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Interest in high‐entropy inorganic compounds originates from their ability to stabilize cations and anions in local environments that rarely occur at standard temperature and pressure. This leads to new crystalline phases in many‐cation formulations with structures and properties that depart from conventional trends. The highest‐entropy homogeneous and random solid solution is a parent structure from which a continuum of lower‐entropy offspring can originate by adopting chemical and/or structural order. This report demonstrates how synthesis conditions, thermal history, and elastic and chemical boundary conditions conspire to regulate this process in Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O, during which coherent CuO nanotweeds and spinel nanocuboids evolve. We do so by combining structured synthesis routes, atomic‐resolution microscopy and spectroscopy, density functional theory, and a phase field modeling framework that accurately predicts the emergent structure and local chemistry. This establishes a framework to appreciate, understand, and predict the macrostate spectrum available to a high‐entropy system that is critical to rationalizing property engineering opportunities. [ABSTRACT FROM AUTHOR]

We report the interface structures of CdO thin films on 001 -MgO and 0001 -Al 2 O 3 substrates. Using aberration corrected scanning transmission electron microscopy, we show that epitaxial growth of (001)-CdO ∥ (001)-MgO occurs with a lattice misfit greater than 10%. A high density of interface misfit dislocations is found to form. In combination with molecular dynamics simulations, we show that dislocation strain fields form and overlap in very thin heterostructures of CdO and MgO (< 3 nm). On the c-Al 2 O 3 substrate, we find that CdO grows with a surface normal of 025. We show that three rotation variants form due to the symmetry of the sapphire surface. These results contribute insights into the epitaxial growth of these rock-salt oxides. [ABSTRACT FROM AUTHOR]

Chemical solution deposition is used to grow biaxially textured NiFe2O4 (NFO) thin films on (0001) sapphire substrates; a high degree of out-of-plane orientation in the <111> direction is confirmed by θ-2θ X-ray diffraction and pole figures. X-ray φ-scanning indicates in-plane texture and an epitaxial relationship between NFO (111) and Al2O3 (0001) in two crystallographic variants. The out-of-plane magnetization exhibits improved Mr/Ms from 0.5 in 110 nm-thick films to 0.8 in 60 nm-thick films. Compared to uniaxially textured NFO films on platinized silicon, the out-of-plane coercivity is reduced by 20%. The improved out-of-plane magnetic anisotropy is comparable to epitaxial NFO films of similar thickness deposited by pulsed laser deposition and sputtering. [ABSTRACT FROM AUTHOR]

The authors report a study of molecular beam deposition of MgO films on amorphous SiO2 and (0001) GaN surfaces over a large range of temperatures (25–400 °C) and molecular oxygen growth pressures (10−7–10−4 Torr). This study provides insight into the growth behavior of an oxide with volatile metal constituents. Unlike other materials containing volatile constituents (e.g., GaAs, PbTiO3), all components of MgO become volatile at normal epitaxial growth temperatures (=250 °C). Consequently, defining which species is the adsorption controller becomes ambiguous. Different growth regimes are delineated by the critical substrate temperature for Mg re-evaporation and the Mg:O flux ratio. These regimes have impact on phase purity, quartz crystal microbalance calibration, and film microstructure. The universal decay in deposition rate above growth 10−5 Torr O2 is also considered. By introducing a third flux of inert argon gas, rate reduction is attributed to increased molecular scattering and not oxidation of the metal source. [ABSTRACT FROM AUTHOR]

