Interfacial charge transfer and its impact on transport properties of LaNiO/LaFeO superlattices.

Charge transfer or redistribution at oxide heterointerfaces is a critical phenomenon, often leading to remarkable properties such as two-dimensional electron gas and interfacial ferromagnetism. Despite studies on LaNiO/LaFeO superlattices and heterostructures, the direction and magnitude of the charge transfer remain debated, with some suggesting no charge transfer due to the high stability of Fe (3d). Here, we synthesized a series of epitaxial LaNiO/LaFeO superlattices and demonstrated partial (up to ~0.

Guided anisotropic oxygen transport in vacancy ordered oxides.

Anisotropic and efficient transport of ions under external stimuli governs the operation and failure mechanisms of energy-conversion systems and microelectronics devices. However, fundamental understanding of ion hopping processes is impeded by the lack of atomically precise materials and probes that allow for the monitoring and control at the appropriate time- and length- scales. In this work, using in-situ transmission electron microscopy, we directly show that oxygen ion migration in vacancy ordered, semiconducting SrFeO epitaxial thin films can be guided to proceed through two distinctly different diffusion pathways, each resulting in different polymorphs of SrFeO with different ground electronic properties before reaching a fully oxidized, metallic SrFeO phase.

Correlation between oxygen evolution reaction activity and surface compositional evolution in epitaxial LaSrNiFeO thin films.

Water electrolysis can use renewable electricity to produce green hydrogen, a portable fuel and sustainable chemical precursor. Improving electrolyzer efficiency hinges on the activity of the oxygen evolution reaction (OER) catalyst. Earth-abundant, ABO-type perovskite oxides offer great compositional, structural, and electronic tunability, with previous studies showing compositional substitution can increase the OER activity drastically.

Freestanding epitaxial SrTiO nanomembranes via remote epitaxy using hybrid molecular beam epitaxy.

The epitaxial growth of functional oxides using a substrate with a graphene layer is a highly desirable method for improving structural quality and obtaining freestanding epitaxial nanomembranes for scientific study, applications, and economical reuse of substrates. However, the aggressive oxidizing conditions typically used in growing epitaxial oxides can damage graphene. Here, we demonstrate the successful use of hybrid molecular beam epitaxy for SrTiO growth that does not require an independent oxygen source, thus avoiding graphene damage.

Ultra-flat and long-lived plasmons in a strongly correlated oxide.

Plasmons in strongly correlated systems are attracting considerable attention due to their unconventional behavior caused by electronic correlation effects. Recently, flat plasmons with nearly dispersionless frequency-wave vector relations have drawn significant interest because of their intriguing physical origin and promising applications. However, these flat plasmons exist primarily in low-dimensional materials with limited wave vector magnitudes (q < ~0.

Spontaneous Lithiation of Binary Oxides during Epitaxial Growth on LiCoO.

Epitaxial growth is a powerful tool for synthesizing heterostructures and integrating multiple functionalities. However, interfacial mixing can readily occur and significantly modify the properties of layered structures, particularly for those containing energy storage materials with smaller cations. Here, we show a two-step sequence involving the growth of an epitaxial LiCoO cathode layer followed by the deposition of a binary transition metal oxide.

Spironolactone Ameliorates Cochlear Implant Induced Endolymphatic Hydrops.

Background: Endolymphatic hydrops (EH) has been observed in both animal and human cochleae following cochlear implant (CI) surgery. We tested whether EH could be eliminated by administration of mineralocorticoid steroid antagonist spironolactone and explored the electrophysiological consequences of this.

Methods: Sixty-four adult guinea pigs underwent cochlear implantation with a dummy electrode.

Epitaxial SrTiO films with dielectric constants exceeding 25,000.

SignificanceSemiconductor interfaces are among the most important in use in modern technology. The properties they exhibit can either enable or disable the characteristics of the materials they connect for functional performance. While much is known about important junctions involving conventional semiconductors such as Si and GaAs, there are several unsolved mysteries surrounding interfaces between oxide semiconductors.

Room-Temperature Ferromagnetism at an Oxide-Nitride Interface.

