The thermal stability and degradation mechanism of Cu/Mo nanomultilayers.

The microstructural evolution of Cu/Mo nanomultilayers upon annealing was investigated by X-ray diffraction and transmission electron microscopy. The isothermal annealing process in the temperature ranges of 300-850°C was conducted to understand the thermal behavior of the sample and follow the transformation into a nanocomposite. Annealing at 600°C led to the initiation of grain grooving in the investigated nanomultilayer, and it degraded into a spheroidized nanocomposite structure at 800°C. The sample kept the as-deposited Cu {111}//Mo{110} fiber texture up to 850°C. The residual stress was investigated to explain microstructure changes. The activation energy of degradation kinetics of Cu/Mo nanomultilayers was determined to understand the rate-determining mechanism for the degradation of nanolaminate structures.

This study investigates the microstructural evolution of Cu/Mo nanomultilayers during vacuum annealing up to 85°C and provides important insights into their thermal stability and degradation mechanisms for development and application.

Bio-Inspired Micro- and Nano-Scale Surface Features Produced by Femtosecond Laser-Texturing Enhance TiZr-Implant Osseointegration.

Surface design plays a critical role in determining the integration of dental implants with bone tissue. Femtosecond laser-texturing has emerged as a breakthrough technology offering excellent uniformity and reproducibility in implant surface features. However, when compared to state-of-the-art sandblasted and acid-etched surfaces, laser-textured surface designs typically underperform in terms of osseointegration. This study investigated the capacity of a bio-inspired femtosecond laser-textured surface design to enhance osseointegration compared to state-of-the-art sandblasted & acid-etched surfaces. Laser-texturing facilitates the production of an organized trabeculae-like microarchitecture with superimposed nano-scale laser-induced periodic surface structures on both 2D and 3D samples of titanium-zirconium-alloy. Following a boiling treatment to modify the surface chemistry, improving wettability to a contact angle of 10°, laser-textured surfaces enhance fibrin network formation when in contact with human whole blood, comparable to state-of-the-art surfaces. In vitro experiments demonstrate that laser-textured surfaces significantly outperform state-of-the-art surfaces with a 2.5-fold higher level of mineralization by bone progenitor cells after 28 days of culture. Furthermore, in vivo evaluations reveal superior biomechanical integration of laser-textured surfaces after 28 days of implantation. Notably, during abiological pull-out tests, laser-textured surfaces exhibit comparable performance, suggesting that the observed enhanced osseointegration is primarily driven by the biological response to the surface. This article is protected by copyright. All rights reserved.

Intrinsic Formamidinium Tin Iodide Nanocrystals by Suppressing the Sn(IV) Impurities.

The long search for nontoxic alternatives to lead halide perovskites (LHPs) has shown that some compelling properties of LHPs, such as low effective masses of carriers, can only be attained in their closest Sn(II) and Ge(II) analogues, despite their tendency toward oxidation. Judicious choice of chemistry allowed formamidinium tin iodide (FASnI3) to reach a power conversion efficiency of 14.81% in photovoltaic devices. This progress motivated us to develop a synthesis of colloidal FASnI3 NCs with a concentration of Sn(IV) reduced to an insignificant level and to probe their intrinsic structural and optical properties. Intrinsic FASnI3 NCs exhibit unusually low absorption coefficients of 4 × 103 cm-1 at the first excitonic transition, a 190 meV increase of the band gap as compared to the bulk material, and a lack of excitonic resonances. These features are attributed to a highly disordered lattice, distinct from the bulk FASnI3 as supported by structural characterizations and first-principles calculations.

Bilayer Dense-Porous Li7 La3 Zr2 O12 Membranes for High-Performance Li-Garnet Solid-State Batteries.

