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Analytical sensitivity versus analytical volume for APT compared with other commonly used geoscience characterisation techniques. Figure modified from an original version by Cameca.
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Atom probe tomography is an analytical technique that provides quantitative three‐dimensional elemental and isotopic analyses at sub‐nanometre resolution across the whole periodic table. Although developed and mostly used in the materials science and semiconductor fields, recent years have seen increasing development and application in the geoscien...
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... geological processes are fundamentally controlled by element interactions at this scale, so the ability to quantify elemental and isotopic compositions with nanometre resolution has the potential to greatly increase our understanding of fundamental geological processes. However, few analytical techniques are capable of providing such resolution (Figure 1). One such technique is atom probe tomography (APT), a timeof-flight mass spectrometry system that characterises atomic species and position with sub-nanometre spatial resolution. ...
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... histogram of the mass-to-charge values (measured in Daltons, Da) is generated as a 'mass spectrum', and the mass values are calibrated from known mass peaks. A typical spectrum collected from a feldspar sample indicates the presence of single and molecular ions at different multiple charge states and further illustrates the ability to distinguish between different isotopes ( Figure 10). The capacity to identify and separate mass peaks is dependent on the mass resolving power (MRP), defined as an inverse measure of the mass peak width (Dm) with respect to the mass-to-charge value (m): ...
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... effects, for example, due to local field distortions at atomic terrace step-edges in crystalline samples, are referred to as trajectory aberrations ( Waugh et al. 1976, Vurpillot et al. 2000b). Larger-scale distortions can occur wherever there are differences in the field strength required to evaporate atoms from local regions on the surface ( Figure 11). These effects, known as 'local magnification', illustrate an important limitation in obtaining an accurate spatial reconstruction. ...
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... of sample selection is initially similar to other microanalysis techniques, with rock samples from wellcharacterised igneous, sedimentary or metamorphic terrains being collected during fieldwork, and progressively smaller regions of interest then being selected and sequentially characterised ( Figure 12). Thin sections or grain mounts are commonly used, though unpolished fracture surfaces or powders can also be utilised. ...
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... addition, ToF-SIMS instruments provide mass-to-charge ratio spectra like those generated by APT, but the different acquisition conditions mean that some m/q peaks are found in different positions. This can help with identification of peaks and highlight potential interferences in the atom probe data (Figure 13). Furthermore, the incorporation of ToF-SIMS systems into focussed ion-beam scanning electron microscopes (FIB-SEM) used for atom probe specimen preparation enables compositional information to be in used for targeting ( Rickard et al. 2020). ...
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... recent years, site-specific sample preparation of both conductive and non-conductive materials has increasingly utilised FIB-SEM ( Waugh et al. 1984, Alexander et al. 1989, Larson et al. 1999), and a number of methods for FIB-based specimen preparation have been developed (e.g., see reviews by , McKenzie et al. 2010, Blum et al. 2016. However, most facilities now use a similar methodology for site-specific atom probe specimens ( Figure 14). This method involves the deposition of a small, rectangular, protective Pt capping layer over the region of interest followed by the removal of a 2.5 µm wide triangular prism, with a length dependent on the number of required APT tips. ...
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... method involves the deposition of a small, rectangular, protective Pt capping layer over the region of interest followed by the removal of a 2.5 µm wide triangular prism, with a length dependent on the number of required APT tips. Segments of the prism (approximately 2 µm wide) are then mounted on pre-sharpened posts on a silicon coupon and ion beam milled with an annular mask to produce a needle shape with a final tip diameter < 100 nm ( Figure 14). The mounting of regions of interest onto 'microtips' on a single coupon simplifies specimen preparation and handling (Thompson et al. 2005), while mounting onto a TEM grid enables correlative microscopy studies (Gorman et al. 2008). ...
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... cases where atom probe acquisition is stopped prior to tip failure, reimaging of the specimen after the analysis, and comparison with images taken before the analysis allow the analysed volume to be precisely measured (Figure 15). This information can be used to establish, or refine, the correct reconstruction parameters for a particular mineral. ...
