Abstract

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Abstract

The half-Heusler alloy TiNiSn is a promising material for thermoelectric applications that is inexpensive and non-toxic. We demonstrate the epitaxial growth of smooth TiNiSn thin films on MgO(001) single crystal substrates by pulsed laser deposition, using transmission electron microscopy to investigate nanoscale structural and chemical inhomogeneities. In particular, an interfacial reaction results in the formation of a titanium-rich oxide nanolayer at the substrate interface, and this maintains epitaxy but perturbs film composition. Segregation effects are observed throughout the film, producing a narrow range of off-stoichiometric, half-Heusler compositions. The propensity of titanium to oxidise also leads to the commensurate formation of parasitic titanium oxide nanostructures which may be overlooked in bulk techniques but are a key feature that drives both the formation of Ni-enriched, full-Heusler phases and the local decomposition of the half-Heusler to form additional nickel-stannide phases.

The ability to electrically control the optical properties of metamaterials is an essential capability required for technological innovation. The creation of dynamic electrically tunable metamaterials in the visible and near infrared regions is important for a range of imaging and fiber optic technologies. However, current approaches require complex nanofabrication processes which are incompatible for low‐cost device production. Herein, a novel simple approach is reported for electrical control of optical properties which uses a flexoelectric dielectric element to electromechanically manipulate the form factor of a chiral nanostructure. By altering the dimensions of the chiral nanostructure, the polarization properties of light are allowed to be electrically controlled. The flexoelectric element is part of a composite metafilm that is templated onto a nanostructured polymer substrate. As 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 dielectrics and low‐cost polymer‐based materials provides a route to the high throughput production of electrically responsive disposable metadevices.