ORCID Profile
0000-0002-9256-0966
Current Organisation
University of Oxford
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Publisher: Springer Science and Business Media LLC
Date: 10-05-2019
DOI: 10.1007/S11661-019-05246-5
Abstract: Titanium is commonly added to nickel superalloys but has a well-documented detrimental effect on oxidation resistance. The present work constitutes the first atomistic-scale quantitative measurements of grain boundary and bulk compositions in the oxide scale of a current generation polycrystalline nickel superalloy performed through atom probe tomography. Titanium was found to be particularly detrimental to oxide scale growth through grain boundary diffusion.
Publisher: IOP Publishing
Date: 07-2022
Abstract: Traditional reconstruction protocols in atom probe tomography frequently feature image distortions for multiphase materials, due to inaccurate geometric assumptions regarding specimen evolution. In this work, the authors’ outline a new reconstruction protocol capable of correcting for many of these distortions. This new method uses predictions from a previously developed physical model for specimen field evaporation. The application of this new model-driven approach to both an experimental semiconductor multilayer system and a fin field-effect transistor device (finFET) is considered. In both systems, a significant reduction in multiphase image distortions when using this new algorithm is clearly demonstrated. By being able to quantitatively compare model predictions with experiment, such a method could also be applied to testing and validating new developments in field evaporation theory.
Publisher: Oxford University Press (OUP)
Date: 14-11-2003
DOI: 10.1017/S1431927607070900
Abstract: Nanoscale atomic clusters in atom probe tomographic data are not universally defined but instead are characterized by the clustering algorithm used and the parameter values controlling the algorithmic process. A new core-linkage clustering algorithm is developed, combining fundamental elements of the conventional maximum separation method with density-based analyses. A key improvement to the algorithm is the independence of algorithmic parameters inherently unified in previous techniques, enabling a more accurate analysis to be applied across a wider range of material systems. Further, an objective procedure for the selection of parameters based on approximating the data with a model of complete spatial randomness is developed and applied. The use of higher nearest neighbor distributions is highlighted to give insight into the nature of the clustering phenomena present in a system and to generalize the clustering algorithms used to analyze it. Maximum separation, density-based scanning, and the core linkage algorithm, developed within this study, were separately applied to the investigation of fine solute clustering of solute atoms in an Al-1.9Zn-1.7Mg (at.%) at two distinct states of early phase decomposition and the results of these analyses were evaluated.
Publisher: Elsevier BV
Date: 06-2009
DOI: 10.1016/J.ULTRAMIC.2009.03.016
Abstract: New and improved spatial distribution map (SDM) methods are developed to identify and extract crystallographic information within atom probe tomography three-dimensional (3D) reconstructions. Detailed structural information is retrieved by combining z-SDM offset distribution analyses computed in multiple crystallographic directions, accurately determining inter-planar spacings and crystallographic angles. The advantages of this technique in comparison to applying the complete z-SDM and complementary xy-SDM analysis to a single crystallographic direction are investigated. Further, in determining these multidirectional z-SDM and xy-SDM profiles, background noise reduction and automatic peak identification algorithms are adapted to attain increased accuracy and is shown to be particularly effective in cases where crystal structure is present but poorly resolved. These techniques may be used to calibrate the reconstruction parameters and investigate their dependence on the design of in idual atom probe experiments.
Publisher: Elsevier BV
Date: 04-2016
Publisher: Informa UK Limited
Date: 21-04-2010
Publisher: Elsevier BV
Date: 10-2013
Publisher: Elsevier BV
Date: 03-2015
Publisher: Oxford University Press (OUP)
Date: 13-02-2019
DOI: 10.1017/S1431927618016240
Abstract: In this work, we demonstrate a new system for the examination of gas interactions with surfaces via atom probe tomography. This system provides capability of examining the surface and subsurface interactions of gases with a wide range of specimens, as well as a selection of input gas types. This system has been primarily developed to aid the investigation of hydrogen interactions with metallurgical s les, to better understand the phenomenon of hydrogen embrittlement. In its current form, it is able to operate at pressures from 10 −6 to 1000 mbar (abs), can use a variety of gasses, and is equipped with heating and cryogenic quenching capabilities. We use this system to examine the interaction of hydrogen with Pd, as well as the interaction of water vapor and oxygen in Mg s les.
Publisher: Elsevier BV
Date: 11-2011
DOI: 10.1016/J.ULTRAMIC.2011.08.005
Abstract: Progress in the reconstruction for atom probe tomography has been limited since the first implementation of the protocol proposed by Bas et al. in 1995. This approach and those subsequently developed assume that the geometric parameters used to build the three-dimensional atom map are constant over the course of an analysis. Here, we test this assumption within the analyses of low-alloyed materials. By building upon methods recently proposed to measure the tomographic reconstruction parameters, we demonstrate that this assumption can introduce significant limitations in the accuracy of the analysis. Moreover, we propose a strategy to alleviate this problem through the implementation of a new reconstruction algorithm that dynamically accommodates variations in the tomographic reconstruction parameters.
Publisher: Oxford University Press (OUP)
Date: 29-07-2014
DOI: 10.1017/S1431927614012872
Abstract: Atom probe is a powerful technique for studying the composition of nano-precipitates, but their morphology within the reconstructed data is distorted due to the so-called local magnification effect. A new technique has been developed to mitigate this limitation by characterizing the distribution of the surrounding matrix atoms, rather than those contained within the nano-precipitates themselves. A comprehensive chemical analysis enables further information on size and chemistry to be obtained. The method enables new insight into the morphology and chemistry of niobium carbonitride nano-precipitates within ferrite for a series of Nb-microalloyed ultra-thin cast strip steels. The results are supported by complementary high-resolution transmission electron microscopy.
Publisher: Informa UK Limited
Date: 27-04-2016
Publisher: Elsevier BV
Date: 05-2017
DOI: 10.1016/J.ULTRAMIC.2017.01.019
Abstract: We have used high resolution transmission electron microscopy (HRTEM), aberration-corrected quantitative scanning transmission electron microscopy (Q-STEM), atom probe tomography (APT) and X-ray diffraction (XRD) to study the atomic structure of (0001) polar and (11-20) non-polar InGaN quantum wells (QWs). This paper provides an overview of the results. Polar (0001) InGaN in QWs is a random alloy, with In replacing Ga randomly. The InGaN QWs have atomic height interface steps, resulting in QW width fluctuations. The electrons are localised at the top QW interface by the built-in electric field and the well-width fluctuations, with a localisation energy of typically 20meV. The holes are localised near the bottom QW interface, by indium fluctuations in the random alloy, with a localisation energy of typically 60meV. On the other hand, the non-polar (11-20) InGaN QWs contain nanometre-scale indium-rich clusters which we suggest localise the carriers and produce longer wavelength (lower energy) emission than from random alloy non-polar InGaN QWs of the same average composition. The reason for the indium-rich clusters in non-polar (11-20) InGaN QWs is not yet clear, but may be connected to the lower QW growth temperature for the (11-20) InGaN QWs compared to the (0001) polar InGaN QWs.
Publisher: AIP Publishing
Date: 09-01-2018
DOI: 10.1063/1.5006255
Abstract: We investigate the impact of a fluorine plasma treatment used to obtain enhancement-mode operation on the structure and chemistry at the nanometer and atomic scales of an InAlN/GaN field effect transistor. The fluorine plasma treatment is successful in that enhancement mode operation is achieved with a +2.8 V threshold voltage. However, the InAlN barrier layers are observed to have been damaged by the fluorine treatment with their thickness being reduced by up to 50%. The treatment also led to oxygen incorporation within the InAlN barrier layers. Furthermore, even in the as-grown structure, Ga was unintentionally incorporated during the growth of the InAlN barrier. The impact of both the reduced barrier thickness and the incorporated Ga within the barrier on the transistor properties has been evaluated theoretically and compared to the experimentally determined two-dimensional electron gas density and threshold voltage of the transistor. For devices without fluorine treatment, the two-dimensional electron gas density is better predicted if the quaternary nature of the barrier is taken into account. For the fluorine treated device, not only the changes to the barrier layer thickness and composition, but also the fluorine doping needs to be considered to predict device performance. These studies reveal the factors influencing the performance of these specific transistor structures and highlight the strengths of the applied nanoscale characterisation techniques in revealing information relevant to device performance.
Publisher: Oxford University Press (OUP)
Date: 31-07-2006
DOI: 10.1017/S1431927606068346
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005
Publisher: Springer Science and Business Media LLC
Date: 12-07-2016
DOI: 10.1038/SREP25618
Abstract: Understanding the corrosion of uranium is important for its safe, long-term storage. Uranium metal corrodes rapidly in air, but the exact mechanism remains subject to debate. Atom Probe Tomography was used to investigate the surface microstructure of metallic depleted uranium specimens following polishing and exposure to moist air. A complex, corrugated metal-oxide interface was observed, with approximately 60 at.% oxygen content within the oxide. Interestingly, a very thin (~5 nm) interfacial layer of uranium hydride was observed at the oxide-metal interface. Exposure to deuterated water vapour produced an equivalent deuteride signal at the metal-oxide interface, confirming the hydride as originating via the water vapour oxidation mechanism. Hydroxide ions were detected uniformly throughout the oxide, yet showed reduced prominence at the metal interface. These results support a proposed mechanism for the oxidation of uranium in water vapour environments where the transport of hydroxyl species and the formation of hydride are key to understanding the observed behaviour.
