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Electrochemically converting nitrate ions, a widely distributed nitrogen source in industrial wastewater and polluted groundwater, into ammonia represents a sustainable route for both wastewater treatment and ammonia generation. However, it is currently hindered by low catalytic activities, especially under low nitrate concentrations. Here we report a high-performance Ru-dispersed Cu nanowire catalyst that delivers an industrial-relevant nitrate reduction current of 1 A cm

The large surface areas in porous organic matter (OM) and on the surface of altered minerals control the sequestration of metal(loid)s in contaminated soils and sediments. This study explores the sequestration of Cu by OM in surficial forest soil in close proximity to the Horne smelter, Rouyn-Noranda, Quebec, Canada. The organic-rich soils have elevated concentrations of Cu (Cu = 〈0.75〉 wt%) but lack associations between organic matter (OM) and Cu-sulfides, commonly observed in organic-rich Cu-contaminated soils. This provides a unique opportunity to study the sequestration of Cu by OM in a sulfur-depleted environment using a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT). In two examined OM particles, Cu is predominantly sequestered as (I) nano- to micrometer-size Cu-bearing spinels, (II) as cuprite (Cu

We report a unique in situ instrument development effort dedicated to studying gas/solid interactions relevant to heterogeneous catalysis and early stages of oxidation of materials via atom probe tomography and microscopy (APM). An in situ reactor cell, similar in concept to other reports, has been developed to expose nanoscale volumes of material to reactive gas environments, in which temperature, pressure, and gas chemistry are well controlled. We demonstrate that the combination of this reactor cell with APM techniques can aid in building a better mechanistic understanding of resultant composition and surface and subsurface structure changes accompanying gas/surface reactions in metal and metal alloy systems through a series of case studies: O2/Rh, O2/Co, and O2/Zircaloy-4. In addition, the basis of a novel operando mode of analysis within an atom probe instrument is also reported. The work presented here supports the implementation of APM techniques dedicated to atomic to near-atomically resolved gas/surface interaction studies of materials broadly relevant to heterogeneous catalysis and oxidation.

A multimodal chemical imaging approach has been developed and applied to detail the dynamic, atomic-scale changes associated with oxidation of a zirconium alloy (Zircaloy-4). Scanning transmission electron microscopy, a gas-phase reactor chamber attached to an atom probe tomography instrument, and synchrotron-based X-ray absorption near-edge spectroscopy were employed to reveal morphology, composition, crystal, and electronic structure changes that occur during initial stages of oxidation at 300 °C. Oxidation was carried out in 10 mbar O2 gas for short exposure times of 1 and 5 min. A multilayered oxide film with a cubic ZrO adjacent to the oxide/metal interface, a nanoscopic transition region with a graded composition of ZrO2−x (where 0 x 2 in the outermost oxide were formed. Partitioning of the major alloying element (tin) to the oxide/metal interface and heterogeneously within the oxide accompanied the development of the layered oxide. Our work provides a rapid, high-throughput approach for detailed characterisation of initial stages of zirconium alloy oxidation at an accelerated time scale, with implications for several other alloy systems.

Northwest Africa (NWA) 7042 is an intermediate, permafic shergottite consisting of two generations of olivine (early zoned olivine Fo41-76, and late-stage fayalitic olivine Fo46-56), complexly zoned pyroxene (En35-64Fs22-46Wo5-34), shock-melted or maskelynitized feldspar (An5-30Ab16-61Or1-47), and accessory merrillite, apatite, ilmenite, titanomagnetite, Fe-Cr-Ti spinels, pyrrhotite, and baddeleyite. The zoned olivine grains have been pervasively modified, containing conspicuous brown Mg-rich cores surrounded by colorless, unaltered Fe-rich overgrowth rims. This textural relationship suggests that the cores were altered at magmatic temperatures prior to crystallization of the rims on Mars. Launch-generated shock veins in NWA 7042 also crosscut and displace several of the altered olivine grains indicating that alteration occurred before ejection of the meteorite. While this type of olivine alteration is rare in shergottites, it is similar to deuterically altered olivine in basalts and gabbros on Earth, caused by residual water-rich magmatic fluids. Transmission electron microscopy analysis of the olivine alteration did not reveal the high-temperature phases expected from this process; however, NWA 7042 has also been subjected to extensive terrestrial weathering, which may explain their absence. The potential presence of deuterically altered olivine in NWA 7042 has significant implications, as it is the third martian meteorite where deuteric alteration of olivine has been observed (the others being NWA 10416, and Allan Hills 77005). The different mantle sources for the parental melts of these three meteorites would suggest many, if not all martian mantle reservoirs have the potential to produce water-rich magmas.

