Four dimensional-scanning transmission electron microscopy study on relationship between crystallographic orientation and spontaneous polarization in epitaxial BiFeO.

Spontaneous polarization and crystallographic orientations within ferroelectric domains are investigated using an epitaxially grown BiFeO thin film under bi-axial tensile strain. Four dimensional-scanning transmission electron microscopy (4D-STEM) and atomic resolution STEM techniques revealed that the tensile strain applied is not enough to cause breakdown of equilibrium BiFeO symmetry (rhombohedral with space group: R3c). 4D-STEM data exhibit two types of BiFeO ferroelectric domains: one with projected polarization vector possessing out-of-plane component only, and the other with that consisting of both in-plane and out-of-plane components.

Limits to the strain engineering of layered square-planar nickelate thin films.

The layered square-planar nickelates, NdNiO, are an appealing system to tune the electronic properties of square-planar nickelates via dimensionality; indeed, superconductivity was recently observed in NdNiO thin films. Here, we investigate the role of epitaxial strain in the competing requirements for the synthesis of the n = 3 Ruddlesden-Popper compound, NdNiO, and subsequent reduction to the square-planar phase, NdNiO. We synthesize our highest quality NdNiO films under compressive strain on LaAlO (001), while NdNiO on NdGaO (110) exhibits tensile strain-induced rock salt faults but retains bulk-like transport properties.

High Mobility Two-Dimensional Electron Gas at the BaSnO/SrNbO Interface.

Oxide two-dimensional electron gases (2DEGs) promise high charge carrier concentrations and low-loss electronic transport in semiconductors such as BaSnO (BSO). ACBN0 computations for BSO/SrNbO (SNO) interfaces show Nb- electron injection into extended Sn- electronic states. The conduction band minimum consists of Sn- states ∼1.

Ferroelectric Modulation of Surface Electronic States in BaTiO for Enhanced Hydrogen Evolution Activity.

Ferroelectric nanomaterials offer the promise of switchable electronic properties at the surface, with implications for photo- and electrocatalysis. Studies to date on the effect of ferroelectric surfaces in electrocatalysis have been primarily limited to nanoparticle systems where complex interfaces arise. Here, we use MBE-grown epitaxial BaTiO thin films with atomically sharp interfaces as model surfaces to demonstrate the effect of ferroelectric polarization on the electronic structure, intermediate binding energy, and electrochemical activity toward the hydrogen evolution reaction (HER).

Oxide Two-Dimensional Electron Gas with High Mobility at Room-Temperature.

The prospect of 2-dimensional electron gases (2DEGs) possessing high mobility at room temperature in wide-bandgap perovskite stannates is enticing for oxide electronics, particularly to realize transparent and high-electron mobility transistors. Nonetheless only a small number of studies to date report 2DEGs in BaSnO -based heterostructures. Here, 2DEG formation at the LaScO /BaSnO (LSO/BSO) interface with a room-temperature mobility of 60 cm  V  s at a carrier concentration of 1.

Superconductivity in a quintuple-layer square-planar nickelate.

Since the discovery of high-temperature superconductivity in copper oxide materials, there have been sustained efforts to both understand the origins of this phase and discover new cuprate-like superconducting materials. One prime materials platform has been the rare-earth nickelates and, indeed, superconductivity was recently discovered in the doped compound NdSrNiO (ref. ).

Enthalpy and entropy of oxygen electroadsorption on RuO(110) in alkaline media.

We report the temperature influence of the OH and O electroadsorption on RuO(110) films grown on TiO(110) crystals in alkaline media. From the temperature effect, we evaluate the enthalpy and entropy of the OH and O electroadsorption, including the adsorbate-adsorbate interactions that we analyze using the interaction parameters of the Frumkin-isotherm model. We found that the adsorbates repel each other enthalpically but attract each other entropically.

Directly measuring the structural transition pathways of strain-engineered VO thin films.

Epitaxial films of vanadium dioxide (VO) on rutile TiO substrates provide a means of strain-engineering the transition pathways and stabilizing of the intermediate phases between monoclinic (insulating) M1 and rutile (metal) R end phases. In this work, we investigate structural behavior of epitaxial VO thin films deposited on isostructural MgF (001) and (110) substrates via temperature-dependent Raman microscopy analysis. The choice of MgF substrate clearly reveals how elongation of V-V dimers accompanied by the shortening of V-O bonds triggers the intermediate M2 phase in the temperature range between 70-80 °C upon the heating-cooling cycles.