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... tomography by TEM and STEM (K€ ubel et al. 2005) also provides new opportunities for better reconstruction parameters. Cross-correlating electron tomography results with atom probe analyses has been shown to ensure the better specimen radius, shank angle, and zdirection scaling of atom probe reconstructions ( Arslan et al. 2008, Gorman et al. 2008) (Figure 16). In addition, and in a similar way to the SEM, TEM can be performed after APT analysis on analysed specimens to measure the amount of material that has been removed during the atom probe analysis and determine reconstruction parameters. ...
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... the development of laser-assisted APT, there has been growing interest in applying nanoscale geochemical characterisation to a broad range of geological materials including glass ( Gin et al. 2013, Hellmann et al. 2015, Gin et al. 2017), diamond (Heck et al. 2014, Lewis et al. 2015, Schirhagl et al. 2015, Mukherjee et al. 2016), Fe-Ni metal alloys ( Einsle et al. 2018) and silicides ( Gopon et al. 2017), platinum-group alloys ( Parman et al. 2015, Daly et al. 2017, oxides ( Bachhav et al. 2011, Fahey et al. 2016, Taylor et al. 2018, Frierdich et al. 2019 analyses by SIMS were disturbed at the nanoscale, but the disturbance could be temporally constrained through the characterisation of isotopic ratios in different Pb domains (Valley et al. 2014(Valley et al. , 2015; Figure 18a). A similar study on discrete Pb reservoirs in discordant zircon provided some insights into the mechanisms of Pb segregation and the role of defects in forming discrete Pb isotopic reservoirs (Peterman et al. 2016(Peterman et al. , 2019; Figure 18b). ...
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... the development of laser-assisted APT, there has been growing interest in applying nanoscale geochemical characterisation to a broad range of geological materials including glass ( Gin et al. 2013, Hellmann et al. 2015, Gin et al. 2017), diamond (Heck et al. 2014, Lewis et al. 2015, Schirhagl et al. 2015, Mukherjee et al. 2016), Fe-Ni metal alloys ( Einsle et al. 2018) and silicides ( Gopon et al. 2017), platinum-group alloys ( Parman et al. 2015, Daly et al. 2017, oxides ( Bachhav et al. 2011, Fahey et al. 2016, Taylor et al. 2018, Frierdich et al. 2019 analyses by SIMS were disturbed at the nanoscale, but the disturbance could be temporally constrained through the characterisation of isotopic ratios in different Pb domains (Valley et al. 2014(Valley et al. , 2015; Figure 18a). A similar study on discrete Pb reservoirs in discordant zircon provided some insights into the mechanisms of Pb segregation and the role of defects in forming discrete Pb isotopic reservoirs (Peterman et al. 2016(Peterman et al. , 2019; Figure 18b). Trace element mobility has been studied in undeformed zircon ( Piazolo et al. 2017, Peterman et al. 2019) and deformed zircon ( Piazolo et al. 2016, and similar studies have been undertaken on baddeleyite (White et al. 2017, White et al. 2018a, b), monazite ( Fougerouse et al. 2018, Seydoux-Guillaume et al. 2019), titanite ) and rutile ( Verberne et al. 2019). ...
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... these varying properties also have the potential to affect the ability of specific minerals to be analysed by APT due to difficulties in sample preparation and/or a propensity to rupture in the high electric fields required for field emission. To date, published atom probe data exist for a limited number of minerals ( Figure 17; Table 2) and, in most cases, analysed minerals have tended to have high crystal symmetry and reasonable Mohs' hardness. However, experiments on galena (Pb sulfide) and zinnwaldite (Li-bearing mica) show that APT can also be successfully applied to relatively soft minerals, which in the latter case are also strongly anisotropic, cleaved and has low crystal symmetry (Fig- ure 19). ...