Publisher: Elsevier BV
Date: 09-2018
Publisher: Elsevier BV
Date: 09-2020
Publisher: Oxford University Press (OUP)
Date: 14-11-2007
DOI: 10.1017/S1431927607070912
Abstract: In February 2006, in conjunction with the 19th Australian Conference on Microscopy and Microanalysis held in Sydney, the 2nd Australian Workshop on Atom Probe Tomography was convened by S.P. Ringer, M.K. Miller, D.A. Saxey, and R. Zheng at the Australian Key Centre for Microscopy and Microanalysis at The University of Sydney. The topics covered at that workshop included specimen preparation data acquisition and data analysis methods for atom probe tomography applications to spinodal alloys, phase transformations, light metals, atomic clustering, and detection methods, as well as future directions of the science and technology of atom probe tomography. The presentations and discussions that took place at this workshop, which was attended by more than 30 people, provided the inspiration for this special issue of Microscopy and Microanalysis .
Publisher: Elsevier BV
Date: 2021
Publisher: Springer Science and Business Media LLC
Date: 22-06-2020
DOI: 10.1007/S11661-020-05845-7
Abstract: Industrial gas turbines (IGT) require novel single-crystal superalloys with demonstrably superior corrosion resistance to those used for aerospace applications and thus higher Cr contents. Multi-scale modeling approaches are aiding in the design of new alloy grades however, the CALPHAD databases on which these rely remain unproven in this composition regime. A set of trial nickel-based superalloys for IGT blades is investigated, with carefully designed chemistries which isolate the influence of in idual additions. Results from an extensive experimental characterization c aign are compared with CALPHAD predictions. Insights gained from this study are used to derive guidelines for optimized gas turbine alloy design and to gauge the reliability of the CALPHAD databases.
Publisher: Springer Science and Business Media LLC
Date: 15-06-2021
DOI: 10.1038/S41377-021-00564-Z
Abstract: We investigated metal-organic vapor phase epitaxy grown (InGa)(AsSb)/GaAs/GaP Stranski–Krastanov quantum dots (QDs) with potential applications in QD-Flash memories by cross-sectional scanning tunneling microscopy (X-STM) and atom probe tomography (APT). The combination of X-STM and APT is a very powerful approach to study semiconductor heterostructures with atomic resolution, which provides detailed structural and compositional information on the system. The rather small QDs are found to be of truncated pyramid shape with a very small top facet and occur in our s le with a very high density of ∼4 × 10 11 cm −2 . APT experiments revealed that the QDs are GaAs rich with smaller amounts of In and Sb. Finite element (FE) simulations are performed using structural data from X-STM to calculate the lattice constant and the outward relaxation of the cleaved surface. The composition of the QDs is estimated by combining the results from X-STM and the FE simulations, yielding ∼In x Ga 1 − x As 1 − y Sb y , where x = 0.25–0.30 and y = 0.10–0.15. Noticeably, the reported composition is in good agreement with the experimental results obtained by APT, previous optical, electrical, and theoretical analysis carried out on this material system. This confirms that the InGaSb and GaAs layers involved in the QD formation have strongly intermixed. A detailed analysis of the QD capping layer shows the segregation of Sb and In from the QD layer, where both APT and X-STM show that the Sb mainly resides outside the QDs proving that Sb has mainly acted as a surfactant during the dot formation. Our structural and compositional analysis provides a valuable insight into this novel QD system and a path for further growth optimization to improve the storage time of the QD-Flash memory devices.
Publisher: Oxford University Press (OUP)
Date: 08-2019
Publisher: American Physical Society (APS)
Date: 10-12-2015
Publisher: Elsevier BV
Date: 06-2019
Publisher: Elsevier BV
Date: 02-2020
Publisher: Oxford University Press (OUP)
Date: 31-07-2006
DOI: 10.1017/S1431927606069030
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2005
Publisher: Springer Science and Business Media LLC
Date: 13-03-2018
DOI: 10.1007/S11661-018-4558-7
Abstract: A family of novel polycrystalline Ni-based superalloys with varying Ti:Nb ratios has been created using computational alloy design techniques, and subsequently characterized using atom probe tomography and electron microscopy. Phase chemistry, elemental partitioning, and γ ′ character have been analyzed and compared with thermodynamic predictions created using Thermo-Calc. Phase compositions and γ ′ volume fraction were found to compare favorably with the thermodynamically predicted values, while predicted partitioning behavior for Ti, Nb, Cr, and Co tended to overestimate γ ′ preference over the γ matrix, often with opposing trends vs Nb concentration.
Publisher: Wiley
Date: 2007
DOI: 10.1002/JEMT.20412
Abstract: A contingency table analysis procedure is developed and applied to three dimensional atom probe data sets for the investigation of fine-scale solute co-/anti-segregation effects in multicomponent alloys. Potential sources of error and inaccuracy are identified and eliminated from the technique. The conventional P value testing techniques associated with chi(2) are shown to be unsatisfactory and can become ambiguous in cases of large block numbers or high solute concentrations. The coefficient of contingency is demonstrated to be an acceptable and useful basis of comparison for contingency table analyses of differently-conditioned materials. However, care must be taken in choice of block size and to maintain a consistent overall composition between experiments. The coefficient is dependent upon block size and solute composition, and cannot be used to compare analyses with significantly different solute compositions or to assess the extent of clustering without reference to that of the randomly ordered case. It is shown that as clustering evolves into larger precipitates and phases, contingency table analysis becomes inappropriate. Random labeling techniques are introduced to infer further meaning from the coefficient of contingency. We propose the comparison of experimental result, mu(exp), to the randomized value, micro(rand), as a new method by which to interpret the quantity of solute clustering present in a material. It is demonstrated that how this method may be utilized to identify an appropriate size of contingency table analysis blocks into which the data set is partitioned to optimize the significance of the results.
Publisher: Elsevier BV
Date: 04-2020
Publisher: Elsevier BV
Date: 08-2020
Publisher: AIP Publishing
Date: 05-04-2004
DOI: 10.1063/1.1687313
Abstract: A globally uniform time-independent semiclassical wave function for nonadiabatic scattering is presented. This wave function, which takes the form of a surface-hopping expansion, is motivated by the globally uniform semiclassical wave function of Kay and co-workers for the single-surface case. The surface-hopping expansion is similar to a previously presented primitive semiclassical wave function for nonadiabatic problems. This earlier wave function has the important feature that it correctly incorporates all phase terms, allowing for an accurate treatment of quantum interference effects. The globally uniform expression has important numerical advantages over the primitive formulation. The globally uniform wave function does not have caustic singularities, and the globally uniform calculation avoids a root search for trajectories obeying double-ended boundary conditions that is required by the primitive semiclassical calculation.
Publisher: Elsevier BV
Date: 12-2014
DOI: 10.1016/J.ULTRAMIC.2014.06.004
Abstract: Carbon quantification and the standardisation in a pure cementite were conducted using pulsed-laser atom probe tomography (APT). The results were analysed to investigate a dependence on three distinct experimental parameters the laser pulse energy, the cryogenic specimen temperature and the laser pulse frequency. All the measurements returned an apparent carbon content of 25.0±1.0at%. Carbon content measurements showed no clear dependence on the cryogenic temperature or the laser pulse frequency. However, the results did demonstrate a strong correlation with the laser pulse energy. For lower laser pulse energies, the analysis returned carbon contents higher than the stoichiometric ratio. It was suggested that this effect is due to pile up of (56)Fe(++) at the detector and as a consequence there is a systematic preferential loss of these ions throughout the course of the experiment. Conversely, in experiments utilising higher laser pulse energies, it was found that the carbon contents were smaller than the stoichiometric ratio. In these experiments an increasing fraction of the larger carbon molecular ions (e.g., C5 ions) were detected as part of a multiple detection events, which could affect the quantification measurements.