Sodium yttrium fluoride (NaYF4) is an important upconverting material with many potential uses in chemistry, materials science, and biology, which can be synthesized hydrothermally in both cubic (α...

New cryogenic characterization techniques for exploring the nanoscale structure and chemistry of intact solid–liquid interfaces have recently been developed. These techniques provide high-resolution information about buried interfaces from large samples or devices that cannot be obtained by other means. These advancements were enabled by the development of instrumentation for cryogenic focused ion beam liftout, which allows intact solid–liquid interfaces to be extracted from large samples and thinned to electron-transparent thicknesses for characterization by cryogenic scanning transmission electron microscopy or atom probe tomography. Future implementation of these techniques will complement current strides in imaging of materials in fluid environments by in situ liquid-phase electron microscopy, providing a more complete understanding of the morphology, surface chemistry, and dynamic processes that occur at solid–liquid interfaces.

A site-specific, cryogenic, focused ion beam (FIB) method is presented for the preparation of atom probe tomography (APT) specimens from a frozen liquid/solid interface. As a practical example, the interface between water and a corroded boroaluminosilicate glass has been characterized by APT for the first time. The water/glass interface is preserved throughout specimen preparation by plunge freezing the corroding glass particles with the corrosion solution into slush nitrogen. Site-specific specimen preparation is enabled through a new approach to extract and mount a small volume of material using a cryogenically cooled FIB stage and micromanipulator. The prepared APT specimens are subsequently transferred from the FIB to APT under cryogenic and high-vacuum conditions using a novel FIB/APT transfer shuttle and home-built environmental transfer hub attached to the APT system. Particular focus is given to the technical methods for specimen fabrication under cryogenic conditions. Persistent challenges are discussed in addition to future opportunities for this new specimen preparation method.

Recent discovery of superconductivity in Nd0.8Sr0.2NiO2 motivates the synthesis of other nickelates for providing insights into the origin of high-temperature superconductivity. However, the synthesis of stoichiometric R1−xSrxNiO3 thin films over a range of x has proven challenging. Moreover, little is known about the structures and properties of the end member SrNiO3. Here, we show that spontaneous phase segregation occurs while depositing SrNiO3 thin films on perovskite oxide substrates by molecular beam epitaxy. Two coexisting oxygen-deficient Ruddlesden-Popper phases, Sr2NiO3 and SrNi2O3, are formed to balance the stoichiometry and stabilize the energetically preferred Ni2+ cation. Our study sheds light on an unusual oxide thin-film nucleation process driven by the instability in perovskite structured SrNiO3 and the tendency of transition metal cations to form their most stable valence (i.e., Ni2+ in this case). The resulting metastable reduced Ruddlesden-Popper structures offer a testbed for further studying emerging phenomena in nickel-based oxides.

Dynamic phase segregation, driven by the instability of Ni2+, occurs during SrNiO3 heteroepitaxy growth., Recent discovery of superconductivity in Nd0.8Sr0.2NiO2 motivates the synthesis of other nickelates for providing insights into the origin of high-temperature superconductivity. However, the synthesis of stoichiometric R1−xSrxNiO3 thin films over a range of x has proven challenging. Moreover, little is known about the structures and properties of the end member SrNiO3. Here, we show that spontaneous phase segregation occurs while depositing SrNiO3 thin films on perovskite oxide substrates by molecular beam epitaxy. Two coexisting oxygen-deficient Ruddlesden-Popper phases, Sr2NiO3 and SrNi2O3, are formed to balance the stoichiometry and stabilize the energetically preferred Ni2+ cation. Our study sheds light on an unusual oxide thin-film nucleation process driven by the instability in perovskite structured SrNiO3 and the tendency of transition metal cations to form their most stable valence (i.e., Ni2+ in this case). The resulting metastable reduced Ruddlesden-Popper structures offer a testbed for further studying emerging phenomena in nickel-based oxides.

