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Fe1−xRhx layers are grown with varying rhodium fraction x on (001)-oriented MgO substrates by molecular-beam epitaxy. Film structural, morphological, magnetic, and transport properties are investigated. At room temperature, layers are ferromagnetic (FM) for x < 0.48 and antiferromagnetic (AF) for x > 0.48. Separating the two magnetically ordered phases at x = 0.48 is an abrupt change in the Fe1−xRhx lattice parameter of Δa = 0.0028 nm (Δa/a = −0.9%). For AF layers, the FM state is recovered by heating across a first-order phase transition. The transition leads to a large resistivity modulation, Δρ/ρ = 80%, over a narrow temperature range, ΔT = 3 K, in stoichiometric Fe0.50Rh0.50/MgO(001). For samples with compositions deviating from x = 0.50, fluctuations broaden ΔT and defect scattering reduces Δρ/ρ. [ABSTRACT FROM AUTHOR]

Generalized ellipsometry measurements are used to extract the complex dielectric function (ε = ε 1 + i ε 2) spectra of GdScO3 single crystals over the 0.7–8.5 eV photon energy range. GdScO3 is a wide bandgap semiconductor with a high dielectric constant, and potential applications include replacing SiO2 in silicon-based transistors and as an epitaxial substrate for thin film growth. This work presents the anisotropic optical properties for electric fields oscillating parallel to the a-, b-, and c-crystallographic axes. A direct bandgap is identified at 6.44 eV along the direction parallel to the a-axis, with additional critical points observed at 6.74 and 7.42 eV in the same direction. Additional above gap critical point transitions are found at 6.72, 7.31, and 7.96 along the direction parallel to the b-axis and 6.83 and 8.00 eV along the direction parallel to the c-axis. [ABSTRACT FROM AUTHOR]

Recent research work on searching for high mobility p -type oxides has identified substantial promising p -type oxide candidates. However, very few of them have been experimentally proven with high p -type conductivity, due to their limited p -type dopability caused by the deep valence band edge (VBE). In this work, we report amorphous phase Ta 2 SnO 6 (a -Ta 2 SnO 6) possessing unusually shallow VBE that permits high p -type doping without hole-killing oxygen vacancy defects spontaneous formation, contrasting to crystalline Ta 2 SnO 6 (c -Ta 2 SnO 6). The shallow VBE in a -Ta 2 SnO 6 also allows a low Schottky barrier height with contact metals and unique a −/ c - Ta 2 SnO 6 heterostructure device. The shallow VBE in a -Ta 2 SnO 6 is due to the local structure disorder that circumvents the strong electrostatic Coulombic interaction between positively charged Ta5+ and Sn-5 s lone-pair electrons which accounts for the deep VBE and low p -type dopability in c -Ta 2 SnO 6. [Display omitted] • Many high hole mobility oxides cannot be p -type doped because of their deep valence band edge positions. • Band alignments and band edge positions are investigated to access the p -type dopability of oxides. • Amorphous Ta 2 SnO 6 has different electronic structure and carrier transport property than its crystalline counterpart. • Shallow valence band edge in amorphous Ta 2 SnO 6 allows a low Schottky barrier with contact metal. • A novel heterostructure device based on amorphous/crystalline Ta 2 SnO 6 is designed for better electron transport. [ABSTRACT FROM AUTHOR]

Abstract: We review recent developments and advances in the synthesis of thin-film multiferroic and magnetoelectric heterostructures. Driven by the promise of new materials with built-in useful phenomena (i.e., electric field control of ferromagnetism), extensive research has been centered on the search for and characterization of new single-phase multiferroic materials. In this review we provide a brief overview of recent developments in the synthesis of thin film versions of these materials. Advances in modern film growth processes have provided access to high-quality materials for in-depth study. We highlight the use of epitaxial thin-film strain to stabilize metastable phases, drive multiferroic properties, and produce new structures and properties in materials including case studies of EuTiO3 and BiFeO3. [Copyright &y& Elsevier]

The broad spectrum of electronic and optical properties exhibited by oxides offers tremendous opportunities for microelectronic devices, especially when a combination of properties in a single device is desired. Here we describe the use of reactive molecular-beam epitaxy and pulsed-laser deposition to synthesize functional oxides, including ferroelectrics, ferromagnets, and materials that are both at the same time. Owing to the dependence of properties on direction, it is often optimal to grow functional oxides in particular directions to maximize their properties for a specific application. But these thin film techniques offer more than orientation control; customization of the film structure down to the atomic-layer level is possible. Numerous examples of the controlled epitaxial growth of oxides with perovskite and perovskite-related structures, including superlattices and metastable phases, are shown. In addition to integrating functional oxides with conventional semiconductors, standard semiconductor practices involving epitaxial strain, confined thickness, and modulation doping can also be applied to oxide thin films. Results of fundamental scientific importance as well as results revealing the tremendous potential of utilizing functional oxide thin films to create devices with enhanced performance are described. [ABSTRACT FROM AUTHOR]

