Stratospheric aerosol injection could mitigate harmful effects of global warming, but could have undesirable side effects, such as warming the stratosphere and depleting the ozone layer. We explore the potential benefits of solid alumina and calcite particles as alternatives to sulfate aerosols by using an experimentally informed aerosol-chemistry-climate model. Compared to sulfur dioxide, injection of solids reduces stratospheric warming by up to 70% and diffuse radiation by up to 40%, highlighting their potential benefits. Achieving -1 W m-2 of radiative forcing would likely result in very small ozone changes, but sizable uncertainties remain. These arise from poorly understood heterogeneous chemical and microphysical processes, which, under less likely assumptions, could lead to larger global ozone column changes between -14% and +4%. Our work provides recommendations for improving the understanding of stratospheric aerosol injection using materials other than sulfur dioxide, and underscores the need for kinetic laboratory studies.

A Pt skin effect, i.e., an enrichment of Pt within the first 1-2 nm from the surface, is observed in as-prepared electrodeposited Ni-rich Ni-Pt thin films. This effect, revealed by Rutherford backscattering (RBS), is present for both dense thin films and mesoporous thin films synthesized by micelle-assisted electrodeposition from a chloride-based electrolyte. Due to the Pt skin effect, the Ni-rich thin films show excellent stability at the hydrogen evolution reaction (HER) in acidic media, during which a gradient in the Pt/Ni ratio is established along the thickness of the thin films, while the activity at the HER remains unaffected by this structural change. Further characterization by elastic recoil detection with He ions analysis shows that hydrogen profiles are similar to those of Pt: a surface hydrogen peak coincides with the Pt skin, and a gradient in hydrogen concentration is established during HER in acidic media, together with a considerable uptake in hydrogen. A comparative study shows that in alkaline media, hydrogen evolution has little to no effect on the structural properties of the thin films, even for much longer times of exposure. The mesoporous thin films, in addition to their higher efficiency at HER compared to dense thin films, also show lower internal stress, as determined by Rietveld refinement of grazing incidence X-ray diffraction patterns. The latter also reveal a fully single-phase and nanocrystalline structure for all thin films with varying Ni contents.

<p>Recent studies have suggested that injection of solid particles such as alumina (Al<sub>2</sub>O<sub>3</sub>) and calcite (CaCO<sub>3</sub>) instead of SO<sub>2</sub> for stratospheric aerosol intervention could reduce some of the adverse side effects of SAI such as ozone depletion, stratospheric heating, and changes in diffuse radiation. However, the expected improvements from alteration of stratospheric chemistry are subject to large uncertainties. We constrain some of these uncertainties by experimental work on calcite particles using elastic recoil detection analysis (ERDA) and in-situ experiments using X-ray photoelectron spectroscopy (XPS). Subsequently, we use a global aerosol-chemistry climate model that, for the first time, interactively couples microphysical and chemical processes of solid calcite and alumina particles as well as liquid sulfuric acid aerosols with model radiation and transport. Notably, SAI by solid particles only leads to more effective radiative forcing per aerosol burden compared to sulfuric acid aerosols, not per injected mass. However, reduced stratospheric warming remains a major advantage of solid particles. Furthermore, different assumptions on the heterogeneous chemistry of solid particles, based on the available experimental data, result in drastically different impacts on stratospheric composition, in particular, ozone. For alumina particles, which are thought to not undergo chemical aging during their stratospheric residence time we present a sensitivity analysis for heterogenous reactions to quantify uncertainty. For the alkaline calcite particles, which are thought to undergo chemical aging in the stratosphere via reaction with acids (e.g., HCl, HNO<sub>3</sub>, H<sub>2</sub>SO<sub>4</sub>) we find even larger uncertainties due to unknown reaction pathways and highly uncertain rates under stratospheric conditions. The large uncertainty in predicted stratospheric ozone changes can only be reduced via substantial additional laboratory experiments under stratospheric conditions, i.e., partial pressures of relevant gases (e.g., HCl, HNO<sub>3</sub>, H<sub>2</sub>SO<sub>4</sub>), temperatures < 220 K, relative humidity < 1% and realistic UV irradiance. From the present perspective, sulfur-based SAI has significantly lower uncertainty than injection of solid particles, which have significantly reduced stratospheric heating but very large uncertainties in impacts on stratospheric composition.</p>

