The harsh anodic environment in proton exchange membrane water electrolyzers (PEMWEs) necessitates surface modification of titanium bipolar plates (BPPs) to prevent corrosion-induced ion release and formation of non-conductive oxides. Platinum coatings are a commonly used approach, providing electrically conductive corrosion protection. However, their limited availability and high material cost highlight the need to reduce Pt utilization for large-scale application. Therefore, this study systematically investigates the electrochemical performance and durability of nanometer-scale Pt coatings on grade 2 Ti substrates, aiming to minimize film thickness while maintaining functional integrity. Using a comprehensive set of high-resolution characterization techniques, this work provides detailed insights into the interplay between Pt film thickness, coating defects, and substrate degradation. Overall, the results demonstrate that Pt coatings with a thickness of about 24 nm (≈57 μg cm-2 Pt loading) can effectively protect titanium BPP, highlighting that nanometer-thin coatings preserve performance while enabling a significant reduction in Pt usage for PEMWE bipolar plate design.

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.

Graphene has been suggested as an ultimately thin functional coating for metallurgical alloys, such as steels. However, even on pure iron (Fe), the parent phase of steels, the growth of high quality graphene films remains largely elusive to date. We here report scalable chemical vapor deposition (CVD) of high quality monolayer graphene films on Fe substrates. To achieve this, we here elucidate the mechanisms of graphene growth on Fe using complementary in situ X-ray diffractometry (XRD) and in situ near ambient pressure X-ray photoelectron spectroscopy (NAP XPS) during our scalable CVD conditions. As key factors that set Fe apart from other common graphene CVD catalyst supports such as Ni or Cu, we identify that for Fe (i) carbothermal reduction of persistent Fe-oxides and (ii) kinetic balancing of carbon uptake into the Fe during CVD near the Fe-C eutectoid because of the complex multiphased Fe-C phase diagram are critical. Additionally, we establish that the carbon uptake into the Fe during graphene CVD is not only important in terms of growth mechanism but can also be advantageously utilized for concurrent surface hardening of the Fe during the graphene CVD process, akin to carburization/case hardening. Our work thereby forms a framework for controlled and scalable high-quality monolayer graphene film CVD on Fe including the introduction of concurrent surface hardening during graphene CVD.

We studied high-temperature cyclic voltammetry (HT-CV) and high-temperature chronoamperometry for diffusion (HT-CAD) as fast and reliable techniques for investigating the interdiffusion behavior of different material combinations. Diffusion of nickel through a gold layer is used as a model system. HT-CAD detects inhomogeneous diffusion in-situ and in real time without requiring high vacuum conditions. The diffused species is assigned reliably by applying HT-CV. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to analyze the elemental composition and the spatial distribution of elements within the sample. The electrochemical cell consists of a disc made of yttria-stabilized zirconium dioxide (YSZ) as a solid electrolyte conductive for oxygen ions, with a working-, reference- and counter electrode. A platinum plate is pressed onto the YSZ as a reference electrode. A multilayer structure consisting of sputtered gold and nickel has been fabricated to serve as the working electrode. On the reverse side, a porous platinum layer serves as a counter electrode. Chronoamperometric and cyclic voltammetric measurements are carried out at elevated temperatures of around 300°C. These methods enable targeted oxidation of the diffused nickel by controlling the potential. This research enhances understanding of diffusion in metallic multilayers, providing insights into diffusion behavior.

ABSTRACTThe combination of different surface‐sensitive techniques is frequently used in material sciences to analyze complex systems. How these methods compare in terms of quantitative and qualitative information is often unclear. In this study, we directly compare low‐energy ion scattering spectroscopy (LEIS), secondary ion mass spectrometry (SIMS), and angle‐resolved X‐ray photoelectron spectroscopy (AR‐XPS) depth profiling analyses. Therefore, we use the Zn–Al–Mg model coatings after alkaline and acidic treatments in model solutions. The combined use of AR‐XPS and LEIS depth profiling proved effective in studying compositional and elemental changes in the surface oxides of Zn–Al–Mg coatings after alkaline and acidic treatments. Additionally, by combining these methods, SIMS depth profiling can be effectively calibrated for matrix effects. Here, we find that, for example, Mg is considerably more sensitive to SIMS detection, based on effective secondary ionisation. Such effects must be considered for data interpretation.