Predictions and measurements of the effect of biaxial strain on the properties of epitaxial ferroelectric thin films and superlattices are reviewed. Results for single-layer ferroelectric films of biaxially strained SrTiO3, BaTiO3, and PbTiO3 as well as PbTiO3/SrTiO3 and BaTiO3/SrTiO3 superlattices are described. Theoretical approaches, including first principles, thermodynamic analysis, and phase-field models, are applied to these biaxially strained materials, the assumptions and limitations of each technique are explained, and the predictions are compared. Measurements of the effect of biaxial strain on the paraelectric-to-ferroelectric transition temperature (TC) are shown, demonstrating the ability of percent-level strains to shift TC by hundreds of degrees in agreement with the predictions that predated such experiments. Along the way, important experimental techniques for characterizing the properties of strained ferroelectric thin films and superlattices, as well as appropriate substrates on which to grow them, are mentioned. [ABSTRACT FROM AUTHOR]

In this study, we investigate in situ etching of β-Ga2O3 in a metalorganic chemical vapor deposition system using tert-butyl chloride (TBCl). We report etching of both heteroepitaxial 2 ¯ 01 -oriented and homoepitaxial (010)-oriented β-Ga2O3 films over a wide range of substrate temperatures, TBCl molar flows, and reactor pressures. We infer that the likely etchant is HCl (g), formed by the pyrolysis of TBCl in the hydrodynamic boundary layer above the substrate. The temperature dependence of the etch rate reveals two distinct regimes characterized by markedly different apparent activation energies. The extracted apparent activation energies suggest that at temperatures below ∼800 °C, the etch rate is likely limited by desorption of etch products. The relative etch rates of heteroepitaxial 2 ¯ 01 and homoepitaxial (010) β-Ga2O3 were observed to scale by the ratio of the surface energies, indicating an anisotropic etch. Relatively smooth post-etch surface morphology was achieved by tuning the etching parameters for (010) homoepitaxial films. [ABSTRACT FROM AUTHOR]

The article reports on the application of technological innovation through oxide electronic devices with sufficient purity showing quantum Hall Effect. It mentions the use of electron transport as a better sensitive test for the measurement of electrical cleanliness in materials compared to other chemical characterization. It notes the achievement of highest mobility in synthetic Zinc oxide single crystals, in which the mobile electrons are provided while the scattering effect is prevented.

Transport properties of electron-doped cuprate Sr 1 − x La x CuO 2 thin films have been investigated as a function of doping. In particular, optimal- and over-doped samples were obtained by tuning the Sr:La stoichiometric ratio. Optimal-doped samples show a non-Fermi liquid behavior characterized by linear dependence of the resistivity from room temperature down to intermediate temperature (about 150–170 K). However, by approaching temperatures in the superconducting transition, a Fermi-liquid behavior-characterized by a T 2 -scaling law-was observed. Once established, the transition from a linear-T to a quadratic- T 2 behavior was successfully traced back in over-doped samples, even occurring at lower temperatures. In addition, the over-doped samples show a crossover to a linear-T to a logarithmic dependence at high temperatures compatible with anti-ferromagnetic spin fluctuations dominating the normal state properties of electron-doped cuprates. [ABSTRACT FROM AUTHOR]

The article discusses the report by Jin Wang and colleagues on the application of negative pressure to ferroelectric lead titanate (PbTiO3) to increase its spontaneous polarization and ferroelectric transition temperature. The authors created a stable phase PbTiO3 using a lower density, metastable polymorph of PbTiO3. Also provided are the features of the stable polymorph including the density and transition temperature.

Flexoelectricity is a property of dielectric materials whereby they exhibit electric polarization induced by strain gradients; while this effect can be negligible at the macroscale, it can become dominant at the nanoscale, where strain gradients can turn out to be tremendous. Previous works have demonstrated that flexoelectricity coupled with piezoelectricity enables the mechanical writing of ferroelectric polarization. When considering ferroelectric materials with out-of-plane polarization, the coupling of piezoelectricity with flexoelectricity can insert a mechanical asymmetry to the system and enable the distinction of oppositely polarized domains, based on their nanomechanical response. Using atomic force microscopy and, more specifically, contact resonance techniques, the coupling of flexoelectricity to piezoelectricity can be exploited to mechanically read the sign of ferroelectric polarization in a non-destructive way. We have measured a variety of ferroelectric materials, from a single crystal to thin films, and domains that are polarized down always appear to be stiffer than oppositely polarized domains. In this article, we demonstrate experimentally that the phenomenon is size-dependent and strongly enhanced when the dimension of the material is reduced to nanoscale in thin films. Ultimately, we demonstrate how the sensitivity in mechanical reading of ferroelectric polarization can be improved by appropriately tuning the mechanical stiffness of the cantilevers. [ABSTRACT FROM AUTHOR]

The article offers the authors' insights on the study conducted by Jae-Wan Park and colleagues on the integration of functional oxide interface on silicon. The authors state that oxide system has a remarkable property on transitioning conductors to its insulating state by using techniques based on atomic force microscopy. Furthermore, they mention that correlated electrons have the ability to integrate functionalities to oxide which are absent to conventional semiconductors and silicon.