Heterointerfaces have led to the discovery of novel electronic and magnetic states because of their strongly entangled electronic degrees of freedom. Single-phase chromium compounds always exhibit antiferromagnetism following the prediction of the Goodenough-Kanamori rules. So far, exchange coupling between chromium ions via heteroanions has not been explored and the associated quantum states are unknown.

Understanding the Electronic Structure Evolution of Epitaxial LaNiFeO Thin Films for Water Oxidation.

Rare earth nickelates including LaNiO are promising catalysts for water electrolysis to produce oxygen gas. Recent studies report that Fe substitution for Ni can significantly enhance the oxygen evolution reaction (OER) activity of LaNiO. However, the role of Fe in increasing the activity remains ambiguous, with potential origins that are both structural and electronic in nature.

Incorporation of Ti in epitaxial FeTiOthin films.

The titanomagnetites (FeTiO,⩽ 1) are a family of reducible spinel-structure oxides of interest for their favorable magnetic, catalytic, and electrical transport properties. To understand the stability of the system during low temperature deposition, epitaxial thin films of FeTiOwere deposited by molecular beam epitaxy (MBE) on MgO(001) at 250-375 °C. The homogeneous incorporation of Ti, Fe valence state, and film morphology were all found to be strongly dependent on the oxidation conditions at the low substrate temperatures employed.

Spontaneous phase segregation of SrNiO and SrNiO during SrNiO heteroepitaxy.

Recent discovery of superconductivity in NdSrNiO motivates the synthesis of other nickelates for providing insights into the origin of high-temperature superconductivity. However, the synthesis of stoichiometric Sr NiO thin films over a range of has proven challenging. Moreover, little is known about the structures and properties of the end member SrNiO Here, we show that spontaneous phase segregation occurs while depositing SrNiO thin films on perovskite oxide substrates by molecular beam epitaxy.

Identifying Ionic and Electronic Charge Transfer at Oxide Heterointerfaces.

The ability to tailor oxide heterointerfaces has led to novel properties in low-dimensional oxide systems. A fundamental understanding of these properties is based on the concept of electronic charge transfer. However, the electronic properties of oxide heterointerfaces crucially depend on their ionic constitution and defect structure: ionic charges contribute to charge transfer and screening at oxide interfaces, triggering a thermodynamic balance of ionic and electronic structures.

Hole-Trapping-Induced Stabilization of Ni in SrNiO /LaFeO Superlattices.

Creating new functionality in materials containing transition metals is predicated on the ability to control the associated charge states. For a given transition metal, there is an upper limit on valence that is not exceeded under normal conditions. Here, it is demonstrated that this limit of 3+ for Ni and Fe can be exceeded via synthesis of (SrNiO ) /(LaFeO ) superlattices by tuning n and m.

Extracting band edge profiles at semiconductor heterostructures from hard-x-ray core-level photoelectron spectra.

Internal electric fields that underpin functioning of multi-component materials systems and devices are coupled to structural and compositional inhomogeneities associated with interfaces in these systems. Hard-x-ray photoelectron spectroscopy is a valuable source of information on band-edge profiles, governed by the distribution of internal fields, deep inside semiconductor thin films and heterojunctions. However, extracting this information requires robust and physically meaningful decomposition of spectra into contributions from individual atomic planes.

Reversible Oxidation Quantified by Optical Properties in Epitaxial FeCrO Films on (001) MgAlO.

We report on the structural and optical properties of FeCrO epitaxial films grown by molecular beam epitaxy on MgAlO (001) as a function of δ (average cation valence). The average Fe valence is linked to the out-of-plane lattice parameter and the extent of light absorption in the infrared spectral region. Over-oxidized films (0 < δ < 0.

Tuning the Electronic Structure of LaNiO through Alloying with Strontium to Enhance Oxygen Evolution Activity.

The perovskite oxide LaNiO is a promising oxygen electrocatalyst for renewable energy storage and conversion technologies. Here, it is shown that strontium substitution for lanthanum in coherently strained, epitaxial LaNiO films (La Sr NiO) significantly enhances the oxygen evolution reaction (OER) activity, resulting in performance at = 0.5 comparable to the state-of-the-art catalyst BaSrCoFeO .

Tuning Photovoltaic Performance of Perovskite Nickelates Heterostructures by Changing the A-Site Rare-Earth Element.