Oxynitrides are promising materials for visible light-driven water splitting. However, limited information regarding their electron-momentum resolved electronic structure exists. Here, with the advantage of the enhanced probing depth and chemical state specificity of soft-X-ray ARPES, we determine the electronic structure of the photocatalyst oxynitride LaTiO 2 N and monitor its evolution as a consequence of the oxygen evolution reaction. After the photoelectrochemical reactions, we observe a partial loss of Ti- and La-N 2p states, distortions surrounding the local environment of titanium atoms and, unexpectedly, an indication of an electron accumulation layer at or near the surface, which may be connected with either a large density of metallic surface states or downward band bending. The distortions and defects associated with the titanium 3d states lead to the trapping of electrons and charge recombination, which is a major limitation for the oxynitride LaTiO 2 N. The presence of an accumulation layer and its evolution suggests complex mechanisms of the photoelectrochemical reaction, especially in cases where co-catalysts or passivation layers are used.

Atomic layer deposition is an appealing deposition technology for the fabrication of protective coatings for various applications, including semiconductor manufacturing chambers and related metallic parts with complex three-dimensional topographies, where a key requirement is (thermo)mechanical robustness of the coatings. Here, we study the mechanical properties of atomic-layer-deposited Al2O3, Y2O3, and their nanolaminate (NL) coatings on an Al metal substrate. Tensile straining experiments accompanied by in situ optical and scanning electron microscopy indicate that the fragmentation onset of 100 nm thick coatings can be tailored in the strain range of 1.3–2.1% by controlling the layer structure and composition of the NLs, such that a higher Al2O3 content, denser layer spacing, and amorphization favor higher crack onset strain. Although the fracture toughness of Al2O3 and Y2O3 is found to be similar, KIC = 1.3 MPa·m1/2, the (substantially tensile) intrinsic residual stress for Y2O3 is a disadvantage for applications, where applied tensile stresses are to be expected. The films adhere well to the Al substrate as significant delamination of the films is not observed in the tensile experiments; the analysis of the fragmentation patterns indicates that insertion of an Al2O3 layer at the film/substrate interface can enhance the interface toughness. High-temperature (425 °C) tensile experiments for the Al2O3 films indicate good temperature tolerance for the coatings, and in comparison to the room-temperature data, a significant difference is seen in the increase of saturation crack spacing. Moreover, the structure and composition of the films are studied in detail through X-ray reflection and diffraction, transmission electron microscopy, Rutherford backscattering spectrometry, and elastic recoil detection analysis. The results are particularly interesting for protective coating applications.

Different SrTiO3 thin films are investigated to unravel the nature of ultra-low conductivities recently found in SrTiO3 films prepared by pulsed laser deposition. Impedance spectroscopy reveals electronically pseudo-intrinsic conductivities for a broad range of different dopants (Fe, Al, Ni) and partly high dopant concentrations up to several percent. Using inductively-coupled plasma optical emission spectroscopy and reciprocal space mapping, a severe Sr deficiency is found and positron annihilation lifetime spectroscopy revealed Sr vacancies as predominant point defects. From synchrotron-based X-ray standing wave and X-ray absorption spectroscopy measurements, a change in site occupation is deduced for Fe-doped SrTiO3 films, accompanied by a change in the dopant type. Based on these experiments, a model is deduced, which explains the almost ubiquitous pseudo-intrinsic conductivity of these films. Sr deficiency is suggested as key driver by introducing Sr vacancies and causing site changes (Fe-Sr and Ti-Sr) to accommodate nonstoichiometry. Sr vacancies act as mid-gap acceptor states, pinning the Fermi level, provided that additional donor states (most probably TiSr center dot center dot\[{\rm{Ti}}_{{\rm{Sr}}}<^>{ \bullet \bullet }\]) are present. Defect chemical modeling revealed that such a Fermi level pinning also causes a self-limitation of the Ti site change and leads to a very robust pseudo-intrinsic situation, irrespective of Sr/Ti ratios and doping.

