Modifying mixed ionic and electronic conductor (MIEC) surfaces has gained attention as a strategy to enhance oxygen exchange reaction kinetics and attenuate surface degradation. This study investigates the high-temperature stability and cation segregation behavior of La0.6Sr0.4CoO3-delta (LSC) thin films modified with similar to 0.5 nm CaO and SnO2 overlayers after annealing at 800 degrees C. Combining Time-of-flight secondary ion mass spectrometry (ToF-SIMS), X-ray photoelectron spectroscopy (XPS), Secondary electron microscopy (SEM)/Energy dispersive X-ray analysis (EDX), and Auger-Meitner electron spectroscopy (AMES), we provide a comprehensive picture of surface and sub-surface changes, segregation, interdiffusion, and secondary phase formation. Our results show that Sr enrichment during high-temperature annealing occurs at the surface regardless of the overlayer. However, significant differences in surface morphology emerge depending on the overlayer. Our results indicate that surface acidity, modulated by the oxide overlayer, is of fundamental importance for the formation of secondary phases and determines the interaction with acidic gas-phase impurities. These findings suggest that surface modifications are not a viable strategy to prevent Sr segregation at high temperatures. However, they can lead to complicated surface dynamics and significantly change the secondary phase formation processes induced by Sr segregation.

Silicon nitride SiN_x nanomechanical resonators are central to sensing, quantum technologies, and fundamental physics experiments due to their exceptional mechanical quality factors (Q). However, as resonator thickness approaches the nano-scale, surface-related dissipation limits performance. Here, we investigate the role of surface chemistry in low-stress Si-rich SiNx membranes through a combination of hydrofluoric acid (HF) etching and trimethylchlorosilane (TMCS) silanization, correlated with surface characterization and mechanical measurements. Preliminary analysis by TEM-EELS, XPS, RBS/ERDA, and XRR reveals a native oxide surface layer (1-2 nm). Surface modification by HF and TMCS was subsequently evaluated using XPS, photothermal FTIR, contact-angle measurements, and intrinsic quality factor (Q_int) characterization. While HF etching effectively removes the native oxide and TMCS introduces hydrophobic Si-(CH_3)_3 termination, neither oxide thickness nor surface energy correlates with mechanical dissipation. TMCS treatments produce the largest enhancements, increasing Q_int by up to 50

Insulating oxides are among the most abundant solid materials in the universe1-3. Of the many ways in which they influence natural phenomena, perhaps the most consequential is their capacity to transfer electrical charge during contact4-10-which occurs even between samples of the same oxide-yet the symmetry-breaking parameter that causes this remains unidentified11,12. Here we show that adventitious carbonaceous molecules adsorbed from the environment are the symmetry-breaking factor in same-material oxide contact electrification (CE). We use acoustic levitation to measure charge exchange between a sphere and a plate composed of identical amorphous silicon dioxide (SiO2). Although charging polarity is random for co-prepared samples, we control it with baking or plasma treatment. Observing the charge-exchange relaxation afterwards, we see dynamics over a timescale of hours and connect this directly to the presence of adventitious carbon with time-of-flight mass spectrometry, low-energy ion scattering and infrared spectroscopy. Going further, we confirm that adventitious carbon can even determine charge exchange among different oxides. Our results identify the symmetry-breaking parameter that causes insulating oxides to exchange charge in settings ranging from desert sands4 to volcanic plumes5,6, while simultaneously highlighting an overlooked factor in CE more broadly.

Two-dimensional (2D) layered materials such as transition metal dichalcogenides (e.g., MoS2, WS2) and MXenes (e.g., Ti3C2Tx), as well as hybrids of these materials are the focus of current research in solid lubrication due to their outstanding performance. Transition metal carbo-chalcogenides (TMCCs), consisting of an MXene core and a TMD-like surface, represent an inherent combination of TMDs and MXenes without the need to construct hybrids out of the individual layers. Due to their layered structure and surface chemistry, favorable tribological properties can be expected from these novel materials. Here, multilayer Ta2S2C and Nb2S2C TMCCs are deposited solely as a powder onto a steel substrate and their tribological properties under linear sliding against different counterbodies, i.e., Al2O3, SiC, 100Cr6, and polytetrafluoroethylene (PTFE) are discussed. Advanced materials characterization techniques are used to detect the presence of TMCCs inside the wear tracks and to reveal their 2D structure within the tribofilm. Finally, density functional theory (DFT) simulations are used to unravel the easy shearability of TMCCs at the nanoscale. The results demonstrate the great potential of this new 2D material family, which also offers many possibilities for defined tuning of the solid-solid interface.

