Towards predictive modelling of near-edge structures in electron energy loss spectra of AlN based ternary alloys

Although electron energy loss near edge structure analysis provides a tool for experimentally probing unoccupied density of states, a detailed comparison with simulations is necessary in order to understand the origin of individual peaks. This paper presents a density functional theory based technique for predicting the N K-edge for ternary (quasi-binary) nitrogen alloys by adopting a core hole approach, a methodology that has been successful for binary nitride compounds. It is demonstrated that using the spectra of binary compounds for optimising the core hole charge ($0.35\,\mathrm{e}$ for cubic Ti$_{1-x}$Al$_x$N and $0.45\,\mathrm{e}$ for wurtzite Al$_x$Ga$_{1-x}$N), the predicted spectra evolutions of the ternary alloys agree well with the experiments. The spectral features are subsequently discussed in terms of the electronic structure and bonding of the alloys.Comment: 11 pages, 9 figures, 1 tabl

Managing dose-, damage- and data-rates in multi-frame spectrum-imaging

As an instrument, the scanning transmission electron microscope is unique in being able to simultaneously explore both local structural and chemical variations in materials at the atomic scale. This is made possible as both types of data are acquired serially, originating simultaneously from sample interactions with a sharply focused electron probe. Unfortunately, such scanned data can be distorted by environmental factors, though recently fast-scanned multi-frame imaging approaches have been shown to mitigate these effects. Here, we demonstrate the same approach but optimized for spectroscopic data; we offer some perspectives on the new potential of multi-frame spectrum-imaging (MFSI) and show how dose-sharing approaches can reduce sample damage, improve crystallographic fidelity, increase data signal-to-noise, or maximize usable field of view. Further, we discuss the potential issue of excessive data-rates in MFSI, and demonstrate a file-compression approach to significantly reduce data storage and transmission burdens

Cost Overruns in Hydrocarbon Megaprojects: A Critical Review and Implications for Research

Cost overruns are prevalent in hydrocarbon (oil and gas) megaprojects. A recent report indicates that 64% of ongoing megaprojects globally are facing cost overruns. Despite their increasing occurrence, there has been limited published research in the mainstream literature that has specifically examined why and how they occur. Consequently, suggestions regarding how to constructively address cost overruns in hydrocarbon megaprojects are scant. To better understand the causal nature of cost overruns in hydrocarbon megaprojects, this article provides a critical review of the extant literature. Findings from the research indicate that complex interactions between project characteristics, people, technology, and structure and culture contribute to cost overruns occurring. As a result, it is suggested that chaos theory can be used to explain how cost overruns arise in hydrocarbon megaprojects. This article provides a reference point for engendering future research in this pervasive and fertile area