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... date, published atom probe data exist for a limited number of minerals ( Figure 17; Table 2) and, in most cases, analysed minerals have tended to have high crystal symmetry and reasonable Mohs' hardness. However, experiments on galena (Pb sulfide) and zinnwaldite (Li-bearing mica) show that APT can also be successfully applied to relatively soft minerals, which in the latter case are also strongly anisotropic, cleaved and has low crystal symmetry (Fig- ure 19). Despite such success, assessment of the crystallographic orientation dependence on atom probe acquisition parameters and yield may be needed in minerals, such as micas, where there is a high degree of crystallographic anisotropy. ...
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... ( Fougerouse et al. 2016; Figure 21a). In cases such as this, where compositionally distinct inclusions are present, the reconstruction of spatial relationships is critical. ...
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... cases such as this, where compositionally distinct inclusions are present, the reconstruction of spatial relationships is critical. However, these data illustrated potential issues in the reconstruction of such small compositional features because the field required for evaporation differs markedly between the nanoscale inclusion ( Figure 11), in this case gold, and the host arsenopyrite matrix (Figure 21a). Similar features have been seen in atom probe studies of synthetic specimens of spherical gold nanoparticles in MgO (Devaraj et al. 2014). ...
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... cases such as this, where compositionally distinct inclusions are present, the reconstruction of spatial relationships is critical. However, these data illustrated potential issues in the reconstruction of such small compositional features because the field required for evaporation differs markedly between the nanoscale inclusion ( Figure 11), in this case gold, and the host arsenopyrite matrix (Figure 21a). Similar features have been seen in atom probe studies of synthetic specimens of spherical gold nanoparticles in MgO (Devaraj et al. 2014). ...
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... features have been seen in atom probe studies of synthetic specimens of spherical gold nanoparticles in MgO (Devaraj et al. 2014). The alternative scenario of nanoparticles requiring a lower field for evaporation than the host has also been reported for Pb clusters in zircon (Figure 18b; Peterman et al. 2016). Such studies serve to illustrate that care should be taken in interpreting reconstructed inclusion morphologies when the field required for evaporation is markedly different between host and inclusion. ...
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... advantage of APT is its ability to place compositional constraints on the trace element and isotope geochemistry of the included phase. For example, Ca-rich clusters in monazite (Figure 21b), interpreted to represent inclusions of nanoscale apatite ( Fougerouse et al. 2018), also contain trace amounts of Si and Pb which is enriched when compared with the host monazite. The apatite inclusions have been interpreted to segregate shortly after monazite growth and they preferentially partition common Pb within the monazite lattice. ...
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... potential area of future research is in the analysis of nanoscale fluid inclusions within minerals. A likely example is the presence of OH 3 peaks associated with the tips of segregated Fe-rich lamellae in rutile (Figure 21c). In this case, the reconstruction of OH 3 distribution shows an unusual pattern of dispersion that likely represents trajectory aberrations associated with rapid evaporation of the inclusion contents once the inclusion has been breached. ...
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... of these clusters, using 3D volumes defined by isoconcentration surfaces (Hellman et al. 2000) or cluster analysis routines (e.g., Stephenson et al. 2007, Dong et al. 2019, significantly reduces the analytical background and permits quantification of compositional and isotopic analysis of these clusters. 207 Pb/ 206 Pb measurements of clusters in both concordant and discordant zircon (Figure 18) have been shown to be distinct from bulk isotopic compositions outside the cluster and this has allowed the isotopic compositions of the clusters to be used to constrain the timing of geological events ( Valley et al. 2014, Peterman et al. 2016). ...
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... clusters have also been found in other minerals and again the mechanisms of cluster formation are notably different. As outlined earlier, Pb associated with nanoinclusions of apatite in monazite (Figure 21b) have been interpreted to reflect partitioning of Pb into apatite during unmixing of phosphate end-member compositions immediately after growth ( Fougerouse et al. 2018). However, APT and TEM data from high-temperature monazite grains from Rogaland, Norway, contain CaSO 4 nanoclusters that appear to be linked to Pb mobility associated with cluster formation during a younger, high-temperature metamorphic event ( Laurent et al. 2016, Seydoux-Guillaume et al. 2019). ...