The article offers information on highly resistive ferrite magnet, where a ferroelectric polarization is induced with low magnetic field at room temperature. It states that multiferroic phase plays the key role in the observed magnetic field-induced polarization. It mentions several drawbacks of magnetoelectrics and multiferroics including induced polarizations value may be smaller than required for the application and instead of magnetic fields, electric field are easier to route in devices.

The article discusses electric fields and their innovative means of controlling systems of condensed matter. The focus of the article is research by Caviglia and colleagues researching the way an electric field can be employed in the modification of electron concentrations of transparent electron gases. Topics include an analysis of the major challenge to the study, which is nanoscale oxide interfaces, and the research methodology used by Caviglia and colleagues.

Examines the role of oxides in semiconductor electronics. Possibility of controlling the electronic properties of oxides with the nanoscale precision necessary for the information industry; Identification of some oxides as excellent insulators and others as superconductors; Prediction that oxides such as hafnium dioxide are to replace silicon dioxide in the transistors of laptop computers.

Low resistance non-alloyed ohmic contacts are realized by a metal-first process on homoepitaxial, heavily n+ doped (010) β-Ga2O3. The resulting contacts have a contact resistance (Rc) as low as 0.23 Ω-mm on an as-grown sample and exhibit nearly linear ohmic behavior even without a post-metallization anneal. The metal-first process was applied to form non-alloyed contacts on n+ (010) β-Ga2O3 grown by metal-organic chemical vapor deposition (MOCVD) as well as suboxide molecular beam epitaxy. Identical contacts fabricated on similar MOCVD samples by conventional liftoff processing exhibit highly rectifying Schottky behavior. Re-processing using the metal-first process after removal of the poor contacts by conventional methods does not improve the contacts; however, addition of a Ga-flux polishing step followed by re-processing using a metal-first process again results in low resistance, nearly linear ohmic contacts. The liftoff process, therefore, does not reliably render nearly linear ohmic behavior in non-alloyed contacts. Furthermore, no interface contamination was detected by x-ray photoelectron spectroscopy. This suggests that during the initial liftoff processing, a detrimental layer may form at the interface, likely modification of the Ga2O3 surface, that is not removable during the contact removal process but that can be removed by Ga-flux polishing. [ABSTRACT FROM AUTHOR]

Through mapping of the spatiotemporal strain profile in ferroelectric BiFeO3 epitaxial thin films, we report an optically initiated dynamic enhancement of the strain gradient of 105-106 m−1 that lasts up to a few ns depending on the film thickness. Correlating with transient optical absorption measurements, the enhancement of the strain gradient is attributed to a piezoelectric effect driven by a transient screening field mediated by excitons. These findings not only demonstrate a new possible way of controlling the flexoelectric effect, but also reveal the important role of exciton dynamics in photostriction and photovoltaic effects in ferroelectrics. [ABSTRACT FROM AUTHOR]

We report the temperature influence of the OHad and Oad electroadsorption on RuO2(110) films grown on TiO2(110) crystals in alkaline media. From the temperature effect, we evaluate the enthalpy and entropy of the OHad and Oad 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. Our result suggests that an entropy analysis is necessary to capture the electroadsorption behavior on RuO2 since the enthalpy–entropy competition strongly influences the electroadsorption behavior. Our observation of an entropic force is consistent with the view that water may be a mediator for adsorbate–adsorbate interactions. [ABSTRACT FROM AUTHOR]

TbScO3 is a wide bandgap semiconductor with potential applications in charge trap memory devices and acts as an alternate gate dielectric in fully depleted transistors and also a substrate for epitaxial thin film growth. TbScO3 has an orthorhombic crystal structure, which gives rise to optical anisotropy. Generalized ellipsometric spectra are measured for multiple in-plane rotations of (110) and (001) oriented TbScO3 single crystals over a photon energy range of 0.7–8.5 eV to determine the complex dielectric function (ε = ε1 + iε2) spectra for electric fields oscillating along each axis. A direct bandgap is identified at 6.50 eV, and above gap critical point transitions are found at 6.99, 7.14, 7.16, 7.21, and 7.42 eV. [ABSTRACT FROM AUTHOR]

New properties and exotic quantum phenomena can form due to periodic nanotextures, including Moire patterns, ferroic domains, and topologically protected magnetization and polarization textures. Despite the availability of powerful tools to characterize the atomic crystal structure, the visualization of nanoscale strain-modulated structural motifs remains challenging. Here, we develop nondestructive real-space imaging of periodic lattice distortions in thin epitaxial films and report an emergent periodic nanotexture in a Mott insulator. Specifically, we combine iterative phase retrieval with unsupervised machine learning to invert the diffuse scattering pattern from conventional X-ray reciprocal-space maps into real-space images of crystalline displacements. Our imaging in PbTiO3/SrTiO3 superlattices exhibiting checkerboard strain modulation substantiates published phase-field model calculations. Furthermore, the imaging of biaxially strained Mott insulator Ca2RuO4 reveals a strain-induced nanotexture comprised of nanometer-thin metallic-structure wires separated by nanometer-thin Mott-insulating-structure walls, as confirmed by cryogenic scanning transmission electron microscopy (cryo-STEM). The nanotexture in Ca2RuO4 film is induced by the metal-to-insulator transition and has not been reported in bulk crystals. We expect the phasing of diffuse X-ray scattering from thin crystalline films in combination with cryo-STEM to open a powerful avenue for discovering, visualizing, and quantifying the periodic strain-modulated structures in quantum materials. [ABSTRACT FROM AUTHOR]