The wettability and the control of the contact angle of surfaces are important for various applications. Materials with a water contact angle less than or greater than 90 deg are hydrophilic or hydrophobic, respectively. Most of the binary oxides are hydrophilic, but oxides of rare earth metals and metal atoms with low electronegativity have hydrophobic surfaces. Yttria is one of the materials predicted to have hydrophobic properties. In this work, we investigated the wettability of ion-beam-sputtered Yttria thin films. The measured water contact angles were between 67 degrees and 96 degrees. The concentration of the embedded argon atoms was found to influence the contact angle.

Perovskite oxynitride semiconductors have attracted huge interest recently as promising photoelectrode materials for photoelectrochemical (PEC) water splitting. Depicted by, the extensive studies of the PEC activity of oxynitride powder-based photoelectrodes and/or deposited thin-film electrodes. High-crystalline-quality, oxynitride thin films grown by physical vapor deposition are ideal model systems to study the fundamental physical and chemical properties of the surface of these materials, including their evolution. In this work, using a combination of high-sensitivity low-energy ion scattering (LEIS) and X-ray photoelectron spectroscopy (XPS), we monitor surface evolution of LaTiOxNy (LTON) and CaNbOxNy (CNON) thin films before and after the PEC characterizations. The as-prepared epitaxial LTON films show a preferential LaO termination at the surface layers, followed by a Ti-enriched subsurface. Whereas, the polycrystalline CNON thin films exhibit a non-uniform surface, with a mixed surface termination and a significant Ca-segregated subsurface. After the PEC characterizations, additional precipitated LaO species are found on the outer surface of the LTON epitaxial films. However, no significant surface change is observed on the polycrystalline CNON films by LEIS. The XPS analysis shows, an increase of the oxidized Ti and Nb cations (Ti4+ and Nb5+) after the PEC reaction in the LTON and CNON films, respectively. The initial drops in photocurrent for the LTON and CNON films are attributed to the changes in the surface chemical status. This work provides insight into the surface characteristics and evolution of LTON and CNON oxynitride thin films as photoelectrodes for PEC applications.

A B S T R A C T A special gilding material called Zwischgold has been frequently observed in medieval gilded artefacts. As a bilayer metal leaf made from gold and silver, it exhibits similar but slightly paler golden colour tone compared to pure gold. Zwischgold surface can be darkened quickly due to the corrosion of its silver base. Despite its frequent mentions in medieval guild statutes, the production of Zwischgold and its important technological parameters have been under a veil of secrecy since the Middle Ages. Here, we examine the thicknesses and materials proportions of medieval Zwischgold, through high-resolution scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX) on a large number of samples taken from late medieval gilded sculptures. We observe that medieval Zwischgold contains ultra-thin gold layers in a thickness range of ca. 20-50 nm, indicating the employment of high-precision technologies in manufacturing of delicate art materials in the late medieval period. It further clarifies some ambiguity in gilding history, regarding the colour appearance of medieval Zwischgold. As supportive data, Rutherford backscattering spectrometry (RBS) and scanning transmission electron microscopy (STEM) were applied, in order to confirm the precision and accuracy of the sample preparation and the SEM analysis. (c) 2021 The Author(s). Publi? par Elsevier Masson SAS. Cet article est publi? en Open Access sous licence CC BY (http://creativecommons.org/licenses/by/4.0/).