Li dendrites form in Li7 La3 Zr2 O12 (LLZO) solid electrolytes due to intrinsic volume changes of Li and the appearance of voids at the Li metal/LLZO interface. Bilayer dense-porous LLZO membranes make for a compelling solution of this pertinent challenge in the field of Li-garnet solid-state batteries (SSB). Lithium is thus stored in the pores of the LLZO, thereby avoiding i) dynamic changes of the anode volume and ii) the formation of voids during Li stripping due to increased surface area of the Li/LLZO interface. The dense layer then additionally reduces the probability of short circuits during cell charging. In this work, a method for producing such bilayer membranes utilizing sequential tape-casting of porous and dense layers is reported. The minimum attainable thicknesses are 8-10 µm for dense and 32-35 µm for porous layers, enabling gravimetric and volumetric energy densities of Li-garnet SSBs of 279 Wh kg-1 and 1003 Wh L-1 , respectively. Bilayer LLZO membranes in symmetrical cell configuration exhibit high critical current density up to 6 mA cm-2 and cycling stability of over 160 cycles at a current density of 0.5 mA cm-2 at an areal capacity limitation of 0.25 mAh cm-2 .

Fluorinated ether electrolyte with controlled solvation structure for high voltage lithium metal batteries.

The development of new solvents is imperative in lithium metal batteries due to the incompatibility of conventional carbonate and narrow electrochemical windows of ether-based electrolytes. Whereas the fluorinated ethers showed improved electrochemical stabilities, they can hardly solvate lithium ions. Thus, the challenge in electrolyte chemistry is to combine the high voltage stability of fluorinated ethers with high lithium ion solvation ability of ethers in a single molecule. Herein, we report a new solvent, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane (DTDL), combining a cyclic fluorinated ether with a linear ether segment to simultaneously achieve high voltage stability and tune lithium ion solvation ability and structure. High oxidation stability up to 5.5 V, large lithium ion transference number of 0.75 and stable Coulombic efficiency of 99.2% after 500 cycles proved the potential of DTDL in high-voltage lithium metal batteries. Furthermore, 20 µm thick lithium paired LiNi0.8Co0.1Mn0.1O2 full cell incorporating 2 M LiFSI-DTDL electrolyte retained 84% of the original capacity after 200 cycles at 0.5 C.

Impact of Electrolyte Incorporation in Anodized Niobium on Its Resistive Switching.

The aim of this study was to develop memristors based on Nb2O5 grown by a simple and inexpensive electrochemical anodization process. It was confirmed that the electrolyte selection plays a crucial role in resistive switching due to electrolyte species incorporation in oxide, thus influencing the formation of conductive filaments. Anodic memristors grown in phosphate buffer showed improved electrical characteristics, while those formed in citrated buffer exhibited excellent memory capabilities. The chemical composition of oxides was successfully determined using HAXPES, while their phase composition and crystal structure with conductive filaments was assessed by TEM at the nanoscale. Overall, understanding the switching mechanism leads towards a wide range of possible applications for Nb memristors either as selector devices or nonvolatile memories.

Microstructure-Property Control in Functional Materials by Multilayer Design.

Smart microstructure and interface design in nanomultilayers allows to tailor physical properties like thermal stability, thermal conductivity and directional metal outflow for targeted applications. In this work, selected examples of nanomultilayer systems, constituted of alternating nanolayers of metals and/or nitrides, as precisely fabricated with variable textures, microstructures, grain sizes and internal stresses are presented. The role of the microstructure and stress state on selected functional properties is shown.

Hard x-ray photoelectron spectroscopy: a snapshot of the state-of-the-art in 2020.

Hard x-ray photoelectron spectroscopy (HAXPES) is establishing itself as an essential technique for the characterisation of materials. The number of specialised photoelectron spectroscopy techniques making use of hard x-rays is steadily increasing and ever more complex experimental designs enable truly transformative insights into the chemical, electronic, magnetic, and structural nature of materials. This paper begins with a short historic perspective of HAXPES and spans from developments in the early days of photoelectron spectroscopy to provide an understanding of the origin and initial development of the technique to state-of-the-art instrumentation and experimental capabilities. The main motivation for and focus of this paper is to provide a picture of the technique in 2020, including a detailed overview of available experimental systems worldwide and insights into a range of specific measurement modi and approaches. We also aim to provide a glimpse into the future of the technique including possible developments and opportunities.