We report a synthetic route to achieve high electron mobility at room temperature in epitaxial La:BaSnO3/SrZrO3 heterostructures prepared on several oxide substrates. Room-temperature mobilities of 157, 145, and 143 cm2 V−1 s−1 are achieved for heterostructures grown on DyScO3 (110), MgO (001), and TbScO3 (110) crystalline substrates, respectively. This is realized by first employing pulsed laser deposition to grow at very high temperature the SrZrO3 buffer layer to reduce dislocation density in the active layer, then followed by the epitaxial growth of an overlaying La:BaSnO3 active layer by molecular-beam epitaxy. Structural properties of these heterostructures are investigated, and the extracted upper limit of threading dislocations is well below 1.0 × 10 10 cm−2 for buffered films on DyScO3, MgO, and TbScO3 substrates. The present results provide a promising route toward achieving high mobility in buffered La:BaSnO3 films prepared on most, if not all, oxide substrates with large compressive or tensile lattice mismatches to the film. [ABSTRACT FROM AUTHOR]

The development of high-performance p-type oxides with high hole mobility and a wide bandgap is critical for the applications of metal oxide semiconductors in vertically integrated CMOS devices [Salahuddin et al., Nat. Electron. 1, 442 (2018)]. Sn2+-based oxides such as SnO and K2Sn2O3 have recently been proposed as high-mobility p-type oxides due to their relatively low effective hole masses, which result from delocalized Sn s-orbital character at the valence band edge. Here, we introduce a promising ternary Sn-O-X compound, Ta2SnO6, which exhibits strong valence band dispersion and a large bandgap. In order to evaluate the performance of this oxide as a p-type semiconductor, we perform first-principles calculations of the phonon-limited room-temperature carrier mobilities in SnO, SnO2, and Ta2SnO6. Electron relaxation time is evaluated, accounting for the scatterings from acoustic deformation potentials and polar optical phonons (POP), within the isotropic and dispersionless approximation. At room temperature, the electron/hole mobilities in a given material (SnO, SnO2, and Ta2SnO6) are found to be limited by POP scattering. SnO2 shows high room-temperature electron mobility of 192 cm2/(V s), while SnO and Ta2SnO6 exhibit impressive hole mobilities, with the upper limit at 60 and 33 cm2/(V s), respectively. We find that carrier effective mass largely accounts for the differences in mobility between these oxides with correspondingly different POP scattering rates. The theoretically predicted intrinsic mobilities of each material will provide the upper limit to the real mobilities for their device applications. Our findings also suggest a necessity of further investigation to identify even higher mobility p-type oxides with smaller hole effective masses. [ABSTRACT FROM AUTHOR]

We report the electrocatalysis of the chlorine evolution reaction (CER) on well-defined RuO2(110) and IrO2(110) surfaces. RuO2 and IrO2 are known for their capabilities to catalyze the CER. Until now, the CER measurements have only been reported on well-defined RuO2 surfaces and only at high Cl− concentrations. We present the CER measurement and the role of Cl− at lower concentration on single-orientation RuO2(110) and IrO2(110) films. We find that RuO2(110) is two orders of magnitude more active than IrO2(110). Moreover, we observe the correlation between the CER activity and the Oad formation potential on RuO2 and IrO2, supporting the prior suggestion that the Oad is the active site for the CER. We further use the reaction order analysis to support the Volmer-Heyrovsky mechanism of the CER, which was previously suggested from the Tafel slope analysis. Our finding highlights the importance of the surface Oad species on oxides for the CER electrocatalysis and suggests the electrochemical formation of Clad on Oad (for example, Cl− + Oad ↔ OClad + e−) as the crucial step in the CER electrocatalysis. [ABSTRACT FROM AUTHOR]

Functional properties of transition-metal oxides strongly depend on crystallographic defects; crystallographic lattice deviations can affect ionic diffusion and adsorbate binding energies. Scanning x-ray nanodiffraction enables imaging of local structural distortions across an extended spatial region of thin samples. Yet, localized lattice distortions remain challenging to detect and localize using nanodiffraction, due to their weak diffuse scattering. Here, we apply an unsupervised machine learning clustering algorithm to isolate the low-intensity diffuse scattering in as-grown and alkaline-treated thin epitaxially strained SrIrO3 films. We pinpoint the defect locations, find additional strain variation in the morphology of electrochemically cycled SrIrO3, and interpret the defect type by analyzing the diffraction profile through clustering. Our findings demonstrate the use of a machine learning clustering algorithm for identifying and characterizing hard-to-find crystallographic defects in thin films of electrocatalysts and highlight the potential to study electrochemical reactions at defect sites in operando experiments. [ABSTRACT FROM AUTHOR]

