Prof. Driscoll’s group works in the area of Oxide Energy Materials And Electronics based on advanced thin films. Oxides are of interest as they possess the whole range of materials functions, all the way from insulators to superconductors (with ferroelectrics, semiconductors, and magnetic materials, and a range of other functions in between) (Fig. 1). In the vast majority of cases, they are environmentally stable and benign. There are a large number of possible applications
Fig. 1. Diagrammatic representation of the many properties of nanoengineered oxide films.
Thin films, nanostructuring and interfaces.
The Driscoll group uses nanoscience to engineer oxide materials and they focus on basic science through to application. We are interested in both understanding of basic functionalities and in engineering new interfacial- driven properties. We design and fabricated novel nanostructured films (both standard superlattice approaches) and self-assembled ordered nanocomposite films.
We fabricate high quality thin films using advanced pulsed laser deposition with laser heating and in-situ XPS (Fig. 2). We also use atmospheric pressure spatial atomic layer deposition (AP-SALD), ALD and state-of-the-art oxide sputtering. We also do wide-ranging in-depth characterisation (range of electrical and magnetic measurements from cryogenic temperature, up to ~700°C) to fully understand the materials properties. We collaborate with groups to do density functional theory (DFT) calculations to determine interface structures. This is necessary since interfaces play a very important role is determining the functional properties.
Fig. 2. Advanced pulsed laser deposition systems (one system with in-situ XPS) used in Prof. Driscoll’s group.
Some example structures and fascinating properties stemming from the nanoengineered thin film composites we make are:
a) Artificial Superlattice Structures
We create artificial superlattice structures by advanced PLD. These structures enable us to learn about emergent interface phenomena, as well as to create new properties through interface engineering. An example is the perovskite system: La0.9Ba0.1MnO3:SrTiO3 (LBMO/ STO) (Fig. 3). In thin films, LBMO is a ferromagnetic metal although in bulk it is a ferromagnetic insulator. Through interface engineering to control the octahedral rotations in the LBMO using the STO as a pinning layer, we reinstate the bulk properties.
Fig. 3. Structure and Properties of the LBMO/STO superlattice system. Layers of LBMO and STO are shown in different formats with real images in centre and right hand side/ 40 uc and 5 uc LBMO show different levels of octahedral tilting depending on ability of the STO layer to pin the LBMO. Magnetisation and resistivity versus temperature of the 40 uc films show Tc above room temperature and critically an insulating behaviour also. Such ferromagnetic insulating films are required for a range of spintronic devices. Images adapted from 10.1002/advs.201901606.
b) Vertically aligned nanocomposite (VAN) films
Designer nanocomposite films have been developed over more than 15 years by Prof. Driscoll. Such films show unprecedented properties for many wide ranging functionalities, from ultrahigh density memory systems to superconductors, optoelectronics, to photonics, 3D microbatteries, photocatalysts, electrocatalysts, micro-solid oxide fuel cells, etc.
An example VAN film is below show. In fact, it is a mesoporous structured single-crystalline epitaxial (La0.60Sr0.40)0.95(Co0.20Fe0.80)O3 (LSCF) film made by a simple etching process using acetic acid at room temperature. Thus, MgO was etched out of a vertically aligned nanocomposite film of LSCF/MgO.
Fig. 4 below we show an example nanocomposite film which gives much superior performance (reduced activation energy for oxygen exchange and order of magnitude increases oxygen exchange kinetics). These materials could have potential for superior performance cathodes in fuel cells.
Fig. 4. Etched Self-assembled nanocomposite film giving mesoporous LCSF film showing markedly increased oxygen reduction kinetics. https://doi.org/10.1016/j.jpowsour.2022.230983