Mineral-organic matter (OM) studies have predominantly focused on acidic soils that are abundant in iron (Fe) oxides and aluminum (Al) oxides. We have probed mineral-OM interactions in an alkaline or calcareous soil of the Aridisols class. Unlike the role of Fe and Al, the role of Ca-minerals (particularly calcite), which are ubiquitous in alkaline soils, in OM sequestration is not well understood. Multiple recent model studies with aqueous Ca2+ or synthetic calcite and a suite of OM compounds have shown Ca-OM assemblages to be spatially correlated with calcite at the microscale. To study the chemical state of both Ca and Fe and their competing role in soil organic matter (SOM) stabilization, we performed laboratory characterization using x-ray diffraction, Mossbauer spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, and scanning transmission electron microscopy, alongside synchrotron-based microscale chemical imaging using scanning transmission xray microscopy combined with near-edge x-ray absorption fine structure. Ca mineral-organic associations were found to be ubiquitous in this system and are likely critical for understanding SOM stabilization/degradation in alkaline soils. From our findings on mineralogy, speciation, and the nature of Ca-OM bridging, we identified differences in C and Ca chemistry based on the relative location of OM to Ca minerals. The OM near the calcite crystal was enriched in lipid and protein moieties, Ca-OM next to Fe minerals displayed a strong contribution from aromatic compounds, while on the surface of microbes, the carbonate was believed to be of microbial in origin, as also suggested by preliminary works reporting on the formation of amorphous calcite or nano-calcite. In Ca-OM admixed with carbonate, it was difficult to distinguish Ca-associated OM from amorphous calcite or nano-calcite.

We quantify the effects of intensely applied electric fields on the Fe oxidation mechanism. The specimen are pristine Fe single crystals exposing a variety of surface structures identified by field ion microscopy. These crystals are simultaneously exposed to low pressures of pure oxygen gas, on the order of 10‐7 mbar, while applying intense electric fields on their surface of several tens of volts per nanometer. The local composition of the different surface structures is probed directly and in real time using an Environmental Atom Probe and successfully compared with first principles‐based models. We found that rough Fe{244} and Fe{112} facets are more reactive toward oxygen than compact Fe{024} and Fe{011} facets. Results demonstrate that the influence of an electric field on the oxidation kinetics depends on the timescales that are involved as the system evolves toward equilibrium. The initial oxidation kinetics show that strong increases in electric fields facilitate the formation of an oxide. However, as one approaches equilibrium, high field values mitigate this formation. Ultimately, this study elucidates how high externally applied electric fields can be utilized to dynamically exploit reaction dynamics at the nanoscale towards desired products in a catalytic reaction at mild reaction conditions.

Hydrogen embrittlement mechanisms of steels have been studied for several decades. Understanding hydrogen diffusion behavior in steels is crucial towards both developing predictive models for hydrogen embrittlement and identifying mitigation strategies. However, because hydrogen has a low atomic mass, it is extremely challenging to detect by most analytical methods. In recent years, cryogenic-transfer atom probe tomography (APT) of electrochemically-deuterium-charged steels has provided invaluable qualitative analysis of nanoscale deuterium traps such as carbides, dislocations, grain boundaries and interfaces between ferrite and cementite. Independently, cyclic voltammetry (CV) has provided valuable analysis of bulk hydrogen diffusion in steels. In this work, we use a combination of CV and cryogenic-transfer APT for quantitative analysis of deuterium pickup in electrolytically charged pure Fe (ferrite) and a model austenitic Fe18Cr14Ni alloy without any second phase. The high solubility and low diffusivity of hydrogen in austenite versus ferrite and potential influence of oxide layer are highlighted to result in clear observable signatures in CV and cryogenic-transfer APT results. The remaining challenges and pathway for enabling quantitative analysis of hydrogen pick up in steels is also discussed.