LaTiO x N y oxynitride thin films are employed to study the surface modifications at the solid-liquid interface that occur during photoelectrocatalytic water splitting. Neutron reflectometry and grazing incidence x-ray absorption spectroscopy were utilised to distinguish between the surface and bulk signals, with a surface sensitivity of 3 nm. Here we show, contrary to what is typically assumed, that the A cations are active sites that undergo oxidation at the surface as a consequence of the water splitting process. Whereas, the B cations undergo local disordering with the valence state remaining unchanged. This surface modification reduces the overall water splitting efficiency, but is suppressed when the oxynitride thin films are decorated with a co-catalyst. With this example we present the possibilities of surface sensitive studies using techniques capable of operando measurements in water, opening up new opportunities for applications to other materials and for surface sensitive, operando studies of the water splitting process.

In the previous paper (Part I), the colorimetry and interferometric microscopy measurements on modern gold leaf models have revealed that the visual appearance of a gilded surface, both burnished and unburnished, depends strongly on the substrate type, surface roughness and texture, but not on the colour of the substrate. In this second part, we investigate the materials compositions and technical specifications of medieval gold leaf through combining literature sources and materials analysis such as scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM-EDX) on samples taken from gilded artefacts. Our study shows that the late medieval gold leaf has a high purity of about 23.7 carat and has an average thickness of 160 nm (with a peak value of 138 nm), purer and thicker than the modern gold leaves studies in Part I. Supportive Rutherford backscattering spectrometry (RBS) measurements on gilded models confirms the accuracy and reliability of the SEM-EDX observations on the medieval gold leaf samples. We additionally present observations of a rarely recorded special variant of medieval gold leaf – “fine reinforced gold leaf”. Combined with the findings from Part I, we conclude that light penetrating the medieval gold leaf and reflected from the substrate could not be a significant, or even perceptible contribution to the visual appearance of the gilding. We argue that the misconception surrounding the correlation between the substrate colour and the gilded surface appearance can be attributed to the historical development of gilding and polychromy technologies.

TiO$_2$ and WO$_3$ are two of the most important earth-abundant electronic materials with applications in countless industries. Recently alloys of WO$_3$ and TiO$_2$ have been investigated leading to improvements of key performance indicators for a variety of applications ranging from photo-electrochemical water splitting to electrochromic smart windows. These positive reports and the complexity of the ternary W-Ti-O phase diagram motivate a comprehensive experimental screening of this phase space. Using combinatorial thermal oxidation of solid solution W$_{1-x}$Ti$_{x}$ precursors combined with bulk and surface analysis mapping we investigate the oxide phase formation and surface passivation of tungsten titanium oxide in the entire compositional range from pure WO$_3$ to TiO$_2$. The system shows a remarkable structural transition from monoclinic over cubic to tetragonal symmetry with increasing Ti concentration. In addition, a strong Ti surface enrichment is observed for precursor Ti-concentrations in excess of 55 at.%, resulting in the formation of a protective rutile-structured TiO$_2$ surface layer. Despite the structural transitions, the optical properties of the oxide alloys remain largely unaltered demonstrating an independent control of multiple functional properties in W$_{1-x}$Ti$_{x}$O$_{n}$. The results from this study provide valuable guidelines for future development of W$_{1-x}$Ti$_{x}$O$_{n}$ for electronic and energy applications, but also novel engineering approaches for surface functionalization and additive manufacturing of Ti-based alloys.