Modifications of mixed ionic electronic conductor (MIEC) surfaces are a promising approach to improve oxygen exchange reaction (OER) kinetics and can have a tremendous impact on surface charges and secondary ion yields. Utilizing time-of-flight secondary ion mass spectrometry (ToF-SIMS), we examined degradation, segregation, and cation interdiffusion behaviors on La0.6Sr0.4CoO3-delta (LSC) and Pr0.2Ce0.8O2-delta (PCO) thin films modified with similar to 0.5 nm CaO, TiO2, and SnO2 overlayers after annealing at 700 degrees C and 800 degrees C, respectively. Surface profiles (AFM; ToF-SIMS) and depth profiles (ToF-SIMS) revealed structural and chemical transformations, including particle formation and surface roughening. The overlayer stability varied significantly for different overlayers on the same material and for the same overlayer on LSC and PCO. All oxidic overlayers were more stable on PCO than LSC. Depth profiling indicated that Ca-40(+) ions penetrated the entire LSC and PCO layers (30 nm). Ti-48(+) aligns more accurately with a typical analytical solution to Fick's diffusion equation for finite systems, showing higher diffusion coefficients in LSC than PCO. Sn-120(+) exhibited minimal penetration, indicating high stability on the surface and less intermixing with either MIEC. These results hint at the need to differentiate between the stability of the binary oxides on the surface and the bulk diffusivity.

Physical vapor deposited coatings are widely utilized as surface protection for metal and ceramic components operating in harsh environments. However, research on the high-cycle fatigue (HCF) life of hard-coated metal substrates has reached contradictory conclusions, leaving it unclear whether ceramic coatings enhance or compromise their fatigue resistance. To improve reliability and extend service life, this study explores the residual stress-dependent influence of arc evaporated TiAlN-based thin films on the fatigue life of Ti-6Al-4V. Therefore, different stress-modifying approaches were implemented, including a substrate bias variation, a Tantalum based alloying strategy, and a specific interlayer design. The combination of high-cycle fatigue tests, synchrotron-based experiments providing depth-resolved stress profiles, and the formulation of a linear-elastic stress-failure model resulted in the following identified relationships: (i) A threshold level in the residual compressive stress state must be present in TiAlN-based coatings to prevent deteriorating HCF performance introduced by failure of the ceramic nitride. (ii) Once the residual compressive stress field is able to shift fatigue crack nucleation into the bulk titanium alloy, the HCF life increases. (iii) The further the residual tensile stress peak is shifted from the bulk material surface — achieved through an optimized residual stress design implementing a metallic interlayer beneath the TiAlN-based top coating — the greater the improvement in HCF strength. Overall, this approach achieved an unprecedented HCF enhancement exceeding 50 % compared to uncoated Ti-6Al-4V (from 420 MPa to 628 MPa at 107 load cycles), highlighting the importance of an in-depth understanding of stress gradients within coating-substrate combinations.

