Michael Moody
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.
New Research Projects Available
Selected Publications
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Characterization of oxidation mechanisms in a family of polycrystalline chromia-forming nickel-base superalloys
March 2021|Journal article|Acta Materialia -
Observation of Mn-Ni-Si-rich features in thermally-aged model reactor pressure vessel steels
January 2021|Journal article|Scripta Materialia© 2020 Acta Materialia Inc. Atom probe tomography was used to characterise two low-Cu (< 0.04 at. %) model steels after exposure to long-term thermal ageing. Mn-Ni-Si-rich features were observed to form after as little as 20,731 h (∼ 2.4 years) of ageing. The composition of these features were compared to those predicted by thermodynamic models and the similarities and differences are discussed. -
Characterisation of nano-scale precipitates in BOR60 irradiated T91 steel using atom probe tomography
January 2021|Journal article|Journal of Nuclear Materials© 2020 Elsevier B.V. Atom probe tomography has characterised the microstructural changes in T91 steel after BOR60 reactor irradiation at five temperatures between 376 °C and 524 °C to doses between 14.6 dpa and 35.1 dpa. Irradiation-induced precipitation and segregation to carbide/matrix interface induced by neutron irradiation has been characterised. Atom probe tomography characterisation shows that Mn, Ni, Si -rich (MNS-rich) clusters form in T91 steel irradiated in BOR60 reactor at temperatures between 376 °C and 415 °C, which is not observed at higher temperatures 460 °C and 524 °C. The number density, volume fraction and composition of MNS-rich clusters have been characterised. Ni, Mn, Si and P is found to segregate at carbide matrix interface after irradiation at lower temperature and only P segregation is observed at 524 °C. -
Atom probe characterisation of segregation driven Cu and Mn–Ni–Si co-precipitation in neutron irradiated T91 tempered-martensitic steel
December 2020|Journal article|Materialia -
Towards model-driven reconstruction in atom probe tomography
November 2020|Journal article|JOURNAL OF PHYSICS D-APPLIED PHYSICSfield evaporation, boundary element method, panel clustering, atom probe tomography, level set method, data reconstruction, distortion correction -
A more holistic characterisation of internal interfaces in a variety of materials via complementary use of transmission Kikuchi diffraction and Atom probe tomography
October 2020|Journal article|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. -
Processing APT Spectral Backgrounds for Improved Quantification.
October 2020|Journal article|Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of CanadaWe describe a method to estimate background noise in atom probe tomography (APT) mass spectra and to use this information to enhance both background correction and quantification. Our approach is mathematically general in form for any detector exhibiting Poisson noise with a fixed data acquisition time window, at voltages varying through the experiment. We show that this accurately estimates the background observed in real experiments. The method requires, as a minimum, the z-coordinate and mass-to-charge-state data as input and can be applied retrospectively. Further improvements are obtained with additional information such as acquisition voltage. Using this method allows for improved estimation of variance in the background, and more robust quantification, with quantified count limits at parts-per-million concentrations. To demonstrate applications, we show a simple peak detection implementation, which quantitatively suppresses false positives arising from random noise sources. We additionally quantify the detectability of 121-Sb in a standardized-doped Si microtip as (1.5 × 10−5, 3.8 × 10−5) atomic fraction, α = 0.95. This technique is applicable to all modes of APT data acquisition and is highly general in nature, ultimately allowing for improvements in analyzing low ionic count species in datasets. -
Electron microscopy and atom probe tomography of nanoindentation deformation in oxide dispersion strengthened steels
September 2020|Journal article|Materials Characterization -
A study of the interaction of oxygen with the α
2 phase in the model alloy Ti–7wt%AlAugust 2020|Journal article|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
August 2020|Journal article|Acta Materialia