Publisher: Elsevier BV
Date: 05-2018
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 06-2016
Publisher: Oxford University Press (OUP)
Date: 08-03-2011
DOI: 10.1017/S1431927610094535
Abstract: Atom probe tomography (APT) represents a significant step toward atomic resolution microscopy, analytically imaging in idual atoms with highly accurate, though imperfect, chemical identity and three-dimensional (3D) positional information. Here, a technique to retrieve crystallographic information from raw APT data and restore the lattice-specific atomic configuration of the original specimen is presented. This lattice rectification technique has been applied to a pure metal, W, and then to the analysis of a multicomponent Al alloy. Significantly, the atoms are located to their true lattice sites not by an averaging, but by triangulation of each particular atom detected in the 3D atom-by-atom reconstruction. Lattice rectification of raw APT reconstruction provides unprecedented detail as to the fundamental solute hierarchy of the solid solution. Atomic clustering has been recognized as important in affecting alloy behavior, such as for the Al-1.1Cu-1.7Mg (at. %) investigated here, which exhibits a remarkable rapid hardening reaction during the early stages of aging, linked to clustering of solutes. The technique has enabled lattice-site and species-specific radial distribution functions, nearest-neighbor analyses, and short-range order parameters, and we demonstrate a characterization of solute-clustering with unmatched sensitivity and precision.
Publisher: Elsevier BV
Date: 09-2015
Publisher: Elsevier BV
Date: 12-2015
Publisher: Wiley
Date: 15-05-2019
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.ULTRAMIC.2012.12.011
Abstract: Oxide nanoclusters in a consolidated Fe-14Cr-2W-0.3Ti-0.3Y₂O₃ ODS steel and in the alloy powder after mechanical alloying (but before consolidation) are investigated by atom probe tomography (APT). The maximum separation method is a standard method to define and characterise clusters from within APT data, but this work shows that the extent of clustering between the two materials is sufficiently different that the nanoclusters in the mechanically alloyed powder and in the consolidated material cannot be compared directly using the same cluster selection parameters. As the cluster selection parameters influence the size and composition of the clusters significantly, a procedure to optimise the input parameters for the maximum separation method is proposed by sweeping the d(max) and N(min) parameter space. By applying this method of cluster parameter selection combined with a 'matrix correction' to account for trajectory aberrations, differences in the oxide nanoclusters can then be reliably quantified.
Publisher: AIP Publishing
Date: 11-06-2019
DOI: 10.1063/1.5097411
Abstract: We investigate the atomic scale structure of m-plane InGaN quantum wells grown on bulk m-plane GaN templates and reveal that as the indium content increases there is an increased tendency for nonrandom clustering of indium atoms to occur. Based on the atom probe tomography data used to reveal this clustering, we develop a k · p model that takes these features into account and links the observed nanostructure to the optical properties of the quantum wells. The calculations show that electrons and holes tend to colocalize at indium clusters. The transition energies between the electron and hole states are strongly affected by the shape and size of the clusters. Hence, clustering contributes to the very large line widths observed in the experimental low temperature photoluminescence spectra. Also, the emission from m-plane InGaN quantum wells is strongly linearly polarized. Clustering does not alter the theoretically predicted polarization properties, even when the shape of the cluster is strongly asymmetric. Overall, however, we show that the presence of clustering does impact the optical properties, illustrating the importance of careful characterization of the nanoscale structure of m-plane InGaN quantum wells and that atom probe tomography is a useful and important tool to address this problem.
Publisher: AIP Publishing
Date: 02-05-2016
DOI: 10.1063/1.4948299
Abstract: Atom probe tomography and quantitative scanning transmission electron microscopy are used to assess the composition of non-polar a-plane (11-20) InGaN quantum wells for applications in optoelectronics. The average quantum well composition measured by atom probe tomography and quantitative scanning transmission electron microscopy quantitatively agrees with measurements by X-ray diffraction. Atom probe tomography is further applied to study the distribution of indium atoms in non-polar a-plane (11-20) InGaN quantum wells. An inhomogeneous indium distribution is observed by frequency distribution analysis of the atom probe tomography measurements. The optical properties of non-polar (11-20) InGaN quantum wells with indium compositions varying from 7.9% to 20.6% are studied. In contrast to non-polar m-plane (1-100) InGaN quantum wells, the non-polar a-plane (11-20) InGaN quantum wells emit at longer emission wavelengths at the equivalent indium composition. The non-polar a-plane (11-20) quantum wells also show broader spectral linewidths. The longer emission wavelengths and broader spectral linewidths may be related to the observed inhomogeneous indium distribution.
Publisher: Springer Science and Business Media LLC
Date: 2016
DOI: 10.1557/MRS.2015.311
Publisher: Wiley
Date: 18-09-2018
Publisher: Elsevier BV
Date: 05-2021
Publisher: Elsevier BV
Date: 04-2009
Publisher: IOP Publishing
Date: 21-07-2016
Publisher: AIP Publishing
Date: 26-09-2002
DOI: 10.1063/1.1505865
Abstract: An approximate semianalytic theory is developed to describe the homogeneous nucleation of droplets from a supersaturated vapor, beginning with a partition function and including rigorously the translation and surface tension contributions. The liquid and vapor phases are treated as uniform (step density profile) and may be described by any accurate equation of state. It is shown that the classical approximation for the free energy of droplet formation may be derived from the present theory by making additional approximations (ideal gas, incompressible liquid), and the two are compared for the case where the vapor phase forms a reservoir (constant supersaturation). In the case of a finite-sized vapor phase, where the supersaturation decreases as the droplet grows, a free energy minimum exists beyond the critical radius, and this stable droplet equilibrium is examined in detail. Comparison with computer simulations proves the quantitative accuracy of the present theory for a Lennard-Jones system. Also derived is a new, formally exact expression for the surface tension that is useful for computer simulations.
Publisher: IOP Publishing
Date: 28-04-2017
Publisher: ASTM International
Date: 2018
Publisher: Elsevier BV
Date: 05-2017
Publisher: Elsevier BV
Date: 02-2012
Publisher: Springer Science and Business Media LLC
Date: 21-03-2012
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.ULTRAMIC.2015.02.013
Abstract: Oxide dispersion strengthened ferritic steels (ODS) are being considered for structural components of future designs of fission and fusion reactors because of their impressive high-temperature mechanical properties and resistance to radiation damage, both of which arise from the nanoscale oxide particles they contain. Because of the critical importance of these nanoscale phases, significant research activity has been dedicated to analysing their precise size, shape and composition (Odette et al., Annu. Rev. Mater. Res. 38 (2008) 471-503 [1] Miller et al., Mater. Sci. Technol. 29(10) (2013) 1174-1178 [2]). As part of a project to develop new fuel cladding alloys in India, model ODS alloys have been produced with the compositions, Fe-0.3Y2O3, Fe-0.2Ti-0.3Y2O3 and Fe-14Cr-0.2Ti-0.3Y2O3. The oxide particles in these three model alloys have been studied by APT in their as-received state and following ion irradiation (as a proxy for neutron irradiation) at various temperatures. In order to adequately quantify the composition of the oxide clusters, several difficulties must be managed, including issues relating to the chemical identification (ranging and variable peak-overlaps) trajectory aberrations and chemical structure and particle sizing. This paper presents how these issues can be addressed by the application of bespoke data analysis tools and correlative microscopy. A discussion follows concerning the achievable precision in these measurements, with reference to the fundamental limiting factors.
Publisher: AIP Publishing
Date: 15-08-2010
DOI: 10.1063/1.3462399
Abstract: The impact of laser pulsing on the field evaporation process is investigated for Al and W by pulsed laser atom probe tomography. Quantitative analysis reveals the influence on the spatial resolution of the peak temperature reached by the specimen following light absorption from the laser pulse. It is concluded that surface migration processes induce significant degradation of the lateral resolution, changing by 100% and 20%, respectively, for Al and W when the specimen temperature is increased from 4% to 7% of the material’s melting point, while the in-depth resolution is shown to remain nearly constant for both materials.
Publisher: Elsevier BV
Date: 11-2018
Publisher: Springer Science and Business Media LLC
Date: 25-10-2019
DOI: 10.1007/S11661-019-05472-X
Abstract: The kinetics of primary α -Ti colony/Widmanstätten plate growth from the β are examined in Ti-6246, comparing a simple quasi-analytic model to experiment. The plate growth velocity depends sensitively both on the diffusivity D ( T ) of the rate-limiting species and on the supersaturation around the growing plate. These result in a maxima in growth velocity around 40 K below the transus, once sufficient supersaturation is available to drive the plate growth. In Ti-6246, the plate growth velocity was found to be around 0.32 μ m min −1 at 850 °C, which was in good agreement with the model prediction of 0.36 μ m min −1 . The solute field around the growing plates, and the plate thickness, was found to be quite variable, due to the intergrowth of plates and soft impingement. This solute field was found to extend to up to 30 nm, and the interface concentration in the β was found to be around 6.4 at. pct Mo. It was found that the increasing O content from 500 to 1500 wppm will have minimal effect on the plate lengths expected during continuous cooling in contrast, Mo approximately doubles the plate lengths obtained for every 2 wt pct Mo reduction. Alloys using V as the β stabilizer instead of Mo are expected to have much faster plate growth kinetics at nominally equivalent V contents. These findings will provide a useful tool for the integrated design of alloys and process routes to achieve tailored microstructures.