When two insulating, neutral materials are contacted and separated, they exchange electrical charge1. Experiments have long suggested that this 'contact electrification' is transitive, with different materials ordering into 'triboelectric series' based on the sign of charge acquired2. At the same time, the effect is plagued by unpredictability, preventing consensus on the mechanism and casting doubt on the rhyme and reason that series imply3. Here we expose an unanticipated connection between the unpredictability and order in contact electrification: nominally identical materials initially exchange charge randomly and intransitively, but-over repeated experiments-order into triboelectric series. We find that this evolution is driven by the act of contact itself-samples with more contacts in their history charge negatively to ones with fewer contacts. Capturing this 'contact bias' in a minimal model, we recreate both the initial randomness and ultimate order in numerical simulations and use it experimentally to force the appearance of a triboelectric series of our choosing. With a set of surface-sensitive techniques to search for the underlying alterations contact creates, we only find evidence of nanoscale morphological changes, pointing to a mechanism strongly coupled with mechanics. Our results highlight the centrality of contact history in contact electrification and suggest that focusing on the unpredictability that has long plagued the effect may hold the key to understanding it.

In present work, we investigated single-walled carbon nanotubes (SWCNTs) filled with nickelocene utilizing the gas phase method. We investigated the electronic properties of sorted metallic and semiconducting nickelocene-filled SWCNTs using angle-resolved photoemission spectroscopy. This allowed observing the variation of the Fermi level between different measurement angles, which is connected with the modification of the electronic properties of the nanotubes. The Fermi level varied significantly between nanotubes with different metallicity. This is explained by different effectivity of charge transfer in different samples due to different conductivity type, length of nickel clusters and homogeneity of filling of SWCNTs.

We explore the surface properties of Teflon AF1600 films treated by oxygen plasma with various procedure parameters. Contact angle (CA) measurements, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron microscopy (XPS) are employed to investigate the wetting behavior, surface topography, and chemical composition, respectively. While the etched thickness reveals a linear relationship to the applied plasma energy, the surface presents various wetting properties and topographies depending on the plasma energy: low advancing and zero receding CA (1 kJ), super high advancing and zero receding CA (2-3 kJ), and super high advancing and high receding CA (≥4.5 kJ) for the wetting behaviors; pillar-like (≤6 kJ) and fiber-like (>6 kJ) nanoscaled structures for the topographies. The results of XPS analysis reveal slight changes in the presence of O- and F-components (<4%) after oxygen plasma treatment. Furthermore, we discuss the applicability of the Wenzel and Cassie-Baxter equations and employ the Friction-Adsorption (FA) model, where no wetting state and structure-related parameters are needed, to describe the CAs on the plasma-treated surfaces. Additionally, we conduct electrowetting experiments on the treated surfaces and find that the experimental results of the advancing CA are in good agreement with the predictions of the FA model.

Understanding optical absorption in silicon nitride is crucial for cutting-edge technologies like photonic integrated circuits, nanomechanical photothermal infrared sensing and spectroscopy, and cavity optomechanics. Yet, the origin of its strong dependence on film deposition and fabrication process is not fully understood. This Letter leverages nanomechanical photothermal sensing to investigate optical extinction κ_ext at 632.8 nm wavelength in LPCVD SiN strings across a wide range of deposition-related tensile stresses (200-850 MPa). Measurements reveal a reduction in κ_ext from 10^3 to 10^1 ppm with increasing stress, correlated to variations in Si/N content ratio. Within the band-fluctuations framework, this trend indicates an increase of the energy bandgap with the stress, ultimately reducing absorption. Overall, this study showcases the power and simplicity of nanomechanical photothermal sensing for low absorption measurements, offering a sensitive, scattering-free platform for material analysis in nanophotonics and nanomechanics.

This study aims to investigate the photoelectrochemical behavior of the n-type 4H-SiC, focusing on aqueous, hydroxide-based electrolytes. Despite its high stability, this wide-bandgap semiconductor material undergoes electrochemical reactions, such as anodic oxidation or etching, under specific conditions. Since electrons are the majority charge carriers in n-type semiconductors, oxidation processes require above-bandgap illumination. Then, the reaction rate is influenced by the number of electron holes available for an oxidation process and the velocity of the transport of hydroxide ions to/from the surface. The goal is to focus on the essential reaction parameters (i.e., potential and electrolyte concentration) to clarify the reaction mechanism in aqueous (alkaline) electrolytes. Methods with controllable hydrodynamic conditions are required to investigate the transport processes in the electrolyte. Even though the rotating disk electrode (RDE) is a commonly used and powerful method, it is not well suited for our purpose. Photoelectrochemical etching of SiC is extraordinary because it involves both mass transfer phenomena and gas evolution but also needs high-intensity illumination from an appropriate light source. Hence, a new concept for an inverted rotating cell was developed and implemented. This setup was used to study the effect of the mass transport of hydroxide ions on the photoelectrochemical behavior of SiC in each potential region at varying rotation speeds. In order to interpret the experimental findings, a distinct electrical network model was formulated for simulating the results, aiding in unraveling the underlying reaction mechanism. Electrochemical measurements were complemented by surface-sensitive analytical techniques. XPS was the method of choice to investigate the composition of the sample surface before and after etching. SEM and AFM allow the characterization of the surface morphology in the initial stages of etching. The totality of this information provides a complete picture of the complex processes in the vicinity of the semiconductor electrode.