The demand for high-resolution imaging, and high sample throughputs in LA-ICP-MS experiments has led to developing rapid-response ablation cells with low dispersion. These cells can achieve short transient signals called single pulse responses (SPRs), whose width is in the single-digit millisecond range at 1% of the maximum. However, coupled with ICP-Q-MS, recording those short signals poses a problem due to the sequential measurement of selected m/z ratios. If more than one m/z ratio is targeted, the time resolution of quadrupole detection systems is insufficient for accurately determining short SPRs. This work focuses on utilizing rapid response ablation cells for the analysis of multiple elements with quadrupole-based detection systems in the SPR mode. To achieve this, an ArF-excimer laser equipped with a rapid-response ablation chamber is coupled to an ICP-MS with a short settling time of 0.2 ms and below. The two naturally occurring Ag-isotopes were analyzed in the NIST SRM 612 to optimize the dwell times for ideal data acquisition. The data shows that the ratio of the dwell time and the settling time, plays a crucial role. With the optimized parameters, the natural ratio of 107Ag and 109Ag within a 10 ms FW0.01M transient signal could be determined. This concept of LA-ICP-MS was then applied for depth profiling analysis of Al-doped SiC, a wide bandgap semiconductor. This procedure acquired depth profiles on 30 different sample locations in approximately 2 minutes with an exceptional depth resolution of 55 nm. The measurement of single pulse responses (SPRs) in LA-ICP-Q-MS measurements was optimized to analyze more than one m/z ratio.

We report on the barrier performance of a nitride, and three oxynitrides of the system Al-Cr-Nb-Ta-Ti between Cu and Si. Different high-entropy sublattice nitrides have been tested before as diffusion barriers in this system, by depositing thin barriers on single crystalline Si substrates, followed by a thick Cu layer on top, and subsequent vacuum annealing. We investigated a reversed stacking sequence, by sputtering 15-30 nm of (Al,Cr,Nb,Ta,Ti)-O-N (between 0.5 and 63.7 at.% O) on polished polycrystalline Cu substrates, followed by 200 nm of Si. The samples were then vacuum annealed at 600, 700, 800 and 900 degrees C for 30 min. All four investigated coatings perform similar. Secondary Ion Mass Spectrometry depth profiling in high-current-bunched mode (lateral res-olution +/- 1 mu m) shows breakthrough of Si even at 600 degrees C. But 3D constructed images with Burst Alignment mode (lateral resolution of +/- 2 nm) reveal that this failure is a highly localized phenomenon, likely related to coarsening effects at the Cu grain boundaries, leading to punctuation of the diffusion barrier. Aside from this penetration, the majority of the area of each barrier coating retains its function. This in-depth analysis shows that the barrier function of the nitride and oxynitride coatings mostly stays intact up to 800 degrees C and fails completely at 900 degrees C.

Sub-nanometer modifications of mixed ionic electronic conducting (MIEC) materials, like the perovskite La0.6Sr0.4CoO3-delta (LSC), represent a promising approach to improving their oxygen exchange kinetics and degradation stability. The complex interactions between decoration layers and the host material are still not fully understood and are a subject of current research. Under these circumstances, a novel approach using time-offlight secondary ion mass spectrometry (ToF-SIMS) was developed to gain deeper insight into the electronic and chemical interactions of LSC with different oxidic decorations. The investigated samples were prepared by pulsed laser deposition (PLD) on YSZ single crystals, starting with a 100 nm thin LSC layer, which was then modified by sub-nm decorations of CaO, TiO2, and SnO2 (nominally 0.05-0.5 nm) on top. By using ToF-SIMS with a sampling depth of 1-2 nm, it was possible to extract information simultaneously on the decoration layer and the host oxide. Significant differences in secondary ion (SI) intensities of the host material LSC were found that can be attributed to the formation of surface-near dipoles as a consequence of the acidic or basic nature of the decoration oxide. Further, relative stoichiometric variations of the La+, Sr+, and Co+ signals depending on the decoration oxide were observed, suggesting different preferential decoration sites on the LSC surface.

The changes of the surface morphology and the surface chemistry of LSC thin films grown on different substrates were tracked for 100 hours under SOFC operation conditions. Atomic force microscopy was used to monitor the formation of particles at the LSC surface. Depending on the thin film structure (polycrystalline vs. epitaxial), different particle formation dynamics were observed. Electron microscopy was employed to investigate the chemistry of the segregated particles and revealed that the particles were Sr- and S-rich. Secondary ion mass spectrometry and X-ray photoelectron spectroscopy measurements were performed on degraded LSC thin films, which also found significant amounts of sulfur on the LSC surface, despite no deliberate addition of sulfur compounds, as well as A-site cation enrichment. Impedance spectroscopy was used to track the polarization resistance of LSC grown on YSZ over the same degradation period and a strong increase inthe polarization resistance and in its activation energy was revealed (1.09 to 1.73 eV). The experimental results indicate that sulfur adsorption on LSC surfaces is omnipresent in the investigated conditions and even trace amounts of sulfur compounds present in nominally pure measurement gases account for particle formation and multiple degradation effects under operating conditions.

