Michael Moody

Professor Michael Moody
Professor of Materials
+44 1865 273693
michael.moody@materials.ox.ac.uk

My interests are focused upon enabling materials research at the nanoscale via the microscopy techniques of atom probe tomography (APT) and field ion microscopy (FIM). APT is a technique capable of material characterisations at the atomic-scale, in which each atom is identified chemically and located in three-dimensions with very high accuracy. Hence, it is a technique rapidly rising in prominence. The Atom Probe Group in the Department of Materials at the University of Oxford is interested and active in all areas of this research across a broad range of material systems.

In particular, I am developing a variety of new analytical techniques to improve the three dimensional reconstructions generated by APT and the subsequent atom-by-atom analysis of the resulting data.  I am interested in applying these techniques to the characterisation of a wide variety of systems to inform materials research projects.

Selected Publications

  • A more holistic characterisation of internal interfaces in a variety of materials via complementary use of transmission Kikuchi diffraction and Atom probe tomography

    2020
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    Journal article
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    Applied Surface Science
    © 2020 Elsevier B.V. Changes in the chemistry of internal interfaces, particularly grain boundaries, are known to affect the macroscopic properties of a wide range of material systems. Solute segregation to grain boundaries is dependent on, amongst other factors, the physical structure of the grain boundary. We demonstrate how complementary use of transmission Kikuchi diffraction (TKD) and atom probe tomography (APT) can provide a more holistic characterisation of grain boundaries in a variety of materials. Structural information is reported from TKD data for a model steel, a titanium alloy, and a multicrystalline silicon sample. Complementary APT analyses are used to determine the segregation behaviour to these interfaces. A novel specimen preparation protocol allows for the grain boundary to be positioned more reliably within the apex of an APT specimen. Meanwhile, a method that allows a grain boundary's five macroscopic degrees of freedom to be determined from TKD data alone is also proposed.

  • Electron microscopy and atom probe tomography of nanoindentation deformation in oxide dispersion strengthened steels

    2020
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    Journal article
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    Materials Characterization
    © 2020 Elsevier Inc. Oxide Dispersion Strengthened (ODS) steels are candidates for fuel cladding materials in sodium-cooled fast reactors and for structural materials in nuclear fusion power reactors. The effect yttrium-titanium-oxygen (Y-Ti-O) nano-oxide precipitates within ODS steels have on the micromechanical deformation mechanisms has been investigated. The aim is to assess the extent of any direct link between the Y-Ti-O dispersion and nanoindentation hardness, using electron backscatter diffraction, transmission electron microscopy (TEM), and atom probe tomography (APT) studies of a Fe-14Cr-3W-0.2Ti-0.25Y2O3 (wt%) ODS steel at room temperature. Y-Ti-O nanoclusters had a non-uniform distribution and average number density that ranged from 5.8 ± 0.1 × 1023 to 1.3 ± 0.1 × 1024 m−3 and Guinier radii ranging from 1.8 ± 0.2 nm to 2.1 ± 0.2 nm. Surprisingly, the local Y-Ti-O distribution did not correlate strongly with the nanohardness, indicating that the dominant hardening mechanisms was at best only weakly related to the Y-Ti-O distribution. Instead, scanning TEM and APT confirmed that the dominant hardening mechanism was due to the grain boundary refinement, and was further enhanced by tungsten enrichment to ~3.5 at.% at grain boundaries.

  • A study of the interaction of oxygen with the α2 phase in the model alloy Ti–7wt%Al

    2020
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    Journal article
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    Scripta Materialia
    © 2020 Acta Materialia Inc. Atom Probe Tomography is used to show that the α2 phase (Ti3Al) forms upon ageing Ti–7Al at 550 °C with as little as 500 wppm oxygen. Notably, it is found that oxygen consistently partitions away from the α2 precipitates to the α matrix. The role of aluminium concentration and oxygen solubility on oxygen partitioning preference is also investigated. Based on our observations, we propose a mechanism by which oxygen encourages α2 formation despite partitioning away from it. Furthermore, nanohardness systematically measured with respect to ageing time and oxygen concentration suggests that α2 precipitation is not the dominant hardening mechanism during ageing.

  • Microstructural understanding of the oxidation of an austenitic stainless steel in high-temperature steam through advanced characterization

    2020
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    Journal article
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    Acta Materialia

  • New insights into the oxidation mechanisms of a Ferritic-Martensitic steel in high-temperature steam

    2020
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    Journal article
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    Acta Materialia
    © 2020 Acta Materialia Inc. The microstructure of the surface oxide film formed on an Fe-9Cr Ferritic-Martensitic (F-M) steel after exposure to deaerated high-temperature steam at 600°C for 100 h has been analyzed in detail by advanced characterization techniques. The surface oxide film has been revealed to have a triplex structure, including an outer oxide layer, an inner oxide layer, and an internal oxide layer. Although the outer and inner oxide layers are continuous, the internal oxide layer has been proved to consist of interconnected metallic and chromite phases, which is a typical feature of internal oxidation. The formation mechanisms of each layer have been discussed, finding that, contrary to what the available space model suggests, an external oxidation is not the controlling oxidation mechanism of F-M steels in high-temperature steam. The higher resolution used in this study confirms that the controlling mechanism is internal oxidation.

  • The Effect of Composition Variations on the Response of Steels Subjected to High Fluence Neutron Irradiation

    2020
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    Journal article
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    Materialia

  • Atom Probe Tomography Study of Gettering in High-Performance Multicrystalline Silicon

    2020
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    Journal article
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    IEEE Journal of Photovoltaics
    © 2011-2012 IEEE. During the production of high-performance multicrystalline silicon (HPMC-Si) solar cells, gettering occurs inherently during the formation of an emitter. The material benefits with an increase in minority carrier lifetime from the external gettering of impurities into the diffused layer. However, depending on the thermal budget and parameters of the emitter diffusion, as well as the specific material properties, the process can also be detrimental in terms of increased recombination activity of specific crystallographic defects. Thus, it is important to understand the root causes behind the change in recombination activity of defects following gettering. Here, we present a correlative atom probe tomography study of grain boundaries in both p- and n-type HPMC-Si before and after gettering. The presence of nitrogen was found to directly correlate with the increase in recombination activity at grain boundaries. Additionally, an estimation of the atom probe tomography detection limit for transition metals in silicon is made and found to be greater than known impurity levels in commercial HPMC-Si.

  • Reflections on the Analysis of Interfaces and Grain Boundaries by Atom Probe Tomography.

    2020
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    Journal article
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    Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada
    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 example 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.

  • The effect of hydrogen on the early stages of oxidation of a magnesium alloy

    2020
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    Journal article
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    Corrosion Science

  • The effect of hydrogen on the early stages of oxidation of a magnesium alloy

    2020
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    Journal article
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    Corrosion Science
    • More