Publisher: Oxford University Press (OUP)
Date: 16-03-2017
DOI: 10.1017/S1431927616012782
Abstract: Due to the intrinsic evaporation properties of the material studied, insufficient mass-resolving power and lack of knowledge of the kinetic energy of incident ions, peaks in the atom probe mass-to-charge spectrum can overlap and result in incorrect composition measurements. Contributions to these peak overlaps can be deconvoluted globally, by simply examining adjacent peaks combined with knowledge of natural isotopic abundances. However, this strategy does not account for the fact that the relative contributions to this convoluted signal can often vary significantly in different regions of the analysis volume e.g., across interfaces and within clusters. Some progress has been made with spatially localized deconvolution in cases where the discrete microstructural regions can be easily identified within the reconstruction, but this means no further point cloud analyses are possible. Hence, we present an ion-by-ion methodology where the identity of each ion, normally obscured by peak overlap, is resolved by examining the isotopic abundance of their immediate surroundings. The resulting peak-deconvoluted data are a point cloud and can be analyzed with any existing tools. We present two detailed case studies and discussion of the limitations of this new technique.
Publisher: Elsevier BV
Date: 08-2020
Publisher: Elsevier BV
Date: 05-2018
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.ULTRAMIC.2019.04.005
Abstract: A method for the rapid preparation of atom probe tomography (APT) needles using a xenon plasma-focussed ion beam (FIB) instrument is presented and demonstrated on a test s le of Ti-6Al-4V alloy. The method requires significantly less operator input than the standard lift-out protocol, is site-specific and produces needles with minimal ion-beam damage electron microscopy indicated the needle's surface amorphised/oxidised region to be less than 2 nm thick. The resulting needles were routinely analysable by APT, confirming the expected microstructure and showing negligible Xe contamination.
Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.ULTRAMIC.2010.11.014
Abstract: Spatial Distribution Maps (SDM) in their various forms have previously been used to identify and characterize crystallographic structure within APT reconstructions. Importantly, it has been shown that such SDM analyses can also provide the crystallographic orientation of the specimen with respect to the direction of the detector in the original experiment. In this study, we investigate the application of SDMs to the analysis of APT reconstruction of a nanocrystalline Al film. We demonstrate that significant intra-granular crystallographic information is retained in the reconstruction, even in the x-y plane perpendicular to the direction of the detector. Further, the crystallographic orientation of the grains can be characterized highly accurately not only with respect to the bulk specimen but also their misorientation with respect to neighbouring grains.
Publisher: Wiley
Date: 2011
DOI: 10.1002/JEMT.20958
Abstract: A limiting characteristic of the atom-probe technique is the nondetection of ions and this embodies a significant "missing information" problem in investigations of atomic clustering phenomena causing difficulty in the interpretation of any atom-probe experiment. It is shown that the measurable cluster-size distribution can be modeled by a mixed binomial distribution. A deconvolution method based upon expectation-maximization (EM) algorithm is presented to obtain the original physical distribution from an efficiency-degraded distribution, thereby providing means to calculate accurate cluster number densities from atom probe results. The accuracy of this restoration was predominantly dependent upon the detector efficiency and was proved to be highly accurate in the case of conventional atom-probe detector efficiencies (ε = 57%). Such considerations and measures are absolutely necessary when the number density of clusters and small precipitates is in any way regarded as important. We conclude that limitations in detector efficiency are more limiting for cluster-finding analyses via atom-probe techniques than spatial resolution issues, and therefore the current endeavors for improving detector technologies are well found.
Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.ULTRAMIC.2010.11.016
Abstract: Key to the integrity of atom probe microanalysis, the tomographic reconstruction is built atom by atom following a simplistic protocol established for previous generations of instruments. In this paper, after a short review of the main reconstruction protocols, we describe recent improvements originating from the use of exact formulae enabling significant reduction of spatial distortions, especially near the edges of the reconstruction. We also show how predictive values for the reconstruction parameters can be derived from electrostatic simulations, and finally introduce parameters varying throughout the analysis.
Publisher: Wiley
Date: 07-08-2019
DOI: 10.1002/PIP.3184
Abstract: Hydrogen passivation is a key industrial technique used to reduce the recombination activity of defects in multicrystalline silicon (mc‐Si). However, not all dislocations and grain boundaries respond well to traditional hydrogen passivation techniques. In order to understand the reasons for these different behaviours, and how superior passivation might be achieved, a method is required for the direct observation of hydrogen at these defects. Here, we present a novel characterisation technique based on a combination of transmission Kikuchi diffraction (TKD), atom probe tomography (APT), and isotopic substitution that enables unambiguous detection and quantification of hydrogen atoms present at crystallographic defects in mc‐Si.
Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.ULTRAMIC.2010.11.018
Abstract: Whereas the atom probe is regarded almost exclusively as a technique for 3D chemical microanalysis of solids with the highest chemical and spatial resolution, we demonstrate that the technique can be used for detailed crystallographic determinations. We present a new method for the quantitative determination of crystal structure (plane spacings and angles) using a Hough transformation of the reconstructed atom probe data. The resolving power is shown to be high enough to identify poorly established, discontinuous planes that are typical in semiconducting materials. We demonstrate the determination of crystal geometry around a grain boundary and the use of the technique for the optimisation of tomographic reconstruction. We propose that this method will enable automatic spatial analysis and, ultimately, automated tomographic reconstruction in atom probe microscopy.
Publisher: Elsevier BV
Date: 05-2022
Publisher: American Chemical Society (ACS)
Date: 28-01-2014
DOI: 10.1021/CS401117E
Publisher: Elsevier BV
Date: 06-2018
Publisher: Informa UK Limited
Date: 15-03-2011
Publisher: Oxford University Press (OUP)
Date: 20-03-2017
DOI: 10.1017/S1431927617000277
Abstract: An automated procedure has been developed for the reconstruction of field ion microscopy (FIM) data that maintains its atomistic nature. FIM characterizes in idual atoms on the specimen’s surface, evolving subject to field evaporation, in a series of two-dimensional (2D) images. Its unique spatial resolution enables direct imaging of crystal defects as small as single vacancies. To fully exploit FIM’s potential, automated analysis tools are required. The reconstruction algorithm developed here relies on minimal assumptions and is sensitive to atomic coordinates of all imaged atoms. It tracks the atoms across a sequence of images, allocating each to its respective crystallographic plane. The result is a highly accurate 3D lattice-resolved reconstruction. The procedure is applied to over 2000 tungsten atoms, including ion-implanted planes. The approach is further adapted to analyze carbides in a steel matrix, demonstrating its applicability to a range of materials. A vast amount of information is collected during the experiment that can underpin advanced analyses such as automated detection of “out of sequence” events, subangstrom surface displacements and defects effects on neighboring atoms. These analyses have the potential to reveal new insights into the field evaporation process and contribute to improving accuracy and scope of 3D FIM and atom probe characterization.
Publisher: Elsevier BV
Date: 12-2019
Publisher: Elsevier BV
Date: 2012
DOI: 10.1016/J.ULTRAMIC.2011.10.003
Abstract: Nitrided steels are widely used in the engineering field due to their superior hardness and other attractive properties. Atom probe tomography (APT) was employed to study two Nb-microalloyed CASTRIP steels with different N contents. A major challenge of using APT to study this group of materials is the presence of tails after Fe peaks in the mass spectra, which overestimates the composition for alloying elements such as Nb and Cu in the steels. One important factor that contributes to the tails is believed to be delayed field evaporation from Fe²⁺. This artefact of the mass spectrum was observed to be the most severe when voltage pulsing was used. The application of laser pulses with energy ranging from 0.2 to 1.2 nJ successfully reduced the tails and lead to better compositional measurement accuracy. Spatial resolution in the z-direction (along the tip direction) was observed to be less affected by changing laser energy but deteriorates in x-y direction with increasing laser energy. This investigation suggests that pulsed-laser atom probe with ∼0.4 nJ laser energy can be used to study this group of materials with improved mass resolution while still maintaining high spatial resolution.
Publisher: Elsevier BV
Date: 08-2017
Publisher: Elsevier BV
Date: 11-2014
DOI: 10.1016/J.MICRON.2014.04.008
Abstract: Intergranular stress corrosion cracking (IGSCC) in type SUS304 stainless steels, tested under pressurized water reactor (PWR) primary water conditions, has been characterized with unprecedented spatial resolution using scanning electron microscopy (SEM) and novel low-energy (∼3 kV) energy dispersive X-ray spectroscopy (EDX). An advancement of the large area silicon drift detector (SDD) has enhanced its sensitivity for X-rays in the low-energy part of the atomic spectrum. Therefore, it was possible to operate the SEM at lower accelerating voltages in order to reduce the interaction volume of the beam with the material and achieve higher spatial resolution and better signal-to-noise ratio. In addition to studying the oxide chemistry at the surface of intergranular stress corrosion cracks, the technique has proven capable of resolving Ni enrichment ahead of some crack tips. Active cracks could be distinguished from inactive ones due to the presence of oxides in the open crack and Ni-rich regions ahead of the crack tip. Furthermore, it has been established that SCC features can be better resolved with low-energy (3 kV) than high-energy (12 kV) EDX. The low effort in s le preparation, execution and data analysis makes SEM the ideal tool for initial characterization and selection of the most important SCC features such as dominant cracks and interesting crack tips, later to be studied by transmission electron microscopy (TEM) and atom probe tomography (APT).