Understanding optical absorption in silicon nitride is crucial for cutting-edge technologies like photonic integrated circuits, nanomechanical photothermal infrared sensing and spectroscopy, and cavity optomechanics. Yet, the origin of its strong dependence on the film deposition and fabrication process is not fully understood. This Letter leverages nanomechanical photothermal sensing to investigate optical extinction kappa(ext) at a 632.8 nm wavelength in low-pressure chemical vapor deposition (LPCVD) SiN strings across a wide range of deposition-related tensile stresses (200-850 MPa). Measurements reveal a reduction in kappa(ext) from 10(3) to 10(1) ppm with increasing stress, correlated to variations in Si/N content ratio. Within the band-fluctuations framework, this trend indicates an increase of the energy bandgap with the stress, ultimately reducing absorption. Overall, this study showcases the power and simplicity of nanomechanical photothermal sensing for low absorption measurements, offering a sensitive, scattering-free platform for material analysis in nanophotonics and nanomechanics.

Hybrid materials (HMs) combine the high diversity of functionalities of organic compounds with properties typical for inorganic materials, such as high mechanical strength or high thermal stability. Herein, HMs combining organic pigment molecules and TiO2 as inorganic component, with covalently linked components, i.e., so‐called class II HMs, are reported. The synthesis of such HMs is intrinsically challenging, as the apolar organic pigment component and the inorganic polar TiO2 component require different conditions for their respective formation. Herein, we circumvent this issue by employing solvothermal synthesis in superheated isopropanol, which through temperature tunability of the solvent properties allows for both generating and linking both components in one‐pot. First, it is shown that an organic benzimidazole‐based pigment molecule designed for readily binding to Ti can be synthesized solvothermally. Second, new class II titanium‐based HMs are generated from Ti(OiPr)4 and pigment precursors in a solvothermal reaction. The pigment@TiO2 HMs feature significant porosity and are structurally identified as layered structures of lepidocrocite‐like TiO2 linked via pigment molecules. These layered HMs assemble into hierarchical nanoflowers, and depending on the pigment segments, different interlayer spacings in between inorganic layers are observed. Third, the pigment@TiO2 materials are shown to be usable as electrode materials in lithium‐ion batteries.

AbstractMagnesium‐ion batteries (MIBs) are a promising alternative to lithium‐ion batteries due to their higher theoretical energy densities and lower cost. However, fundamental limitations such as the sluggish diffusion of Mg2+ ions into cathode materials have hindered their practical implementation. In this work, the structural, morphological and interfacial changes of H2V3O8, a promising cathode material for MIBs, are elucidated upon Mg2+ intercalation in TFSI‐based electrolytes. Post‐mortem analysis revealed a shrinkage of the interlayer distance, an increase in cell volume, and a decrease of the surface V5+/V4+ ratio during discharge. These changes were only partially reversible upon subsequent charge due to Mg trapping. A cathode electrolyte interphase (CEI) formed mainly of TFSI− anions, its decomposition products, and MgF2 was detected on the surface of H2V3O8. The CEI thickness and chemical composition vary upon charge and discharge as well as during prolonged cycling, and its presence correlates with the additional capacity recorded during discharge. Our study aims to contribute to a better understanding of Mg2+ intercalation and cathode‐electrolyte interaction in high voltage cathode materials for MIBs.

Magnesium-ion batteries (MIBs) are a promising alternative to lithium-ion batteries due to their higher theoretical energy densities and lower cost. However, fundamental limitations such as the sluggish diffusion of Mg2+ ions into cathode materials have hindered their practical implementation. In this work, the structural, morphological and interfacial changes of H2V3O8, a promising cathode material for MIBs, are elucidated upon Mg2+ intercalation in TFSI-based electrolytes. Post-mortem analysis revealed a shrinkage of the interlayer distance, an increase in cell volume, and a decrease of the surface V5+/V4+ ratio during discharge. These changes were only partially reversible upon subsequent charge due to Mg trapping. A cathode electrolyte interphase (CEI) formed mainly of TFSI- anions, its decomposition products, and MgF2 was detected on the surface of H2V3O8. The CEI thickness and chemical composition vary upon charge and discharge as well as during prolonged cycling, and its presence correlates with the additional capacity recorded during discharge. Our study aims to contribute to a better understanding of Mg2+ intercalation and cathode-electrolyte interaction in high voltage cathode materials for MIBs.

