Synthesis and Analysis of Heterostructural Semiconductor Alloy Sn1-xCaxCh (Ch=S, Se) and Nitrides Zn1-xWxN and Zn1-x(W1-yMoy)xN

This work explores the synthesis and characterization of the metastable alloys Sn1-xCaxCh (Ch= S, Se) and nitride compounds Zn-W-Mo-N, which have recently been predicted by theorists. Single phase thin films of Sn1-xCaxS are prepared by pulsed laser deposition and radio-frequency magnetron sputtering and of Sn1-xCaxSe are prepared by pulsed laser deposition. A transition from the rock salt cubic structure at high Ca concentrations to the orthorhombic structure at lower Ca is observed at x = 0.25 for the sulfide and x = 0.18 for the selenide. Optical bandgaps for both Sn1-xCaxCh alloys follow nonlinear trends with a discontinuity near the transition composition range from 1.5-2.45 eV and 0.6-3.5 eV for Sn1-xCaxS and Sn1-xCaxSe respectively. Sn1-xCaxS samples were highly resistive, yielding resistivities of 〖10〗^2 -〖 10〗^4 Ωcm at low Ca concentrations (x < 0.1) and increasing rapidly with added Ca. Sn1-xCaxSe samples were much more conductive with resistivities 〖10〗^(-2) - 5×〖10〗^1 Ωcm over the range of compositions (0 < x < 1) and exhibited excellent thermoelectric properties with a power factor PF = 2 μWcm-1K-2 at x = 0.16. The phase decomposition of these alloys is also explored using STEM EDS (scanning transmission electron microscopy energy dispersive x-ray spectroscopy). Thin films of nitride compounds Zn-W-N and Zn-Mo-W-N are deposited by RFMS and the range of compositions for stabilization of the predicted wurtzite phase (at Zn3WN4) is tested. Single phase crystalline WZ samples were obtained between 60-87% and 50-84% Zn cation percent for the Zn-W-N and Zn-Mo-W-N systems respectively. Optical absorption for samples is calculated from measured transmission and reflectance for 800 < λ < 1100 nm, and samples at low Zn percentages are more absorbing in the IR than at higher Zn. Resistivities are measured for all films and found to be 〖10〗^3- 〖10〗^5 and 〖10〗^(-1) -〖 10〗^5 Ωcm for Zn-W-N and Zn-W-Mo-N respectively. Composition uniformity and crystalline uniformity are explored by STEM EDS and TEM respectively. WZ phase films were found to be compositionally uniform, but films at lower Zn concentrations (around 30% Zn) tended to phase separate. The experimental work presented here shows the viability of computational predictions of metastable materials and materials searches in alternative materials space to expand the number of known materials and understanding of metastable materials

Jahn-Teller-driven Phase Segregation in Mnx_{x}Co3−x_{3-x}O4_{4} Spinel Thin Films

Transition metal spinel oxides comprised of Earth-abundant Mn and Co have long been explored for their use in catalytic reactions and energy storage. However, understanding of functional properties can be challenging due to differences in sample preparation and the ultimate structural properties of the materials. Epitaxial thin film synthesis provides a novel means of producing precisely-controlled materials to explore the variations reported in the literature. In this work, Mn$_{x}$Co$_{3-x}$O$_{4}$ samples from x = 0 to x = 1.28 were synthesized through molecular beam epitaxy and characterized to develop a material properties map as a function of stoichiometry. Films were characterized via in situ X-ray photoelectron spectroscopy, X-ray diffraction, scanning transmission electron microscopy, and polarized K-edge X-ray absorption spectroscopy. Mn cations within this range were found to be octahedrally coordinated, in line with an inverse spinel structure. Samples largely show mixed Mn$^{3+}$ and Mn$^{4+}$ character with evidence of phase segregation tendencies with increasing Mn content and increasing Mn$^{3+}$ formal charge. Phase segregation may occur due to structural incompatibility between cubic and tetragonal crystal structures associated with Mn$^{4+}$ and Jahn-Teller active Mn$^{3+}$ octahedra, respectively. Our results help to explain the reported differences across samples in these promising materials for renewable energy technologies.Comment: 25 pages, 8 figures; Supplemental info and figures, 9 page

