EPOFO

Electron probing of functional oxides

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 Obiettivo del progetto (Objective)

'This project is aimed towards unlocking the properties of functional oxides such as ferroelectric (BaTiO3, BiFeO3 on SrNbxTi1-xO3/SrTiO3) and multiferroic (CoFe2O4 on BaTiO3) thin films. The need for manufacturing such thin films with tailored properties is currently growing immensely due to their potential for a wide range of applications including high frequency electronics, microwave tunable devices, and memory based devices. The key feature of these devices is the speed of tuning and the most inhibiting factor in their usability is the slow relaxation processes which are attributed to the residual polarization caused by the space charge formed due to the injection of electrons from electrodes and its trapping by defects and/or oxygen vacancies on the oxide film-electrode interface and/or inside the film itself. Currently, there is a critical demand for the development and application of characterization methods that are able to probe the physicochemical material parameters on the very local scale. To address this, an integrated multidisciplinary approach will be undertaken. State-of-art nanoanalytical electron microscopy techniques will be applied and developed to determine the films potential for the next-generation nanoscale components pertinent to microwave and memory devices. Specifically the objectives of the proposed research are (1) to investigate the structural defects/domain structure of ferroelectric/ multiferroic thin films, (2) to probe the oxygen deficiencies/vacancies at the interfaces, and (3) to experimentally identify and evaluate the space charge distributions arising from these defects. Finally, all experimental results will be weighed against theoretical predictions. Ultimately, the results of this project will elucidate the switch-ability, i.e. the inherent speed of tuning, of the materials at sub-nanometer scale, by rationalizing the role that each of the above-mentioned, critical attributes play in regulating the relaxation processes.'

Introduzione (Teaser)

EU-funded scientists applied state-of-the-art electron microscopy techniques to provide further insight into the physical and chemical properties that govern the behaviour of functional oxides.

Descrizione progetto (Article)

Current research and industry attention on functional oxides are based on their wide range of applications, including memory devices, high-frequency electronics and tuneable microwave devices. The key feature of these devices is the speed of switching, with slow relaxation processes being a main downside to their use.

Nano-scale structures of active surfaces and interfaces play a critical role in oxide functionality. In the EU-funded project 'Electron probing of functional oxides' (EPOFO), scientists investigated the interface structural defects of functional oxides in thin-film device configurations, and probed oxygen deficiencies at the interfaces. Furthermore, they experimentally identified and evaluated the space charge distributions arising from these defects that inhibit functional properties at the interfaces and surfaces.

Through these activities, EPOFO sought to elucidate the role of structural defects, oxygen deficiencies and space charge distributions in regulating the relaxation processes.

To address important issues that govern the performance of functional oxide nanoparticle systems and thin-film heterostructures, the project evaluated transmission electron microscopy (TEM) techniques. TEM data were thoroughly analysed using theoretical calculations.

Nanoparticle catalytic functionality is known to be directly linked to the active surface sites taking part in the reaction. Through TEM and electron energy-loss spectroscopy, scientists characterised the surface of oxide perovskite catalysts whose reaction mechanisms remained unknown at that time. The conclusions obtained through density functional theory analysis were important given that these catalysts are the best contenders for replacing the conventional costly metal catalysts.

Other project findings concerned the lack of sufficient elastic strain for strong magnetoelectric coupling at the interface of a ferroelectric and a ferromagnetic functional oxide system. Nevertheless, results confirmed a sufficient chemical activity between the two oxides that could lead to synthesising complex engineered interfaces.

EPOFO contributed to optimising future engineered oxide structures that can be successfully implemented in future working devices. Nano-scale control of the structures should be useful to further investigate the device speed of switching.