Template Substrate Research Articles

Oxygen Incorporation in the Molecular Beam Epitaxy Growth of ScxGa1−xN and ScxAl1−xN

Secondary‐ion mass spectrometry (SIMS) is used to determine impurity concentrations of carbon and oxygen in two scandium‐containing nitride semiconductor multilayer heterostructures: ScxGa1−xN/GaN and ScxAl1−xN/AlN grown by molecular beam epitaxy (MBE). In the ScxGa1−xN/GaN heterostructure grown in metal‐rich conditions on GaN–SiC template substrates with Sc contents up to 28 at%, the oxygen concentration is found to be below 1 × 1019 cm−3, with an increase directly correlated with the scandium content. In the ScxAl1−xN–AlN heterostructure grown in nitrogen‐rich conditions on AlN–Al2O3 template substrates with Sc contents up to 26 at%, the oxygen concentration is found to be between 1019 and 1021 cm−3, again directly correlated with the Sc content. The increase in oxygen and carbon takes place during the deposition of scandium‐alloyed layers.

Peptidomimetic Modulators of BACE1

The β-site APP Cleaving enzyme 1 (BACE1) is a membrane-associated aspartyl protease which mediates the production of amyloid-β (Aβ), a major component of amyloid plaques in the Alzheimer’s disease brain. We have synthesised and characterised a series of peptidomimetic analogues of BACE substrates that incorporate two distinct stabilising structures. To demonstrate the potential activity of these compounds, a variety of assaying strategies were used to investigate cleavage susceptibility and inhibition potency under competitive and non-competitive conditions. β-Amino acids and scissile site N-methylation were incorporated into peptide substrate templates as transition state isostere (TSI) substitutes by positional scanning to generate series of non-TSI β-peptidomimetics. The amino acid sequences flanking the β-cleavage site within APP carrying the Swedish double mutation (APPSW), Neuregulin, the synthetic hydroxyethylene-based TSI peptide inhibitor OM99-2, and the high affinity peptide sequence SEISYEVEFR, served as the four substrate templates from which over 60 peptides were designed and synthesised by solid phase peptide synthesis. A quenched fluorescent substrate BACE1 assay in conjunction with liquid chromatography–mass spectrometry (LC-MS) analysis was established to investigate cleavage susceptibility and inhibition potency under competitive and non-competitive conditions. It was determined that β-amino acids substituted at the P1 scissile site position within known peptide substrates were resistant to proteolysis, and particular substitutions induced a concentration-dependent stimulation of BACE1, indicating a possible modulatory role of native BACE1 substrates.

Controls on fine particle retention in experimental streams

The transport and retention of fine particulate organic matter (FPOM) in headwater streams plays a significant role in organic matter processing and represents a critical link between upstream and downstream systems. Benthic biofilms potentially alter substrate characteristics and dynamics. However, the influence of biofilm colonization on FPOM retention has not been well documented, likely due to inherent heterogeneity of natural systems. We expected that biofilm growth would either enhance or diminish FPOM retention in the streambed, whereas biofilm growth would vary depending on the underlying substrate template. We used a short-term FPOM addition technique to estimate transport distances of a fine particle analog (corn pollen: 70 μm) in four 50-m experimental streams (Q = 1.5 L/s) at the Notre Dame Linked Experimental Ecosystem Facility. Streams varied in substrate size (1-cm pea gravel vs 10-cm small cobble) and complexity (homogenous 50/50 mix vs alternating sections). We sampled streams on multiple dates over 5 mo (June–October) of biofilm colonization and senescence. While FPOM transport distances generally increased as biofilm colonization occurred, retention was variable across streams and over time. We found no consistent or simple pattern of FPOM retention in our streams. Rather, one of the strongest effects was an indirect relationship between FPOM removal and transient storage, a factor that is strongly driven by biofilm colonization. These results emphasize the dynamic feedback of the physical and biological environments influencing FPOM retention in streams.