Isolation of Single Donors in ZnO

The shallow donor in zinc oxide (ZnO) is a promising semiconductor spin qubit with optical access. Single indium donors are isolated in a commercial ZnO substrate using plasma focused ion beam (PFIB) milling. Quantum emitters are identified optically by spatial and frequency filtering. The indium donor assignment is based on the optical bound exciton transition energy and magnetic dependence. The single donor emission is intensity and frequency stable with a transition linewidth less than twice the lifetime limit. The isolation of optically stable single donors post-FIB fabrication is promising for optical device integration required for scalable quantum technologies based on single donors in direct band gap semiconductors.Comment: E. R. Hansen and V. Niaouris contributed equally to this work. 13 pages, 11 figure

Unsupervised segmentation of irradiation\unicode{x2010}induced order\unicode{x2010}disorder phase transitions in electron microscopy

We present a method for the unsupervised segmentation of electron microscopy images, which are powerful descriptors of materials and chemical systems. Images are oversegmented into overlapping chips, and similarity graphs are generated from embeddings extracted from a domain\unicode{x2010}pretrained convolutional neural network (CNN). The Louvain method for community detection is then applied to perform segmentation. The graph representation provides an intuitive way of presenting the relationship between chips and communities. We demonstrate our method to track irradiation\unicode{x2010}induced amorphous fronts in thin films used for catalysis and electronics. This method has potential for "on\unicode{x2010}the\unicode{x2010}fly" segmentation to guide emerging automated electron microscopes.Comment: 7 pages, 3 figures. Accepted to Machine Learning and the Physical Sciences Workshop, NeurIPS 202

Resolving diverse oxygen transport pathways across Sr-doped lanthanum ferrite and metal-perovskite heterostructures

Perovskite structured transition metal oxides are important technological materials for catalysis and solid oxide fuel cell applications. Their functionality often depends on oxygen diffusivity and mobility through complex oxide heterostructures, which can be significantly impacted by structural and chemical modifications, such as doping. Further, when utilized within electrochemical cells, interfacial reactions with other components (e.g. Ni- and Cr-based alloy electrodes and interconnects) can influence the perovskite's reactivity and ion transport, leading to complex dependencies that are difficult to control in real-world environments. Here we use isotopic tracers and atom probe tomography to directly visualize oxygen diffusion and transport pathways across perovskite and metal-perovskite heterostructures, i.e. (Ni-Cr coated) Sr-doped lanthanum ferrite (LSFO). Annealing in 18O2(g) results in elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO while Ni-Cr undergoes oxidation via multiple mechanisms and transport pathways. Complementary density functional theory (DFT) calculations at experimental conditions provide rationale for OE reaction mechanisms and reveal a complex interplay of different thermodynamic and kinetic drivers. Our results shed light on the fundamental coupling of defects and oxygen transport in an important class of catalytic materials.Comment: 39 pages, 10 figure

Silicon-lattice-matched boron-doped gallium phosphide: A scalable acousto-optic platform

The compact size, scalability, and strongly confined fields in integrated photonic devices enable new functionalities in photonic networking and information processing, both classical and quantum. Gallium phosphide (GaP) is a promising material for active integrated photonics due to its high refractive index, wide band gap, strong nonlinear properties, and large acousto-optic figure of merit. In this work we demonstrate that silicon-lattice-matched boron-doped GaP (BGaP), grown at the 12-inch wafer scale, provides similar functionalities as GaP. BGaP optical resonators exhibit intrinsic quality factors exceeding 25,000 and 200,000 at visible and telecom wavelengths respectively. We further demonstrate the electromechanical generation of low-loss acoustic waves and an integrated acousto-optic (AO) modulator. High-resolution spatial and compositional mapping, combined with ab initio calculations indicate two candidates for the excess optical loss in the visible band: the silicon-GaP interface and boron dimers. These results demonstrate the promise of the BGaP material platform for the development of scalable AO technologies at telecom and provide potential pathways toward higher performance at shorter wavelengths

Observational and genetic associations between cardiorespiratory fitness and cancer:A UK Biobank and international consortia study