With high resistance against interdiffusion, electromigration, creep and fatigue, single-crystal films of refractory metals are highly desired for applications in opto- and micro-electronic devices. Their fabrication is nevertheless very challenging, primarily due to their high melting points. Requiring no external thermal input, ion-irradiation presents an alternative route for single-crystal films by converting from their polycrystalline counterparts through irradiation-induced selective grain growth. The incomplete poly- to single-crystal conversion is however a common problem which limits the application of this method. Here we use refractory W thin films, the element with the highest melting point, as a model system. We systematically investigate the influences of film microstructure (texture and grain size) and irradiation temperature (77 K and room temperature) on the evolution of selective grain growth under 4.5 MeV Au+ ion-irradiation. We find that the driving force for selective grain growth can be increased by narrowing the texture spread of the films, refining the grain size and decreasing the irradiation temperature. Following this guidance, a complete conversion of a polycrystalline W film into a single crystal is achieved. This study therefore provides insights into the mechanism of selective grain growth and proves that it is an effective technique for microstructure engineering in thin film materials. The concepts can be applied to all crystalline metal films. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cell research, an asymmetric crystallization profile is often obtained after annealing, resulting in a bilayered - or double-layered - CZTSSe absorber. So far, only segregated pieces of research exist to characterize the appearance of this double layer, its formation dynamics, and its effect on the performances of devices. In this work, we review the existing research on double-layered kesterites and evaluate the different mechanisms proposed. Using a cosputtering-based approach, we show that the two layers can differ significantly in morphology, composition, and optoelectronic properties and complement the results with a large statistical data set of over 850 individual CZTS solar cells. By reducing the absorber thickness from above 1000 to 300 nm, we show that the double-layer segregation is alleviated. In turn, we see a progressive improvement in the device performance for lower thickness, which alone would be inconsistent with the well-known case of ultrathin CIGS solar cells. We therefore attribute the improvements to the reduced double-layer occurrence and find that the double layer limits the efficiency of our devices to below 7%. By comparing the results with CZTS grown on monocrystalline Si substrates, without a native Na supply, we show that the alkali metal supply does not determine the double-layer formation but merely reduces the threshold for its occurrence. Instead, we propose that the main formation mechanism is the early migration of Cu to the surface during annealing and formation of Cu2-xS phases in a self-regulating process akin to the Kirkendall effect. Finally, we comment on the generality of the mechanism proposed by comparing our results to other synthesis routes, including our own in-house results from solution processing and pulsed laser deposition of sulfide- and oxide-based targets. We find that although the double-layer occurrence largely depends on the kesterite synthesis route, the common factors determining the double-layer occurrence appear to be the presence of metallic Cu and/or a chalcogen deficiency in the precursor matrix. We suggest that understanding the limitations imposed by the double-layer dynamics could prove useful to pave the way for breaking the 13% efficiency barrier for this technology.

In the previous paper (Part I), the colorimetry and interferometric microscopy measurements on modern gold leaf models have revealed that the visual appearance of a gilded surface, both burnished and unburnished, depends strongly on the substrate type, surface roughness and texture, but not on the colour of the substrate. In this second part, we investigate the materials compositions and technical specifications of medieval gold leaf through combining literature sources and materials analysis such as scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM–EDX) on samples taken from gilded wooden sculptures. Our study shows that the late medieval gold leaf has a high purity of about 23.7 carat and has an average thickness of 160 nm (with a peak value of 138 nm), purer and thicker than the modern gold leaves studies in Part I. Supportive Rutherford backscattering spectrometry (RBS) measurements on gilded models confirms the accuracy and reliability of the SEM–EDX observations on the medieval gold leaf samples. We additionally present observations of a rarely recorded special variant of medieval gold leaf—“fine reinforced gold leaf”. Combined with the findings from Part I, we conclude that light penetrating the medieval gold leaf and reflected from the gilding substrate could not be a significant, or even perceptible contribution to the visual appearance of the gilding. We argue that the misconception surrounding the correlation between the substrate colour and the gilded surface appearance can be attributed to the historical development of gilding and polychromy technologies.