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... materials science studies include stable isotopic characterisation of both anions and cations and include C ( Thuvander et al. 2011), O ( Kinno et al. 2014), S ( Gopon et al. 2019), N ( Kinno et al. 2015), Si ( Shimizu et al. 2009), Fe (Taylor et al. 2018, Frierdich et al. 2019), Zn (Ironside et al. 2017) and Ge ( Shimizu et al. 2013). The sensitivity of isotopic analysis at nanometre scales is fundamentally limited by the number of atoms available within a small analytical volume (Figure 1). For spherical volumes around 100 nm in size, which can be accommodated within a typical APT reconstruction, isotopic sensitivities of 1 per mille may be achieved for elements present at 1-5% concentration. ...
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... of atom probe analysis of U isotopes in certified U 3 O 8 reference materials has shown that major isotopic ratios agree with known compositional values (Fahey et al. 2016) and there are comparative thermal ion mass spectrometry (TIMS) and atom probe studies that show that Re-Os analysis by atom probe may yield similar, though less precise, ages to more traditional TIMS analyses (Daly et al. 2018). A number of studies have also investigated the mechanisms that can affect the distribution of radiogenic 207 Pb/ 206 Pb ratios in zircon (Figure 18; Valley et al. 2014, Peterman et al. 2016, Blum et al. 2018), baddeleyite ( White et al. 2017) and monazite ( Fougerouse et al. 2018, Seydoux-Guillaume et al. 2019). The nanoscale distribution of common Pb associated with deformation-related defects has also been studied in titanite ) and pyrite ( Fougerouse et al. 2019). ...
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... a heterogeneous material, the different constituents of the material rarely have the same field evaporation properties. Differences in these properties will induce the preferential evaporation of the low-field constituent relative to the high-field component and create asperities (or topography) at the surface of the specimen (Figure 11). This nanoscale topography will create ion trajectory aberrations in comparison with a smooth surface. ...
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... Nevertheless, beam sizes are larger which makes the sampling difficult. Few analytical techniques can quantify elemental and isotopic compositions throughout the whole periodic table of elements, with an optimum combination of spatial resolution and detection limit, as APT (Reddy et al., 2020). In metallic phases, the spatial resolution (true 3-D) is less than 1 nm 3 , and the lowest sensitivity (as estimated from steels) is less than 50 atomic ppm. ...
The presence of spheroidized plessite (SP) in mesosiderites was recently reported in the literature. This finding coupled with the poor understanding of this plessite variant, motivated us to investigate its formation process and evaluate its implications in assessing the previous proposals concerning mesosiderites' genesis and cooling history. SP consists of spherulitic taenite particles irregularly distributed, usually surrounded by carbides, and embedded in a kamacite matrix. It has been reported in iron meteorites containing graphite, carbides, and pearlitic plessite (PP), especially in the IAB main group and the sLL and sLH subgroups. From the combination of X‐ray tomography, electron backscatter diffraction, energy‐dispersive spectrometry, and atom probe tomography in three samples of Vaca Muerta mesosiderite (A1, low to moderate metamorphism) from the ICATE (Argentina) collection of meteorites, we were able to identify a common crystallographic orientation between spheroids and retained taenite, the absence of PP and the carbon depletion in the metallic portion contiguous to the spheroids, and the high volumetric connectivity of the metallic portion. Based on these findings: (i) SP likely grew at the expense of pearlite lamellae, with their absence resulting from complete consumption after an extraordinarily slow cooling rate, probably succeeding a deep burial in a breccia of rock fragments. (ii) Carbon introduction would have followed plessite formation in mesosiderites at a temperature low enough to prevent carbon solid‐state diffusion. (iii) Metal would have been poured in silicates, which favors the collision model between a differentiated asteroid and a molten core for mesosiderite genesis.
... In general, the high background and thermal tailing of the 40 Ca 2+ signal cannot be completely suppressed by optimizing the measurement parameters and/or specimen geometries for bone specimens, resulting always in a loss of information. This makes it impossible to identify and quantify trace elements and complicates the determination of isotope ratios, which can be crucial for the quantification for e.g. for the dating of fossils and minerals [88]. ...