Selective C-C Bond Scission of Ketones via Visible-Light-Mediated Cerium Catalysis

Summary Here, we report a general catalytic manifold for the selective C–C bond scission of ketones via the exploitation of the ligand-to-metal charge transfer (LMCT) excitation mode. Through a cooperative utilization of Lewis acid catalysis and LMCT catalysis, the C–C bond of ketones could be selectively and effectively cleaved, enabling the installation of different functionalities at each carbon of the cleaved C–C bond through a sequential and orthogonal manner. This reaction manifold serves as a photocatalytic alternative to the Norrish type I reaction with the combination of visible light and inexpensive cerium salts. Under operationally simple conditions, a wide range of acyclic and cyclic ketones, from simple strained cyclobutanones to complex androsterone with less strained cyclopentanone moiety, could be successfully transformed into versatile chemical building blocks.

High-mobility two-dimensional electron gases at AlGaN/GaN heterostructures grown on GaN bulk wafers and GaN template substrates

We report a comparative study of the mobility of two-dimensional electron gases (2DEG) formed at AlGaN/GaN heterostructures by simultaneously growing on substrates with very different dislocation densities. The mobility is seen to depend on the 2DEG charge density directly, but surprisingly, dislocations do not cause a discernible impact on the mobility of the samples within the measured region <25 000 cm2 V−1 s−1. This experimental observation questions the generally accepted belief that dislocations are one of the dominant low-temperature scattering mechanisms for low-density 2DEG at AlGaN/GaN structures.

A Simple and Rapid Method to Produce SERS Substrates Using Au Nanoparticles Prepared by Laser Ablation and DVD Template

Simple and highly sensitive SERS substrates were produced using Au nanoparticles (AuNPs) prepared by laser ablation in water and available Digital Video Discs (DVDs). We used the simple “drop-cast’’ method to deposit AuNPs on the grating pattern surface of a DVD in place of the other methods such as electrochemical deposition, electrophoretic deposition and sputtering method which require some more equipment. AuNPs were proposed to be synthesized in water by laser ablation to form a nearly circular AuNP stain of small size on a DVD surface. The protecting polycarbonate layer of a DVD was removed from the DVD surface. The bare metallic DVD surface was rinsed carefully with ethanol and distilled water. The width of tracks on a DVD surface is around 300 nm and distance between them is around 450 nm. We prepared AuNPs by pulsed laser ablation of a gold piece in distilled water. The colloidal gold nanoparticles were deposited on DVD templates. We studied to produce an effective layer of AuNPs on DVD template for SERS substrates (AuNPs/DVD). The average SERS enhancement factor of the AuNPs/DVD SERS substrates is about 106. The SERS substrates can detect SERS spectra of Malachite Green and Amoxicillin at low concentrations of around 0.1–1 ppm.

The Many Roles of Binding Cooperativity in the Control of DNA Replication

The Many Roles of Binding Cooperativity in the Control of DNA Replication

Digital- to Analog-Type Terahertz Modulation Controlled by Mosaicity of the Substrate Template in Rare-Earth Nickelate Thin Films.

The extreme sensitivity of the metal-insulator (M-I) transition in RNiO3 (R = rare-earth ion) nickelates to various extrinsic and intrinsic factors rely on mechanisms driving structure-property relations. Here, we demonstrate a unique way to control the M-I transition of epitaxial Pr0.5Sm0.5NiO3 thin films using a mosaic template of the LaAlO3(100) substrate; two sets of epitaxial films were deposited on highly oriented crystals and mosaic (with multiple crystallites) crystals. While the former films exhibit a robust and sharp M-I transition, the films on the mosaic substrate show distinctively much more subtle and broad transition, albeit same factors suggesting compositional purity. Terahertz (THz) dynamic conductivity too behaves very differently for the two types of films; Drude dynamics dominate the conductivity of highly crystalline films, whereas disorder-driven Drude-Smith conductivity prevails in mosaic films. Using this mosaic structure-controlled M-I transition and conductivity dynamics, we propose to implement these two templates of films for digital and analog THz transmission amplitude modulators.

