Appropriate Choice Of Substrate Research Articles

Strain-Induced Domain Structure and Its Impact on Magnetic and Transport Properties of Gd0.6Ca0.4MnO3 Thin Films.

The evolution of lattice strain on crystallographic domain structures and magnetic properties of epitaxial low-bandwidth manganite Gd0.6Ca0.4MnO3 (GCMO) films have been studied with films on different substrates: SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, SrLaAlO3, and MgO. The X-ray diffraction data reveals that all of the films, except the films on MgO, are epitaxial and have an orthorhombic structure. Cross-sectional transmission electron microscopy (TEM) shows lattice mismatch-dependent microstructural defects. Large-enough tensile strain can increase oxygen vacancies concentration near the interface and can induce vacancies in the substrate. In addition, a second phase was observed in the films with tensile strain. However, compressive strain causes dislocations in the interface and a mosaic domain structure. On the other hand, the magnetic properties of the films, including saturation magnetization, coercive field, and transport property depend systematically on the substrate-induced strain. Based on these results, the choice of appropriate substrate is an important key to obtaining high-quality GCMO film, which can affect the functionality of potential device applications.

Phenomenological theory of defect driven flexo-chemical phenomena in ferroics

The review is focused on the phenomenological description of the elastic defects influence on the electrophysical properties of nanosized ferroics. Using the Landau-Ginzburg-Devonshire phenomenological approach we consider the contribution of the elastic defects (e.g. neutral oxygen vacancies) on the phase transitions temperatures, phase diagrams, piezo-resistive, dielectric and polar properties of thin ferroelectric films and nanoparticles. We pay special attention to the role of flexoelectric effect, Vegard strains and stresses, including their synergy, called flexo-chemical coupling, on the defect-driven phenomena in nanoferroics. We explore the influence of mobile charged defects migration (e.g. the drift and diffusion of cations or charged oxygen vacancies) on the domain structure evolution in thin ferroelectric films. Also, we discuss the possibilities of the uncharged elastic defects self-ordering ordering in thin strained oxide films, and show that a thermodynamically stable disordered phase, spatially modulated phases, and long-range ordered phases with defect layers parallel or perpendicular to substrate plane can appear in the phase diagram in dependence on the film-substrate mismatch strain, concentration of elastic defects and Vegard coefficients. Since the long-range ordered ferroic phases can become multiferroic when some elastic dipoles become electric ones, the obtained results open the way to create and control defect-ordered superstructures by the choice of appropriate substrate and defect concentration in thin ferroic films.

Epitaxial fabrication of 2D materials of group IV elements

Experimental fabrication and investigation of unique properties of two-dimensional monoatomic layers of carbon, silicon, germanium, and tin on different surfaces have opened bright perspectives for development of devices of new generation. Wide opportunities to control their exotic electronic and optical properties via appropriate choice of substrate, content and geometry of two-dimensional layer, combined with elastic strain engineering, made them the central theme of research in the field of nanotechnology and materials science. In this work we review epitaxial methods of synthesis of two-dimensional materials of group IV elements: silicene, germanene, and stanene. General structural properties of these materials are also briefly considered. Special attention is paid to the technological growth modes, providing fabrication of high-quality large-area two-dimensional structures necessary for emerging device application.

Use flexibility of perch types by the branch-camouflaged Common Potoo (Nyctibius griseus): why this bird may occasionally dare to perch on artificial substrates

ABSTRACT Animal species gain protection against visually oriented predators when they choose a suitable substrate that maximizes camouflaging. The choice of appropriate substrate may be particularly important during the brooding period when vulnerability of the parents and their progeny is high. The Common Potoo (Nyctibius griseus) is a well-camouflaged bird that blends nearly perfectly into a branch extension. Camouflage may be so effective for this species that perched individuals may wait until the last second before fleeing a potential predator. We compared the features of day perch substrates used by this bird during nesting and nonnesting occasions. We accessed 1,560 photos online and found that Common Potoo predominantly use natural tree substrates for nesting and resting (1,510 photos, 96.8%), except for a small percentage of individuals (50 photos, 3.2%) that choose seemingly risky artificial substrates (e.g., wires, traffic poles, and even plastic bottles) as resting sites. In addition, a random...

