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.
Processing APT Spectral Backgrounds for Improved Quantification.
Microscopy and microanalysis : the official journal of Microscopy Society of America, Microbeam Analysis Society, Microscopical Society of Canada
We 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