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Emergent phenomena at complex oxide interfaces could provide the basis for a wide variety of next-generation devices, including photovoltaics and spintronics. To date, detailed characterization and computational modeling of interfacial defects, cation intermixing, and film stoichiometry have helped to explain many of the novel behaviors observed at a single heterojunction. Unfortunately, many of the techniques employed to characterize a single heterojunction are less effective for a superlattice made up of a repeating series of interfaces that induce collective interfacial phenomena throughout a film. These repeating interfaces present an untapped opportunity to introduce an additional degree of complexity, such as confined electric fields, that cannot be realized in a single heterojunction. In this work, we explore the properties of SrTiO3-LaCrO3 superlattices to understand the role of defects, including variations in cation stoichiometry of individual layers of the superlattice, intermixing across interfaces, and interfacial oxygen vacancies. Using X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy electron energy-loss spectroscopy (STEM-EELS), we quantify the stoichiometry of individual layers of the superlattice and determine the degree of intermixing in these materials. By comparing these results to both density functional theory (DFT) models and STEM-EELS measurements of the Ti and Cr valence in each layer of the superlattice, we correlate different types of defects with the associated materials properties of the superlattice. We show that a combination of ab initio modeling and complementary structural characterization methods can offer unique insight into structure-property relationships in many oxide superlattice systems. [ABSTRACT FROM AUTHOR]

We show that by co-doping SrTiO3(STO) epitaxial thinfilms with equal amounts of La and Cr, it is possible to produce filmswith an optical band gap ∼0.9 eV lower than that of undopedSTO. Sr1–xLaxTi1–xCrxO3thin films were deposited by molecular beam epitaxyand characterized using X-ray photoelectron spectroscopy and X-rayabsorption near-edge spectroscopy to show that the Cr dopants arealmost exclusively in the Cr3+oxidation state. ExtendedX-ray absorption fine structure measurements and theoretical modelingsuggest that it is thermodynamically preferred for La and Cr dopantsto occupy nearest-neighbor A- and B-sites in the lattice. Transportmeasurements show that the material exhibits variable-range hoppingconductivity with high resistivity. These results create new opportunitiesfor the use of doped STO films in photovoltaic and photocatalyticapplications. [ABSTRACT FROM AUTHOR]

CoFe2O4(CFO)–BiFeO3(BFO)nanocomposites are an intriguing option for future memory and logictechnologies due to the magnetoelectric properties of the system.However, these nanocomposites form with CFO pillars randomly locatedwithin a BFO matrix, making implementation in devices difficult. Toovercome this, we present a technique to produce patterned nanocompositesthrough self-assembly. CFO islands are patterned on Nb-doped SrTiO3to direct the self-assembly of epitaxial CFO–BFO nanocomposites,producing square arrays of CFO pillars. [ABSTRACT FROM AUTHOR]

Oxide two-dimensional electron gases (2DEGs) promise high charge carrier concentrations and low-loss electronic transport in semiconductors such as BaSnO 3 (BSO). ACBN0 computations for BSO/SrNbO 3 (SNO) interfaces show Nb- 4d electron injection into extended Sn- 5s electronic states. The conduction band minimum consists of Sn- 5s states ∼1.2 eV below the Fermi level for intermediate thickness 6-unit cell BSO/6-unit cell SNO superlattices, corresponding to an electron density in BSO of ∼10 21 cm -3 . Experimental studies of analogous BSO/SNO interfaces grown by molecular beam epitaxy confirm significant charge transfer from SNO to BSO. In situ angle-resolved X-ray photoelectron spectroscopy studies show an electron density of ∼4 × 10 21 cm -3 . The consistency of theory and experiments show that BSO/SNO interfaces provide a novel materials platform for low loss electron transport in 2DEGs.

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 3 in humid conditions using ambient-pressure X-ray photoelectron spectroscopy. Comparing the two possible terminations of the polar (001)-oriented surface, we find that the LaO-terminated surface is more reactive toward water, forming hydroxyl species and adsorbing molecular water at lower relative humidity than its FeO 2 -terminated counterpart. However, the FeO 2 -terminated surface forms more hydroxyl species during water adsorption at higher humidity, suggesting that adsorbate-adsorbate interactions may impact reactivity. Our results demonstrate how the termination of a complex oxide can dramatically impact its reactivity, providing insight that can aid in the design of catalyst materials.