Duncan N. Johnstone

Microfluidization of Graphite and Formulation of Graphene-Based Conductive Inks

We report the exfoliation of graphite in aqueous solutions under high shear rate [∼ 108 s–1] turbulent flow conditions, with a 100% exfoliation yield. The material is stabilized without centrifugation at concentrations up to 100 g/L using carboxymethylcellulose sodium salt to formulate conductive printable inks. The sheet resistance of blade coated films is below ∼2Ω/□. This is a simple and scalable production route for conductive inks for large-area printing in flexible electronics.

High-resolution scanning precession electron diffraction: Alignment and spatial resolution

Methods are presented for aligning the pivot point of a precessing electron probe in the scanning transmission electron microscope (STEM) and for assessing the spatial resolution in scanning precession electron diffraction (SPED) experiments. The alignment procedure is performed entirely in diffraction mode, minimising probe wander within the bright-field (BF) convergent beam electron diffraction (CBED) disk and is used to obtain high spatial resolution SPED maps. Through analysis of the power spectra of virtual bright-field images extracted from the SPED data, the precession-induced blur was measured as a function of precession angle. At low precession angles, SPED spatial resolution was limited by electronic noise in the scan coils; whereas at high precession angles SPED spatial resolution was limited by tilt-induced two-fold astigmatism caused by the positive spherical aberration of the probe-forming lens.

Electron Microscopy (Big and Small) Data Analysis With the Open Source Software Package HyperSpy

Francisco de la Peña, Tomas Ostasevicius, Vidar Tonaas Fauske, Pierre Burdet, Petras Jokubauskas, Magnus Nord, Mike Sarahan, Eric Prestat, Duncan N. Johnstone, Joshua Taillon, Jan Caron, Tom Furnival, Katherine E. MacArthur, Alberto Eljarrat, Stefano Mazzucco, Vadim Migunov, Thomas Aarholt, Michael Walls, Florian Winkler, Gaël Donval, Ben Martineau, Andreas Garmannslund, Luiz-Fernando Zagonel and Ilya Iyengar

Secondary magnetic inclusions in detrital zircons from the Jack Hills, Western Australia, and implications for the origin of the geodynamo

The time of origin of Earth’s dynamo is unknown. Detrital zircon crystals containing ferromagnetic inclusions from the Jack Hills of Western Australia have the potential to contain the oldest records of the geodynamo. It has recently been argued that magnetization in these zircons indicates that an active dynamo existed as far back as 4.2 Ga. However, the ages of ferromagnetic inclusions in the zircons are unknown. Here we present the first detailed characterization of the mineralogy and spatial distribution of ferromagnetic minerals in Jack Hills detrital zircons. We demonstrate that ferromagnetic minerals in most Jack Hills zircons are commonly located in cracks and on the zircons’ exteriors. Hematite is observed to dominate the magnetization of many zircons, while other zircons also contain significant quantities of magnetite and goethite. This indicates that the magnetization of most zircons is likely to be dominantly carried by secondary minerals that could be hundreds of millions to billions of years younger than the zircons’ crystallization ages. We conclude that the existence of the geodynamo prior to 3.5 Ga has yet to be established.

On three-dimensional misorientation spaces

Determining the local orientation of crystals in engineering and geological materials has become routine with the advent of modern crystallographic mapping techniques. These techniques enable many thousands of orientation measurements to be made, directing attention towards how such orientation data are best studied. Here, we provide a guide to the visualization of misorientation data in three-dimensional vector spaces, reduced by crystal symmetry, to reveal crystallographic orientation relationships. Domains for all point group symmetries are presented and an analysis methodology is developed and applied to identify crystallographic relationships, indicated by clusters in the misorientation space, in examples from materials science and geology. This analysis aids the determination of active deformation mechanisms and evaluation of cluster centres and spread enables more accurate description of transformation processes supporting arguments regarding provenance.

Data Clustering and Scanning Precession Electron Diffraction for Microanalysis

Modern transmission electron microscopes are capable of recording and storing unprecedented amounts of data, which conventional analysis methods are ill-equipped to deal with. However, recent advances in computing power and the birth of ‘big data’ have given rise to a wealth of new statistical techniques to fill the gap. One family of these techniques is data clustering, which we apply to scanning precession electron diffraction (SPED) data.

The Microstructure of Pharmaceutical Materials Revealed by Scanning Electron Diffraction

The microstructure of pharmaceutical materials influences important physical properties [1] such as compaction behavior, dissolution rate, bioavailability, hygroscopicity, dehydration, chemical stability and physical stability. However, few techniques are capable of directly revealing the underlying microstructure and associated defects. Transmission electron microscopy (TEM) provides an obvious means to image and characterize microstructure and defects. Whilst previous TEM studies of pharmaceutical materials have been insightful [2] the level of detail attained has been necessarily limited because of the sensitivity of the sample to damage by electron irradiation. Scanning electron diffraction (SED) provides a new paradigm in which the data required for detailed analysis is acquired rapidly and before the specimen is destroyed. Insight is gleaned post-facto through the application of versatile computational analysis enabling maximal information to be extracted from the data.

Inter-phase Relationships Revealed in 3-Dimensional Orientation Spaces

Spatially resolved orientation mapping is increasingly performed using electron microscopy techniques, including: electron backscatter diffraction, transmission Kikuchi diffraction and scanning precession electron diffraction. The resulting orientation maps contain a wealth of information with crystal phase and orientation specified at each pixel. However, the depth of this data is often underutilized owing to challenges posed by the analysis of such large quantities of data. In the context of understanding complex and multi-phase materials it is important to characterize inter-phase relationships between nanoscale precipitates and the surrounding matrix, which both affect properties and are indicative of formation pathways. Revealing inter-phase relationships requires statistical assessment of the orientation relationship across the phase boundary, the spatial occurrence of particular boundaries and the surfaces of contact at interfaces. Analysis procedures that highlight relationships in both spatial and orientation dimensions are therefore required. Here, we present an approach to revealing inter-phase relationships, based on considering orientation data in 3-dimensional vector spaces constrained to fundamental zones defined by the crystal symmetry of both crystals.

Scanning Precession Electron Diffraction Study of Hybrid Precipitates in a 6xxx Series Aluminium Alloy

Obtaining reliable and statistical assessment of nanoscale precipitates to link the microstructure with material properties is a primary objective of transmission electron microscopy (TEM) studies of agehardenable aluminium (Al) alloys. Here, it is demonstrated that nanometer-resolution scanning precession electron diffraction (SPED) [1] combined with versatile post-facto computational analysis provides a route to extract improved precipitate statistics in Al alloys. The approach developed is automated, and offers more objective assessment compared to conventional imaging procedures which require manual identification, counting and measurements. The material studied here is a common 6xxx series industrial alloy (6082, Al-0.72Mg-0.88Si-0.03Cu (wt %)) and the methods developed are generic and applicable to any material containing nanoscale precipitates.

Local Layer Stacking and Structural Disorder in Graphene Oxide Studied via Scanning Electron Diffraction.

Graphene oxide (GO) is a structurally complex and variable material comprising sheets of carbon atoms functionalized with a variety of moieties, including carboxyl, epoxy and hydroxyl groups. Potential applications span optoelectronics, energy storage, environmental science and biotechnology. The structural complexity necessitates the application of versatile and information rich characterization techniques. Conventional and scanning transmission electron microscopy [(S)TEM] has provided numerous insights into GO structure [e.g. 1-3], but the detail attained has not reached those familiar from studies of more pristine graphene [4-6]. Here, scanning electron diffraction (SED) is applied to obtain more comprehensive insights into the local layer stacking and structural disorder in GO.