Cost-effective sol-gel synthesis of porous CuO nanoparticle aggregates with tunable specific surface area.

CuO nanoparticles (NPs) are applied in various key technologies, such as catalysis, energy conversion, printable electronics and nanojoining. In this study, an economic, green and easy-scalable sol-gel synthesis method was adopted to produce submicron-sized nanoporous CuO NP aggregates with a specific surface area > 18 m²/g. To this end, a copper-carbonate containing precursor was precipitated from a mixed solution of copper acetate and ammonia carbonate and subsequently calcinated at T ≥ 250 °C. The thus obtained CuO nanopowder is composed of weakly-bounded agglomerates, which are constituted of aggregated CuO NPs with a tunable size in the range of 100-140 nm. The CuO aggregates, in turn, are composed of equi-axed primary crystallites with a tunable crystallite size in the range of 20-40 nm. The size and shape of the primary CuO crystallites, as well as the nanoporosity of their fused CuO aggregates, can be tuned by controlled variation of the degree of supersaturation of the solution via the pH and the carbonate concentration. The synthesized submicron-sized CuO aggregates can be more easily and safely processed in the form of a solution, dispersion or paste than individual NPs, while still offering the same enhanced reactivity due to their nanoporous architecture.

Structural properties of ultrathin SrO film deposited on SrTiO3.

The role of epitaxial strain and chemical termination in selected interfaces of perovskite oxide heterostructures is under intensive investigation because of emerging novel electronic properties. SrTiO   3 (STO) is one of the most used substrates for these compounds, and along its < 001 > direction allows for two nonpolar chemical terminations: TiO2 and SrO. In this paper, we investigate the surface morphology and crystal structure of SrO epitaxial ultrathin films: from 1 to about 25 layers grown onto TiO   2 -terminated STO substrates. X-ray diffraction and transmission electron microscopy analysis reveal that SrO grows along its [ 111 ] direction with a 4% out-of-plane elongation. This large strain may underlay the mechanism of the formation of self-organized pattern of stripes that we observed in the initial growth. We found that the distance between the TiO   2 plane and the first deposited SrO layer is 0.27 ( 3 ) nm, a value which is about 40% bigger than in the STO bulk. We demonstrate that a single SrO-deposited layer has a different morphology compared to an ideal atomically flat chemical termination.

Anodizing of Self-Passivating W xTi1- x Precursors for W xTi1- xO n Oxide Alloys with Tailored Stability.

TiO2 and WO3 are two of the most important, industrially relevant earth-abundant oxides. Although both materials show complementary functionality and are promising candidates for similar types of applications such as catalysis, sensor technology, and energy conversion, their chemical stability in reactive environments differs remarkably. In this study, anodic barrier oxides are grown on solid-solution W xTi1- x alloy precursors covering a wide compositional range (0 ≤ x ≤ 1) with the goal of creating functional oxides with tailored stability. A strong Ti-cation enrichment in the surface region of the grown W xTi1- xO n layer is observed, which can be controlled by both the anodizing conditions and precursor composition. For Ti concentrations above 50 at. %, a continuous nanometer-thick TiO2 protective coating is achieved on top of a homogeneous W xTi1- xO n film as evidenced by X-ray photoelectron spectroscopy and transmission electron microscopy analyses. A comprehensive electrochemical assessment demonstrates a very stable passivation of the surface in both acidic and alkaline environments. This increase in chemical stability correlates directly with the presence of this protective TiO2 film. The results of this work provide insights into the oxidation behavior of W1- xTi x alloys, but more importantly demonstrate how controlled oxidation of self-passivating alloys can lead to oxide alloys with thin, protective surface layers that otherwise would require more sophisticated deposition methods.

Tailoring Fast Directional Mass Transport of Nano-Confined Ag-Cu Alloys upon Heating: Effect of the AlN Barrier Thickness.