There has been a recent surge in the use of cryo and/or vacuum specimen preparation and transfer systems to broaden the scope of research enabled by the microscopy technique of atom probe tomography. This is driven by the fact that, as for many microscopes, the application of atom probes to air- and temperature-sensitive materials or wet biological specimens has previously been limited by transfer through air at room temperature. Here we provide an overview of areas of research that benefit from these new transfer and analysis protocols, as well as a review of current advances in transfer devices, environmental cells, and glove boxes for controlled specimen manipulation. This includes the study of catalysis and corrosion, biological samples, liquid-solid interfaces, natural aging, and the distribution of hydrogen in materials.

The interaction of oxygen with a reactive metal is ubiquitous, yet the precise atomic-level mechanisms and pathways leading to the formation of a surface oxide are not well-understood. We report oxygen atom distributions inside Rh single nanoparticles using atom probe microscopy (APM) and demonstrate that mainly facets of the «022¯» crystallographic directions act as oxygen-permeable gateways. The highly anisotropic spatial distribution of incorporated oxygen atoms is in agreement with video-field emission analyses according to which {113} facets of the «022¯» zones act as portals for subsurface diffusion. In addition to providing a more fundamental understanding of the precursor states to metal corrosion, in particular for the case of nanosized metal particles, our studies are also relevant for heterogeneous catalysis where catalytic activity and selectivity conform to reaction-induced structural changes of metal nanoparticles., SCOPUS: ar.j, info:eu-repo/semantics/published

Cryo-based atom probe tomography has been applied to directly reveal the water-solid interface and hydrated corrosion layers making up the nanoscale porous structure of a corroded borosilicate glass in its native aqueous environment. The analysis includes morphology and compositional mapping of the inner gel/glass interface, isolation of a tomographic sub-volume of the tortuous water-filled gel, and comparison of the gel structure with simulations. The nanoscale porous structure is qualitatively consistent with that of the molecular dynamics simulation, enabling in greater confidence in both interrogations. Comparison of the gel/glass interface between desiccated and cryogenically preserved samples reveals consistently abrupt B dissolution behavior and quantitative differences in the apparent H ingress into the glass. These comparisons give some guidance to future experimental approaches to understanding glass corrosion behavior. More broadly, the cryogenic preservation and 3D visualization of the native water/solid structure in 3D at the nanoscale has direct relevance to a wide range of materials systems beyond glass science.

Sodium yttrium fluoride (NaYF4) is an upconverting material with many potential uses in chemistry, materials science, and biology that can be synthesized hydrothermally in both cubic (α) and hexagonal (β) crystallographic polymorphs. Understanding the mechanisms underlying the phase conversion between the cubic and hexagonal polymorphs is of great interest to help inform future efforts to synthesize atomically-precise quantum materials with well-defined sizes and morphologies. In this work, we use a combination of analytical transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), powder X-ray diffraction (XRD), in situ liquid cell TEM, atom probe tomography (APT), and extended x-ray absorption fine structure (EXAFS) measurements to show evidence suggesting that the hexagonal NaYF4 nanowires form through a non-classical crystal growth mechanism involving the formation and subsequent oriented attachment of mesocrystals consisting of cubic (α) plase units. EXAFS spectroscopy also suggests that substitutional Yb3+ point defects within NaYF4 are distributed evenly throughout the crystal lattice without clustering, and also that they may exhibit selective substitution into one of the two possible trivalent yttrium sites in the unit cell for hydrothermally synthesized NaYF4.

Element redistributions after initial oxidation of a Ni38Cr22Fe20Mn10Co10 (at. %) multi-principle element alloy at 120 °C and 300 °C is captured via in situ atom probe tomography. All cations contribute to the oxide in both conditions, consisting of Cr-rich inner oxide and Fe, Mn, Co and Ni-rich outer oxide. At lower temperature, Ni tends to be trapped at the outer/inner oxide interface, while Ni enriches at the oxide/metal interface at higher temperature in tandem with Cr metal depletion. These observations confirm oxidation of complex alloys involves the formation of metastable, multi-layered oxide films, with a distinct tendency for solute trapping.