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 BaSnO3‐based heterostructures. Here, 2DEG formation at the LaScO3/BaSnO3 (LSO/BSO) interface with a room‐temperature mobility of 60 cm2 V−1 s−1 at a carrier concentration of 1.7 × 1013 cm–2 is reported. This is an order of magnitude higher mobility at room temperature than achieved in SrTiO3‐based 2DEGs. This is achieved by combining a thick BSO buffer layer with an ex situ high‐temperature treatment, which not only reduces the dislocation density but also produces a SnO2‐terminated atomically flat surface, followed by the growth of an overlying BSO/LSO interface. Using weak beam dark‐field transmission electron microscopy imaging and in‐line electron holography technique, a reduction of the threading dislocation density is revealed, and direct evidence for the spatial confinement of a 2DEG at the BSO/LSO interface is provided. This work opens a new pathway to explore the exciting physics of stannate‐based 2DEGs at application‐relevant temperatures for oxide nanoelectronics. [ABSTRACT FROM AUTHOR]

We grew Sr1-xLaxCuO2 thin films and SrCuO2/Sr0.9La0.1CuO2/SrCuO2 trilayers by reflection high-energy diffraction-calibrated layer-by-layer molecular beam epitaxy, to study their electrical transport properties as a function of the doping and thickness of the central Sr0.9La0.1CuO2 layer. For the trilayer samples, as already observed in underdoped SLCO films, the electrical resistivity versus temperature curves as a function of the central layer thickness show, for thicknesses thinner than 20 unit cells, sudden upturns in the low temperature range with the possibility for identifying, in the normal state, the T* and a T** temperatures, respectively, separating high-temperature linear behavior and low-temperature quadratic dependence. By plotting the T* and T** values as a function of TConset for both the thin films and the trilayers, the data fall on the same curves. This result suggests that, for the investigated trilayers, the superconducting critical temperature is the important parameter able to describe the normal state properties and that, in the limit of very thin central layers, such properties are mainly influenced by the modification of the energy band structure and not by interface-related disorder. [ABSTRACT FROM AUTHOR]

The article presents a study that explores liberating a hidden antiferroelectric phase with interfacial electrostatic engineering. It mentions that antiferroelectric materials have seen a resurgence of interest because of proposed applications in a number of energy-efficient technologies. It discusses that use of electrostatic confinement provides an untapped pathway for the design of engineered antiferroelectric materials with large and potentially coupled responses.

We report the growth of thin films of the mixed valence compound YbAl3 on MgO using molecular-beam epitaxy. Employing an aluminum buffer layer, epitaxial (001) films can be grown with sub-nm surface roughness. Using x-ray diffraction, in situ low-energy electron diffraction, and aberration-corrected scanning transmission electron microscopy, we establish that the films are ordered in the bulk as well as at the surface. Our films show a coherence temperature of 37 K, comparable to that reported for bulk single crystals. Photoelectron spectroscopy reveals contributions from both f13 and f12 final states establishing that YbAl3 is a mixed valence compound and shows the presence of a Kondo Resonance peak near the Fermi-level. [ABSTRACT FROM AUTHOR]

A fundamental understanding of materials' structural dynamics, with fine spatial and temporal control, underpins future developments in electronic and quantum materials. Here, we introduce an optical transient grating pump and focused X-ray diffraction probe technique (TGXD) to examine the structural evolution of materials excited by modulated light with a precisely controlled spatial profile. This method adds spatial resolution and direct structural sensitivity to the established utility of a sinusoidal transient-grating excitation. We demonstrate TGXD using two thin-film samples: epitaxial BiFeO3, which exhibits a photoinduced strain (structural grating) with an amplitude proportional to the optical fluence, and FeRh, which undergoes a magnetostructural phase transformation. In BiFeO3, structural relaxation is location independent, and the strain persists on the order of microseconds, consistent with the optical excitation of long-lived charge carriers. The strain profile of the structural grating in FeRh, in comparison, deviates from the sinusoidal excitation and exhibits both higher-order spatial frequencies and a location-dependent relaxation. The focused X-ray probe provides spatial resolution within the engineered optical excitation profile, resolving the spatiotemporal flow of heat through FeRh locally heated above the phase transition temperature. TGXD successfully characterizes mesoscopic energy transport in functional materials without relying on a specific transport model. [ABSTRACT FROM AUTHOR]

• Perovskite solid solutions can produce indifferent points with a congruently melting minimum. • Pair selection criteria include a Goldschmidt perovskite tolerance factor close to unity. • Seven solid solution pairs with cubic crystal structure were identified in this study. • These materials have favorable lattice parameters for perovskite substrate applications. • Czochralski/Bridgman growth show that sodium evaporation and attendant hazards are a problem. Single-crystal substrate materials with crystal structures and lattice parameters matching a desired epitaxial film are an enabling technology for many critical materials. Such substrates are best grown by bulk techniques that benefit from the substrate material being congruently melting. The shortage of congruently melting perovskites in critical lattice parameter ranges has been addressed herein by a search for new congruently melting compositions. A solid solution of two perovskites can be congruently melting at a minimum temperature under specified thermodynamic conditions where the coefficient matrix has a zero determinant. This is called an indifferent point. A wide variety of perovskite solid solutions were investigated to identify compounds that have an indifferent melting minimum and a cubic crystal structure with favorable lattice constants in the range of 0.390–0.412 nm. Solid solution pairs that form such indifferent points include, but are not limited to, seven compositions identified in this study. The lattice parameters of the new materials show a broad range of desirable lattice constants. A perovskite tolerance factor close to unity gave a favorable contribution to the free energy and makes a cubic crystal structure favorable. These solid solutions constitute a broad and important class of compounds not previously anticipated. The only significant drawback is the high vapor pressure of sodium, which is present in most of these materials and requires special growth conditions and equipment for safety. [ABSTRACT FROM AUTHOR]