Solid solutions of rocksalt oxides are proposed for lattice-matched dielectrics in gallium nitride (GaN) electronics. This article explores the epitaxial growth of the rocksalt oxide calcium oxide (CaO) by molecular beam epitaxy on gallium nitride surfaces. As a possible end member to a rocksalt oxide solid solution, it is important to understand the processing space that allows for epitaxial CaO growth. Exposing the GaN surface to the oxidant flux prior to the metal flux is shown to be critical in eliminating polycrystalline growth. The effect of deposition temperature, metal flux, and oxidant flux on the film’s epitaxial crystalline quality is also examined. Optimal epitaxial quality is found for growth temperatures of >=600 °C and near oxygen pressures of 10-6 Torr. Thermal stability of the CaO/GaN interface is experimentally evaluated. No reaction phases are observed by x-ray diffraction up to 850 °C in air and >1100 °C in a reducing atmosphere. However, CaO films are found to be extremely reactive with H2O, forming Ca(OH)2 within a few hours when exposed to ambient atmosphere at room temperature. [ABSTRACT FROM AUTHOR]

Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN–PT) (70/30) thin films were deposited by pulsed laser deposition using two growth strategies: adsorption controlled deposition from lead-rich targets (∼25–30 mass%) and lower-temperature deposition (Td≤600°C) from targets containing a small amount of excess lead oxide (≤3 mass %). The substrates used were (001) SrRuO3/LaAlO3. Typical remanent polarization values ranged between 12 and 14 μC/cm2 for these films. The longitudinal piezoelectric coefficient (d33,f) was measured usingin situfour-circle X-ray diffraction, and the transverse coefficient (d31,f ore31,f) was measured using the wafer flexure method.d33,f ande31,f coefficients of∼300–350 pm/V and∼−11 C/m2 were calculated, respectively. In general, the piezoelectric coefficients and aging rates were strongly asymmetric, suggesting the presence of a polarization bias. The large, extremely stable piezoelectric response that results from poling parallel to the preferred polarization direction is attractive for miniaturized sensors and actuators. [ABSTRACT FROM AUTHOR]

Deposition of lanthanide oxides on GaN is investigated as a means to produce stable dielectric with good interface quality. Epitaxial growth of cubic <111>-oriented Sc2O3 is observed on GaN [0001] with a lattice mismatch of 7.2%, whereas La2O3 growth, with a lattice mismatch of ∼21%, results in a mixed phase epitaxial film comprised of the bixbyite and hexagonal allotropes. Substantial roughening accompanies this mixed phase film. By inserting a thin Sc2O3 interfacial layer between La2O3 and GaN and a Sc2O3 capping layer, the crystal quality of the predominantly La2O3 layer is improved and the stack is stabilized against hydroxide formation under ambient conditions. [ABSTRACT FROM AUTHOR]

GaN surface and near-surface chemistry influence on band offsets of oxide overlayers is demonstrated through X-ray photoelectron spectroscopy measurements using epitaxial (111)-oriented MgO films on (0001)-oriented Ga-polar GaN as a case study. For identical cleaning and MgO growth conditions, GaN subsurface oxygen impurities influence the GaN bare surface band bending and the ultimate band offset to MgO heterolayers. As the GaN surface oxygen concentration increases from an atomic concentration of 0.9% to 3.4%, the valence band offset to MgO decreases from 1.68 eV to 1.29 eV, respectively. This study highlights the sensitivity of the oxide/nitride interface electronic structure to GaN epilayer preparation and growth conditions. [ABSTRACT FROM AUTHOR]

Abstract: Molecular beam deposition systems allow for unparalleled control of film composition and structure. This article addresses the capacity for controlling metal and oxidant fluxes in the Yb/O2 system to access the metastable phase ytterbium monoxide (YbO). Experiments exploring the growth of polycrystalline YbO x films by molecular beam deposition demonstrate that a 2:1 molar ratio of Yb:O2 fluxes is necessary to achieve preferential growth of the divalent oxide. Applying similar deposition conditions to a (001) GaN surface leads to the growth of epitaxial (111) YbO films. Similar to other rocksalt oxides grown on GaN surfaces, YbO films display a 3D growth mechanism that leads to a grainy morphology with crystallites of 50nm lateral dimensions. Rocking curves in ω and φ have full-width half-maximum values of 1.77° and 4.1°, respectively; further improvements in crystal quality appear to be limited by the thermal stability of the YbO phase. [Copyright &y& Elsevier]