Abstract: Polarons, that is lattice distortions associated with the stabilization of electronic states, are thought to play a pivotal role in the physics and chemistry of metal oxides. They are implicated in phenomena as diverse as high-Tc superconductivity, resistive switching and photocatalysis. Although it is difficult to access polarons in the bulk material, in principle they can be probed and manipulated at the surface in order to test models of their formation and properties. Here this is exploited using scanning tunnelling microscopy to examine polarons on TiO₂(110), with oxygen vacancies (O_b-vacs) as the electron source. By manipulating the lateral positions of O_b-vacs using electrical pulses in STM, we show that the polarons follow the O_b-vac and are therefore not directly associated with a particular donor centre in the selvedge. Polaron hopping is not observed below 16 K. By forming O_b-vac dimers, trimers and tetramers it is possible to examine the interaction between polarons. We compare these data to the results of calculations.

About the Speaker: Prof. Geoff Thornton’s research focuses on the nanoscience and surface science of metal oxides, which play a crucial role in technologies such as catalysis and molecular electronics. The targets of our experiments include developing single molecule spectroscopy on oxide surfaces, imaging single molecule chemistry, and nanofabrication of functional devices. This work employs a suite of scanning probe microscopes, spectrometers, and diffractometers in London together with synchrotron radiation techniques at the Diamond Light Source and ESRF, Grenoble.