Bone structure is generally hierarchically organized into organic (collagen, proteins,...), inorganic (hydroxyapatite (HAP)) components. However, many fundamental mechanisms of the biomineralization processes such as HAP formation, the influence of trace elements, the mineral-collagen arrangement, etc., are not clearly understood. This is partly due to the analytical challenge of simultaneously characterizing the three-dimensional (3D) structure and chemical composition of biominerals in general at the nanometer scale, which can, in principle be achieved by atom probe tomography (APT). Yet, the hierarchical structures of bone represent a critical hurdle for APT analysis in terms of sample yield and analytical resolution, particularly for trace elements, and organic components from the collagen appear to systematically get lost from the analysis. Here, we applied in-situ metallic coating of APT specimens within the focused ion beam (FIB) used for preparing specimens, and demonstrate that the sample yield and chemical sensitivity are tremendously improved, allowing the analysis of individual collagen fibrils and trace elements such as Mg and Na. We explored a range of measurement parameters with and without coating, in terms of analytical resolution performance and determined the best practice parameters for analyzing bone samples in APT. To decipher the complex mass spectra of the bone specimens, reference spectra from pure HAP and collagen were acquired to unambiguously identify the signals, allowing us to analyze entire collagen fibrils and interfaces at the near-atomic scale. Our results open new possibilities for understanding the hierarchical structure and chemical heterogeneity of bone structures at the near-atomic level and demonstrate the potential of this new method to provide new, unexplored insights into biomineralization processes in the future.
... This inverse problem and the situational ambiguity cause the data interpretation for SAXS to be more extensive than for TEM and represents the key trade-off in regard to using other techniques. [283], [287], [288] . ...
... The dotted arrows indicate the potential extensibility. Adapted and modified from sources [283], [287], [288] . Figure 11: A illustrates the electron density distribution of a spherical core particle enveloped by a shell/ligand and surrounded by a solvent. ...
The rising demand for quantum dots (QDs) necessitates swift and reliable quality verification methods. This work focuses on the synthesis of organically passivated CdSe core QDs and their comprehensive characterization via UV/Vis spectroscopy, transmission electron microscopy, and small-angle X-ray scattering (SAXS). The aim was to correlate data to ISO/TS 17466 (data standard deviation ~15%) and to validate SAXS as a reliable method for sizing data modeling. This was achieved by obtaining the number-weighted hard-sphere parameter Dn with a relative deviation percentage of 6.9 ± 4.4 %. Additionally, the volume-weighted gyradius Dg, the model-free mode of the pair-distribution function Dmode, and the volume-weighted hard-sphere parameter Dv were derived and expressed as readily applicable tight-binding model functions. This work utilized laboratory SAXS to measure sub-2 nm particles and various bimodal size distributions of mixed particle samples between 2 and 7 nm. The traceable results significantly enhanced the certainty of characterizing such small particles near the instrumental resolution limit. The generalized indirect Fourier transform method consistently identified mean values for bimodal samples, demonstrating SAXS as a viable method. However, individual population modes were only revealed using experimentally weak Lagrange multiplier.
Additionally, this work addresses the longevity of colloidal QDs by preserving their size distribution through embedding in epoxy resin, yielding easily manageable casts of great value for various SAXS applications. The method for epoxy resin embedment supports the proof-of-concept of core CdSe nanoparticles as a sub-10 nm standard, although homogenizing cast processing optimizations are necessary to reduce uncertainties. Hence, an alternative design concept for vertical instead of horizontal casting is proposed. Furthermore, it was observed that the surrounding matrix blue-shifts the band edge energy proportional to the number fraction of surface atoms, highlighting the necessity of understanding matrix-dependent sizing data. Surface reconstruction effects are indicated as the main cause, with follow-up experiments proposed for probing the impact of stress by alternating the matrix. Critical factors for establishing a CdSe QD standard from pre-synthesis to post-evaluation are discussed, emphasizing the importance of handling and process unification. These metrological discussions are essential to delimit the size-dependent property range and uncertainty inherent in the quantum dot material itself.
