Welcome to the Thin films and Interface Materials Research Group website. We investigate interfacial phenomena in a number of functional materials, predominantly fabricated in thin film form. Most of our research is on complex metal oxides with a special emphasis on ferroelectrics and multiferroics, although more recently we have also explored non-oxide phosphides and sulfide multilayers for solar applications . Our group spends hours trying make these materials at very tiny dimensions to the size of a few nanometers. The challenge is not only in making them but also visually "seeing" them and measuring their properties. At such length scales, the background noise often overrides the signal of interest- therefore a large part of our research involves highly sensitive instrumentation to detect very weak signals and advanced microscopy techniques.
Our research
In our group we are interested in the properties of a material at an interface. In fact, often the system of interest is so small that the surface area dominates over the volume 鈥 leading to what is called as surface and interface mediated phenomena. We study interface morphology, chemistry and structure and its effect ultimately on the functional response听for applications such as piezoelectric sensors, computer memory, solar energy and ultrasonic transducers.听Current areas of research include:
Development of domain wall nanoelectronics
In 2009 it was demonstrated that certain types of domain walls in an otherwise insulating material are able to conduct current. We have developed devices based on domain wall nanoelectronics, a new avenue to design functional materials by using nanofabrication to artificially engineer domain walls in ferroelectrics. This program, funded by the ARC, led to a breakthrough paper published in Science Advances and coverage by a number of media outlets. A follow-up paper, showing that the charge state of the wall can be used to access multi-level data storage, was recently published in Advanced Functional Materials.
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Using specially designed nanofabricated electrodes and scanning probe techniques, we demonstrate a prototype non-volatile ferroelectric domain wall memory, scalable to below 100nm, whose binary state is defined by the existence or absence of conductive walls. The device can be read out non-destructively at moderate voltages (<3 V), exhibits relatively high OFF-ON ratios (~103) with excellent endurance and retention characteristics, and has multilevel data storage capacity. Our work thus constitutes an important step toward integrated nanoscale ferroelectric domain wall memory devices.
Relevant papers:
Science Advances 2017, 3: e1700512
Adv. Funct. Mater.听2019,听29, 1807523.
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Development of topological nanoelectronics
All ferroic materials show regions called domains, which are separated by naturally occurring domain walls. Domains and domain walls are called 鈥渢opological defects鈥澨 our research funded by ARC Centre of Excellence FLEET has now demonstrated a new avenue to design functional materials by using real space topologies to artificially engineer the net ferroelectric polarisation.听 Following demonstration of the world鈥檚 first multistate ferroelectric domain wall memory (see above) we are currently studying the synthesis, manipulation and control of polar bubles and electrical skyrmions.
Relevant papers
Freestanding Ferroelectric Bubble Domains. Advanced Materials 2021, 2105432.
Topology and control of self-assembled domain patterns in low-dimensional ferroelectrics. Nature communications 2020, 11 (1), 1-8.
Deterministic switching of ferroelectric bubble nanodomains. Advanced Functional Materials 2019, 29 (28), 1808573.
Interface engineering of ferroelectric domains in thin films with colossal piezoelectric properties
Nanofabrication and interface engineering of the electrical and mechanical constraints can lead to ferroelectric thin films with superior electromechanical properties, suitable for sensors and actuators. This work has been published in a series of high-impact journals, most recently in听Nature听Materials.
Relevant papers
Anisotropic epitaxial stabilisation of a low-symmetry ferroelectric with enhanced electromechanical response. Nature Materials 2021, 1-7.
Deterministic ferroelastic domain switching using ferroelectric bilayers. Nano letters 2019, 19 (8), 5319-5326.
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Effect of atomic scale inhomogeneity on polar interfaces
Given the aggressive trend for miniaturisation, even the presence of a single atomic level defect can adversely affect the nanoscale device performance. We used highly sophisticated aberration-corrected microscopy and atomic-scale spectroscopy techniques to investigate the consequences of the defects associated with materials lattice. We have shown that defects can be exploited to stabilise new phases and hence properties
Relevant papers
Superior polarisation retention through engineered domain wall pinning. Nature communications 2020, 11 (1), 1-8.
Interfacial strain gradients control nanoscale domain morphology in epitaxial BiFeO3 multiferroic films. Advanced Functional Materials 2020, 30 (22), 2000343.
Controlled Nucleation and Stabilization of Ferroelectric Domain Wall Patterns in Epitaxial (110) Bismuth Ferrite Heterostructures. Advanced Functional Materials 2020, 30 (48), 2003571.
New quantum materials through nanostructured polar oxide thin film interfaces听(ZnS-GaP)
As semiconductor devices are shrunk towards the atomic-scale regime, quantum mechanical effects move from becoming a small correction to dominating device performance 鈥 and offering entirely new functionalities. Using complex oxide heterostructures we show new ways to听exploit such quantum properties including exploiting the coupling between spin and polarisation.
Relevant papers
The Experimentalist's Guide to the Cycloid, or Noncollinear Antiferromagnetism in Epitaxial BiFeO3. Advanced Materials 2020, 32 (45), 2003711.
Fowler鈥揘ordheim tunneling-assisted enhancement of tunneling electroresistance effect through a composite barrier, Appl. Phys. Lett.听听2020, 116, 202901
A perspective on electrode engineering in ultrathin ferroelectric heterostructures for enhanced tunneling electroresistance, Applied Physics Reviews 2020, 7, 041316
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