Transmission electron microscopes use electrons with wavelengths of a few picometers, potentially capable of imaging individual atoms in solids at a resolution ultimately set by the intrinsic size of an atom. However, owing to lens aberrations and multiple scattering of electrons in the sample, the image resolution is reduced by a factor of 3 to 10. By inversely solving the multiple scattering problem and overcoming the electron-probe aberrations using electron ptychography, we demonstrate an instrumental blurring of less than 20 picometers and a linear phase response in thick samples. The measured widths of atomic columns are limited by thermal fluctuations of the atoms. Our method is also capable of locating embedded atomic dopant atoms in all three dimensions with subnanometer precision from only a single projection measurement. [ABSTRACT FROM AUTHOR]

Bandgap engineering is central to the design of heterojunction devices. For heterojunctions involving monolayer-thick materials like MoS2, the carrier concentration of the atomically thin film can vary significantly depending on the amount of charge transfer between MoS2 and the substrate. This makes substrates with a range of charge neutrality levels—as is the case for complex oxide substrates—a powerful addition to electrostatic gating or chemical doping to control the doping of overlying MoS2 layers. We demonstrate this approach by growing monolayer MoS2 on perovskite (SrTiO3 and LaAlO3), spinel (MgAl2O4), and SiO2 substrates with multi-inch uniformity. The as-grown MoS2 films on these substrates exhibit a controlled, reproducible, and uniform carrier concentration ranging from (1–4) ×1013 cm−2, depending on the oxide substrate employed. The observed carrier concentrations are further confirmed by our density-functional theory calculations based on ab initio mismatched interface theory (MINT). This approach is relevant to large-scale heterostructures involving monolayer-thick materials in which it is desired to precisely control carrier concentrations for applications. [ABSTRACT FROM AUTHOR]

Unlike many superlattice structures, Ruddlesden–Popper phases have atomically abrupt interfaces useful for interrogating how periodic atomic layers affect thermal properties. Here, we measure the thermal conductivity in thin films of the n = 1–5 and 10 members of the (SrTiO3)nSrO Ruddlesden–Popper superlattices grown by molecular-beam epitaxy and compare the results to a single crystal of the n = 1 Ruddlesden–Popper SrLaAlO4. The thermal conductivity cross-plane to the superlattice layering (k33) is measured using time-domain thermoreflectance as a function of temperature and the results are compared to first-principles calculations. The thermal conductivity of this homologous series decreases with increasing interface density. Characterization by x-ray diffraction and scanning transmission electron microscopy confirms that these samples have a Ruddlesden–Popper superlattice structure. [ABSTRACT FROM AUTHOR]

The thermal conductivity of an epitaxial layer of CsBiNb2O7 grown by pulsed-laser deposition is measured by time-domain thermoreflectance in the temperature range 100

There has been significant progress on the fundamental science and technological applications of complex oxides and multiferroics. Among complex oxide thin films, barium strontium titanate (BST) has become the material of choice for room-temperature-based voltage-tunable dielectric thin films, due to its large dielectric tunability and low microwave loss at room temperature. BST thin film varactor technology based reconfigurable radio frequency (RF)/microwave components have been demonstrated with the potential to lower the size, weight, and power needs of a future generation of communication and radar systems. Low-power multiferroic devices have also been recently demonstrated. Strong magneto-electric coupling has also been demonstrated in different multiferroic heterostructures, which show giant voltage control of the ferromagnetic resonance frequency of more than two octaves. This manuscript reviews recent advances in the processing, and application development for the complex oxides and multiferroics, with the focus on voltage tunable RF/microwave components. The over-arching goal of this review is to provide a synopsis of the current state-of the-art of complex oxide and multiferroic thin film materials and devices, identify technical issues and technical challenges that need to be overcome for successful insertion of the technology for both military and commercial applications, and provide mitigation strategies to address these technical challenges. [ABSTRACT FROM AUTHOR]

Epitaxial Sc2O3 films with the cubic bixbyite structure were grown on (111) Si by reactive molecular beam epitaxy. High-resolution transmission electron microscopy (HRTEM) revealed an abrupt, reaction-layer free interface between Sc2O3 and Si. The ∼10% lattice mismatch between Si and Sc2O3 was relieved by the formation of a hexagonal misfit dislocation network with Burgers vectors of 1/2,〈 &1macr;10〉Si and line directions parallel to 〈11&2macr;&rangSi. A high density of planar defects and threading dislocations was observed. Analysis of lattice shifts across the planar defects in HRTEM showed that these faults were likely antiphase boundaries (APBs). ABPs form when film islands coalesce during growth because films nucleate with no unique arrangement of the ordered oxygen vacancies in the bixbyite structure relative to the Si lattice. [ABSTRACT FROM AUTHOR]

The article discusses that ultrawide-bandgap semiconductors as ushering in the next generation of high-power electronics. It mentions that phase transition of the epitaxial layers from the alpha to the narrower bandgap beta-phase is catalyzed by the c-plane of the crystal. It discusses about the epitaxial stabilization of the bandgap.