... In general, the high background and thermal tailing of the 40 Ca 2+ signal cannot be completely suppressed by optimizing the measurement parameters and/or specimen geometries for bone specimens, resulting always in a loss of information. This makes it impossible to identify and quantify trace elements and complicates the determination of isotope ratios, which can be crucial for the quantification for e.g. for the dating of fossils and minerals [88]. ...
Bone structure is generally hierarchically organized into organic (collagen, proteins, ...), inorganic (hydroxyapatite (HAP)) components. However, many fundamental mechanisms of the biomineralization processes such as HAP formation, the influence of trace elements, the mineral-collagen arrangement, etc., are not clearly understood. This is partly due to the analytical challenge of simultaneously characterizing the three-dimensional (3D) structure and chemical composition of biominerals in general at the nanometer scale, which can, in principle be achieved by atom probe tomography (APT). Yet, the hierarchical structures of bone represent a critical hurdle for APT analysis in terms of sample yield and analytical resolution, particularly for trace elements, and organic components from the collagen appear to systematically get lost from the analysis. Here, we applied in-situ metallic coating of APT specimens within the focused ion beam (FIB) used for preparing specimens, and demonstrate that the sample yield and chemical sensitivity are tremendously improved, allowing the analysis of individual collagen fibrils and trace elements such as Mg and Na. We explored a range of measurement parameters with and without coating, in terms of analytical resolution performance and determined the best practice parameters for analyzing bone samples in APT. To decipher the complex mass spectra of the bone specimens, reference spectra from pure HAP and collagen were acquired to unambiguously identify the signals, allowing us to analyze entire collagen fibrils and interfaces at the near-atomic scale. Our results open new possibilities for understanding the hierarchical structure and chemical heterogeneity of bone structures at the near-atomic level and demonstrate the potential of this new method to provide new, unexplored insights into biomineralization processes in the future.
... Quantifying the particle compositions is challenging, mainly due to their small sizes. The atom positions in the reconstructed map may be slightly delocalized, making it difficult to define the boundary of the particles that best represents their compositions (Vurpillot et al. 2000;Fougerouse et al. 2016;Reddy et al. 2020). APT analysis is also Bright-field TEM images of the foil prepared in the vicinity of the APT specimens show a high density of butterflyshaped strain fields typical for coherent particle inclusions (Fig. 9A). ...
In natural corundum, a strong geochemical correlation is sometimes observed between Be and heavy high field strength elements (HHFSEs) such as Nb, Ta and W, and it has been hypothesized that trace elements are hosted in primary inclusions. However, no known mineral enriched in both Be and HHFSEs stable at these geological conditions can explain this correlation. To understand how Be and HHFSEs are distributed in natural corundum down to the atomic scale, two natural Be-bearing sapphire crystals from Afghanistan and Nigeria are studied using laser ablation inductively coupled plasma and time-of-flights secondary ion mass spectrometry, atom probe tomography and transmission electron microscopy. In addition to common trace elements such as Mg, Ti, and Fe, Be and W are detected in the metamorphic sapphire from Afghanistan, whereas Be, Nb and Ta are detected in the magmatic sapphire from Nigeria. Nanoclustering in both samples shows fractionation of Be and high field strength elements (including Ti) by atomic mass, suggesting a secondary process controlled by solid-state diffusion. The homogeneously distributed W and the secondary nano-precipitates bearing Nb and Ta indicates that HHFSEs can be incorporated into the corundum structure during crystallization, most likely through preferred adsorption on the growth surface. The strong correlation between Be and HHFSEs across the growth zones is probably due to Be being attracted by HHFSEs to partially balance the charge when incorporated into the corundum structure. The enrichment of high field strength elements by growth kinetics may result in supersaturated concentrations during crystallization, allowing them to precipitate out when the host corundum is heated above its formation temperature by basaltic magma. Comparison with previous transmission electron microscope studies suggests the same process for incorporating Be and HHFSEs also applies to other natural corundums from different localities.