Fe(Se,Te) coated conductors deposited on simple rolling-assisted biaxially textured substrate templates

In this paper we study the feasibility of Fe(Se, Te) coated conductors on a simple rolling-assisted biaxially textured substrate (RABiTS) template. Starting from commercially available Ni–5 at% W tapes which show an out-of-plane orientation of about 7° and an in-plane orientation around 5°, we realized a RABiTS template for Fe(Se, Te) coated conductor fabrication by depositing CeO2 thin films on the metallic tape. The oxide buffer layers, deposited via pulsed laser ablation, exhibit an out-of-plane and an in-plane orientation suitable for Fe(Se, Te) deposition and act as a chemical barrier against Ni diffusion. Fe(Se, Te) thin films deposited on such a simple template show a superconducting transition at 16 K and very high upper critical field values with a ΔTc,0 of only 3 K in 18 T. The transport critical current reaches values of 1.7 × 105 A cm−2 at 4.2 K in self-field and is reduced by less than one order of magnitude up to 18 T, remaining isotropic with respect to the magnetic field direction.

Growth of ReS2 thin films by pulsed laser deposition

We present results on growth of ReS2 thin film both on c plane sapphire substrate and MoS2 template by pulsed laser deposition (PLD). Films tend to grow with (0001)ReS2 ⊥ (0001)Al2O3 and (0001)ReS2 ⊥ (0001)MoS2 ∥ (0001)Al2O3 at deposition temperature below 300 °C. Films are polycrystalline grown at temperature above 300 °C. The smoothness and epitaxial quality of the films are significantly improved when grown on MoS2 template compared to sapphire substrate. The results show that PLD is suitable to grow ReS2 thin film over large area (10 × 10 mm2) for practical device application.

Nanogold Biosynthesis Mediated by Mixed Flower Pollen Grains.

Physical and chemical methods for nanoparticle synthesis are disadvantageous to less energy demanding and more efficient and environmentally friendly biological approaches. Thus, in this paper, we designed simple, bottom-up, in vitro, static experiment under laboratory conditions using suspension of mixed flower pollen grains for nanoparticle synthesis. Pollen grains provided template substrates for gold nanoparticles synthesis from dissolved Au(III). Transmission and scanning electron microscopy along with ultraviolet-visible spectra confirmed the gold nanoparticles formation. The biosynthesized/phytosynthesized gold nanoparticles had relative narrow size distribution (from 3 to 11 nm) with dominant spherical morphology with no aggregated forms. Thus, the gold nanoparticles in pollen dispersion provides excellent stability and dispersity.

The effects of interaction between vermiculite and manganese dioxide on the environmental geochemical process of thallium

The interaction among various soil minerals can significantly impact on the environmental geochemical process of contaminants. Therefore, this study investigated the effects of interaction between vermiculite (VER) and manganese dioxide (MnO2) on the migration and transformation of Tl(I). The VER exhibited typical layered structure and MnO2 possessed a flower-like structure with serious reunion phenomenon, while the production of interaction between vermiculite and manganese dioxide, labeled VER-MnO2, illustrated as fish scales evenly spread over a large sheet, suggesting that MnO2 could triumphantly be anchored on the VER and the aggregation of MnO2 was prevented. Compared with the pure MnO2, VER acted as template substrate contributed the higher specific surface area (298.18 m2·g−1) and the oxidation degree of Mn. VER-MnO2 showed the highest fixation capacity (144.29 mg·g−1) than other two materials in the order VER-MnO2 > MnO2 > VER, and there was no risk derived from Mn dissolution. The influence mechanism of VER-MnO2 on Tl(I) migration and transformation lied in immobilization, ion exchange and oxidization. Fixed-bed column immobilization experiments showed that VER-MnO2 could purify drinking water contaminated by Tl (20 μg·L−1) and the effective breakthrough volumes were 900 bed volumes until reaching the maximum limits allowed in drinking water (0.1 μg·L−1). VER-MnO2 excellently catches Tl to prevent groundwater pollution. This study provides a theoretical guidance for environmental fate and restoration of soil heavy metal pollution.

