Pakes - Quantum materials for electronics, spintronics and biosensing
Our team is interested in the functionalisation of technologically interesting materials such as diamond, graphene, silicon and organic semiconductors via the chemical modification of the surface and surface transfer doping. We have a strong focus on the functionalisation of diamond surfaces at the atomic-scale to engineer two-dimensional devices with applications in quantum electronics and biosensing.
The group is based in La Trobe's Atom-scale Research Laboratory which houses three ultra-high vacuum (UHV) scanning probe microscopes for atomic scale imaging and manipulation, and suite of UHV instrumentation for the functionalisation and characterisation of surfaces. We work closely with partners at the Australian Synchrotron, University of Erlangen, University of Nottingham, National University of Singapore, and a number of Australian Institutions. We utilise synchrotron-based X-ray facilities at the Australian Synchrotron, BESSY and the Singapore Synchrotron Light Source, and facilities for device fabrication and quantum measurement at the University of Melbourne.
Spintronics in two-dimensional surface conducting diamond
When hydrogen-terminated diamond surfaces are exposed to air, electrons are transferred from the diamond into an absorbed water layer resulting in a sub-surface hole accumulation layer and a high p-type surface conductivity. This allows high hole sheet densities to be achieved and has led to significant interest for chemical and biological sensor applications. Through the preparation of high-quality, low disorder hydrogenated surfaces, surface conducting diamond devices can be prepared with metallic conductivity permitting the study of magnetotransport effects at temperatures as low as 50 mK.
Magnetotransport measurements have revealed the presence of phase coherent backscattering effects, in the form of weak localisation and weak anti-localisation. By exploring quantum transport in fabricated diamond devices, we have shown that the hole accumulation layer forms a two-dimensional system with a strong spin-orbit interaction (Edmonds et al., 2015). Surface conducting diamond is a spin-3/2 p-type semiconductor, offering interesting spin properties that differ to those of graphene and other two-dimensional systems. We are developing this project through a number of avenues that seek to explore these properties and to engineer devices that permit the control of spin as a route towards carbon-based semiconductor spintronics.
New heterostructured materials created by surface functionalisation of diamond
Hydrogen and oxygen terminated diamond surfaces have been studied extensively over the last two decades and the unique properties of these systems have been exploited across a diverse range of applications. Recently, we have established new methodologies for functionalising the diamond surface with other species, including fluorine and silicon. The demonstration that an atomically smooth and well-ordered silicon-diamond interface can be formed (Schenk et al., 2015) opens a path to the preparation of new semiconductor heterostructured materials involving carbon; such materials have a variety of potential applications in the areas of quantum information, high-precision magnetometry and sensing.
We are extending this project by exploring other semiconductor-diamond interfaces and by developing protocols for the functionalisation of the heterostructured interface using ex-situ chemical processing. These experiments are aimed at facilitating the ordered bonding of biomolecules to the diamond surface to realise high sensitivity sensing. Additionally, through the use of cryogenic ultra-high scanning tunnelling microscopy techniques, the atomic-scale imaging and manipulation of these new heterostructured surfaces is being investigated.
Meet the team
Professor Chris Pakes
Dr Alex Schenk
Alex Tsai (University of Melbourne, co-supervised with Dr Jeff McCallum)
Professor Lothar Ley (University of Erlangen)