Strain dependent anisotropy in photoluminescence of heteroepitaxial nonpolar a-plane ZnO layers

Nonpolar a-plane ZnO layers with anisotropic in-plane strains were prepared on the three substrates of r-sapphire, a-GaN, and a-Al0.08GaN templates via a pulsed laser deposition system, to investigate the distinguishing anisotropic photoluminescence properties of a-ZnO grown on foreign substrates. The optical anisotropy of nonpolar ZnO grown on GaN and AlGaN templates was investigated via polarization-dependent photoluminescence (PL) measurement and polarization transmission spectra measurement. The 0.3 μm a-ZnO layer grown on the a-GaN template has significant anisotropic optical properties with a degree of polarization (DOP) of the photoluminescence (PL) spectrum of about 0.8907, larger than 0.8786 of ZnO on a-Al0.08GaN or 0.8408 of a-ZnO on r-sapphire, revealing that the a-GaN may be the best candidate for the fabrication of modulators and that the increase of the Al component x of p-AlxGa1-xN will attenuate the anisotropic properties of the heteroepitaxial a-ZnO layer, providing a valuable basis for the choice of appropriate substrate for nonpolar a-plane ZnO based polarized optoelectronic devices. Moreover, the relationship between crystal quality anisotropy and optical anisotropy was proposed.

Flexible ultrathin-body single-photon avalanche diode sensors and CMOS integration.

We proposed the world's first flexible ultrathin-body single-photon avalanche diode (SPAD) as photon counting device providing a suitable solution to advanced implantable bio-compatible chronic medical monitoring, diagnostics and other applications. In this paper, we investigate the Geiger-mode performance of this flexible ultrathin-body SPAD comprehensively and we extend this work to the first flexible SPAD image sensor with in-pixel and off-pixel electronics integrated in CMOS. Experimental results show that dark count rate (DCR) by band-to-band tunneling can be reduced by optimizing multiplication doping. DCR by trap-assisted avalanche, which is believed to be originated from the trench etching process, could be further reduced, resulting in a DCR density of tens to hundreds of Hertz per micrometer square at cryogenic temperature. The influence of the trench etching process onto DCR is also proved by comparison with planar ultrathin-body SPAD structures without trench. Photon detection probability (PDP) can be achieved by wider depletion and drift regions and by carefully optimizing body thickness. PDP in frontside- (FSI) and backside-illumination (BSI) are comparable, thus making this technology suitable for both modes of illumination. Afterpulsing and crosstalk are negligible at 2µs dead time, while it has been proved, for the first time, that a CMOS SPAD pixel of this kind could work in a cryogenic environment. By appropriate choice of substrate, this technology is amenable to implantation for biocompatible photon-counting applications and wherever bended imaging sensors are essential.

Plant performance on Mediterranean green roofs: interaction of species-specific hydraulic strategies and substrate water relations.

Recent studies have highlighted the ecological, economic and social benefits assured by green roof technology to urban areas. However, green roofs are very hostile environments for plant growth because of shallow substrate depths, high temperatures and irradiance and wind exposure. This study provides experimental evidence for the importance of accurate selection of plant species and substrates for implementing green roofs in hot and arid regions, like the Mediterranean area. Experiments were performed on two shrub species (Arbutus unedo L. and Salvia officinalis L.) grown in green roof experimental modules with two substrates slightly differing in their water retention properties, as derived from moisture release curves. Physiological measurements were performed on both well-watered and drought-stressed plants. Gas exchange, leaf and xylem water potential and also plant hydraulic conductance were measured at different time intervals following the last irrigation. The substrate type significantly affected water status. Arbutus unedo and S. officinalis showed different hydraulic responses to drought stress, with the former species being substantially isohydric and the latter one anisohydric. Both A. unedo and S. officinalis were found to be suitable species for green roofs in the Mediterranean area. However, our data suggest that appropriate choice of substrate is key to the success of green roof installations in arid environments, especially if anisohydric species are employed.