Publisher: AIP Publishing
Date: 11-2011
DOI: 10.1063/1.3657846
Abstract: Modern atom probes typically incorporate an ultrafast pulsed-laser source with wavelength ranging from infrared (IR) to ultraviolet (UV) depending on the specific instrument. In order to estimate the influence of the wavelength on the accuracy of the technique, the achievable in-depth spatial resolution has been measured for atom probe analyses of the same pure W specimen using three different wavelengths and across a range of laser pulse energies. UV illumination is shown to yield superior spatial resolution to both IR and visible (green) wavelengths. We propose that this improvement relates to a faster decay of temperature enabled by light absorption confined to the near apex region.
Publisher: Elsevier BV
Date: 08-2017
Publisher: Elsevier BV
Date: 02-2017
Publisher: American Physical Society (APS)
Date: 11-10-2010
Publisher: American Physical Society (APS)
Date: 15-06-2011
Publisher: Springer Science and Business Media LLC
Date: 17-10-2014
Publisher: Elsevier BV
Date: 02-2017
Publisher: Oxford University Press (OUP)
Date: 31-01-2019
DOI: 10.1017/S1431927618015507
Abstract: We report on a new algorithm for the detection of crystallographic information in three-dimensional, as retained in atom probe tomography (APT), with improved robustness and signal detection performance. The algorithm is underpinned by one-dimensional distribution functions (DFs), as per existing algorithms, but eliminates an unnecessary parameter as compared to current methods. By examining traditional DFs in an automated fashion in real space, rather than using Fourier transform approaches, we utilize an error metric based upon the expected value for a spatially random distribution for detecting crystallography. We show cases where the metric is able to successfully obtain orientation information, and show that it can function with high levels of additive and displacive background noise. We additionally compare this metric to Fourier transform methods, showing fewer artifacts when examining simulated datasets. An extension of the approach is used to aid the automatic detection of high-quality data regions within an entire dataset, albeit with a large increase in computational cost. This extension is demonstrated on acquired aluminum and tungsten APT datasets, and shown to be able to discern regions of the data which have relatively improved spatial data quality. Finally, this program has been made available for use in other laboratories undertaking their own analyses.
Publisher: Springer Science and Business Media LLC
Date: 22-07-2021
Publisher: Elsevier BV
Date: 08-2015
DOI: 10.1016/J.MICRON.2015.04.011
Abstract: Transmission Kikuchi diffraction (TKD), also known as transmission-electron backscatter diffraction (t-EBSD) is a novel method for orientation mapping of electron transparent transmission electron microscopy specimen in the scanning electron microscope and has been utilized for stress corrosion cracking characterization of type 316 stainless steels. The main advantage of TKD is a significantly higher spatial resolution compared to the conventional EBSD due to the smaller interaction volume of the incident beam with the specimen. Two 316 stainless steel specimen, tested for stress corrosion cracking in hydrogenated and oxygenated pressurized water reactor chemistry, were characterized via TKD. The results include inverse pole figure (IPFZ) maps, image quality maps and misorientation maps, all acquired in very short time (<60 min) and with remarkable spatial resolution (up to 5 nm step size possible). They have been used in order to determine the location of the open crack with respect to the grain boundary, deformation bands, twinning and slip. Furthermore, TKD has been used to measure the grain boundary misorientation and establish a gauge for quantifying plastic deformation at the crack tip and other regions in the surrounding matrix. Both grain boundary migration and slip transfer have been detected as well.
Publisher: Oxford University Press (OUP)
Date: 19-08-2020
Publisher: Elsevier BV
Date: 12-2019
Publisher: Elsevier BV
Date: 2016
Publisher: American Chemical Society (ACS)
Date: 04-10-2019
Publisher: Elsevier BV
Date: 2021
Publisher: American Association for the Advancement of Science (AAAS)
Date: 17-03-2017
Abstract: The design of atomic-scale microstructural traps to limit the diffusion of hydrogen is one key strategy in the development of hydrogen-embrittlement-resistant materials. In the case of bearing steels, an effective trapping mechanism may be the incorporation of finely dispersed V-Mo-Nb carbides in a ferrite matrix. First, we charged a ferritic steel with deuterium by means of electrolytic loading to achieve a high hydrogen concentration. We then immobilized it in the microstructure with a cryogenic transfer protocol before atom probe tomography (APT) analysis. Using APT, we show trapping of hydrogen within the core of these carbides with quantitative composition profiles. Furthermore, with this method the experiment can be feasibly replicated in any APT-equipped laboratory by using a simple cold chain.
Publisher: Maney Publishing
Date: 11-02-2016
Publisher: Springer Science and Business Media LLC
Date: 19-11-2014
DOI: 10.1038/NCOMMS6501
Abstract: Microscopy encompasses a wide variety of forms and scales. So too does the array of simulation techniques developed that correlate to and build upon microstructural information. Nevertheless, a true nexus between microscopy and atomistic simulations is lacking. Atom probe has emerged as a potential means of achieving this goal. Atom probe generates three-dimensional atomistic images in a format almost identical to many atomistic simulations. However, this data is imperfect, preventing input into computational algorithms to predict material properties. Here we describe a methodology to overcome these limitations, based on a hybrid data format, blending atom probe and predictive Monte Carlo simulations. We create atomically complete and lattice-bound models of material specimens. This hybrid data can then be used as direct input into density functional theory simulations to calculate local energetics and elastic properties. This research demonstrates the role that atom probe combined with theoretical approaches can play in modern materials engineering.
Publisher: Elsevier BV
Date: 05-2011
DOI: 10.1016/J.ULTRAMIC.2010.12.027
Abstract: Though the atom probe has provided unprecedented atomic identification and spatial imaging capability, the basic reconstruction assumption of a smooth hemispherical tip shape creates significant challenges in yielding high fidelity chemical information for atomic species with extreme differences in fields required for field evaporation. In the present study, the evaporation behavior and accompanying artifacts are examined for the super-cell lattice structure of L1(0) FePt, where alternating Fe and Pt planes exist in the [0 0 1] orientation. Elemental Fe and Pt have significant differences in field strengths providing a candidate system to quantify these issues. Though alloys can result in changes in the elemental field strength, the intrinsic nature of elemental planes in [0 0 1] L1(0) provides a system to determine to what extent basic assumptions of elemental field strengths can break down in understanding reconstruction artifacts in this intermetallic alloy. The reconstruction of field evaporation experiments has shown depletion of Fe at the (0 0 2) pole and zone axes. Compositional profiles revealed an increase in Fe and atom count moving outward from the pole. The depletion at the low indexed pole and zone axes was determined to be the result of local magnification and electrostatic effects. The experimental results are compared to an electrostatic simulation model.
Publisher: Oxford University Press (OUP)
Date: 04-2017
DOI: 10.1017/S1431927617000320
Abstract: Accurately identifying and extracting clusters from atom probe tomography (APT) reconstructions is extremely challenging, yet critical to many applications. Currently, the most prevalent approach to detect clusters is the maximum separation method, a heuristic that relies heavily upon parameters manually chosen by the user. In this work, a new clustering algorithm, Gaussian mixture model Expectation Maximization Algorithm (GEMA), was developed. GEMA utilizes a Gaussian mixture model to probabilistically distinguish clusters from random fluctuations in the matrix. This machine learning approach maximizes the data likelihood via expectation maximization: given atomic positions, the algorithm learns the position, size, and width of each cluster. A key advantage of GEMA is that atoms are probabilistically assigned to clusters, thus reflecting scientifically meaningful uncertainty regarding atoms located near precipitate/matrix interfaces. GEMA outperforms the maximum separation method in cluster detection accuracy when applied to several realistically simulated data sets. Lastly, GEMA was successfully applied to real APT data.
Publisher: Elsevier BV
Date: 09-2023
Publisher: Elsevier BV
Date: 10-2020
Publisher: Oxford University Press (OUP)
Date: 30-04-2015
DOI: 10.1017/S1431927615000422
Abstract: Various practical issues affecting atom probe tomography (APT) analysis of III-nitride semiconductors have been studied as part of an investigation using a c -plane InAlN/GaN heterostructure. Specimen preparation was undertaken using a focused ion beam microscope with a mono-isotopic Ga source. This enabled the unambiguous observation of implantation damage induced by s le preparation. In the reconstructed InAlN layer Ga implantation was demonstrated for the standard “clean-up” voltage (5 kV), but this was significantly reduced by using a lower voltage (e.g., 1 kV). The characteristics of APT data from the desorption maps to the mass spectra and measured chemical compositions were examined within the GaN buffer layer underlying the InAlN layer in both pulsed laser and pulsed voltage modes. The measured Ga content increased monotonically with increasing laser pulse energy and voltage pulse fraction within the examined ranges. The best results were obtained at very low laser energy, with the Ga content close to the expected stoichiometric value for GaN and the associated desorption map showing a clear crystallographic pole structure.
