single flakes, this study establishes SME as a robust platform for quantitative MXene analyses, enabling precise optical metrology of MXene based optoelectronic and electrochemical device
The role of iron in the electronic configuration of mixed nickel iron oxides for the oxygen evolution reaction
No full textNickel based oxides are among the best performing catalysts for the alkaline O2 evolution reaction OER . It has long been recognized that iron enhances the catalytic activity of nickel based catalysts, though only recently has intensive research been done on the interplay between the two transition metals, leading to the excellent performance, surpassing that of either pure metal. It is still not clear how the electronic configuration in these mixed metal compounds changes to enhance their catalytic activity for the OER. We carried out a systematic study of the electronic configuration of thin film mixed metal oxides Ni 1 amp; 8722;x FexOyHz with varying contents x of iron. In this investigation we employed X ray absorption and resonant valence photoelectron spectroscopy XAS and resPES to gain knowledge on the changes induced in the electronic structure by introduction of iron, both before and after electrochemical activation. Based on density functional theory calculations we found iron species to induce a highly oxidizing environment that facilitates generation of oxo species on iron and neighbouring nickel sites. The reduced electron density around Ni O bonds creates in gap states near the Fermi level. The magnitude of these in gap states scales linearly with the OER performance and thus can be used as an activity descriptor. Contrary to literature, we see the in gap states even before electrochemical activation and conclude that they are a consequence of Ni O Fe motifs already present before anodization. Beyond 50 metal content the number of Ni O Fe motifs is decreasing again, resulting in an interval of 10 30 iron metal content to be optimal for the OE
Dynamic control of X ray core exciton resonances by Coulomb screening in photoexcited semiconductors
Full text linkExcitonics is an emerging field focused on exploiting and manipulating excitons generated through light matter interactions. Advancing the field into X ray excitonics requires precise energy and time control of core exciton resonances, enabling non linear X ray phenomena such as element specific X ray transient gratings, and advancing material characterization. To achieve these objectives, it is essential to comprehend the role of many body effects governing core exciton dynamics. In this work, we address this challenge by combining experiments with an ab initio approach specifically developed to interpret pump probe excitations. Applied to the prototypical wide bandgap semiconductor ZnO, first principles calculations reproduce experimental results and unveil how the density and distribution of photoexcited carriers dynamically tune Coulomb screening, thereby controlling core exciton binding energies, while Pauli blocking remains negligible. These insights inform a method for dynamically controlling core exciton resonances at absorption edges, achieving either a uniform spectral blue shift caused by thermalized carrier distributions on picosecond timescales, or distinct blue shifts for individual resonances, driven by time dependent carrier distributions on femtosecond timescale
Mimicking Outdoor Ion Migration in Perovskite Solar Cells A Forward Bias, No Light Accelerated Aging Approach
Full text linkPerovskite solar cells PSCs are expected to transform the photo voltaic market; however, their unproven operational stability requires urgent attention, particularly accelerated aging tests. Currently, illumination is the primary stressor in such tests. In this work, we present an accelerated aging procedure consisting of prolonged forward biasing followed by a dark storage postbias rest phase, conducted entirely in the dark. During aging under forward bias, ion migration led to impeded charge transport, macroscopic defect growth, and an adverse response of the cells to short light soaking, all of which recovered in the postbias rest phase, yet resulted in increased recombination due to redistribution of ions. We found that outdoor operation of PSCs in Berlin, Germany, over a 20 month period exhibited similar dynamics, with periods of higher temperature and irradiance spring summer aligning with the forward bias phase and cooler, dimmer periods fall amp; 8722;winter aligning with the postbias rest phase. This paves the way for accelerated aging tests that can mimic ion migration induced degradation outdoors without requiring an illumination sourc
Resolving Peak Overlap in HPLC Analysis of Glycerol Oxidation Products by Utilizing Various Detectors Application to BiVO4 Photoanodes
Full text linkGlycerol, often considered a waste byproduct of biodiesel production, holds the potential for conversion into chemicals of varying economic value, such as dihydroxyacetone DHA and formic acid FA . Hence, accurate identification and quantification of glycerol oxidation reaction GOR products are crucial for glycerol valorization research and practical deployment. High performance liquid chromatography HPLC is the preferred analytical method for these purposes due to its proficiency in separating and quantifying components in liquid mixtures, even in the presence of diluted solutes. On the other hand, peak overlap in chromatograms, especially among glycerol, DHA, and FA, poses a notable challenge in the analysis of GOR products. This study introduces a quantification method aimed at resolving peak overlaps in HPLC analysis of GOR products. Initially, we examine the optical properties of glycerol and GOR products to identify optimal wavelengths for spectrophotometric HPLC analysis and detection. Subsequently, we propose an algebraic approach to resolve the peak overlap of glycerol, DHA, and FA using various detectors, including the refractive index detector RID and the variable wavelength detector VWD . This method is applied to analyze the GOR products of undoped, nonco catalyzed nanoporous BiVO4 photoanodes, which have shown an intrinsic catalytic activity toward GOR products in previous studie
An Interdisciplinary Perspective to the Application of In Situ Operando Techniques in Photocatalytic and Electrocatalytic Processes and its Future
No full textElectro and photodriven catalysis are emerging as viable alternatives to traditional catalytic methods for producing key global consumer products across various applications. The emergence of this class of catalysis is attributable to increasing need for sustainable and ecofriendly pathways to value added chemical synthesis. The roadmap for the highly diverse and multifaceted field of catalysis continues to evolve, highlighting the growing need of understanding their physical and chemical reaction mechanism. Among the many available characterization techniques, in amp; 8201;situ and operando investigations stand out for their ability to provide detailed insights into fundamental physicochemical processes under realistic working conditions. In this article, a select group of representative energy material is discussed, where the application of different in amp; 8201;situ operando techniques successfully generates improved understanding. The primary goal is to emphasize the significance of these techniques, particularly those, which have been commonly employed in studying materials relevant to energy and environmental application
Efficient Chemo Mechanical Actuator Driven by Generation of Prestress via Glycosaminoglycans Accelerating Intrafibrillar Mineralization of Calcium Carbonate
No full textOn the optimization of the non linear lattice of BESSY III
Full text linkHelmholtz Zentrum Berlin plans to construct a fourthgeneration greenfield synchrotron light source in the early 2030s to replace BESSY II, a 1.7 GeV machine that has been running since 1998. The optimization of the linear lattice already considers non linear aspects, such as minimizing the necessary sextupole strength and, for the minimal case of two families of sextupoles, phase cancellation to reduce the resonant driving terms. In preparation for the final optimization of 8 sextupole families and the single octupole, different approaches are compared multi objective genetic optimization, for a lattice with given error sets and orbit correction on the one hand, and the minimization of the resonant driving terms and the detuning terms on the other hand. Here, analytic formulas are used, so after a single evaluation of the Twiss parameters, the driving terms can be determined for different combinations of sextupole and octupole values. The results will determine the strategy for optimizing the lattice s non linear behavior, i.e., dynamic aperture and momentum acceptance, taking the efficiency of the optimization into accoun