Realization of Epitaxial Thin Films of the Topological Crystalline Insulator Sr SnO.

Topological materials are derived from the interplay between symmetry and topology. Advances in topological band theories have led to the prediction that the antiperovskite oxide Sr SnO is a topological crystalline insulator, a new electronic phase of matter where the conductivity in its (001) crystallographic planes is protected by crystallographic point group symmetries. Realization of this material, however, is challenging.

Simultaneous Structural and Electronic Transitions in Epitaxial VO_{2}/TiO_{2}(001).

Recent reports have identified new metaphases of VO_{2} with strain and/or doping, suggesting the structural phase transition and the metal-to-insulator transition might be decoupled. Using epitaxially strained VO_{2}/TiO_{2} (001) thin films, which display a bulklike abrupt metal-to-insulator transition and rutile to monoclinic transition structural phase transition, we employ x-ray standing waves combined with hard x-ray photoelectron spectroscopy to simultaneously measure the structural and electronic transitions. This x-ray standing waves study elegantly demonstrates the structural and electronic transitions occur concurrently within experimental limits (±1  K).

Ferroelectric Domain Walls in PbTiO Are Effective Regulators of Heat Flow at Room Temperature.

Achieving efficient spatial modulation of phonon transmission is an essential step on the path to phononic circuits using "phonon currents". With their intrinsic and reconfigurable interfaces, domain walls (DWs), ferroelectrics are alluring candidates to be harnessed as dynamic heat modulators. This paper reports the thermal conductivity of single-crystal PbTiO thin films over a wide variety of epitaxial-strain-engineered ferroelectric domain configurations.

Chlorine evolution reaction electrocatalysis on RuO(110) and IrO(110) grown using molecular-beam epitaxy.

We report the electrocatalysis of the chlorine evolution reaction (CER) on well-defined RuO(110) and IrO(110) surfaces. RuO and IrO are known for their capabilities to catalyze the CER. Until now, the CER measurements have only been reported on well-defined RuO surfaces and only at high Cl concentrations.

ON-state evolution in lateral and vertical VO threshold switching devices.

We report the results of finite element simulations of the ON state characteristic of VO-based threshold switching devices and compare the results with experimental data. The model is based on thermally induced threshold switching (thermal runaway) and successfully reproduces the I-V characteristics showing the formation and growth of the conductive filament in the ON state. Furthermore, we compare the I-V characteristics for two VO films with different electrical conductivities in the insulating and metallic phases as well as those based on TaO and NbO functional layers.

Mesoscopic quantum effects in a bad metal, hydrogen-doped vanadium dioxide.

The standard treatment of quantum corrections to semiclassical electronic conduction assumes that charge carriers propagate many wavelengths between scattering events, and succeeds in explaining multiple phenomena (weak localization magnetoresistance (WLMR), universal conductance fluctuations, Aharonov-Bohm oscillations) observed in polycrystalline metals and doped semiconductors in various dimensionalities. We report apparent WLMR and conductance fluctuations in H VO, a poor metal (in violation of the Mott-Ioffe-Regel limit) stabilized by the suppression of the VO metal-insulator transition through atomic hydrogen doping. Epitaxial thin films, single-crystal nanobeams, and nanosheets show similar phenomenology, though the details of the apparent WLMR seem to depend on the combined effects of the strain environment and presumed doping level.

Atomically engineered ferroic layers yield a room-temperature magnetoelectric multiferroic.

Materials that exhibit simultaneous order in their electric and magnetic ground states hold promise for use in next-generation memory devices in which electric fields control magnetism. Such materials are exceedingly rare, however, owing to competing requirements for displacive ferroelectricity and magnetism. Despite the recent identification of several new multiferroic materials and magnetoelectric coupling mechanisms, known single-phase multiferroics remain limited by antiferromagnetic or weak ferromagnetic alignments, by a lack of coupling between the order parameters, or by having properties that emerge only well below room temperature, precluding device applications.