A large variety of transport properties have been observed at the interface between the insulating oxides SrTiO3 and LaAlO3 such as insulation, 2D interface metallicity, 3D bulk metallicity, magnetic ...scattering, and superconductivity. The relation between the structure and the properties of the SrTiO3/LaAlO3 interface can be explained in a meaningful way by taking into account the relative contribution of three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. The emerging phase diagram is much richer than for related bulk oxides due to the occurrence of interface electronic reconstruction. The observation of this interface phenomenon is a display of recent advances in thin film deposition and characterization techniques, and provides an extension to the range of exceptional electronic properties of complex oxides.
The interface between the insulating oxides SrTiO3 and LaAlO3 shows a variety of transport properties. The properties of the interface can be explained by three structural aspects: oxygen vacancies, structural deformations (including cation disorder), and electronic interface reconstruction. Irrespective of the origin of mobile charge at these heterointerfaces, once harnessed and controlled all could lead to heterostructures, where the properties are determined by strong correlation effects, and therefore full of surprises.
Topological defects in ferroic materials are attracting much attention both as a playground of unique physical phenomena and for potential applications in reconfigurable electronic devices. Here, we ...explore electronic transport at artificially created ferroelectric vortices in BiFeO3 thin films. The creation of one-dimensional conductive channels activated at voltages as low as 1 V is demonstrated. We study the electronic as well as the static and dynamic polarization structure of several topological defects using a combination of first-principles and phase-field modelling. The modelling predicts that the core structure can undergo a reversible transformation into a metastable twist structure, extending charged domain walls segments through the film thickness. The vortex core is therefore a dynamic conductor controlled by the coupled response of polarization and electron-mobile-vacancy subsystems with external bias. This controlled creation of conductive one-dimensional channels suggests a pathway for the design and implementation of integrated oxide electronic devices based on domain patterning. PUBLICATION ABSTRACT
A promising cathode material for rechargeable batteries is LiMn2O4, which exhibits higher operating voltage, reduced toxicity and lower costs as compared to commonly used LiCoO2 cathodes. However, ...LiMn2O4 suffers from limited cycle life, as excessive capacity fading occurs during battery cycling due to dissolution of Mn into the acidic electrolyte. Here, we show that by structural engineering of stable, epitaxial LiMn2O4 thin films the electrochemical properties can be enhanced as compared to polycrystalline samples. Control of the specific crystal orientation of the LiMn2O4 thin films resulted in dramatic differences in surface morphology with pyramidal, rooftop or flat features for respectively (100), (110), and (111) orientations. All three types of LiMn2O4 films expose predominantly ⟨111⟩ crystal facets, which is the lowest energy state surface for this spinel structure. The (100)-oriented LiMn2O4 films exhibited the highest capacities and (dis)charging rates up to 33C, and good cyclability over a thousand cycles, demonstrating enhanced cycle life without excessive capacity fading as compared to previous polycrystalline studies.
Ferroelectric domain formation is an essential feature in ferroelectric thin films. These domains and domain walls can be manipulated depending on the growth conditions. In rhombohedral BiFeO3 thin ...films, the ordering of the domains and the presence of specific types of domain walls play a crucial role in attaining unique ferroelectric and magnetic properties. In this study, controlled ordering of domains in BiFeO3 film is presented, as well as a controlled selectivity between two types of domain walls is presented, i.e., 71° and 109°, by modifying the substrate termination. The experiments on two different substrates, namely SrTiO3 and TbScO3, strongly indicate that the domain selectivity is determined by the growth kinetics of the initial BiFeO3 layers.
Growth of the BiFeO3 thin films is shown to depend on the atomic termination of the SrTiO3 and TbScO3 substrates. Interface engineering with a single SrO layer on substrate surfaces enables the control of domain ordering and selectivity between 71° and 109° domain walls. Underlying mechanism is claimed to be growth dynamic during the initial phase of growth.
Designing a broad-spectrum gas sensor capable of identifying gas components in complex environments, such as mixed atmospheres or extreme temperatures, is a significant concern for various ...technologies, including energy, geological science, and planetary exploration. The main challenge lies in finding materials that exhibit high chemical stability and wide working temperature range. Materials that amplify signals through non-chemical methods could open up new sensing avenues. Here, we present the discovery of a broad-spectrum gas sensor utilizing correlated two-dimensional electron gas at a delta-doped LaAlO
/SrTiO
interface with LaFeO
. Our study reveals that a back-gating on this two-dimensional electron gas can induce a non-volatile metal to insulator transition, which consequently can activate the two-dimensional electron gas to sensitively and quantitatively probe very broad gas species, no matter whether they are polar, non-polar, or inert gases. Different gas species cause resistance change at their sublimation or boiling temperature and a well-defined phase transition angle can quantitatively determine their partial pressures. Such unique correlated two-dimensional electron gas sensor is not affected by gas mixtures and maintains a wide operating temperature range. Furthermore, its readout is a simple measurement of electric resistance change, thus providing a very low-cost and high-efficient broad-spectrum sensing technique.
Abstract
In order to bring the diverse functionalities of transition metal oxides into modern electronics, it is imperative to integrate oxide films with controllable properties onto the silicon ...platform. Here, we present asymmetric LaMnO
3
/BaTiO
3
/SrTiO
3
superlattices fabricated on silicon with layer thickness control at the unit-cell level. By harnessing the coherent strain between the constituent layers, we overcome the biaxial thermal tension from silicon and stabilize
c
-axis oriented BaTiO
3
layers with substantially enhanced tetragonality, as revealed by atomically resolved scanning transmission electron microscopy. Optical second harmonic generation measurements signify a predominant out-of-plane polarized state with strongly enhanced net polarization in the tricolor superlattices, as compared to the BaTiO
3
single film and conventional BaTiO
3
/SrTiO
3
superlattice grown on silicon. Meanwhile, this coherent strain in turn suppresses the magnetism of LaMnO
3
as the thickness of BaTiO
3
increases. Our study raises the prospect of designing artificial oxide superlattices on silicon with tailored functionalities.
Ceramic-based nanocomposites are a rapidly evolving research area as they are currently being used in a wide range of applications. Epitaxial vertically aligned nanocomposites (VANs) offer promising ...advantages over conventional planar multilayers as key functionalities are tailored by the strong coupling at their vertical interfaces. However, limited knowledge exists of which material systems are compatible in composite films and which types of structures are optimal for a given functionality. No lithium-based VANs have yet been explored for energy storage, while 3D solid-state batteries offer great promise for enhanced energy and power densities. Although solid-on-solid kinetic Monte Carlo simulation (KMCS) models of VAN growth have previously been developed, phase separation was forced into the systems by limiting hopping directions and/or tuning the activation energies for hopping. Here, we study the influence of the temperature and deposition rate on the morphology evolution of lithium-based VANs, consisting of a promising LiMn2O4 cathode and a Li0.5La0.5TiO3 electrolyte, by applying a KMCS model with activation energies for hopping obtained experimentally and with minimum restrictions for hopping directions. Although the model considers only the kinetic processes away from thermodynamic equilibrium, which would determine the final shape of the pillars within the matrix, the trends in pillar size and distribution within the simulated VANs are in good agreement with experiments. This provides an elegant tool to predict the growth of VAN materials as the experimental activation energies and higher degrees of freedom for hopping result in a more realistic and low computational cost model to obtain accurate simulations of VAN materials.
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