Publisher: Elsevier BV
Date: 2018
Publisher: Oxford University Press (OUP)
Date: 04-07-2008
DOI: 10.1017/S1431927608080690
Abstract: The application of wide field-of-view detection systems to atom probe experiments emphasizes the importance of careful parameter selection in the tomographic reconstruction of the analyzed volume, as the sensitivity to errors rises steeply with increases in analysis dimensions. In this article, a self-consistent method is presented for the systematic determination of the main reconstruction parameters. In the proposed approach, the compression factor and the field factor are determined using geometrical projections from the desorption images. A three-dimensional Fourier transform is then applied to a series of reconstructions, and after comparing to the known material crystallography, the efficiency of the detector is estimated. The final results demonstrate a significant improvement in the accuracy of the reconstructed volumes.
Publisher: AIP Publishing
Date: 10-11-2003
DOI: 10.1063/1.1622662
Abstract: A time independent semiclassical surface hopping model was previously derived for the numerical evaluation of the transition litudes for multisurface problems. This analysis is revisited and a new method incorporating phase information disregarded by the previous model is derived. The coordinate axis is partitioned into a finite number of intervals. The propagation of the wavefront across an interval is again described by a flux conserving transformation. For the one dimensional case transition litudes across many intervals can be evaluated via matrix multiplication of the in idual interval transforms. Comparison with exact quantum mechanical calculations show that the results generated by this new model are highly accurate. Further this new approach offers a significant increase in computational efficiency. Accurate results can be obtained in calculations employing larger and hence fewer intervals to partition the system where the original model fails. This increase in efficiency has important implications for multidimensional surface hopping problems.
Publisher: Elsevier BV
Date: 12-2014
Publisher: Oxford University Press (OUP)
Date: 07-2009
DOI: 10.1017/S1431927609092599
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009
Publisher: Trans Tech Publications, Ltd.
Date: 06-2010
DOI: 10.4028/WWW.SCIENTIFIC.NET/MSF.654-656.2366
Abstract: Atom probe tomography provides compositional information in three dimensions at the atomic scale, and is therefore extremely suited to the study of nanocrystalline materials. In this paper we present atom probe results from the investigation of nanocomposite TiSi¬Nx coatings and nanocrystalline Al. We address some of the major challenges associated with the study of nanocrystalline materials, including specimen preparation, visualisation, common artefacts in the data and approaches to quantitative analysis. We also discuss the potential for the technique to relate crystallographic information to the compositional maps.
Publisher: IOP Publishing
Date: 09-2020
Abstract: Reconstructions in atom probe tomography (APT) are plagued by image distortions arising from changes in the specimen geometry throughout the experiment. The simplistic and inaccurate geometrical assumptions that underpin the conventional reconstruction approach account for much of this distortion. Here we extend our previous work of modelling APT experiments using level set methods to three dimensions (3D). This model is used to generate and subsequently reconstruct synthetic APT datasets from electron tomography (ET) of an A l - M g - S i multiphase specimen. Finally, we apply our model to the reconstruction of an experimental field-effect transistor (finFET) dataset. This model-driven reconstruction successfully reduces density distortions compared to conventional methods. By combining prior knowledge about the specimen geometry from sources such as ET, such an approach promises new distortion correcting APT reconstruction applicable to complex specimen geometries.
Publisher: Oxford University Press (OUP)
Date: 15-03-2023
Abstract: A large number of atom probe tomography (APT) datasets from past experiments were collected into a database to conduct statistical analyses. An effective way of handling the data is shown, and a study on hydrogen is conducted to illustrate the usefulness of this approach. We propose to handle a large collection of APT spectra as a point cloud and use a city block distance–based metric to measure dissimilarity between spectra. This enables quick and automated searching for spectra by similarity. Since spectra from APT experiments on similar materials are similar, the point cloud of spectra contains clusters. Analysis of these clusters of spectra in this point cloud allows us to infer the s le materials. The behavior of contaminant hydrogen is analyzed and correlated with voltage, electric field, and s le base material. Across several materials, the H2+ /H+ ratio is found to decrease with increasing field, likely an indication of postionization of H2+ ions. The absolute amounts of H2+ and H+ are found to frequently increase throughout APT experiments.
Publisher: Elsevier BV
Date: 2017
Publisher: Elsevier BV
Date: 09-2019
Publisher: Oxford University Press (OUP)
Date: 18-01-2010
DOI: 10.1017/S1431927609991267
Abstract: This article addresses gaps in definitions and a lack of standard measurement techniques to assess the spatial resolution in atom probe tomography. This resolution is known to be anisotropic, being better in-depth than laterally. Generally the presence of atomic planes in the tomographic reconstruction is considered as being a sufficient proof of the quality of the spatial resolution of the instrument. Based on advanced spatial distribution maps, an analysis methodology that interrogates the local neighborhood of the atoms within the tomographic reconstruction, it is shown how both the in-depth and the lateral resolution can be quantified. The influences of the crystallography and the temperature are investigated, and models are proposed to explain the observed results. We demonstrate that the absolute value of resolution is specimen specific.
Publisher: Springer Science and Business Media LLC
Date: 03-08-2014
Publisher: Informa UK Limited
Date: 07-12-2017
Publisher: Oxford University Press (OUP)
Date: 18-03-2020
DOI: 10.1017/S1431927620000197
Abstract: Interfaces play critical roles in materials and are usually both structurally and compositionally complex microstructural features. The precise characterization of their nature in three-dimensions at the atomic scale is one of the grand challenges for microscopy and microanalysis, as this information is crucial to establish structure–property relationships. Atom probe tomography is well suited to analyzing the chemistry of interfaces at the nanoscale. However, optimizing such microanalysis of interfaces requires great care in the implementation across all aspects of the technique from specimen preparation to data analysis and ultimately the interpretation of this information. This article provides critical perspectives on key aspects pertaining to spatial resolution limits and the issues with the compositional analysis that can limit the quantification of interface measurements. Here, we use the ex le of grain boundaries in steels however, the results are applicable for the characterization of grain boundaries and transformation interfaces in a very wide range of industrially relevant engineering materials.
Publisher: Elsevier BV
Date: 09-2012
Publisher: Elsevier BV
Date: 12-2023
Publisher: Elsevier BV
Date: 04-2018
Publisher: Oxford University Press (OUP)
Date: 08-2018
DOI: 10.1017/S1431927618012370
Abstract: Understanding oxide–metal interfaces is crucial to the advancement of materials and components for many industries, most notably for semiconductor devices and power generation. Atom probe tomography provides three-dimensional, atomic scale information about chemical composition, making it an excellent technique for interface analysis. However, difficulties arise when analyzing interfacial regions due to trajectory aberrations, such as local magnification, and reconstruction artifacts. Correlative microscopy and field simulation techniques have revealed that nonuniform evolution of the tip geometry, caused by heterogeneous field evaporation, is partly responsible for these artifacts. Here we attempt to understand these trajectory artifacts through a study of the local evaporation field conditions. With a better understanding of the local evaporation field, it may be possible to account for some of the local magnification effects during the reconstruction process, eliminating these artifacts before data analysis.
Publisher: Informa UK Limited
Date: 03-07-2015
Publisher: Elsevier BV
Date: 11-2002
Publisher: Elsevier BV
Date: 02-2019
Publisher: AIP Publishing
Date: 02-2009
DOI: 10.1063/1.3068197
Abstract: Modern wide field-of-view atom probes permit observation of a wide range of crystallographic features that can be used to calibrate the tomographic reconstruction of the analyzed volume. In this study, methodologies to determine values of the geometric parameters involved in the tomographic reconstruction of atom probe data sets are presented and discussed. The influence of the tip to electrode distance and specimen temperature on these parameters is explored. Significantly, their influence is demonstrated to be very limited, indicating a relatively wide regime of experimental parameters space for sound atom probe tomography (APT) experiments. These methods have been used on several specimens and material types, and the results indicate that the reconstruction parameters are specific to each specimen. Finally, it is shown how an accurate calibration of the reconstruction enables improvements to the quality and reliability of the microscopy and microanalysis capabilities of the atom probe.
Publisher: Oxford University Press (OUP)
Date: 07-2009
DOI: 10.1017/S1431927609092988
Abstract: Extended abstract of a paper presented at Microscopy and Microanalysis 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009
Publisher: Informa UK Limited
Date: 03-2013
Publisher: Elsevier BV
Date: 08-2010
DOI: 10.1016/J.ULTRAMIC.2010.04.017
Abstract: The implementation of fast pulsed laser has significantly improved the performance of the atom probe technique by enabling near-atomic-scale three-dimensional analysis of poorly conducting materials. This has broadened the range of applications for the atom probe, addressing a major limitation of the technique. Despite this, the implications of lasing on the tomographic reconstruction of atom probe data have yet to be fully characterised. Here, we demonstrate how changes in the shape of the specimen surface, induced by laser pulsing, affect the ion trajectories, and hence the projection parameters used to build the three-dimensional map.
