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A series of LaAlO3 thin films with different thicknesses were deposited by pulsed laser deposition at temperatures from 720 °C to 800 °C. The results from grazing incidence x-ray diffraction and reciprocal space mapping indicate that a thin layer of LaAlO3 adjacent to the SrTiO3 substrate remains almost coherently strained to the substrate, while the top layer starts to relax quickly above a certain critical thickness, followed by a gradual relaxation at larger film thickness when they are grown at lower temperatures. The atomic force microscopy results show that the fast relaxation is accompanied by the formation of cracks on the film surface. This can be ascribed to the larger energy release rate when compared with the resistance of LaAlO3 to cracking, according to calculations from the Griffith fracture theory. For films grown at 720 °C, a drop in sheet resistance by two orders of magnitude is observed when the top layer starts to relax, indicating a relationship between the strain and the conductivity of the two-dimensional electron gas at the LaAlO3/SrTiO3 interface. The strain engineered by growth temperature provides a useful tool for the manipulation of the electronic properties of oxide heterointerfaces. [ABSTRACT FROM AUTHOR]

The article discusses about the self-assembly of nanostructures from conjugates of elastin-like peptides and collagen-like peptides (ELP-CLP) has studied as means to produce thermoresponsive, collagen-binding drug delivery vehicles. Topics include the lower transition temperature of conjugates with ELP or CLP domains enables the formation of nanoparticles physiological temperature; and the chemical structure, molecular geometry, and solvent conditions has tuned to affect the size, and shape.

For potential applications in superconducting RF cavities, we have investigated the properties of polycrystalline MgB2 films, including the thickness dependence of the lower critical field Hc1. MgB2 thin films were fabricated by hybrid physical-chemical vapor deposition on (0001) SiC substrate either directly (for epitaxial films) or with a MgO buffer layer (for polycrystalline films). When the film thickness decreased from 300 nm to 100 nm, Hc1 at 5 K increased from around 600 Oe to 1880 Oe in epitaxial films and to 1520 Oe in polycrystalline films. The result is promising for using MgB2/MgO multilayers to enhance the vortex penetration field. [ABSTRACT FROM AUTHOR]

Abstract: The optical properties and structure of anodic oxides are dependent on the anodization conditions. For tantalum oxide formed in dilute phosphoric acid, the anodic oxide forms as two chemically distinct layers, referred to as a bi-layer, where the inner layer is pure tantalum oxide and the outer layer contains incorporated phosphate. The complex dielectric functions of the individual inner and outer layers are determined using spectroscopic ellipsometry. The dielectric functions of the bi-layers are compared to mono-layer oxides formed in sodium sulfate, and the effects of hydrothermal sealing are explored. For bi-layer oxides formed to 70V in phosphoric acid, the inner layer band gap is 4.37±0.02eV and the outer layer band gap is 3.86±0.06eV. Thin anodic oxides (∼6–15nm) are best described by a mono-layer oxide model and exhibit higher optical absorption with a band gap of 3.98±0.08eV. This study shows that spectroscopic ellipsometry is a valuable tool in assessing processing–property relationships of multi-layer anodic films. [Copyright &y& Elsevier]

Fe-MgO tunnel junctions have received much attention for their use in hard drive read heads and other spintronic applications. The system is particularly interesting because of its magnetoresistive behavior and the abundance and low cost of its constituent elements. However, many questions remain about how the structure and chemistry of the Fe-MgO interface mediates magnetic behavior. In this study, we report on transmission electron microscopy, electron energy loss spectroscopy, and magnetic characterization of Fe-MgO composite films with various morphologies. We explore relationships between film morphology, intermixing, and the resulting effects on magnetic structure. We find the presence of oxidation at the Fe-MgO interface, with a detrimental impact on the saturation magnetization of the composite. We also observe changes in coercivity and magnetocrystalline anisotropy with film morphology and thickness. These results will inform the design of MgO-based tunnel junctions and improve our understanding of how processing conditions, resulting in morphological and chemical changes such as oxidation, affect magnetization. [ABSTRACT FROM AUTHOR]

High-throughput synthesis of a series of monometallic and bimetallic catalysts (45 bimetallic and 50 monometallic samples) consisting of nickel and one of nine different metal promoters (B, Co, Cu, Fe, Mg, Mn, Sn, V and Zn) supported on one of five different metal oxides (alumina, ceria, magnesia, silica and titania) is carried out via organometallic grafting using a robotic platform. The catalysts are evaluated for their activity and selectivity for the dry reforming of methane at a feed ratio of CH 4 :CO 2 of 1 at 650–800 °C in a parallel flow reactor system. The type of oxide support prevails over the type of additive for both catalyst activity and stability. On Al 2 O 3 and MgO, Fe was found to be the best promoter; on SiO 2 , Cu is the best promoter at 700 °C and higher, while on TiO 2 , Mn is found to enhance the conversion at 800 °C. On CeO 2 , all additives except Fe have beneficial effects. Twenty-five catalysts show > 90% methane conversion with ten catalysts showing > 95% conversion at 800 °C with the H 2 :CO ratios ranging from 0.8 to 1.2. Amongst the ten highest performers, NiFe/Al 2 O 3 and NiFe/MgO are more active than Ni/Al 2 O 3 and Ni/MgO, respectively and were stable over a period of 25 h at 800 °C. Characterization on the as-prepared samples reveals highly dispersed phase, while after reduction in H 2 , highly dispersed and reduced nickel particles up to 10 nm are formed. The particles do not increase in size under dry reforming reaction conditions at 800 °C. An increased hydrogen consumption observed during H 2 -TPR of the nickel particles is positively correlated with methane conversion for Al 2 O 3 -based catalysts. The resistance to deactivation by coking and variation in coke structure are investigated by spectroscopic and microscopic methods to identify the relationship between metal promoters, alloy formation, and type of surface carbon deposits. Carbon whiskers were observed on the ten selected spent samples and are preferentially deposited on Ni rather than on the promoters. Carbon nanotube formation and metal particle removal from support were not observed to cause deactivation while amorphous carbon formation was clearly linked to catalyst deactivation, as amorphous carbon could encapsulate Ni, either on the support or at the end of the carbon nanotube. The organometallic grafting technique is an efficient and suitable technique for synthesizing highly dispersed and homogeneous phases which lead to high conversion and high durability for dry reforming of methane. [Display omitted] • Monometallic and bimetallic Ni DRM catalysts on Al 2 O 3 , CeO 2 , SiO 2 and TiO 2 were synthesized using organometallic grafting. • 10 catalysts, especially NiFe/Al 2 O 3 and NiFe/MgO, showed stable and high methane conversion > 95 % at 800 °C. • Highly dispersed phase led to highly dispersed nickel particles after in-situ reduction that retain size after DRM. • Amorphous carbon formation is linked to catalyst deactivation by encapsulation of the nickel nanoparticles. [ABSTRACT FROM AUTHOR]