... APT has the capability of determining the distribution of major and trace elements at sub-nanometer resolution for mineral samples (38). The APT needle-shaped specimens were prepared using a Tescan Lyra3 Ga + focused ion beam coupled with a scanning electron microscope (FIB-SEM) at Curtin University. ...
Finding direct evidence for hydrous fluids on early Mars is of interest for understanding the origin of water on rocky planets, surface processes, and conditions essential for habitability, but it is challenging to obtain from martian meteorites. Micro- to nanoscale microscopy of a unique impact-shocked zircon from the regolith breccia meteorite NWA7034 reveals textural and chemical indicators of hydrothermal conditions on Mars during crystallization 4.45 billion years ago. Element distribution maps show sharp alternating zoning defined by marked enrichments of non-formula elements, such as Fe, Al, and Na, and ubiquitous nanoscale magnetite inclusions. The zoning and inclusions are similar to those reported in terrestrial zircon crystallizing in the presence of aqueous fluid and are here interpreted as primary features recording zircon growth from exsolved hydrous fluids at ~4.45 billion years. The unique record of crustal processes preserved in this grain survived early impact bombardment and provides previously unidentified petrological evidence for a wet pre-Noachian martian crust.
... To address this limitation, nanoscale isotopic dating using Atom Probe Tomography (APT) has been developed in recent years. Reddy et al. (2020) demonstrated that APT requires an analytical volume of <0.0007 μm 3 , i.e. four to six orders of magnitude smaller than other high spatial resolution techniques. Fougerouse et al. (2020) showed that accurate 208 Pb/ 232 Th dates in monazite, positioned at different textural locations within rocks, can be obtained through APT. ...
The Greater Himalayan Sequence (GHS) constitutes a pivotal unit within the Himalayan meta-morphic core and positions between the South Tibetan Detachment System (STDS) at its upper boundary and the Main Central Thrust Zone (MCTz) at its lower boundary. Numerous studies on monazite geochronology have been conducted across different segments (Northwest, Central and Eastern Himalayas) of the GHS to determine the dates related to MCTz and STDS, pro-peak-retrograde metamorphic conditions, crustal anatexis, and generation of leucogranite. However, these studies have yielded contrasting interpretations, deviating from the general patterns, suggesting refined local responses to explain the evolution of the orogen. Recent discovery of the High Himalayan Discontinuity within the GHS has significantly changed our understanding of the evolution of GHS and demarcated the beginning of a new era in the Himalayan literature, emphasizing its chronological link to MCTz and STDS. Several tectonic models exist with differing predictions to elucidate the exhumation of the GHS, but each model faces both defence and challenge across different Himalayan segments, based on similar geochronological, metamorphic, and structural data. This study aims to comprehensively review published monazite dates from all the Himalayan segments alongside exhumation models to address existing inconsistencies along the length of the orogen. ARTICLE HISTORY
... Atom probe tomography allows the three-dimensional compositional mapping of elements and isotopes in NMassociations (Gault et al. 2012, Lefebvre et al. 2016, Saxey et al. 2018, Reddy et al. 2020. In a process called field evaporation, either ultra-fast voltage or laser pulses are used to erode and convert the atoms on the tip of a needleshaped specimen into charged ions (Figure 4d). ...
... In a process called field evaporation, either ultra-fast voltage or laser pulses are used to erode and convert the atoms on the tip of a needleshaped specimen into charged ions (Figure 4d). An electric field accelerates the ions towards a position-sensitive detector that registers the time of flight and impact position of individual ion or species (Gault et al. 2012, Lefebvre et al. 2016, Saxey et al. 2018, Reddy et al. 2020). The energy applied to the surface of a specimen is used to calculate the mass-to-charge ratios of the ions based on their travel time, which is almost always sufficient for the identification of an individual atom. ...