The article offers information on the Amorphization mechanism of SrIrO3 electrocatalyst. It mentions that how oxygen redox initiates ionic diffusion and structural reorganization. It discusses that use of renewable electricity to prepare materials and fuels from abundant molecules offers a tantalizing opportunity to address concerns over energy and materials sustainability.

The low dielectric loss underlying the record performance of strained (SrTiO3)nSrO Ruddlesden–Popper films as tunable microwave dielectrics was postulated to arise from (SrO)2 faults accommodating local non-stoichiometric defects. Here, we explore the effect of non-stoichiometry on (SrTiO3)nSrO using positron annihilation lifetime spectroscopy on a composition series of 300 nm thick n = 6 (Sr1+δTiO3)nSrO thin films. These films show titanium-site vacancies across the stoichiometry series, with evidence that TiOx vacancy complexes dominate. Little change in defect populations is observed across the series, indicating the ability of Ruddlesden–Popper phases to accommodate ± 5% off-stoichiometry. This ability for defect accommodation is corroborated by scanning transmission electron microscopy with electron energy loss spectroscopy. [ABSTRACT FROM AUTHOR]

Spin-based memories are attractive for their non-volatility and high durability but provide modest resistance changes, whereas semiconductor logic transistors are capable of providing large resistance changes, but lack memory function with high durability. The recent availability of multiferroic materials provides an opportunity to directly couple the change in spin states of a magnetic memory to a charge change in a semiconductor transistor. In this work, we propose and analyze the spin–orbit torque field-effect transistor, a device with the potential to significantly boost the energy efficiency of spin-based memories and to simultaneously offer a palette of functionalities. [ABSTRACT FROM AUTHOR]

We have measured the angle-resolved transverse resistivity (ARTR), a sensitive indicator of electronic anisotropy, in highquality thin films of the unconventional superconductor Sr2RuO4 grown on various substrates. The ARTR signal, heralding the electronic nematicity or a large nematic susceptibility, is present and substantial already at room temperature and grows by an order of magnitude upon cooling down to 4 K. In Sr2RuO4 films deposited on tetragonal substrates the highest-conductivity direction does not coincide with any crystallographic axis. In films deposited on orthorhombic substrates it tends to align with the shorter axis; however, the magnitude of the anisotropy stays the same despite the large lattice distortion. These are strong indications of actual or incipient electronic nematicity in Sr2RuO4. [ABSTRACT FROM AUTHOR]

Hexagonal LuFeO3 exhibiting ferroelectricity and weak ferromagnetism is grown on metal-polar GaN by molecular-beam epitaxy. The oxide films exhibit smooth surface morphologies and are found to be single crystalline with an epitaxial relationship related by a 30° in-plane rotation relative to the GaN crystal structure. The LuFeO3 layers grown on GaN exhibit room-temperature ferroelectricity and low-temperature magnetic ordering. This epitaxial integration creates a heterostructure platform to explore and exploit the coupling of the ferroelectricity and magnetism of oxides with the strong spontaneous and piezoelectric polarization and the unique electronic and photonic properties of nitride semiconductors. [ABSTRACT FROM AUTHOR]

The electro-optic response of epitaxially strained SrTiO3 grown on bulk DyScO3 substrates is measured as a function of applied in-plane bias (both magnitude and direction) and light polarization. The effective electro-optic coefficients are bias-field dependent. Hysteresis is observed at room temperature, indicative of residual polarity, which is believed to be due to long-lived alignment of nanopolar regions possibly due to defects. A simple model incorporating non-180°-nanoscale domains can account for most of the experimental observations. [ABSTRACT FROM AUTHOR]

Microwave tunable dielectric properties of strained (001) SrTiO3 thin films epitaxially deposited on (110) DyScO3 substrates were studied for in-plane film orientations ([100], [010], [110], and [-110]). A significant in-plane anisotropy in dielectric constant and tuning was observed in these SrTiO3 films. The highest dielectric constant and tuning at room temperature are observed along the [010] direction of the SrTiO3 film (1000 Å thick) (3500 and 70% at 1 V/μm, respectively), the lowest ones are observed along the [100] direction (i.e., 2000 and 50% at 1 V/μm, respectively). The dielectric constant and tuning along [-110] and [110] are about 2500 and 30% at 1 V/μm, respectively, which are intermediary to those along the [010] and [100] directions. The dielectric Q(=1/tan δ) does not show any large difference for the four directions (i.e., Q∼10-20). Also, the phase-transition peak for the [-110] and [110] directions of the SrTiO3 film (300 Å thick) is observed at 275 K, which is lower than that for the [010] and [100] directions. The observed in-plane anisotropic dielectric properties have been interpreted based on the phenomenological thermodynamics of film strain. [ABSTRACT FROM AUTHOR]

