Speaker: Chris Pakes
Affiliation: La Trobe University, Australia
Abstract Details: When hydrogenated 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 high p-type surface conductivity. This allows hole sheet densities as high as 7 x 1013 cm-2 to be achieved and has led to interest for chemical and biological sensor applications and the development of high-power field effect transistors. Many experiments have reported an exponential decrease in the sheet conductivity as the temperature is reduced, driven by carrier freeze-out, which prohibits the exploration of the electronic behaviour of the system at low temperature. However, we shall show that surface transfer doping of H-terminated diamond occurs with no activation energy so a high sheet conductivity can be maintained at low temperature in low disorder samples consistent with metallic conduction in a conventional two-dimensional Fermi liquid, permitting exploration of extended states in the predicted 2D hole band. Magnetotransport measurements have revealed the presence of quantum corrections in the Drude conductivity arising from phase coherent backscattering in the form of weak localisation and weak anti-localisation, the latter arising from a strong spin-orbit interaction at the diamond surface. By gating the surface-conducting layer, the sheet conductivity may be tuned from insulating to metallic conduction, with a concurrent modulation in the hole sheet density. Through an analysis of the evolution of the phase coherent backscattering effects as the hole sheet density is modulated, we show that the spin-orbit splitting can be engineered from 4.6 – 24.5 meV using an electrostatic gate. We shall discuss the potential to realise devices using H-terminated diamond in which spin coherent transport can be studied.

About The Speaker: Chris Pakes received his Ph.D. from the University of Birmingham (UK) in 1999. He held positions at the National Physical Laboratory (UK) and The University of Melbourne before joining La Trobe University in 2007. He has served as Associate Dean (Research) in the Faculty of Science, Technology and Engineering and in 2014 was appointed inaugural Dean of the La Trobe Graduate Research School. Chris leads La Trobe’s Atom-scale Research Laboratory, using a combination of ultra-high vacuum scanning probe microscopy, synchrotron-based photoemission and low-temperature transport to explore 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. His group has a strong focus on the functionalisation of diamond surfaces at the atomic-scale to engineer two-dimensional devices for quantum electronics and spintronics.

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