... Future studies on the identification of cluster-size precursors in NM-associations may be conducted with new generations of APT instruments, which have high detection efficiency (100%) and spatial resolution (Reddy et al. 2020). Targeted NM-associations may be mineral surface coatings in contaminated soils or ore deposits, in which Cu-, Pb-, As-Au-bearing precursors form and grow towards their corresponding NMs. ...
Nanomaterials (NMs) have unique properties and control processes relevant to the fate of contaminants in soils, air, and aquatic systems and within the carbon cycle. Many NMs often occur in association with larger mineral grains, organic matter, or living organisms such as microbes, plants and fungi. The preservation of the spatial, textural, chemical, and mineralogical relations between NMs and minerals, organic matter, and organism (NM‐associations) is of fundamental importance as it provides information about the origin and formation mechanisms of NMs. Here we review analytical approaches and techniques to study NM‐associations at the bulk‐, micro‐, nano‐ and atomic‐scale. We will focus on (a) X‐ray diffraction and mass‐spectroscopy techniques; (2) automatisms within software packages that permit the search of features without operators; (3) preparation and analytical techniques such as the focused‐ion beam technology, transmission electron microscopy and atom probe tomography; (4) nano‐spectroscopic techniques such as tip‐enhanced Raman spectroscopy, synchrotron infrared nanospectroscopy, and nano‐X‐ray fluorescence spectroscopy; (5) ptychographic X‐ray computer tomography. This review paper concludes with selected new perspectives such as (a) the characterisation of NM‐precursors, (b) the role of NM‐associations in the stabilisation of soil organic matter and (c) the interaction of NM‐associations in wildfire smoke with contaminants from other sources.
... In polycrystalline aggregates, the presence of grain boundaries may increase the effective diffusivity of Nd by 10 3 10 6 above the lattice value (Hiraga et al., 2007a(Hiraga et al., , 2007b, possibly up to a factor of 10 8 (Shewmon, 1989, although this is not well-constrained for mantle minerals; J. van Orman, personal communication). Additionally, segregation of incompatible elements into high-diffusivity grain boundaries can also play an important role in enhancing their mobility (Demouchy & Alard, 2021;Reddy et al., 2020). ...
This study is motivated by the observed variability in trace element isotopic and chemical compositions of primitive (SiO2< 52 wt %) basalts in southwest North America (SWNA) during the Cenozoic transition from subduction to extension. Specifically, we focus on processes that may explain the enigmatic observation that in some localities, basalts with low Ta/Th, consistent with parental melts in a subduction setting, have εNd signatures consistent with continental lithospheric mantle (CLM). In locations with the oldest CLM (Proterozoic and Archean), Cenozoic basalts with low Ta/Th have εNd well below zero. We model channelized magma transport through the CLM using simple 1D transport models to explore the extent to which diffusive and reactive mass exchange can modify Nd isotopic compositions via open system melt‐wallrock interactions. For geologically reasonable channel spacings and volume fractions, we quantify the reactive assimilation rates required for incoming melt with a different εNd than the wall‐rock to undergo a substantial isotopic shift during ≈ 10 km channelized melt transport. In the presence of grain boundaries, enhanced diffusion between melt‐rich channels and melt‐poor surrounding rock contributes to isotopic equilibration, however this effect is not enough to explain observations; our models suggest a significant contribution from reactive assimilation of wall‐rock. Additionally our models support the idea that the observed covariability in Ta/Th and εNd in Cenozoic basalts cannot be attributed to transport alone and must also reflect the transition from subduction‐related to extension‐related parental melts in SWNA.
... In situ analysis of minor and trace elements content in single magnetite particles is still not possible due to their small size (i.e. <100 nm) but the development of new techniques such as Atome Probe Tomography (APT), with nm scaleresolution, is very promising(Reddy et al., 2020).To summarize, we highlight that magnetofossils in ancient sedimentary rocks could be identified from their enrichment in Mo and Sn, as well as Se and Al. Strong depletion is expected in Co, Mn and Pb relative to abiotic magnetite. ...