Structural distortion of ferroelectric thin films caused by film strain has a strong impact on the microwave dielectric properties. SrTiO3 thin films epitaxially grown on (110) DyScO3 substrates using molecular beam epitaxy are extremely strained (i.e., ∼1% in-plane tensional strain) from 3.905 Å of bulk SrTiO3. The room-temperature in-plane dielectric constant and its tuning of the films at 10 GHz are observed to be 6000 and 75% with an electric field of 1 V/μm, respectively. The control of strain in SrTiO3 provides a basis for room-temperature tunable microwave applications by elevating its phase-transition peak to room temperature. [ABSTRACT FROM AUTHOR]

Electric-field induced rearrangement of domain microstructure in an epitaxial thin film of Bi[sub 4]Ti[sub 3]O[sub 12] on a SrTiO[sub 3] (001) substrate is studied by optical second harmonic generation measurements. The input polarization dependence of the second harmonic signal exhibits spatial symmetries that reflect the presence of eight different domain variants present in the film. Changes in these symmetries with the application of electric field are experimentally studied at 23° C and 60 °C, and theoretically modeled to extract the hysteresis loops that reflect quantitative changes in the fraction of domain variants. A strong correlation is observed between the dc electrical conductance (as distinct from transient currents) and the ferroelectric domain state of the film, which is proposed to arise from the creation and destruction of charged domain walls within the film with applied field. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The domain microstructure in an epitaxial thin film of Bi[sub 4]Ti[sub 3]O[sub 12] on a SrTiO[sub 3](001) substrate is studied by second harmonic generation measurements. The input polarization dependence of the second harmonic signal exhibits spatial symmetries that reflect the presence of eight different domain variants present in the film. A theoretical model is presented that explains the observed symmetries and extracts quantitative information on the nonlinear optical coefficients of the material and statistics of domain variants present in the film area being probed. The following ratios of nonlinear coefficients and birefringence was determined: d[sub 12]/d[sub 11]=-3.498±0.171, |d[sub 26]/d[sub 12]|=0.365±0.010, |d[sub 26]/d[sub 11]|=1.273±0.036, and |n[sub b]-n[sub a]|=0.101±0.018 (at 532 nm). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Intense hard x-ray pulses from a free-electron laser induce irreversible structural damage in a perovskite oxide epitaxial heterostructure when pulse fluences exceed a threshold value. The intensity of x-ray diffraction from a 25-nm thick epitaxial BiFeO3 layer on a SrTiO3 (STO) substrate measured using a series of pulses decreases abruptly with a per-pulse fluence of 2.7 × 106 photons μm−2 at a photon energy of 9.7 keV but remains constant for 1.3 × 106 photons μm−2 or less. The damage resulted in the destruction of the BiFeO3 thin film within the focal spot area and the formation of a deep cavity penetrating into the STO substrate via the removal of tens of nanometers of material per pulse. The damage threshold occurs at a fluence that is insufficient to heat the absorption volume to the melting point. The morphology of the ablated sample is consistent with fracture rather than melting. Together, these results indicate that the damage occurs via a nonthermal process consistent with ultrafast ionization of the absorption volume. [ABSTRACT FROM AUTHOR]

Single Fe(001) films (30 nm thick) have been epitaxially grown on ferroelectric BaTiO3/SrTiO3(001) substrates at different growth temperatures to study the mutual interaction between the multiferroic components. This paper reports on the as-grown magnetic properties of the structures as a precursor to a full investigation of the multiferroic interactions. Ferromagnetic resonance measurements were carried out at 36 GHz cavity and variable frequency microstrip resonators. Dual resonance modes are observed in the film, which are attributed to relaxed Fe in the film interior and strained Fe at the interface. Fourfold anisotropy is present for both modes with energy density consistent with that of bulk Fe. The interface mode is characterized by a large out-of-plane anisotropy comparable and opposite in sign to the shape anisotropy. This strained interfacial Fe should serve to couple the multiferroic components in this system. Dispersion curves show both optic and acoustic branches along the hard axis [110], with the optic branch resulting from resonance below saturation, indicating high quality Fe in these samples. Growth temperature has minimal influence on the observed anisotropy energies. [ABSTRACT FROM AUTHOR]

Combining multiple fast image acquisitions to mitigate scan noise and drift artifacts has proven essential for picometer precision, quantitative analysis of atomic resolution scanning transmission electron microscopy (STEM) data. For very low signal-to-noise ratio (SNR) image stacks – frequently required for undistorted imaging at liquid nitrogen temperatures – image registration is particularly delicate, and standard approaches may either fail, or produce subtly specious reconstructed lattice images. We present an approach which effectively registers and averages image stacks which are challenging due to their low-SNR and propensity for unit cell misalignments. Registering all possible image pairs in a multi-image stack leads to significant information surplus. In combination with a simple physical picture of stage drift, this enables identification of incorrect image registrations, and determination of the optimal image shifts from the complete set of relative shifts. We demonstrate the effectiveness of our approach on experimental, cryogenic STEM datasets, highlighting subtle artifacts endemic to low-SNR lattice images and how they can be avoided. High-SNR average images with information transfer out to 0.72 Å are achieved at 300 kV and with the sample cooled to near liquid nitrogen temperature. [ABSTRACT FROM AUTHOR]