Publisher: Oxford University Press (OUP)
Date: 08-2022
DOI: 10.1017/S1431927621012162
Abstract: Cu-doping and crystallographic site occupations within the half-Heusler (HH) TiNiSn, a promising thermoelectric material, have been examined by atom probe tomography. In particular, this investigation aims to better understand the influence of atom probe analysis conditions on the measured chemical composition. Under a voltage-pulsing mode, atomic planes are clearly resolved and suggest an arrangement of elements in-line with the expected HH (F-43m space group) crystal structure. The Cu dopant is also distributed uniformly throughout the bulk material. For operation under laser-pulsed modes, the returned composition is highly dependent on the selected laser energy, with high energies resulting in the measurement of excessively high absolute Ti counts at the expense of Sn and in particular Ni. High laser energies also appear to be correlated with the detection of a high fraction of partial hits, indicating nonideal evaporation behavior. The possible mechanisms for these trends are discussed, along with suggestions for optimal analysis conditions for these and similar thermoelectric materials.
Publisher: Elsevier BV
Date: 08-2020
Publisher: Elsevier BV
Date: 09-2018
Publisher: Elsevier BV
Date: 03-2021
Publisher: International Union of Crystallography (IUCr)
Date: 20-07-2012
Publisher: ASTM International
Date: 07-2021
Publisher: Elsevier BV
Date: 08-2015
Publisher: Elsevier BV
Date: 12-2019
Publisher: AIP Publishing
Date: 15-11-2001
DOI: 10.1063/1.1413514
Abstract: Monte Carlo simulations have been used to calculate the surface tension of a planar liquid–vapor interface of a Lennard-Jones fluid using a new cylindrical truncation correction procedure. A bubble was mimicked by simulating a Lennard-Jones liquid close to coexistence containing a single immobile hard-sphere cavity. From the density profile of this system the curvature dependent surface tension has been estimated via calculation of the Helmholtz free energy of the system and separately using a large cavity contact density expansion. Evidence is presented that the Tolman length becomes increasingly negative as the critical temperature is approached and possibly changes sign.
Publisher: Elsevier BV
Date: 05-2016
Publisher: Oxford University Press (OUP)
Date: 31-01-2017
DOI: 10.1017/S1431927616012757
Abstract: The functional properties of the high-temperature superconductor Y 1 Ba 2 Cu 3 O 7− δ (Y-123) are closely correlated to the exact stoichiometry and oxygen content. Exceeding the critical value of 1 oxygen vacancy for every five unit cells ( δ .2, which translates to a 1.5 at% deviation from the nominal oxygen stoichiometry of Y 7.7 Ba 15.3 Cu 23 O 54− δ ) is sufficient to alter the superconducting properties. Stoichiometry at the nanometer scale, particularly of oxygen and other lighter elements, is extremely difficult to quantify in complex functional ceramics by most currently available analytical techniques. The present study is an analysis and optimization of the experimental conditions required to quantify the local nanoscale stoichiometry of single crystal yttrium barium copper oxide (YBCO) s les in three dimensions by atom probe tomography (APT). APT analysis required systematic exploration of a wide range of data acquisition and processing conditions to calibrate the measurements. Laser pulse energy, ion identification, and the choice of range widths were all found to influence composition measurements. The final composition obtained from melt-grown crystals with optimized superconducting properties was Y 7.9 Ba 10.4 Cu 24.4 O 57.2 .
Publisher: Elsevier BV
Date: 2020
Publisher: Springer Science and Business Media LLC
Date: 18-01-2019
DOI: 10.1007/S11661-018-5098-X
Abstract: The formation and evolution of nanoscale γ ″ (Ni 3 (Nb, Ti, Al)) precipitates formed during thermal aging in the nickel superalloy Inconel 625 has been characterized using Atom Probe Tomography. The onset of γ ″ precipitation has been found to occur after only one hour, markedly shorter than the aging time reported in the current literature. Evolution of precipitate composition and morphology during aging has been analyzed, and the potential onset of the γ ″ → δ (Ni 3 (Nb, Mo, Cr, Fe, Ti)) transformation after long aging times is discussed.
Publisher: Elsevier BV
Date: 08-2016
Publisher: Elsevier BV
Date: 12-2020
Publisher: Oxford University Press (OUP)
Date: 30-01-2017
DOI: 10.1017/S1431927616012630
Abstract: In this work, we report on the atom probe tomography analysis of two metallic hydrides formed by pressurized charging using an ex situ hydrogen charging cell, in the pressure range of 200–500 kPa (2–5 bar). Specifically we report on the deuterium charging of Pd/Rh and V systems. Using this ex situ system, we demonstrate the successful loading and subsequent atom probe analysis of deuterium within a Pd/Rh alloy, and demonstrate that deuterium is likely present within the oxide–metal interface of a native oxide formed on vanadium. Through these experiments, we demonstrate the feasibility of ex situ hydrogen analysis for hydrides via atom probe tomography, and thus a practical route to three-dimensional imaging of hydrogen in hydrides at the atomic scale.
Publisher: Springer Science and Business Media LLC
Date: 10-2019
DOI: 10.1140/EPJB/E2019-100244-Y
Abstract: A viable fusion power station is reliant on the development of plasma facing materials that can withstand the combined effects of high temperature operation and high neutron doses. In this study we focus on W, the most promising candidate material. Re is the primary transmutation product and has been shown to induce embrittlement through cluster formation and precipitation below its predicted solubility limit in W. We investigate the mechanism behind this using a kinetic Monte Carlo model, implemented into Stochastic Parallel PARticle Kinetic Simulator (SPPARKS) code and parameterised with a pairwise energy model for both interstitial and vacancy type defects. By introducing point defect sinks into our simulation cell, we observe the formation of Re rich clusters which have a concentration similar to that observed in ion irradiation experiments. We also compliment our computational work with atom probe tomography (APT) of ion implanted, model W-Re alloys. The segregation of Re to grain boundaries is observed in both our APT and KMC simulations.
Publisher: AIP Publishing
Date: 22-01-2004
DOI: 10.1063/1.1635801
Abstract: A novel “ghost interface” expression for the surface tension of a planar liquid–vapor interface is derived in detail from consideration of the free energy of the system, and a methodology for utilization of this new technique is given. An augmented Monte Carlo computer simulation procedure is developed specifically for the ghost interface, including derivation of long-range corrections resulting from potential truncation and a modified Gibbs ensemble technique for the simulation of adjacent coexisting phases. Results generated from the ghost interface theory for the surface tension are presented and found to be in good quantitative agreement with those resulting from the Kirkwood–Buff equation. Applications of this new approach to curved and to supersaturated systems are also discussed.
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.ULTRAMIC.2015.05.011
Abstract: The following manuscript presents a novel approach for creating lattice based models of Sb-doped Si directly from atom probe reconstructions for the purposes of improving information on dopant positioning and directly informing quantum mechanics based materials modeling approaches. Sophisticated crystallographic analysis techniques are used to detect latent crystal structure within the atom probe reconstructions with unprecedented accuracy. A distortion correction algorithm is then developed to precisely calibrate the detected crystal structure to the theoretically known diamond cubic lattice. The reconstructed atoms are then positioned on their most likely lattice positions. Simulations are then used to determine the accuracy of such an approach and show that improvements to short-range order measurements are possible for noise levels and detector efficiencies comparable with experimentally collected atom probe data.
Publisher: IEEE
Date: 09-2008
DOI: 10.1109/ICPP.2008.73
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2020
Publisher: Elsevier BV
Date: 03-2016
Publisher: American Chemical Society (ACS)
Date: 31-10-2014
DOI: 10.1021/JP508144Z
Publisher: Oxford University Press (OUP)
Date: 28-08-2013
DOI: 10.1017/S1431927613013299
Abstract: Atom probe is a nanoscale technique for creating three-dimensional spatially and chemically resolved point datasets, primarily of metallic or semiconductor materials. While atom probe can achieve local high-level resolution, the spatial coherence of the technique is highly dependent upon the evaporative physics in the material and can often result in large geometric distortions in experimental results. The distortions originate from uncertainties in the projection function between the field evaporating specimen and the ion detector. Here we explore the possibility of continuum numerical approximations to the evaporative behavior during an atom probe experiment, and the subsequent propagation of ions to the detector, with particular emphasis placed on the solution of axisymmetric systems, such as isolated particles and multilayer systems. Ultimately, this method may prove critical in rapid modeling of tip shape evolution in atom probe tomography, which itself is a key factor in the rapid generation of spatially accurate reconstructions in atom probe datasets.