An improved understanding of high-temperature alloy oxidation is key to the design of structural materials for next-generation energy conversion technologies. An often overlooked, yet fundamental aspect of this oxidation process concerns the fate of the metal vacancies created when metal atoms are ionized and enter the growing oxide layer. In this work, we provide direct experimental evidence showing that these metal vacancies can be inseparably linked to the oxidation process beginning at the very early stages. The coalescence of metal vacancies at the oxide/alloy interface results initially in the formation of low-density metal and eventually in nm-sized voids. The simultaneous and subsequent oxidation of these regions fills the vacated space and promotes adhesion between the growing oxide and the alloy substrate. These structural transformations represent an important deviation from conventional metal oxidation theory, and this improved understanding will aid in the development of new structural alloys with enhanced oxidation resistance. Instead of annihilating, vacancies created early during high-temperature oxidation of a nickel superalloy coalesce into low-density regions. A team led by Richard Oleksak from the National Energy Technology Laboratory in Oregon, USA, used scanning transmission electron microscopy and atom probe tomography to characterize the surface of a nickel superalloy early in the oxidation process. Under the oxide layer, the metal substrate had many voids, and was rich in aluminum oxide. Contrary to conventional metal oxidation theory, vacancies coalesced to form clusters and nanovoids near the oxide/alloy interface while aluminum was selectively oxidized, creating a region of low-density metal rich in aluminum oxide under the surface, which was then incorporated into the growing surface oxide. Research into early and long-term oxidation mechanisms will help better design stable alloys.

The need for a sustainable energy supply in the face of depleting oil reserves has reignited the importance of Fischer–Tropsch (FT) synthesis technology. Presently, the FT process is practiced at the industrial scale to predominately produce synthetic diesel-type fuels and lubricants. More recently, the possibility of hydrogenating CO toward oxygenates, and not just hydrocarbons, has been explored. We have developed a series of CoCuMn and CoMnK catalysts prepared via the oxalate co-precipitation route that are capable of forming oxygenates with desirable selectivity. Upon H2-assisted thermal decomposition of the resultant mixed metal Co1Cu1Mn1 oxalates, catalysts naturally exhibited a cobalt core–copper shell configuration with Mn5O8 dispersed throughout the catalyst nanoparticle as determined via Atom Probe Tomography (APT). We suggest structural changes are induced by the CO and H2 reactants to form the catalytically active phase under real-time reaction conditions as demonstrated by corroborative Density Functional Theory calculations and experimental evidence. APT studies also show that a Co4Mn1K0.1 catalyst post reaction contained a cobalt carbide phase as determined from a Co/C ratio of 2/1. Manganese and potassium were found only in the outermost part of the particle. Both catalysts were found to contain the presence of a Mn5O8 oxidic phase before and post reaction which we attribute to the high activity toward oxygenates of these two catalysts.

Ferritic-austenitic cast duplex stainless steels (CDSS) undergo significant thermal aging embrittlement in service in light water nuclear reactors. Cast CF–3 and CF–8 duplex stainless steels have been laboratory aged for up to 17,200 h at four different temperatures (280 °C, 320 °C, 360 °C, 400 °C) in order to characterize the evolution of microstructure and mechanical properties. Standard Charpy V-Notch (CVN) impact testing and tensile testing have been conducted to measure the progression of embrittlement of the steels. Concurrently, nanoindentation measurements were performed to measure the hardening of the individual ferrite and austenite phases. Atom probe tomography (APT) analysis of the constituent phases is used to investigate the relationship between spinodal decomposition of the ferrite and the mechanical property evolution during aging. The effects of the local microstructure and property changes in the ferrite phase on the overall bulk mechanical property degradation of these steels are discussed.

The distribution of Fe resulting from the autocatalytic interaction of aqueous Fe(II) with the hematite (α-Fe2O3) (001) surface was directly mapped in three dimensions (3D) for the first time, using Fe isotopic labeling and atom probe tomography (APT). Micrometer-sized hematite platelets were reacted with aqueous Fe(II) enriched in 57Fe and prepared for APT using conventional focused ion beam lift-out techniques. Mass spectrum analyses show that specific Fe-ionic species (i.e., Fe2+ and FeO+) accurately reproduce isotopic ratios within natural abundance in the hematite bulk, and thus were utilized to characterize the distribution of 57Fe and quantify Fe isotopic concentrations. 3D reconstructions of Fe isotopic positions along the surface normal direction showed a zone enriched in 57Fe, consistent with oxidative adsorption of Fe(II) and growth at the relict hematite surface reacted with 57Fe(II)aq. An average net adsorption of 3.2–4.3 57Fe atoms nm–2 was estimated using Gibbsian interfacial excess princip...