Background: The association of fitness with cancer risk is not clear. Methods: We used Cox proportional hazards models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for risk of lung, colorectal, endometrial, breast, and prostate cancer in a subset of UK Biobank participants who completed a submaximal fitness test in 2009-12 (N = 72,572). We also investigated relationships using two-sample Mendelian randomisation (MR), odds ratios (ORs) were estimated using the inverse-variance weighted method. Results: After a median of 11 years of follow-up, 4290 cancers of interest were diagnosed. A 3.5 ml O 2⋅min −1⋅kg −1 total-body mass increase in fitness (equivalent to 1 metabolic equivalent of task (MET), approximately 0.5 standard deviation (SD)) was associated with lower risks of endometrial (HR = 0.81, 95% CI: 0.73–0.89), colorectal (0.94, 0.90–0.99), and breast cancer (0.96, 0.92–0.99). In MR analyses, a 0.5 SD increase in genetically predicted O 2⋅min −1⋅kg −1 fat-free mass was associated with a lower risk of breast cancer (OR = 0.92, 95% CI: 0.86–0.98). After adjusting for adiposity, both the observational and genetic associations were attenuated. Discussion: Higher fitness levels may reduce risks of endometrial, colorectal, and breast cancer, though relationships with adiposity are complex and may mediate these relationships. Increasing fitness, including via changes in body composition, may be an effective strategy for cancer prevention.</p

Novel phase diagram behavior and materials design in heterostructural semiconductor alloys

Structure and composition control the behavior of materials. Isostructural alloying is historically an extremely successful approach for tuning materials properties, but it is often limited by binodal and spinodal decomposition, which correspond to the thermodynamic solubility limit and the stability against composition fluctuations, respectively. We show that heterostructural alloys can exhibit a markedly increased range of metastable alloy compositions between the binodal and spinodal lines, thereby opening up a vast phase space for novel homogeneous single-phase alloys. We distinguish two types of heterostructural alloys, that is, those between commensurate and incommensurate phases. Because of the structural transition around the critical composition, the properties change in a highly nonlinear or even discontinuous fashion, providing a mechanism for materials design that does not exist in conventional isostructural alloys. The novel phase diagram behavior follows from standard alloy models using mixing enthalpies from first-principles calculations. Thin-film deposition demonstrates the viability of the synthesis of these metastable single-phase domains and validates the computationally predicted phase separation mechanism above the upper temperature bound of the nonequilibrium single-phase region

Landscape Movements of Migratory Birds and Bats Reveal an Expanded Scale of Stopover

Many species of birds and bats undertake seasonal migrations between breeding and over-wintering sites. En-route, migrants alternate periods of flight with time spent at stopover – the time and space where individuals rest and refuel for subsequent flights. We assessed the spatial scale of movements made by migrants during stopover by using an array of automated telemetry receivers with multiple antennae to track the daily location of individuals over a geographic area ∼20×40 km. We tracked the movements of 322 individuals of seven migratory vertebrate species (5 passerines, 1 owl and 1 bat) during spring and fall migratory stopover on and adjacent to a large lake peninsula. Our results show that many individuals leaving their capture site relocate within the same landscape at some point during stopover, moving as much as 30 km distant from their site of initial capture. We show that many apparent nocturnal departures from stopover sites are not a resumption of migration in the strictest sense, but are instead relocations that represent continued stopover at a broader spatial scale

Counteractive effects of antenatal glucocorticoid treatment on D1 receptor modulation of spatial working memory

RATIONALE: Antenatal exposure to the glucocorticoid dexamethasone dramatically increases the number of mesencephalic dopaminergic neurons in rat offspring. However, the consequences of this expansion in midbrain dopamine (DA) neurons for behavioural processes in adulthood are poorly understood, including working memory that depends on DA transmission in the prefrontal cortex (PFC). OBJECTIVES: We therefore investigated the influence of antenatal glucocorticoid treatment (AGT) on the modulation of spatial working memory by a D1 receptor agonist and on D1 receptor binding and DA content in the PFC and striatum. METHODS: Pregnant rats received AGT on gestational days 16-19 by adding dexamethasone to their drinking water. Male offspring reared to adulthood were trained on a delayed alternation spatial working memory task and administered the partial D1 agonist SKF38393 (0.3-3 mg/kg) by systemic injection. In separate groups of control and AGT animals, D1 receptor binding and DA content were measured post-mortem in the PFC and striatum. RESULTS: SKF38393 impaired spatial working memory performance in control rats but had no effect in AGT rats. D1 binding was significantly reduced in the anterior cingulate cortex, prelimbic cortex, dorsal striatum and ventral pallidum of AGT rats compared with control animals. However, AGT had no significant effect on brain monoamine levels. CONCLUSIONS: These findings demonstrate that D1 receptors in corticostriatal circuitry down-regulate in response to AGT. This compensatory effect in D1 receptors may result from increased DA-ergic tone in AGT rats and underlie the resilience of these animals to the disruptive effects of D1 receptor activation on spatial working memory