Publisher: Author(s)
Date: 2018
DOI: 10.1063/1.5049338
Publisher: Elsevier BV
Date: 09-2017
Publisher: Elsevier BV
Date: 08-2016
Publisher: Wiley
Date: 07-2008
DOI: 10.1002/JEMT.20582
Abstract: The applicability of the binomial frequency distribution is outlined for the analysis of the evolution nanoscale atomic clustering of dilute solute in an alloy subject to thermal ageing in 3D atom probe data. The conventional chi(2) statistics and significance testing are demonstrated to be inappropriate for comparison of quantity of solute segregation present in two or more different sized system. Pearson coefficient, mu, is shown to normalize chi(2) with respect to s le size over an order of magnitude. A simple computer simulation is implemented to investigate the binomial analysis and infer meaning in the measured value of mu over a series of systems at different solute concentrations and degree of clustering. The simulations replicate the form of experimental data and demonstrate the effect of detector efficiency to significantly underestimate the measured segregation. The binomial analysis is applied to experimental atom probe data sets and complementary simulations are used to interpret the results.
Publisher: Elsevier BV
Date: 03-2019
Publisher: AIP Publishing
Date: 16-02-2015
DOI: 10.1063/1.4909514
Abstract: Atom probe tomography (APT) has been used to characterize the distribution of In atoms within non-polar a-plane InGaN quantum wells (QWs) grown on a GaN pseudo-substrate produced using epitaxial lateral overgrowth. Application of the focused ion beam microscope enabled APT needles to be prepared from the low defect density regions of the grown s le. A complementary analysis was also undertaken on QWs having comparable In contents grown on polar c-plane s le pseudo-substrates. Both frequency distribution and modified nearest neighbor analyses indicate a statistically non-randomized In distribution in the a-plane QWs, but a random distribution in the c-plane QWs. This work not only provides insights into the structure of non-polar a-plane QWs but also shows that APT is capable of detecting as-grown nanoscale clustering in InGaN and thus validates the reliability of earlier APT analyses of the In distribution in c-plane InGaN QWs which show no such clustering.
Publisher: American Physical Society (APS)
Date: 08-2003
Publisher: Elsevier BV
Date: 10-2023
Publisher: Elsevier BV
Date: 12-2018
Publisher: Statistica Sinica (Institute of Statistical Science)
Date: 2021
Publisher: Elsevier BV
Date: 08-2016
Publisher: Elsevier BV
Date: 08-2017
Publisher: Elsevier BV
Date: 10-2013
Publisher: Elsevier BV
Date: 09-2013
DOI: 10.1016/J.ULTRAMIC.2013.02.014
Abstract: Two methods for separating the constituent atoms of molecular ions within atom probe tomography reconstructions are presented. The Gaussian Separation Method efficiently deconvolutes molecular ions containing two constituent atoms and is tested on simulated data before being applied to an experimental HSLA steel dataset containing NbN. The Delaunay Separation Method extends separation to larger complex ions and is also tested on simulated data before being applied to an experimental GaAs dataset containing many large (>3 atoms) complex ions. First nearest neighbour (1NN) distributions and images of the reconstruction before and after the separations are used to show the effect of the algorithms and their validity and practicality are also discussed.
Publisher: AIP Publishing
Date: 25-02-2005
DOI: 10.1063/1.1855313
Abstract: A one-dimensional, two-state model problem with two well-separated avoided crossing points is employed to test the efficiency and accuracy of a semiclassical surface hopping technique. The use of a one-dimensional model allows for the accurate numerical evaluation of both fully quantum-mechanical and semiclassical transition probabilities. The calculations demonstrate that the surface hopping procedure employed accounts for the interference between different hopping trajectories very well and provides highly accurate transition probabilities. It is, in general, not computationally feasible to completely sum over all hopping trajectories in the semiclassical calculations for multidimensional problems. In this case, a Monte Carlo procedure for selecting important trajectories can be employed. However, the cancellation due to the different phases associated with different trajectories limits the accuracy and efficiency of the Monte Carlo procedure. Various approaches for improving the accuracy and efficiency of Monte Carlo surface hopping procedures are investigated. These methods are found to significantly reduce the statistical s ling errors in the calculations, thereby increasing the accuracy of the transition probabilities obtained with a fixed number of trajectories s led.
Publisher: Elsevier BV
Date: 06-2020
Publisher: IOP Publishing
Date: 18-03-2016
Publisher: Elsevier BV
Date: 06-2012
Publisher: Elsevier BV
Date: 06-2012
Publisher: Society of Economic Geologists
Date: 09-2019
DOI: 10.5382/ECONGEO.4676
Abstract: Carlin-type gold deposits are one of the most important gold mineralization styles in the world. Despite their economic importance and the large volume of work that has been published, there remain crucial questions regarding their metallogenesis. Much of this uncertainty is due to the cryptic nature of the gold occurrence, with gold occurring as dispersed nanoscale inclusions within host pyrite rims that formed on earlier formed barren pyrite cores. The small size of the gold inclusions has made determining their nature within the host sulfides and the mechanisms by which they precipitated from the ore fluids particularly problematic. This study combines high-resolution electron probe microanalysis (EPMA) with atom probe tomography (APT) to constrain whether the gold occurs as nanospheres or is dispersed within the Carlin pyrites. APT offers the unique capability of obtaining major, minor, trace, and isotopic chemical information at near-atomic spatial resolution. We use this capability to investigate the atomic-scale distribution of trace elements within Carlin-type pyrite rims, as well as the relative differences of sulfur isotopes within the rim and core of gold-hosting pyrite. We show that gold within a s le from the Turquoise Ridge deposit (Nevada) occurs within arsenian pyrite overgrowth (rims) that formed on a pyrite core. Furthermore, this As-rich rim does not contain nanonuggets of gold and instead contains dispersed lattice-bound Au within the pyrite crystal structure. The spatial correlation of gold and arsenic within our s les is consistent with increased local arsenic concentrations that enhanced the ability of arsenian pyrite to host dispersed gold (Kusebauch et al., 2019). We hypothesize that point defects in the lattice induced by the addition of arsenic to the pyrite structure facilitate the dissemination of gold. The lack of gold nanospheres in our study is consistent with previous work showing that dispersed gold in arsenian pyrite can occur in concentrations up to ~1:200 (gold/arsenic). We also report a method for determining the sulfur isotope ratios from atom probe data sets of pyrite (±As) that illustrates a relative change between the pyrite core and its Au and arsenian pyrite rim. This spatial variation confirms that the observed pyrite core-rim structure is due to two-stage growth involving a sedimentary or magmatic-hydrothermal core and hydrothermal rim, as opposed to precipitation from an evolving hydrothermal fluid.
Publisher: Elsevier BV
Date: 04-2017
Publisher: Elsevier BV
Date: 12-2015
DOI: 10.1016/J.ULTRAMIC.2015.05.006
Abstract: Whilst atom probe tomography (APT) is a powerful technique with the capacity to gather information containing hundreds of millions of atoms from a single specimen, the ability to effectively use this information creates significant challenges. The main technological bottleneck lies in handling the extremely large amounts of data on spatial-chemical correlations, as well as developing new quantitative computational foundations for image reconstruction that target critical and transformative problems in materials science. The power to explore materials at the atomic scale with the extraordinary level of sensitivity of detection offered by atom probe tomography has not been not fully harnessed due to the challenges of dealing with missing, sparse and often noisy data. Hence there is a profound need to couple the analytical tools to deal with the data challenges with the experimental issues associated with this instrument. In this paper we provide a summary of some key issues associated with the challenges, and solutions to extract or "mine" fundamental materials science information from that data.
Publisher: Oxford University Press (OUP)
Date: 04-2017
DOI: 10.1017/S1431927617000356
Abstract: The local electrode atom probe (LEAP) has become the primary instrument used for atom probe tomography measurements. Recent advances in detector and laser design, together with updated hit detection algorithms, have been incorporated into the latest LEAP 5000 instrument, but the implications of these changes on measurements, particularly the size and chemistry of small clusters and elemental segregations, have not been explored. In this study, we compare data sets from a variety of materials with small-scale chemical heterogeneity using both a LEAP 3000 instrument with 37% detector efficiency and a 532-nm green laser and a new LEAP 5000 instrument with a manufacturer estimated increase to 52% detector efficiency, and a 355-nm ultraviolet laser. In general, it was found that the number of atoms within small clusters or surface segregation increased in the LEAP 5000, as would be expected by the reported increase in detector efficiency from the LEAP 3000 architecture, but subtle differences in chemistry were observed which are attributed to changes in the way multiple hit detection is calculated using the LEAP 5000.
Publisher: Elsevier BV
Date: 02-2017
Publisher: IOP Publishing
Date: 19-02-2018
Publisher: IOP Publishing
Date: 14-08-2019
Publisher: AIP Publishing
Date: 20-07-2009
DOI: 10.1063/1.3182351
Publisher: Elsevier BV
Date: 11-2023
Location: United Kingdom of Great Britain and Northern Ireland
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Funder: Engineering and Physical Sciences Research Council
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