This work presents a multisensor hyperspectral approach for the characterization of ultramarine blue, a valuable historical pigment, at the microscopic scale combining the information of four analytical techniques at the elemental and molecular levels. The hyperspectral images collected were combined in a single hypercube, where the pixels of the various spectral components are aligned on top of each other. Selected spectral descriptors have been defined to reduce data dimensionality before applying unsupervised chemometric data analysis approaches. Lazurite, responsible for the blue color of the pigment, was detected as the major mineral phase present in synthetic and good quality pigments. Impurities like pyrite were detected in lower quality samples, although the clear identification of other mineral phases with silicate basis was more difficult. There is no correlation between the spatial distribution of the bands arising in the Raman spectra of natural samples in the region 1200–1850 cm −1 and any of the transition metals or rare earth elements (REE). With this information, the previous hypothesis (based on bulk analysis) attributing these bands to luminescence emissions due to impurities of these elements must be revised. We propose the consideration of CO 2 molecules trapped in the cages of the aluminosilicate structure of sodalite-type. Additionally, correlation between certain Raman features and the combined presence of Ca, P, and REE, in particular Nd, was detected for the lowest quality pigment. Our results highlight the usefulness of fusing chemical images obtained via different imaging techniques to obtain relevant information on chemical structure and properties.

Semiconducting BaTiO3-based ceramics with varying manganese (Mn) acceptor concentrations (0.048-0.112 mol%) are systematically examined. By optimizing the Mn content, ceramics with electrical breakdown field strengths as high as 600 V/mm with simultaneous low decrease of resistance below phase transition (R-min/R-25 = 0.78) temperature are achieved. The observed differences in electrical properties are ascribed to modifications in grain boundary surface state properties. O-18 tracer experiments at 800 degrees C reveal a clear enhancement of oxygen diffusivity with increasing Mn concentration. The comparison with resistance-temperature (R-T) characteristics indicates the simultaneous presence of various acceptors (e.g., adsorbed gases, Mn4+/3+, Mn3+/2+) with different energy levels and suggests a direct correlation between surface trap formation and oxygen diffusivity. We propose that the interaction of Mn with oxygen determines the number of surface states but also the depth of their energy level within bandgap, defining the resulting form of the R-T characteristic.

Epoxy molding compounds are typically used for the encapsulation of modern-day electronic devices. These protect the semiconductor components from environmental influences, such as humidity and oxygen, which could harm the device. However, there is still a risk for corrosion phenomena, when the device is used in harsh conditions (e.g. high humidity and temperature). Electrochemical migration is a mechanism that can occur in the semiconductor device. For instance, silver wires, glues, solders or leadframe-platings used in the package combined with high humidity contact are a huge risk. For this type of corrosion to happen, Ag ions need to migrate through the molding compound. Therefore, measurement of the diffusion coefficient of silver ions in molding compounds can help to better predict the risk of silver migration and corrosion. In this study silver(I)salts were used source for Ag + ions. An Arrhenius correlation was found in the range from 298 K to 393 K. The diffusion coefficient as well as the activation energy of silver ions in four different molding compounds have been evaluated. The investigated activation energies as well as diffusion coefficients are in the range of 0.12 to 0.50 eV.