The self-assembly of nanostructures from conjugates of elastin-like peptides and collagen-like peptides (ELP-CLP) has been studied as means to produce thermoresponsive, collagen-binding drug delivery vehicles. Motivated by our previous work in which ELP-CLP conjugates successfully self-assembled into vesicles and platelet-like nanostructures, here, we extend our library of ELP-CLP bioconjugates to a series of tryptophan/phenylalanine-containing ELPs and GPO-based CLPs [W 2 F x - b -(GPO) y ] with various domain lengths to determine the impact of these modifications on the thermoresponsiveness and morphology. The lower transition temperature of the conjugates with longer ELP or CLP domains enables the formation of well-defined nanoparticles near physiological temperature. Moreover, the morphological transition from vesicles to platelet-like nanostructures occurred when the ratio of the lengths of ELP/CLP decreased. Given the previously demonstrated ability of many ELP-CLP bioconjugates to bind to both hydrophobic drugs and collagen-containing materials, our results suggest new opportunities for designing specific thermoresponsive nanostructures for targeted biological applications., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Conjugated polymers are electronically and ionically active organic materials of interest for use in a variety of devices. Electrochemical deposition is a convenient method for precisely fabricating conjugated polymer thin films, yet a detailed, quantitative understanding of nucleation and growth mechanisms has remained elusive. Here, we report direct imaging of the in situ electrochemical deposition of poly(3,4-ethylenedioxythiophene) (PEDOT) from an aqueous solution of EDOT monomer using Transmission Electron Microscopy with an electrochemical liquid flow cell. We found that PEDOT deposition began preferentially at the edge of the glassy carbon anodes at the beginning of the reaction. Fluctuating clusters of liquid-like oligomers were observed to form near the electrode surfaces. As the reaction continued, both the nucleation of new domains as well as the growth of pre-existing PEDOT deposits were observed, leading to systematic increases in film thickness and roughness.

Ionic liquids (ILs) have received considerable interest for use in electrostatic gating in complex oxide systems. Understanding the ionic liquid/oxide interface, and any bias-induced electrochemical degradation, is critical for the interpretation of transport phenomena. The integrity of the interface between ionic liquid 1-ethyl-3-methylimidazolium hexafluorophosphate and La1/3Sr2/3FeO3 under various biasing conditions was examined by analytical transmission electron microscopy, and we report film degradation in the form of an irreversible chemical reaction regardless of the applied bias. This results in an intermixing region of 4-6 nm at the IL/oxide interface. Electron energy loss spectroscopy shows La and Fe migration into the ionic liquid, resulting in secondary phase formation under negative bias. Our approach can be extended to other ionic liquid/oxide systems in order to better understand the electrochemical stability window of these device structures.

Magnetoelectric oxide heterostructures are proposed active layers for spintronic memory and logic devices, where information is conveyed through spin transport in the solid state. Incomplete theories of the coupling between local strain, charge, and magnetic order have limited their deployment into new information and communication technologies. In this study, we report direct, local measurements of strain- and charge-mediated magnetization changes in the La0.7Sr0.3MnO3/PbZr0.2Ti0.8O3 system using spatially resolved characterization techniques in both real and reciprocal space. Polarized neutron reflectometry reveals a graded magnetization that results from both local structural distortions and interfacial screening of bound surface charge from the adjacent ferroelectric. Density functional theory calculations support the experimental observation that strain locally suppresses the magnetization through a change in the Mn-eg orbital polarization. We suggest that this local coupling and magnetization suppression may be tuned by controlling the manganite and ferroelectric layer thicknesses, with direct implications for device applications.

Photocorrosion stable WO(3) nanowire arrays are synthesized by a solvothermal technique on fluorine-doped tin oxide coated glass. WO(3) morphologies of hexagonal and monoclinic structure, ranging from nanowire to nanoflake arrays, are tailored by adjusting solution composition with growth along the (001) direction. Photoelectrochemical measurements of illustrative films show incident photon-to-current conversion efficiencies higher than 60% at 400 nm with a photocurrent of 1.43 mA/cm(2) under AM 1.5G illumination. Our solvothermal film growth technique offers an exciting opportunity for growth of one-dimensional metal oxide nanostructures with practical application in photoelectrochemical energy conversion.