We demonstrate the dramatic effect of film thickness on the ferroelectric phase transition temperature Tc in strained BaTiO3 films grown on SrTiO3 substrates. Using variable-temperature ultraviolet Raman spectroscopy enables measuring Tc in films as thin as 1.6 nm, and a film thickness variation from 1.6 to 10 nm leads to Tc tuning from 70 to about 925 K. Raman data are consistent with synchrotron x-ray scattering results, which indicate the presence of 180 degrees domains below Tc, and thermodynamic phase-field model calculations of Tc as a function of thickness.

Kelvin probe force microscopy (KPFM) has been used to directly and quantitatively measure Hall voltages, developed at conducting tail-to-tail domain walls in ErMnO single crystals, when current is driven in the presence of an approximately perpendicular magnetic field. Measurements across a number of walls, taken using two different atomic force microscope platforms, consistently suggest that the active p-type carriers have unusually large room temperature mobilities of the order of hundreds of square centimeters per volt second. Associated carrier densities were estimated to be of the order of 10 cm. Such mobilities, at room temperature, are high in comparison with both bulk oxide conductors and LaAlO-SrTiO sheet conductors. High carrier mobilities are encouraging for the future of domain-wall nanoelectronics and, significantly, also suggest the feasibility of meaningful investigations into dimensional confinement effects in these novel domain-wall systems.

In ferroelectric tunnel junctions, the tunnel resistance depends on the polarization orientation of the ferroelectric tunnel barrier, giving rise to tunnel electroresistance. These devices are promising to be used as memristors in neuromorphic architectures and as non-volatile memory elements. For both applications device scalability is essential, which requires a clear understanding of the relationship between polarization reversal and resistance change as junction size shrinks. Here we show robust tunnel electroresistance in BiFeO 3 -based junctions with diameters ranging from 1200 to 180 nm. We demonstrate that the tunnel electroresistance and the corresponding fraction of reversed ferroelectric domains change 1 Electronic mail: vincent.garcia@thalesgroup.com 2 drastically with the junction diameter: while micron-size junctions display reversal in less than 10% of the area, the smallest junctions show an almost complete polarization reversal.Modeling the electric-field distribution, we highlight the critical role of the bottom electrode resistance which significantly diminishes the actual electric field applied to the ferroelectric barrier in the mixed polarization state. A polarization-dependent critical electric field below which further reversal is prohibited is found to explain the large differences between the ferroelectric switchability of nano-and micron-size junctions. Our results indicate that ferroelectric junctions are downscalable and suggest that specific junction shapes facilitate complete polarization reversal.Ferroelectric materials possess a spontaneous electrical polarization that is switchable by an external electric field. This enables the use of thin ferroelectric films sandwiched between electrodes as non-volatile memories.1 In such ferroelectric memories, the information is encoded by the polarization orientation and recovered in a destructive capacitive readout.When the thickness of the ferroelectric films is of the order of a few nanometers, electron tunneling becomes possible. In these ferroelectric tunnel junctions, 2,3 the tunnel resistance varies depending on the orientation of the polarization; this tunnel electroresistance effect enables a non-destructive information readout. These interfacial magnetoelectric coupling phenomena can be probed by tunnel magnetoresistance experiments, resulting in a non-volatile control of the spin-polarization. 26-29Moreover, selecting oxide electrodes subject to field-induced electronic phase transitions upon polarization reversal may result in enhanced tunnel electroresistance. 29,30 Hence, ferroelectric tunnel junctions offer a fantastic playground to explore electric-field-driven modifications at the nanoscale. 31 Top electrodes of Pt (10 nm) / Co (10 nm) with diameters ranging from 180 nm to 1200 nm ( Fig. 1(a)) are defined by electron-beam lithography, sputtering, and lift-off. 18 We use the conductive tip of an atomic force microscope (AFM) to connect individual top electrodes and perform electric transport measurements under a constant v...

Since the observation that the properties of ferroic domain walls (DWs) can differ significantly from the bulk materials in which they are formed, it has been realised that domain wall engineering offers exciting new opportunities for nano-electronics and nanodevice architectures. We report a novel improper ferroelectric, CsNbW2O9, with the hexagonal tungsten bronze structure. Powder neutron diffraction and symmetry mode analysis indicates that the improper transition (TC ~ 1100 K) involves unit cell tripling, reminiscent of the hexagonal rare earth manganites. However in contrast to the manganites the symmetry breaking in CsNbW2O9 is electronically-driven (i.e., purely displacive) via the second order Jahn-Teller effect in contrast to the geometrically-driven tilt mechanism of the manganites. Nevertheless CsNbW2O9 displays the same kinds of domain microstructure as those found in the manganites, such as characteristic six-domain 'cloverleaf' vertices and DW sections with polar discontinuities. The discovery of a completely new material system, with domain patterns already known to generate interesting functionality in the manganites, is important for the emerging field of DW nanoelectronics.

Laser-controlled reduction of individual graphene oxide films provide unprecedented work function tuning with millivolt precision.