We report a joint experimental and theoretical study of RuO2/TiO2 heterostructures. In the experimental section, mesoporous RuO2/TiO2 heterostructures were prepared by impregnation of mesoporous TiO2 nanoparticles which were synthesized from a new precursor, Na2[Ti(C2O4)3], in an aqueous solution of ruthenium(III) chloride followed by calcination at 300 °C. Using various techniques, the prepared TiO2 and RuO2/TiO2 heterostructures were extensively characterized. The photoelectocatalytic application of the as-prepared heterostructures was then investigated toward the hydrogen evolution reaction (HER). The results illustrated that RuO2 is dispersed uniformly on the TiO2 surface. The loading of RuO2 on TiO2 decreases the band gap energy and extends the absorption edge to the visible light region. This wide absorption extends the photoelectrocatalytic activity of RuO2/TiO2 heterostructures. To obtain a deeper understanding of the increase of the photoelectrocatalytic activity of RuO2/TiO2 heterostructures compared to pure TiO2, theoretical calculations at the density functional theory (DFT) level were performed on some model clusters of pure TiO2 and the RuO2/TiO2 heterostructure. The theoretical results elucidated that the recombination ratio of electron-hole pairs decreases effectively for RuO2/TiO2 compared to pure TiO2.

Electrochemical water-splitting efficiency is determined by both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) electrocatalysts. Therefore, designing a bifunctional configuration is essential for an efficient HER and OER catalytic performance under the same experimental conditions. In this study, a novel ionic pentanuclear complex of the type [Ru(dmbpy)(3)](3)[Fe(CN)(6)](2), where dmbpy = 4,4 ' -dimethyl-2,2 '-bipyridine, has been synthesized and characterized by structural (X-ray), analytical (CHN), and spectral (FT-IR, UV-Vis) methods. Highly reduced graphene oxide nanosheets (HrGO NSs) supported RuO2-Fe2O3 nanocomposite were prepared by an impregnation method using [Ru(dmbpy)(3)](3)[Fe(CN)(6)](2) as a precursor and HrGO NSs as a support. The RuO2-Fe2O3/HrGO NSs nano-composite was characterized by means of spectroscopy (XPS, FT-IR, and FT-Raman), surface area (BET/BJH), diffraction (XRD), thermal (TGA), and electron microscopy (TEM and FE-SEM) analyses. The electrocatalytic HER, OER, and overall water-splitting activities of RuO2-Fe2O3/HrGO NSs, RuO2-Fe2O3, RuO2/HrGO, Fe2O3/HrGO, and HrGO in 1 M KOH solution were studied. According to the overpotentials of -239 and 386 mV (vs. RHE) at 10 mA cm(-2) current density, the exchange current densities of 0.0641 and 0.389 x 10(-4) mA cm(-2), the Tafel slopes of 97 and 67 mV dec(-1), and the charge-transfer resistance values of 38.57 and 31.5 U for HER and OER, respectively, the RuO2-Fe2O3/HrGO NSs nanocomposite possesses bifunctional catalytic capabilities toward both hydrogen and oxygen evolution reactions. The catalytic performance is enhanced by the high surface area, the high number of catalytically active sites, the presence of nanoparticles with different morphologies, and the synergistic interaction between RuO2-Fe2O3 nanoparticles and HrGO nanosheets.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Li metal electrodes have the potential to increase the energy density of conventional lithium-ion batteries by up to 60%. However, challenges regarding the cycling efficiency and safety of these electrodes still remain. Effective surface treatments seem to be a promising approach for resolving issues such as dendrite formation or excessive reaction with the electrolyte. LiF has been reported to exhibit most of the properties required of a coating material in this context, offering high electro-/chemical stability, mechanical strength, high surface energies, etc. Nevertheless, contradicting reports on the effectiveness of LiF coatings to improve the cycling efficiency of Li metal electrodes raise doubts on its effectiveness to protect the Li metal surface. The mechanism of protection for this material is also not well understood. Thus, a comparative study was conducted, selecting three different approaches for the synthesis of a LiF coating on Li metal and following with detailed electrochemical analysis. Using the same experimental setup for all samples enabled direct comparison between the selected coatings, and subsequently, a reliable evaluation on the effectiveness of LiF as protective coating.