Journal Article Nanoscale Mapping of Hydrogen Distribution in Nuclear Structural Materials Using Cryogenic Transfer Atom Probe Tomography Get access Arun Devaraj, Arun Devaraj Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, United States Corresponding author: arun.devaraj@pnnl.gov Search for other works by this author on: Oxford Academic Google Scholar Dallin J Barton, Dallin J Barton National Security Directorate, Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Mark G Wirth, Mark G Wirth Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Daniel E Perea Daniel E Perea Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, United States Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 1553–1554, https://doi.org/10.1093/micmic/ozad067.799 Published: 22 July 2023

The trace element chemistry of pyrite can be used to determine the origin, timing, and conditions of formation of ore deposits; as a vectoring tool for mineral exploration; and to determine the evolution of the Earth's oceanic and atmospheric chemistry. However, little is known about whether trace elements are held with the pyrite structure or within nano-inclusions of other phases. This distinction is important for two primary reasons. First, trace element incorporation into the pyrite structure can affect the partitioning of other trace elements. Second, if trace elements are held within nano-inclusions, the partition coefficient of the mineral phases that make up the nano-inclusion, rather than pyrite, are the critical consideration in related interpretations. Previous studies addressing this topic have used laser ablation inductively coupled plasma mass spectrometry; however, the resulting data do not provide sufficient spatial resolution to delineate trace element distributions unless the inclusions are large. Further, they use these flat element profiles in time resolved laser ablation output graphs to argue that pyrite trace element content provides a direct relationship between trace element content of seawater and pyrite trace element content. To improve resolution, we have used atom probe tomography to characterize trace element distributions in pyrite framboids from the Cariaco Basin and Demerara Rise in three-dimensions at sub-nanometer resolution. Manganese was found to be concentrated in the pyrite nanocrystal part of the original framboid structure. In contrast, Ni was mostly found along the grain boundary, though it still appeared to be contained within the pyrite structure. Copper was concentrated in later pyrite overgrowths, and As varied in its location. These observations suggest that some important trace elements are incorporated into pyrite during early diagenesis, even in euxinic settings dominated by water-column pyrite formation. Statistical analysis was used to determine whether trace elements were incorporated in the lattice or within nanoscale inclusions (referred to here are nano-inclusions). We found that As, Ni, Cu, and Mn were commonly held within the pyrite structure, but As, Ni, and Cu can also be held as nano-inclusions or within grain interfaces. Incorporation of As is known to enhance the incorporation of other trace elements and in this case appears to correlated to elevated Ni and Cu concentrations in the Cariaco Basin samples. Understanding these relationships strongly impacts our ability to utilize pyrite trace metal concentrations to analyze and quantify early ocean chemistry and its evolution through time.

Pyrite trace element chemistry is important for understanding evolution of ore fluids in mineralizing systems. Much of the understanding of how metals are held in pyrite is based on micro-scale techniques such as LA-ICPMS and electron microprobe. This requires assumptions to be made when interpreting the results regarding whether elements are held as micro-inclusions versus as substitutions into the pyrite lattice. In this contribution, we use micro- to nano-scale analyses including LA-ICPMS, NanoSIMS, and atom probe tomography (APT) to investigate trace element deportment in pyrite from sites characterized by high trace element concentrations (Black Butte SEDEX deposit) and one characterized by medium to low trace element concentrations (Leicester pyrite member, New York). We further use synchrotron based XANES to investigate the redox state of As and how that relates to trace element enrichment. We find that trace elements are highly heterogeneous at all scales investigated and that interpretation of how trace elements are incorporated into pyrite using even micro-scale techniques must be pursued with caution.

Journal Article Elucidating Surface Properties by Correlative TEM and APT Studies of Ideal Mg Specimens Prepared Under Controlled Environments Get access C S Bonifacio, C S Bonifacio E.A. Fischione Instruments, Inc., Export, PA, USA Corresponding author: cs_bonifacio@fischione.com Search for other works by this author on: Oxford Academic Google Scholar D E Perea, D E Perea Pacific Northwest National Laboratory, Richland, WA, USA Search for other works by this author on: Oxford Academic Google Scholar P Nowakowski, P Nowakowski E.A. Fischione Instruments, Inc., Export, PA, USA Search for other works by this author on: Oxford Academic Google Scholar M L Ray, M L Ray E.A. Fischione Instruments, Inc., Export, PA, USA Search for other works by this author on: Oxford Academic Google Scholar P Fischione P Fischione E.A. Fischione Instruments, Inc., Export, PA, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 29, Issue Supplement_1, 1 August 2023, Pages 2073–2074, https://doi.org/10.1093/micmic/ozad067.1073 Published: 22 July 2023