The influence of the non-metal species on the oxidation resistance of transition metal ceramic based thin films is still unclear. For this purpose, we thoroughly investigated the oxide scale formation of a metal (Hf), carbide (HFC0.96), nitride (HfB1.5), and boride (HfB2.3) coating grown by physical vapor deposition. The non-metal species decisively affect the onset temperature of oxidation, ranging between 550 degrees C for HfC0.96 to 840 degrees C for HfN1.5. HfB2.3 and HfN1.5 obtain the slowest oxide scale kinetic following a parabolic law with k(p) values of 4.97.10(-10) and 5.66.10(-11) kg(2) m(-4) s(-1) at 840 degrees C, respectively. A characteristic feature for the oxide scale on Hf coatings, is a columnar morphology and a substantial oxygen inward diffusion. HfC0.96 reveals an ineffective oxycarbide based scale, whereas HfN(1.5 )features a scale with globular HfO2 grains. HfB(2.3 )exhibits a layered scale with a porous boron rich region on top, followed by a highly dense and crystalline HfO2 beneath. Furthermore, HfB(2.3 )presents a hardness of 47.7 +/- 2.7 GPa next to an exceptional low inward diffusion of oxygen during oxidation. This study showcases the strong influence of the non-metallic bonding partner despite the same metallic basis, as well as the huge potential for HfB2 based coatings also for oxidative environments. (C) 2021 Published by Elsevier Ltd.

Artifact‐free depth profiles of alkali ions in SiO 2 were obtained using a time‐of‐flight secondary ion mass spectrometer (ToF‐SIMS) equipped with a Cs + beam as sputter gun. Samples were set to low temperature (~−100°C) using a heating/cooling sample holder. The effects of temperature on the depth profiles was determined with multiple measurements at different temperatures. To validate the described method, obtained depth profiles of alkali metal implanted SiO 2 samples were compared with simulated depth profiles. Evidence for artifact‐free depth profiles is given for potassium, sodium, and lithium, three prominent examples of fast diffusing ions in various materials. This described approach enables more laboratories to acquire depth profiles of alkali metals in non‐conducting samples without time‐consuming sample preparation. It offers artifact‐free depth profiling of alkali metals using a classic ToF‐SIMS without advanced extensions, which are not available in many laboratories.

We present a model for multicomponent diffusion in ionic crystals. The model accounts for vacancy-mediated diffusion on a sub-lattice and for diffusion due to binary exchange of different ionic species without involvement of vacancies on the same sub-lattice. The diffusive flux of a specific ionic species depends on the self-diffusion coefficients, on the diffusion coefficients related to the binary exchanges, and on the site fractions of all ionic species. The model delivers explicit expressions for these dependencies, which lead to a set of coupled non-linear diffusion equations. We applied the model to diffusion of $$^{23}$$Na, $$^{39}$$K, and $$^{41}$$K in alkali feldspar. To this end, gem-quality crystals of alkali feldspar were used together with $$^{41}$$K doped KCl salt as diffusion couples, which were annealed at temperatures between 800$$^\circ$$ and 950$$^\circ$$C. Concentration-distance data for $$^{23}$$Na, $$^{39}$$K, and $$^{41}$$K were obtained by Time of Flight Secondary Ion Mass Spectrometry. Over the entire investigated temperature range the Na self-diffusion coefficient is by a factor of $$\ge 500$$ higher than the K self-diffusion coefficient. Diffusion mediated by binary $$^{39}$$K–$$^{41}$$K exchange is required for obtaining satisfactory fits of the model curves to the experimental data, and the respective kinetic coefficient is well constrained.

Experiments are reported, which allow us to quantify the near-surface cation diffusion in (001) oriented Fe3O4 single crystals at temperatures between 470 and 770 K. Thin homoepitaxial films of magnetite, grown using isotopically labeled Fe-57, were investigated by neutron reflectivity and time-of-flight secondary ion mass spectrometry. By heating the thin films in high vacuum to different temperatures for a well-defined time and determining the Fe-57 distribution along the surface normal, the diffusion lengths are obtained. For the investigated temperature range, diffusion constants of the order of 10(-20) m(2)/s are deduced. These results are important in view of near-surface mass transport induced by oxygen chemical potential differences occurring when magnetite is exposed to different gas atmospheres or by adsorbates.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.