Active chiral plasmonics: flexoelectric control of nanoscale chirality

The ability to electrically control the optical properties of metamaterials is an essential capability required for technological innovation. The creation of dynamic electrically tuneable metamaterials in the visible and near IR region are important for a range of imaging and fibre optic technologies. However current approaches require complex nanofabrication processes which are incompatible for low cost device production. Here, we report a novel simple approach for electrical control of optical properties which utilises a flexoelectric dielectric element to electromechanically manipulate the form factor of a chiral nanostructure. By altering the dimensions of the chiral nanostructure, we allow the polarisation properties of light to be electrically controlled. The flexoelectric element is part of a composite metafilm that is templated on to a nanostructured polymer substrate. Since the flexoelectric element does not require in situ high temperature annealing it can be readily combined with polymer‐based substrates produced by high throughput methods. This is not the case for piezoelectric elements, routinely used in microelectromechanical (MEM) devices which require high temperature processing. Consequently, combining amorphous flexoelectric dielectric and low‐cost polymer‐based materials provides a route to the high throughput production of electrically responsive disposable metadevices

Fast pixelated detectors in scanning transmission electron microscopy. Part II: post acquisition data processing, visualisation, and structural characterisation

Fast pixelated detectors incorporating direct electron detection (DED) technology are increasingly being regarded as universal detectors for scanning transmission electron microscopy (STEM), capable of imaging under multiple modes of operation. However, several issues remain around the post acquisition processing and visualisation of the often very large multidimensional STEM datasets produced by them. We discuss these issues and present open source software libraries to enable efficient processing and visualisation of such datasets. Throughout, we provide examples of the analysis methodologies presented, utilising data from a 256×256 pixel Medipix3 hybrid DED detector, with a particular focus on the STEM characterisation of the structural properties of materials. These include the techniques of virtual detector imaging; higher order Laue zone analysis; nanobeam electron diffraction; and scanning precession electron diffraction. In the latter, we demonstrate nanoscale lattice parameter mapping with a fractional precision ≤6×10−4 (0.06%)

Fast pixelated detectors in scanning transmission electron microscopy. Part I: data acquisition, live processing and storage

The use of fast pixelated detectors and direct electron detection technology is revolutionising many aspects of scanning transmission electron microscopy (STEM). The widespread adoption of these new technologies is impeded by the technical challenges associated them. These include issues related to hardware control, and the acquisition, real-time processing and visualisation, and storage of data from such detectors. We discuss these problems and present software solutions for them, with a view to making the benefits of new detectors in the context of STEM more accessible. Throughout, we provide examples of the application of the technologies presented, using data from a Medipix3 direct electron detector. Most of our software is available under an open source licence, permitting transparency of the implemented algorithms, and allowing the community to freely use and further improve upon them

Correlative chemical and structural nanocharacterization of a pseudo‐binary 0.75Bi(Fe 0.97 Ti 0.03 )O 3 –0.25BaTiO 3 ceramic

Fast-cooling after sintering or annealing of BiFeO3-BaTiO3 mixed oxide ceramics yields core-shell structures that give excellent functional properties, but their precise phase assemblage and nanostructure remains an open question. By comparing conventional electron energy loss spectroscopy (EELS) with scanning precession electron diffraction (SPED) mapping using a direct electron detector, we correlate chemical composition with the presence or absence of octahedral tilting and with changes in lattice parameters. This reveals that some grains have a 3-phase assemblage of a BaTiO3-rich pseudocubic shell; a BiFeO3-rich outer core with octahedral tilting consistent with an R3c structure; and an inner core richer in Ba and even poorer in Ti, which seems to show a pseudocubic structure of slightly smaller lattice parameter than the shell region. This last structure has not been previously identified in these materials, but the composition and structure fit with previous studies. These inner cores are likely to be non-polar and play no part in the ferroelectric properties. Nevertheless, the combination of EELS and SPED clearly provides a novel way to examine heterogeneous microstructures with high spatial resolution, thus revealing the presence of phases that may be too subtle to detect with more conventional techniques.Comment: Section on functional properties altered slightly from previous version before resubmission after reviewers comments. Manuscript: 25 pages, 5 figures; supplemental materials: 6 pages, 1 table, 5 figures (end of document

A correlative study of interfacial segregation in a Cu-doped TiNiSn thermoelectric half-Heusler alloy

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