Perovskite rare-earth nickelates (RNiO) have attracted much attention because of their exotic physical properties and rich potential applications. Here, we report systematic tuning of the electronic structures of RNiO (R = Nd, Sm, Gd, and Lu) by isovalent A-site substitution. By integrating RNiO thin films with Nb-doped SrTiO (NSTO), p-n heterojunction photovoltaic cells have been prepared and their performance has been investigated.

Intracochlear tPA infusion may reduce fibrosis caused by cochlear implantation surgery.

Background: Experiments show that the extent of ongoing fibrotic change within the cochlea can be determined by the volume and pattern of bleeding within the first 24 h following cochlear implantation. Tissue-type plasminogen activator (tPA) is effective at reducing thrombus volume when administered both within and external to the systemic circulation.

Aims/objectives: To determine if tPA delivered into the scala tympani immediately following implantation will reduce thrombus volume within the lower basal turn of the cochlea.

Strain Effect on Oxygen Evolution Reaction Activity of Epitaxial NdNiO Thin Films.

Epitaxial strain can cause both lattice distortion and oxygen nonstoichiometry, effects that are strongly coupled at heterojunctions of complex nickelate oxides. Here we decouple these structural and chemical effects on the oxygen evolution reaction (OER) by using a set of coherently strained epitaxial NdNiO films. We show that within the regime where oxygen vacancies (V) are negligible, compressive strain is favorable for the OER whereas tensile strain is unfavorable; the former induces orbital splitting, resulting in a higher occupancy in the d orbital and weaker Ni-O chemisorption.

An Ultrathin Single Crystalline Relaxor Ferroelectric Integrated on a High Mobility Semiconductor.

The epitaxial growth of multifunctional oxides on semiconductors has opened a pathway to introduce new functionalities to semiconductor device technologies. In particular, the integration of gate materials that enable nonvolatile or hysteretic functionality in field-effect transistors could lead to device technologies that consume less power or allow for novel modalities in computing. Here we present electrical characterization of ultrathin single crystalline SrZrTiO (x = 0.

Coupled Lattice Polarization and Ferromagnetism in Multiferroic NiTiO Thin Films.

Polarization-induced weak ferromagnetism (WFM) was demonstrated a few years back in LiNbO-type compounds, MTiO (M = Fe, Mn, Ni). Although the coexistence of ferroelectric polarization and ferromagnetism has been demonstrated in this rare multiferroic family before, first in bulk FeTiO, then in thin-film NiTiO, the coupling of the two order parameters has not been confirmed. Here, we report the stabilization of polar, ferromagnetic NiTiO by oxide epitaxy on a LiNbO substrate utilizing tensile strain and demonstrate the theoretically predicted coupling between its polarization and ferromagnetism by X-ray magnetic circular dichroism under applied fields.

Measurement Error in Atomic-Scale Scanning Transmission Electron Microscopy-Energy-Dispersive X-Ray Spectroscopy (STEM-EDS) Mapping of a Model Oxide Interface.

With the development of affordable aberration correctors, analytical scanning transmission electron microscopy (STEM) studies of complex interfaces can now be conducted at high spatial resolution at laboratories worldwide. Energy-dispersive X-ray spectroscopy (EDS) in particular has grown in popularity, as it enables elemental mapping over a wide range of ionization energies. However, the interpretation of atomically resolved data is greatly complicated by beam-sample interactions that are often overlooked by novice users.

Influence of LaFeO Surface Termination on Water Reactivity.

The polarity of oxide surfaces can dramatically impact their surface reactivity, in particular, with polar molecules such as water. The surface species that result from this interaction change the oxide electronic structure and chemical reactivity in applications such as photoelectrochemistry but are challenging to probe experimentally. Here, we report a detailed study of the surface chemistry and electronic structure of the perovskite LaFeO in humid conditions using ambient-pressure X-ray photoelectron spectroscopy.

Effect of doping and chemical ordering on the optoelectronic properties of complex oxides: FeO-VO solid solutions and hetero-structures.

The electronic and optical properties of α-(FeV)O at low (x = 0.04) and high (x = 0.5) doping levels are investigated using a combination of periodic and embedded cluster approaches, and time-dependent density functional theory.