This study addresses the phase stability and atomic mobility of Ag-Cu40at.% nano-alloys confined by AlN in a nanomultilayered configuration during thermal treatment. To this end, nanomultilayers (NMLs) with a fixed Ag-Cu40at.% nanolayer thickness of 8 nm and a AlN barrier nanolayer with variable thickness of 4, 8, or 10 nm were deposited by magnetron sputtering on sapphire substrates and subsequently isothermally annealed for 5 or 20 min in air in the range of 200-500 °C. The microstructure of the as-deposited and heat-treated NMLs was analyzed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. Annealing of the thicker AlN barrier layers at T > 300 °C leads to the formation of an interconnected network of line-shaped Cu(O) protrusions on the annealed NML surface. The well-defined outflow pattern of Cu(O) originates from the thermally induced surface cracking of the top AlN barriers with subsequent fast mass transport of Cu along the Cu/AlN interfaces toward the surface cracks. The thinnest (i.e., 4 nm thick) AlN barrier layers exhibit a relatively open grain boundary structure and act as nanoporous membranes upon heating, resulting in the formation of a dense and homogenous distribution of Cu(O) and Ag droplets on the NML surface. These findings demonstrate that the microstructure (i.e., layer thicknesses, interface coherency, and texture) of hybrid nanolaminates can be tuned to provide defined pathways for fast, directional transport of the confined metal to the surface at relatively low temperatures, which might open new routes for low-temperature bonding of micro- and nano-scaled systems.

Orbital Ordering of the Mobile and Localized Electrons at Oxygen-Deficient LaAlO3/SrTiO3 Interfaces.

Interfacing different transition-metal oxides opens a route to functionalizing their rich interplay of electron, spin, orbital, and lattice degrees of freedom for electronic and spintronic devices. Electronic and magnetic properties of SrTiO3-based interfaces hosting a mobile two-dimensional electron system (2DES) are strongly influenced by oxygen vacancies, which form an electronic dichotomy, where strongly correlated localized electrons in the in-gap states (IGSs) coexist with noncorrelated delocalized 2DES. Here, we use resonant soft-X-ray photoelectron spectroscopy to prove the eg character of the IGSs, as opposed to the t2g character of the 2DES in the paradigmatic LaAlO3/SrTiO3 interface. We furthermore separate the d xy and d xz/d xz orbital contributions based on deeper consideration of the resonant photoexcitation process in terms of orbital and momentum selectivity. Supported by a self-consistent combination of density functional theory and dynamical mean field theory calculations, this experiment identifies local orbital reconstruction that goes beyond the conventional eg- vs-t2g band ordering. A hallmark of oxygen-deficient LaAlO3/SrTiO3 is a significant hybridization of the eg and t2g orbitals. Our findings provide routes for tuning the electronic and magnetic properties of oxide interfaces through "defect engineering" with oxygen vacancies.

Modeling of Interface and Internal Disorder Applied to XRD Analysis of Ag-Based Nano-Multilayers.

Multilayered structures are a promising route to tailor electronic, magnetic, optical, and/or mechanical properties and durability of functional materials. Sputter deposition at room temperature, being an out-of-equilibrium process, introduces structural defects and confers to these nanosystems an intrinsic thermodynamical instability. As-deposited materials exhibit a large amount of internal atomic displacements within each constituent block as well as severe interface roughness between different layers. To access and characterize the internal multilayer disorder and its thermal evolution, X-ray diffraction investigation and analysis are performed systematically at differently grown Ag-Ge/aluminum nitride (AlN) multilayers (co-deposited, sequentially deposited with and without radio frequency (RF) bias) samples and after high-temperature annealing treatment. We report here on model calculations based on a kinematic formalism describing the displacement disorder both within the multilayer blocks and at the interfaces to reproduce the experimental X-ray diffraction intensities. Mixing and displacements at the interface are found to be considerably reduced after thermal treatment for co- and sequentially deposited Ag-Ge/AlN samples. The application of a RF bias during the deposition causes the highest interface mixing and introduces random intercalates in the AlN layers. X-ray analysis is contrasted to transmission electron microscopy pictures to validate the approach.