K Atom Promotion of O2 Chemisorption on Au(111) Surface

Alkali atoms are known to promote or poison surface catalytic chemistry. To explore alkali promotion of catalysis and to characterize discharge species in alkali-oxygen batteries, we examine coadsorption of K and O2 on Au(111) surface at the atomic scale by scanning tunneling microscopy (STM) and density functional theory (DFT). On a clean Au(111) surface, O2 molecules may weakly physisorb, but when Au(111) is decorated with K+ ions, they chemisorb into structures that depend on the adsorbate concentrations and substrate templating. At low K coverages, an ordered quantum lattice of K2O2 complexes forms through intramolecular attractive and intermolecule repulsive interactions. For higher K and O2 coverages, the K2O2 complexes condense first into triangular islands, which further coalesce into rhombohedral islands, and ultimately into incommensurate films. No structures display internal contrast possibly because of high structural mutability. DFT calculations explain the alkali-promoted coadsorption in terms of three center, cation-π interactions where pairs of K+ coordinate the π-orbitals on each side of O2 molecules, and in addition O2 forms a covalent bond to Au(111) surface. The K promoted adsorption of O2 is catalyzed by charge transfer from K atoms to Au(111) substrate and ultimately to O2 molecules, forming O2-δ in a redox state between the peroxo and superoxo. Tunneling d I/d V spectra of K2O2 complexes exhibit inordinately intense inelastic progression involving excitation of the O-O stretching vibration, but absence of a Kondo effect suggests that the magnetic moment of O2 is quenched.

Molecular Imprinting with Functional DNA.

Molecular imprinting refers to templated polymerization with rationally designed monomers, and this is a general method to prepare stable and cost-effective ligands. This attractive concept however suffers from low affinity, low specificity, and limited signaling mechanisms for binding. Acrydite-modified DNA oligonucleotides can be readily copolymerized into acrylic polymers. With molecular recognition and catalytic functions, such functional DNAs are recently shown to enhance the performance of molecularly imprinted polymers (MIPs) in a few ways. First, DNA aptamers are used as macromonomers to enhance binding affinity and specificity of MIPs. Second, DNA can help produce optical signals to follow binding events. Third, imprinting can also improve the performance of catalytic DNA by enhancing its activity and specificity toward the template substrate. Finally, MIP is shown to help aptamer selection. Bulk imprinting, nanoparticle imprinting, and surface imprinting are all demonstrated with DNA. Since both DNA and synthetic polymers are cost effective and stable, their hybrid materials still possess such properties while enhancing the function of each component. This review covers recent developments on the abovementioned aspects of DNA-containing MIPs, a field just emerged in the last five years, and future research directions are discussed toward the end.

Chalcogenide glass metasurfaces from fluid instabilities.

Fluid instabilities in chalcogenide glasses can be exploited to self-assemble optical metasurfaces on various template substrates over a large area.

Microstructures and rotational domains in orthorhombic ε-Ga2O3 thin films

In this study, ε-Ga2O3 thin films were grown by mist chemical vapor deposition on a hexagonal (0001) GaN template and a cubic (111) SrTiO3 (STO) substrate. By analyzing the obtained X-ray diffraction (XRD) φ-scans, it was found that the ε-Ga2O3 epitaxial thin films grown on both GaN and STO exhibited an orthorhombic structure. In addition, a method was proposed to distinguish between hexagonal and orthorhombic structures on the basis of the relationships between the 2θ and χ angles for these structures, obtained from the XRD studies. Finally, a mechanism was discussed on the basis of angle relationships, where three rotational domains were observed for orthorhombic ε-Ga2O3 on GaN and STO. Transmission electron microscopy was then employed to determine whether the ε-Ga2O3 thin films on the GaN template and STO substrate consisted of columnar ε-Ga2O3 comprising small domains and intermediate layers between the ε-Ga2O3 film and the substrate.

Structural and Stress Properties of AlGaN Epilayers Grown on AlN-Nanopatterned Sapphire Templates by Hydride Vapor Phase Epitaxy.