A room-temperature synthesis of NiFe oxyfluoride (NiFeOF) holey film, using electrochemical deposition and anodic treatments, has been developed in this work. The developed room-temperature synthetic route can preserve the fine nanoporous structure inside the holey film, providing high surface area and abundant reaction sites for electrocatalytic reactions. Both computational and experimental studies demonstrate that the developed NiFeOF holey film with highly porous structure and metal residuals can be used as a high-efficiency and bifunctional catalyst for overall water splitting. Simulation result indicates that the exposed Ni atom on the NiFeOF surface serves as the active site for water splitting. Fe doping can improve the catalytic activity of the Ni active site due to the partial charge-transfer effect of Fe3+ on Ni2+. Electrochemical performance of the NiFeOF catalyst can be experimentally further enhanced through improved electrical conductivity by the residual NiFe alloy framework inside the hol...

Interfaces and their misfit defects determine the material properties of a wide range of applications, such as electronic devices, photocatalysts, and structural materials. However, current atomic-level understanding of interfacial structures is limited. Here we reveal that a special interfacial structure, a mismatched but oriented interface formed by two differently structured facets, gives rise to Ag3PO4 polypods at room temperature in aqueous solution. Transmission and scanning electron microscopy results suggest that interfaces of {1 0 0} and {1 1 0}({1 0 0}/(1 1 0}), {1 0 0}/{1 1 1}, {1 1 0}/{1 1 1}, and {1 0 0}/{1 0 0} have certain orientation relationships, corresponding to the structural energy minima and coincident site lattices of interfacial atoms, as demonstrated by molecular dynamics simulations. Density functional theory calculations indicate that the formation of pyrophosphates and/or phosphates rotation across the interface, as well as deformation of Ag-O bonds, compensate for the lattice mismatch at the interfaces. Our work opens a new avenue for a much wider range of interfacial structures, allow for a higher diversity of structures, and shines light on tailoring crystal structures, morphologies, and their resulting properties.

The nanoscale microstructure and chemistry of a transparent gahnite glass-ceramic and its precursor glass were investigated using atom probe tomography, transmission electron microscopy, and nuclear magnetic resonance spectroscopy. In the annealed precursor glass, statistically significant ZrO clustering was observed along with Si depletion within 2 nm of the ZrO clusters. This clustering is expected to be the first step in the nucleation and crystallization of the nucleating agent, ZrO2. In the glass-ceramic, gahnite (ZnAl2O4) crystallites were found to exist in proximal locations to ZrO2 and not in a core-shell arrangement. The residual glass composition was directly measured by atom probe, showing higher concentrations of Al, Zn, and Zr than previously expected. At the interfaces between the crystallites and residual glass, no enrichment or depletion zones were found. These findings provide answers to outstanding questions surrounding the nucleation and elemental partitioning, microstructure, and the residual glass composition of transparent gahnite glass-ceramics.

The microstructure and mechanical properties in unaged and thermally aged (at 280 °C, 320 °C, 360 °C, and 400 °C to 4300 h) CF–3 and CF–8 cast duplex stainless steels (CDSS) are investigated. The unaged CF–8 steel has Cr-rich M23C6 carbides located at the δ–ferrite/γ–austenite heterophase interfaces that were not observed in the CF–3 steel and this corresponds to a difference in mechanical properties. Both unaged steels exhibit incipient spinodal decomposition into Fe-rich α–domains and Cr-rich α’–domains. During aging, spinodal decomposition progresses and the mean wavelength (MW) and mean amplitude (MA) of the compositional fluctuations increase as a function of aging temperature. Additionally, G–phase precipitates form between the spinodal decomposition domains in CF–3 at 360 °C and 400 °C and in CF–8 at 400 °C. The microstructural evolution is correlated to changes in mechanical properties.

Emergent phenomena at complex oxide interfaces could provide the basis for a wide variety of next-generation devices, including photovoltaics and spintronics. To date, detailed characterization and computational modeling of interfacial defects, cation intermixing, and film stoichiometry have helped to explain many of the novel behaviors observed at a single heterojunction. Unfortunately, many of the techniques employed to characterize a single heterojunction are less effective for a superlattice made up of a repeating series of interfaces that induce collective interfacial phenomena throughout a film. These repeating interfaces present an untapped opportunity to introduce an additional degree of complexity, such as confined electric fields, that cannot be realized in a single heterojunction. In this work, we explore the properties of SrTiO3–LaCrO3 superlattices to understand the role of defects, including variations in cation stoichiometry of individual layers of the superlattice, intermixing across inter...