AbstractElectron probe and ion probe are the two most used instruments for in situ analysis of halogens in geological materials. The comparison of these two methods on widely distributed glass standards (example: MPI-DING glasses, Jochum et al., G-cubed, 2006) provides a basis for establishing laboratory method, independent geochemical data sets for these elements. We report analyses of F, S, and Cl concentrations in three geological glass samples (EPMA) and 10 referenced standards (EPMA and SIMS). Furthermore, F and Cl absolute abundances have been determined independently for three of the standards (KL2-G, ATHO-G, and KE12), via heavy ion elastic recoil detection analysis (HIERDA), to certify the accuracy of the cross-calibration EPMA-SIMS. The detection limits for EPMA are a 150 μg·g-1 for F, 20 μg·g-1 for S and Cl, and for SIMS < 48 μg·g-1 for F, < 3 μg·g-1 for S, and <19 μg·g-1 for Cl. On SiO2-rich glass-standards, F and Cl measurements by HIERDA highlight a weak matrix effect during SIMS analysis of F and Cl. With the HIERDA independently measured value, we therefore propose an alternative calibration function to empirically correct this matrix effect on the SIMS measurements of F, S, and Cl.

The high ionic conductivity and wide electrochemical stability of the lithium garnet Li 7 La 3 Zr 2 O 12 (LLZO) make it a viable solid electrolyte for all‐solid‐state lithium batteries with superior capacity and power densities. Contrary to common ceramic processing routes of bulk pellets, thin film solid electrolytes could enable large‐area fabrication, and increase energy and power densities by reducing the bulkiness, weight and critically, the area‐specific resistance of the electrolyte. Fabrication of LLZO films has nonetheless been challenging because of lithium losses and formation of impurity phases that result in low densities and poor ionic conductivities as compared to bulk pellets. Here, a scalable method for fabricating submicron films of LLZO employing co‐sputtering from doped LLZO and Li 2 O targets is presented. A record ionic conductivity of 1.9 × 10 −4 S cm –1 is measured for dense and uniform cubic‐phase Ga‐substituted LLZO films annealed at 700 °C in oxygen, which is comparable to the values in high‐temperature sintered pellets and outperforms by one order of magnitude the latest record for LLZO thin films as well as the typical conductivities in the well‐established LiPON electrolyte. This result is an important milestone to realize all‐vacuum deposited solid‐state batteries with higher power density.

Typical low-temperature frustrated triangular antiferromagnet CuFeO2 is attracting extensive interest due to its narrow-band-gap semiconductor properties. High-quality and impurity-free CuFeO2 epitaxial thin films would be preferable for fundamental studies on the physical and chemical properties. However, the heteroepitaxial growth of impurity-free CuFeO2 thin films has been a significant challenge due to its narrow formation window in the Cu–Fe–O system as well as the metastable nature of the Cu1+ cations. This work reports for the first time the fabrication and characterization of high-quality and impurity-free (00.1)-oriented CuFeO2 epitaxial thin films grown with relaxed interfaces on (00.1) sapphire substrates by pulsed laser deposition. Below the critical thickness of around 16 nm, the films exhibit a rhombohedral structure with relatively good crystalline quality where all Cu ions appear to be in the 1+ oxidation state, while the rocking curves display a narrow full width at half maximum of about 0.11°. Increasing the thickness, the (111)-oriented γ-Fe2O3 nanograins grow embedded in the CuFeO2 films. Here, an excess Fe3+-assisted growth mechanism is proposed to explain the iron oxide grain formation. This study provides insight into the heteroepitaxial growth of relaxed CuFeO2 thin films with high purity and crystalline quality as an ideal sample design to characterize the fundamental properties of this material in view of potential device applications.

Photocharge extraction in the visible-light energy range is essential to sustain efficient photoelectrochemical processes driven by solar irradiation of photoanode materials. Recent literature has shown that crystallographic orientation can have a significant impact on the extraction of photocharges, though the difficulty of discriminating bulk and surface orientation effects on charge extraction often complicates any understanding as to the role each orientation may play. Our catalyst-decorated thin-film model system allows us to cleanly separate charge extraction limiting effects of bulk vs. surface orientation. As a result, our study reveals an anisotropic visible-light induced photocharge extraction dependence on the bulk crystallographic orientation in LaTiO2N (LTON) photoanodes. In particular, the visible-light induced photocharge extraction is 30% higher for (011) films than (001) oriented thin films. Computational analysis of the LTON band diagram suggests that this is due to a higher potential energy and photocharge mobility along the (011) direction.