In this paper, we report the epitaxial growth and material characteristics of AlGaN (Al mole fraction of 10%) on an AlN/nanopatterned sapphire substrate (NPSS) template by hydride vapor phase epitaxy (HVPE). The crystalline quality, surface morphology, microstructure, and stress state of the AlGaN/AlN/NPSS epilayers were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The results indicate that the crystal quality of the AlGaN film could be improved when grown on the AlN/NPSS template. The screw threading dislocation (TD) density was reduced to 1.4 × 109 cm−2 for the AlGaN epilayer grown on the AlN/NPSS template, which was lower than that of the sample grown on a flat c-plane sapphire substrate (6.3 × 109 cm−2). As examined by XRD measurements, the biaxial tensile stress of the AlGaN film was significantly reduced from 1,187 MPa (on AlN/NPSS) to 38.41 MPa (on flat c-plane sapphire). In particular, an increase of the Al content in the overgrown AlGaN layer was confirmed by the TEM observation. This could be due to the relaxation of the in-plane stress through the AlGaN and AlN/NPSS template interface.

Poly(dimethylsiloxane)/ZnO Nanoflakes/Three-Dimensional Graphene Heterostructures for High-Performance Flexible Energy Harvesters with Simultaneous Piezoelectric and Triboelectric Generation.

Herein, we report the successful synthesis of poly(dimethylsiloxane)/ZnO nanoflakes/three-dimensional graphene (PDMS/ZnO NFs/3D Gr) heterostructures using Ni foams as the template substrate via a facile route, while adapting a rational material design for a high-performance energy-harvester application. The PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester simultaneously exploits the piezoelectric effect and triboelectrification and shows peak-to-peak output voltages up to 122 V and peak-to-peak current densities up to 51 μA cm-2, resulting in an ultrahigh power density of 6.22 mW cm-2. Furthermore, we have evaluated the performance of the PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester by demonstrating its capacity to instantaneously power up 68 commercially available light-emitting diodes without the need for an additional energy-storage device. The excellent performance of these energy harvesters suggests that PDMS/ZnO NFs/3D Gr heterostructures present a viable strategy for the development of high-performance, flexible, wearable energy-harvesting devices.

Grating-like SERS substrate with tunable gaps based on nanorough Ag nanoislands/moth wing scale arrays for quantitative detection of cypermethrin.

Considering the complexity and high-consumption of the existing approaches to fabricate three-dimensional (3D) regular substrate templates, the scales of the moth wings with evenly-distributed nanoarrays were discovered to provide an ideal bioscaffold for metal silver (Ag) to decorate on to fabricate a flexible, highly-ordered, low-cost and large-scale Ag nanoislands/moth wing (Ag/MW) SERS-active substrate. The grating-like substrate with the optimal morphology of rough and hierarchical Ag nanoislands exhibited high enhancement factor (EF, ~4.16 × 105), low detection limit (10-10 M) to 4-aminothiophenol (4-ATP), outstanding signal uniformity (the relative standard deviations were less than 15%) and superior identification performance in the quantitative detection of pesticide cypermethrin. The three-dimensional finite-difference time-domain (3D-FDTD) method simulated the spatial distribution of the electric field intensity in the substrates with different morphologies, showing a potential strong enhancement of Raman signals in sub-10 nm gaps between two adjacent Ag nanoislands of different layers. These prominent SERS properties of novel Ag/MW SERS-active substrates suggest their potential value in rapid on-side biological and chemical sensing. Meanwhile, the highly-ordered nanoarrays of moth wings provide a new idea for the preparation of regular biomimetic nanomaterials.

Size Control Synthesis of Hydroxyapatite Plates and Their Application in the Preparation of Highly Oriented Films

Hydroxyapatite (HAp) plates were successfully synthesized using dodecanedioic acid (DDDA). Following the preparation of an ethanolic solution of DDDA, solutions of calcium and phosphate were added in succession to produce a white slurry upon mixing. Subsequent processing of this slurry under hydrothermal conditions provided HAp plates of various sizes. Indeed, the plate size could be changed by varying the quantity of DDDA employed in the synthesis, with larger particles being obtained in the presence of larger quantities of DDDA. It was confirmed that a calcium–DDDA complex (Ca-DDD, calcium dodecanedioate) was formed upon mixing of the DDDA and calcium solutions. The observed morphological control could potentially be accounted for by the formation of Ca-DDD. More specifically, during crystal growth, Ca-DDD plays the role of a nucleation substrate (template), a pH buffer, and a calcium reservoir. Finally, we demonstrated that the obtained HAp plates could be employed to prepare a HAp film with high cryst...