The development of three-dimensional (3-D), characterisation techniques with high spatial and mass resolution is crucial for understanding and developing advanced materials for many engineering applications as well as for understanding natural materials. In recent decades, atom probe tomography (APT), which combines a point projection microscope and time-of-flight mass spectrometer, has evolved to be an excellent characterisation technique capable of providing 3-D nanoscale characterisation of materials with sub-nanometer scale spatial resolution, with equal sensitivity for all elements. This review discusses the current state, as of APT instrumentation, new developments in sample preparation methods, experimental procedures for different material classes, reconstruction of APT results, the current status of correlative microscopy, and application of APT for microstructural characterisation in established scientific areas like structural materials as well as new applications in semiconducting nano...

The autocatalytic redox interaction between aqueous Fe(II) and Fe(III)-(oxyhydr)oxide minerals such as goethite and hematite leads to rapid recrystallization marked, in principle, by an atom exchange (AE) front, according to bulk iron isotopic tracer studies. However, direct evidence for this AE front has been elusive given the analytical challenges of mass-resolved imaging at the nanoscale on individual crystallites. We report successful isolation and characterization of the AE front in goethite microrods by 3D atom probe tomography (APT). The microrods were reacted with Fe(II) enriched in tracer 57Fe at conditions consistent with prior bulk studies. APT analyses and 3D reconstructions on cross-sections of the microrods reveal an AE front that is spatially heterogeneous, at times penetrating several nanometers into the lattice, in a manner consistent with defect-accelerated exchange. Evidence for exchange along microstructural domain boundaries was also found, suggesting another important link between exchange extent and initial defect content. The findings provide an unprecedented view into the spatial and temporal characteristics of Fe(II)-catalyzed recrystallization at the atomic scale, and substantiate speculation regarding the role of defects controlling the dynamics of electron transfer and AE interaction at this important redox interface.

Element redistributions after initial oxidation of a Ni38Cr22Fe20Mn10Co10 (at.%) multi-principle element alloy at 120 °C and 300 °C is captured via in situ atom probe tomography. All cations contribute to the oxide in both conditions, consisting of a Cr-rich inner oxide and a Fe, Mn, Co and Ni-rich outer oxide. At lower temperature, Ni tends to be trapped at the outer/inner oxide interface, while Ni enriches at the oxide/metal interface at higher temperature in tandem with Cr metal depletion. These observations confirm oxidation of complex alloys involves the formation of metastable, multi-layered oxide films, with a distinct tendency for solute trapping.

Metal salt films play a critical role in high rate dissolution processes such as within an active pit.1-5 To better understand the film growth mechanism, the salt film structure and composition must be characterized with high resolution, which however, is challenging owing to the dynamic nature of the dissolving interface. In this work, a novel cryogenic specimen preparation approach to preserve the pit solution and salt film was introduced, allowing ex situ characterization of the native structure formed on the dissolving metal surface. The salt film formed on a 304 stainless steel one-dimensional artificial pit electrode was preserved by flash freezing in liquid nitrogen while under an external driving potential, processed using cryo-based focused ion beam, and investigated with cryo-based scanning electron microscopy cross sectional imaging. The salt film exhibits a porous structure, with many voids and gaps between salt crystallite clusters, forming channels to provide ionic connection between the metal/film and film/solution interfaces. A spatial separation of Cr and Fe was observed in the salt film using energy dispersive X-ray spectroscopy, while Ni was found to follow the distribution of Fe, indicating the existence of co-precipitated salt containing Fe2+ and Ni2+. Acknowledgments: This work was supported as part of the Center for Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0016584. Reference G. S. Frankel, T. Li, and J. R. Scully, Journal of the Electrochemical Society, 164 (4), C180-C181 (2017). T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165 (9), C484-C491 (2018). T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 165 (11), C762-C770 (2018). T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 166 (6), C115-C124 (2019). T. Li, J. R. Scully, and G. S. Frankel, Journal of The Electrochemical Society, 166 (11), C3341-C3354 (2019).

Pulsed lasers are used in tandem with one-dimensional nanostructures in a wide range of contemporary physical chemistry experiments, including four-dimensional transmission electron microscopy, scanning probe microscopy, and laser-assisted atom-probe tomography (APT). In this work, closed-form solutions for the pulsed photothermal heating of one-dimensional nanomaterials are compared with experimental time-of-flight APT ion spectra from both amorphous and crystalline silicon targets. Analytical results are given for targets with either a uniform cylindrical morphology or an arbitrary degree of conical tapering. Counterintuitively, increasing a conical specimen’s taper-angle is shown to lead to increases in the maximum temperature reached at the tip of the specimen. In particular, the heat source for tapered targets is affected by internal morphology-dependent cavity resonances that increase the maximum tip temperature relative to an untapered cylindrical structure. Experimental time-of-flight ion spectra ...

