Reporting in Nanotechnology, enhanced domain wall conductance in hexagonal TbMnO3 thin films is revealed by conductive-atomic force microscopy, which is visible only at the boundaries between an upward polarisation (P) region and an unpoled surrounding region. While the ground state of TbMnO3 generally has an orthorhombic structure with a Curie temperature far lower than room temperature, clamping by hexagonal Al2O3 substrate makes a TbMnO3 thin film hexagonal phase and raises significantly the Curie temperature above room temperature. By such strong clamping, it is expected that the polarisation in the hexagonal TbMnO3 thin films is constrained to be normal to the film surface with zero in-plane component of P. This means that, assuming that the film is thin enough (~ 23 nm in this case), there is no domain wall of either head-to-head or tail-to-tail configuration of P, namely no charged domain wall. Therefore, the observed domain walls with enhanced conductivity is concluded to be neutral and, along with enhanced conductivity in charged domain walls of hexagonal manganites, the domain wall conductivity is thought to be a universal property.

Another interesting universal property is the conduction behaviour. Normalised current-voltage curves obtained at each characteristic location (OFF, Unpoled, On boundary, and ON) surprisingly lie on a single fitting curve based on the back-to-back Schottky diodes model. Note that hexagonal TbMnO3 is a narrow bandgap semiconductor. From the fitting results, the Schottky barrier height is a dominant parameter governing the conduction, which is affected by defect chemistry such as oxygen vacancy density. Thus, a pure electrostatic/electronic effect in association with defect chemistry based on the back-to-back Schottky diodes structure should be considered.

More information about this research can be found in the journal Nanotechnology 27 155705.

Further reading

PEDOT-based composites provide electrode materials for supercapacitors (Feb 2016)
How topological defects scatter phonons in graphene nanoribbons (Feb 2016)
Core-shell structure enhances electrochemical properties (Jul 2015)