Development of sputtered AlN thin-film ultrasonic transducers for durable high-temperature applications

This paper presents some of the recent experimental work on developing AlN ultrasonic transducers for high-temperature NDT applications. C-axis oriented AlN films were grown on stainless steel SS316 substrate by RF sputtering deposition. The high-temperature performance and durability of the transducer were examined by pulse-echo experiments after heating to different temperatures. It can be shown that the sputtered AlN film transducer is capable of highly stable and durable performance at 400°C or above, with appropriate choice of substrate, buffer layer, electroding materials and electroding approaches. Experimental evidence also indicates that transducers made of sputtered AlN film and a molybdenum buffer layer on a stainless steel substrate could potentially operate at up to 800°C.

Constrained sintering of BaLa4Ti4O15 thick films: Pore and grain anisotropy

Constrained sintering of BaLa4Ti4O15 (BLT) thick films on flexible platinum foil and on rigid BLT substrate showed enhanced grain growth and anisotropic microstructure development when compared with bulk samples having similar green packing and sintered under the same conditions. The evolution of the microstructural parameters (grain and pore shape, orientation) during densification and their correlation was investigated in films and compared with the morphological evolution in bulk samples. It is then expected that the appropriate choice of substrate will allow designing tailored microstructures of functional thick films with optimized performance.

Optimization of enzyme–substrate pairing for bioluminescence imaging of gene transfer using Renilla and Gaussia luciferases

Bioluminescence imaging (BLI) permits the non-invasive quantification and localization of transduction and expression by gene transfer vectors. The tendency of tissue to attenuate light in the optical region, however, limits the sensitivity of BLI. Improvements in light output from bioluminescent reporter systems would allow the detection of lower levels of expression, smaller numbers of cells and expression from deeper and more attenuating tissues within an animal. With the goal of identifying substrates that allow improved sensitivity with Renilla luciferase (RLuc) and Gaussia luciferase (GLuc) reporter genes, we evaluated native coelenterazine and three of its most promising derivatives in BLI of cultured cells transduced with retroviral vectors encoding these reporters. Of the eight enzyme-substrate pairs tested, the two that performed best were further evaluated in mice to compare their effectiveness for imaging vector-modified cells in live animals. In cell culture, we observed striking differences in luminescence levels from the various enzyme-substrate combinations and found that the two luciferases exhibited markedly distinct abilities to generate light with the substrates. The most effective pairs were RLuc with the synthetic coelenterazine derivative ViviRen, and GLuc with native coelenterazine. In animals, these two pairs allowed similar detection sensitivities, which were eight- to 15-fold higher than that of the prototypical RLuc-native coelenterazine combination. Substrate selection can dramatically influence the detection sensitivity of RLuc and GLuc and appropriate choice of substrate can greatly improve the performance of reporter genes encoding these enzymes for monitoring gene transfer by BLI.

Electrocaloric effect in BaTiO3 thin films

The modified transverse Ising model taking into account the four-spin exchange interaction and quantum fluctuation, as well as the mechanical constraint of the substrate, is constructed and applied to investigate the electrocaloric effect (ECE) in BaTiO3 thin films. It is found that the temperature dependence of ECE strongly depends on both the four-spin exchange interaction and quantum fluctuation. Most importantly, we achieve the adiabatic temperature change ΔT=11.78 K at Tm=490 K, which can be comparable with that observed experimentally in PbZr0.95Ti0.05O3 thin films and ferroelectric polymers. Furthermore, the internal stresses resulting from the clamping effect of the substrate play a crucial role in the ECE of ferroelectric films. Control of the misfit stress by appropriate choice of substrate provides an effective means to improve the adiabatic temperature change for use in cooling or thermodielectric power conversion devices.

Iron silicide nanostructure formation on Au induced superstructures on Si(111)

Using scanning tunnelling microscopy we have investigated the formation of lowdimensional Fe–Si structures on Au covered Si(111) surfaces. The ultrathin Au layerinduces a variety of surface reconstructions, depending on the coverage and temperature:Si(111)-5 × 2, α-, β-, and 6 × 6-Au. The subsequent deposition of 0.28 ML (monolayers) of Fe at400 °C results in the formation of Fe–Si nanostructures whose morphologicalproperties critically depend on the underlying surface. All Au inducedreconstructions give rise to an increase in diffusion length as compared to the bareSi(111)-7 × 7 surface, thereby allowing the growth of well-separated nanostructures at considerably lowertemperatures. Ultimately, the decoupling of surface diffusion and temperature, inducedby the Au layer, can be exploited to tailor the island dimensions and density.With an appropriate choice of substrate, passivating layer and deposited material,nanostructures with the desired properties can be grown in a controlled way.