The compact size, scalability, and strongly confined fields in integrated photonic devices enable new functionalities in photonic networking and information processing, both classical and quantum. Gallium phosphide (GaP) is a promising material for active integrated photonics due to its high refractive index, wide band gap, strong nonlinear properties, and large acousto-optic figure of merit. In this work we demonstrate that silicon-lattice-matched boron-doped GaP (BGaP), grown at the 12-inch wafer scale, provides similar functionalities as GaP. BGaP optical resonators exhibit intrinsic quality factors exceeding 25,000 and 200,000 at visible and telecom wavelengths respectively. We further demonstrate the electromechanical generation of low-loss acoustic waves and an integrated acousto-optic (AO) modulator. High-resolution spatial and compositional mapping, combined with ab initio calculations indicate two candidates for the excess optical loss in the visible band: the silicon-GaP interface and boron dimers. These results demonstrate the promise of the BGaP material platform for the development of scalable AO technologies at telecom and provide potential pathways toward higher performance at shorter wavelengths.

This study investigates the sequestration and transformation of silver (Ag) and arsenic (As) ions in soil organic matter (OM) at the nanoscale using the combination of atom probe tomography (APT), transmission electron microscopy (TEM), focused ion beam (FIB), ion mill thinning and scanning electron microscopy (SEM). Silver-arsenic contaminated organic-rich soils were collected along the shore of Cobalt Lake, a former mining and milling site of the famous Ag deposits at Cobalt, Ontario, Canada. SEM examinations show that particulate organic matter (OM grains) contains mineral inclusions composed of mainly Fe, S, and Si with minor As and traces of Ag. Four OM grains with detectable concentrations of Ag (by SEM-EDS) were further characterized with either a combination of TEM and APT or TEM alone. These examinations show that As is predominantly sequestered by OM through either co-precipitation with Fe-(hydr)oxide inclusions or adsorption on Fe-(hydr)oxides and their subsequent transformation into scorodite (FeAsO4·2H2O)/amorphous Fe-arsenate (AFA). Silver nanoparticles (NPs) with diameters in the range of ∼5-20 nm occur in the organic matrix as well as on the surface of Fe-rich inclusions (Fe-hydroxides, Fe-arsenates, Fe-sulfides), whereas Ag sulfide NPs were only observed on the surfaces of the Fe-rich inclusions. Rims of Ag-sulfides on Ag NPs (TEM data), accumulation of S atoms within and around Ag NPs (APT data), and the occurrence of dendritic as well as euhedral acanthite NPs with diameters in the range of ∼100-400 nm (TEM data) indicate that the sulfidation of the Ag NPs occurred via a mineral-replacement reaction (rims) or a complete dissolution of the Ag NPs, the subsequent precipitation of acanthite NPs and their aggregation (dendrites) and Ostwald ripening (euhedral crystals). These results show the importance of OM and, specifically the mineral inclusions in the sequestration of Ag and As to less bioavailable forms such as acanthite and scorodite, respectively.

Understanding the early stages of interactions between oxygen and material surfaces—especially at very high spatial resolutions—is highly beneficial for fields ranging from materials degradation, corrosion, geological sciences, forensics, and catalysis. The ability of in situ atom probe tomography (APT) is demonstrated to track the diffusion of oxygen and metal ions at nanoscale spatial resolution during the early stages of oxidation of a model Fe–Cr–Ni alloy. Using 18 O isotope tracers in these in situ APT experiments and complementary ex situ multimodal microscopy, spectroscopy, and computational simulations allows to precisely analyze the kinetics of oxidation and determine that outward cation diffusion to oxide/air interface is the primary mechanism for intragranular oxide growth in this alloy at 300 °C. This unique in situ isotopic tracer APT approach and the insights gained can be highly beneficial for studying early stages of gas–surface reactions in a broad array of materials.

An abstract is not available for this content so a preview has been provided. As you have access to this content, a full PDF is available via the ‘Save PDF’ action button.