We report results of measurements of isotopic ratios obtained with atom probe tomography on U3O8 reference materials certified for their isotopic abundances of uranium. The results show good agreement with the certified values. High backgrounds due to tails from adjacent peaks complicate the measurement of the integrated peak areas as well as the fact that only oxides of uranium appear in the spectrum, the most intense of which is doubly charged. In addition, lack of knowledge of other instrumental parameters, such as the dead time, may bias the results. Isotopic ratio measurements can be performed at the nanometer-scale with the expectation of sensible results. The abundance sensitivity and mass resolving power of the mass spectrometer are not sufficient to compete with magnetic-sector instruments but are not far from measurements made by ToF-SIMS of other isotopic systems. The agreement of the major isotope ratios is more than sufficient to distinguish most anthropogenic compositions from natural.

Metal salt films play a critical role in high rate dissolution processes such as within an active pit. However, structural and compositional characterization of salt films is challenging owing to the dynamic nature of the dissolving interface. Here, the salt film formed on SS304 one-dimensional artificial pit surface was preserved by flash freezing and characterized using cryo-based focused ion beam/scanning electron microscopy. The salt film exhibits a porous structure. Ni is co-located with Fe in the salt film, indicating the formation of co-precipitated salt containing Fe2+ and Ni2+. Additionally, a salt film growth model is presented based on ion transport.

Although most studies of organic matter (OM) stabilization in soils have focused on adsorption to aluminosilicate and iron-oxide minerals due to their strong interactions with organic nucleophiles, stabilization within alkaline soils has been empirically correlated with exchangeable Ca. Yet the extent of competing processes within natural soils remains unclear because of inadequate characterization of soil mineralogy and OM distribution within the soil in relation to minerals, particularly in C poor alkaline soils. In this study, we employed bulk and surface-sensitive spectroscopic methods including X-ray diffraction, 57Fe-Mossbauer, and X-ray photoemission spectroscopy (XPS), and transmission electron microscopy (TEM) methods to investigate the minerology and soil organic C and N distribution on individual fine particles within an alkaline soil. Microscopy and XPS analyses demonstrated preferential sorption of Ca-containing OM onto surfaces of Fe-oxides and calcite. This result was unexpected given that the bulk combined amounts of quartz and Fe-containing feldspars of the soil constitute ~90% of total minerals and the surface atomic composition was largely Fe and Al (>10% combined) compared to Ca (4.2%). Soil sorption experiments were conducted with two siderophores, pyoverdine and enterobactin, to evaluate the adsorption of organic molecules with functional groups that strongly and preferentially bind Fe. A greater fraction of pyoverdine was adsorbed compared to enterobactin, which is smaller, less polar, and has a lower aqueous solubility. Using NanoSIMS to map the distribution of isotopically-labeled siderophores, we observed correlations with Ca and Fe, along with strong isotopic dilution with native C, indicating associations with OM coatings rather than with bare mineral surfaces. We propose a mechanism of adsorption by which organics aggregate within alkaline soils via cation bridging, favoring the stabilization of larger molecules with a greater number of nucleophilic functional groups.

Metal catalysts may undergo a series of surface and subsurface structural and chemical transformations during a chemical reaction, which inevitably change the surface properties. Understanding such dynamics from a fundamental science standpoint is important to build rational links between chemical/structural surface properties and the desired catalytic performance. The research presented here addresses, the dynamics of early oxide formation on rhodium (Rh) single nanoparticle during O2 exposures revealing the important role that the subsurface plays. O2 dissociative adsorption, as well as its reaction with H2 mainly imply the Rh{012} regions and is directly observable on Rh nanoparticles with the use of Field Ion and Emission Microscopies (FIM/FEM). Adsorbed oxygen atoms (O(ads)) resulting of the O2 dissociative adsorption can migrate to the bulk through the surface. The combination of our observations by FEM and our observations using Atom Probe Tomography (APT) reveals an inter-facet cooperation between Rh{012} and Rh{113} during this process., info:eu-repo/semantics/published