The exceptional mechanical properties of transition metal carbide coatings are known to be governed by the carbon content and its morphological distribution. Here, we verify the influence of the target peak power density on the chemical composition, microstructure, and mechanical properties of NbCx coatings grown by non-reactive high-power impulse magnetron sputtering (HiPIMS). By tuning the pulse parameters, the power density can be increased from 0.11 to 1.48 kW/cm2 leading to a decrease in the C/Nb ratio from 1.52 to 0.99 within the films - proven by combined elastic backscattering and time-of-flight elastic recoil detection analysis. This decrease in the C/Nb ratio is accompanied by microstructural changes from nanocomposite morphologies with an average grain size of 6.6 +/- 2.5 nm at 0.13 kW/cm2 into more columnar structures with an average column width of 65.2 +/- 18.7 nm at 1.48 kW/cm2. Independent from the C/Nb ratio, all films exhibit a single face-centered cubic structure. The mechanical properties correlate with the enhanced growth behavior dominated by ions at higher peak power densities and the varied C/Nb ratios. A maximum in hardness and fracture toughness of H = 38.7 +/- 3.6 GPa and KIc = 2.78 +/- 0.13 MPa center dot m1/2 (at 3.2 GPa residual compressive stress), is obtained for the nearly stoichiometric NbC coating exhibiting C/Nb ratio of 1.06.

Water electrolysis is one of the most capable processes for supplying clean fuel. Herein, two novel ionic Ru(II)-Fe(II) complexes, [Ru(tmphen)3]2[Fe(CN)6] and [Ru(phen)3][Fe(CN)5(NO)], where tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline and phen = 1,10-phenanthroline, were synthesized and characterized by UV-Vis spectroscopy, elemental analysis, FT-IR, and single-crystal X-ray structural analysis. By thermally decomposing the [Ru(tmphen)3]2[Fe(CN)6] complex at 600 °C for 4 h, a heterostructured RuO2-Fe2O3 nanocomposite was fabricated through a facile one-pot treatment and then characterized by FT-IR, XRD, FT-Raman, UV-Vis (DRS), ICP-OES, FE-SEM, TEM, TGA/DTG, BET, and XPS analyses, which revealed the formation of highly crystalline RuO2-Fe2O3 nanoparticles with an average size of 8-12 nm. The prepared nanocomposite was an efficient heterostructured electrocatalyst for performing water-splitting redox reaction processes, including hydrogen and oxygen evolution reactions (HER and OER) in alkaline solutions. In this regard, RuO2 and Fe2O3 samples were also prepared through thermal decomposition of [Ru(tmphen)3](NO3)2 and K4[Fe(CN)6] precursors, respectively, as control experiments to compare their HER and OER electrocatalytic activity with that of the RuO2-Fe2O3 nanocomposite. Specifically, the RuO2-Fe2O3 nanocomposite exhibited significant electrocatalytic performance, generating 10 mA cm-2 current density at -148 and 292 mV overpotentials, and the Tafel slope results from fitting the LSV curves to the Tafel equation were -43 and 56.08 mV dec-1 for the HER and OER, respectively. Therefore, the heterostructured RuO2-Fe2O3 nanocomposite can be viewed as a bi-functional electrocatalyst for HER and OER because it exploits the synergistic effects of heterostructures and active sites at its interface.

Laterally large ( 3 micrometers), atomically-thin two-dimensional (2D) Bi2O2CO3 nanosheets (2D bismuth oxycarbonate, 2D bismutite) are fabricated via sonochemically-assisted template-free synthesis. Key to the synthesis of the freestanding, laterally large 2D Bi2O2CO3 nanosheets from bulk Bi powder is choice of suspension medium, controlled reaction temperatures and several hours processing time. Lateral sizes of 2D Bi2O2CO3 can be controlled between micrometer-sized nanosheets and tens of nm sized nanoflakes solely based on the choice of suspension medium. The here introduced 2D Bi2O2CO3 nanosheets/-flakes are then hybridized by a simple mix-and-match approach with TiO2 nanoparticles for testing in suspension-type photocatalytic hydrogen production via water splitting. This introduces the 2D Bi2O2CO3 with TiO2 as a promising noble-metal-free co-catalyst for photocatalytic hydrogen evolution. Our results enrich the fabrication toolbox of emerging 2D pnictogen oxycarbonates towards large 2D nanosheets and demonstrate the promising potential of 2D Bi2O2CO3 as an advantageous (co-)catalyst for hydrogen evolution in photocatalytic water splitting.