Influence of mechanical boundary conditions on the electrocaloric properties of ferroelectric thin films

A thermodynamic analysis of the electrocaloric (EC) effect in BaTiO3 ferroelectric thin films has been carried out under differing mechanical boundary conditions. It is shown that both the magnitude of the electrocaloric effect and temperature at which it is maximized depend not only on the extent of the applied field change but also on the value of the initial field. For initial fields smaller than a critical value the EC effect is largest at the phase transition temperature but the effect is a strong function of temperature. For external electrical fields larger than this value, conversely, the EC effect is the largest at a higher temperature and is a weak function of temperature. Perfect lateral clamping transforms the first-order phase transition into a second-order transition, lowering the magnitude of the electrocaloric effect and dependence on temperature. Compressive and tensile misfit strains also alter the nature of the phase transition and affect the electrocaloric properties in an analogous way. A compressive misfit strain shifts the maximum in the EC effect to higher temperatures, reduces its magnitude, and reduces its dependence on temperature, while tensile misfit strain results in the opposite effects. Control of the misfit strain by appropriate choice of substrate provides potential means to vary both the magnitude and the temperature sensitivity of the EC effect for use in cooling or thermodielectric power conversion devices.

Development of Block Co-Polymers as Self-Assembling Templates for Patterned Media

ABSTRACTBlock copolymers that self-organize are of interest as templates for patterned media, as they potentially provide a low cost fabrication route. Poly(styrene)-Poly(methylmethacrylate) block co-polymers (PS-b-PMMA) of appropriate block length and PS to PMMA ratio self-assemble into a 2-D hexagonal phase in which the PS majority phase is continuous and surrounds cylinders of the minority, PMMA phase. For application of this phase to patterned media it is necessary that the cylinders of the minority phase be oriented perpendicular to the substrate surface. This can be achieved by a number of methods, including appropriate choice of substrate and use of a random co-polymer underlayer. Appropriate substrates include H-terminated silicon, some carbon coatings and some ITO glasses. Use of an acetic acid wash causes the minority PMMA component can be induced to be rearranged, giving rise to pores perpendicular to the substrate. Electrodeposition of a metal into the pores produces a hardmask which can be used with ion-milling to transfer the block co-polymer pattern onto a magnetic thin film.

Bi-enzyme sensor based on thick-film carbon electrode modified with electropolymerized tyramine

Bi-enzyme sensor based on thick-film epoxy-carbon electrode modified with polytyramine has been developed and examined for the determination of peroxidase substrates and cholinesterase inhibitors. Polytyramine was obtained on the electrode surface by repeated scanning of the potential from +600 to +1800 mV vs. Ag/AgCl in tyramine solution. The enzymes were immobilized in the polytyramine matrix by cross-linking with glutaraldehyde. The biosensor developed provides a reliable and inexpensive way for preliminary testing of common environmental pollutants with a single sensor in accordance with assumed toxic effect by the choice of appropriate substrate and measurement conditions. The bi-enzyme sensor makes it possible to determine substituted phenols and aromatic amines in the micromolar range of their concentrations and anticholinesterase pesticides with detection limits of 0.1 (Coumaphos) and 0.03 μmol l −1 (Chloropyrifos-methyl).

Generation and detection of pairing bosons : A new method to determine the mechanism of superconductivity in the oxides

We propose a new method to determine the coupling boson in the cuprate superconductors based on the generation and detection of the appropriate boson analogous to the experiments performed on the generation and detection of phonons by conventional BCS superconductors. The appropriate choice of substrate and junction detector will allow the unambiguous determination of the boson that is formed by the recombination of energy gap edge quasiparticles produced by excitations into the normal state of the cuprates.