Island Structure Research Articles

Weak Light-Stimulated Synaptic Hybrid Phototransistors Based on Islandlike Perovskite Films Prepared by Spin Coating.

An artificial synaptic device that can provide color discrimination, image storage, and image recognition is highly required to mimic the human vision for biological robots. All-inorganic halide perovskites have attracted extensive attention for the reason of their high stability and favorable photoelectric properties. In this study, a light-stimulated synaptic phototransistor based on a CsPbBr3/organic semiconductor hybrid film is reported. The fabricated CsPbBr3 film exhibits an island structure, which reduces the hysteresis effectively and at the same time achieves a high specific detectivity of up to 2 × 1015 Jones. The decay of the photocurrent can be delayed by changing the gate bias, which is essential for achieving high-performance light-stimulated synaptic devices. Due to the outstanding detectivity of the device, the obvious synaptic functions can be observed when triggered by a light signal with a power of 1.6 nW that is much weaker than previous most perovskite-based hybrid synaptic phototransistors under a low operating voltage of -1 V. The electrical power consumption of the device could be as low as 0.076 pJ when the power of light spike was 7.36 nW. Taking into account this characterization, with changing of light intensity or wavelength, the contrast of the image was enlarged, which can further promote the image recognition accuracy. More significantly, this CsPbBr3/TIPS hybrid film can be fabricated by facile and low-cost solution processes. This study indicates the great potential of solution-processed perovskite-based light-stimulated synapses for future artificial visual systems.

Study of Surface and Electrical Conductivity of Thin Metal Films of the Ni–Al System

The results of studies of thin Ni–Al films obtained by the resistive thermal evaporation method and having characteristic island sizes of 700–1000 nm with a film thickness of ~500 nm are described. A brief description of the method for producing a film using an installation for creating a high vacuum and subsequent film deposition is presented. The obtained film sample was studied with an optical microscope, a scanning probe microscope, and a Fourier analyzer. The kinetic characteristics of the film, its film, and the characteristic sizes of the islands have been established; regularities in the island structure of the films were sought, and its electrical conductivity has been determined.

Signatures of Jackiw-Rebbi resonance in the thermal conductance of topological Josephson junctions with magnetic islands

Josephson junctions in two-dimensional topological insulators with embedded magnetic domains can host a number of topological phases, in particular, Jackiw-Rebbi solitons and Majorana zero modes. These different non-trivial phases appear in such junctions for multiple-domain magnetic islands, showing a rich multi-gap structure. Features related to the interplay between superconductivity and magnetism in these systems cannot be easily discerned looking at behavior of the Andreev spectrum and the concomitant dc Josephson effect. Instead, the thermal conductance is very sensitive to the nature of the junction and the domain structure of the magnetic island. We present a detailed analysis of these properties in the case of a topological Josephson junction with a single and two-domain magnetic island. Configurations hosting soliton magnetic modes lead to a peculiar behavior of the thermal conductance relative to the thermal quantum, characterized by a negative slope as a function of the temperature, just above the superconducting critical temperature. At low temperatures, these junctions also show characteristic coherence patters in the behavior of the thermal conductance as function of the Josephson phase bias and the angle between the magnetizations of the domains.

Embossed topographic depolarisation maps of biological tissues with different morphological structures

Layered topographic maps of the depolarisation due to diffuse biological tissues are produced using a polarisation-holographic Mueller matrix method approach. Histological sections of myocardial tissue with a spatially structured optically anisotropic fibrillar network, and parenchymal liver tissue with a polycrystalline island structure are successfully mapped. The topography of the myocardium maps relates to the scattering multiplicity within the volume and the specific morphological structures of the biological crystallite networks. The overall depolarisation map is a convolution of the effects of these two factors. Parenchymal liver tissues behave broadly similarly, but the different biological structures present cause the degree of scattering multiplicity to increase more rapidly with increasing phase. Through statistical analysis, the dependences of the magnitudes of the first to fourth order statistical moments are determined. These moments characterise the changing distributions of the depolarisation values through the volume of biological tissues with different morphological structures. Parenchymal liver tissue depolarisation maps are characterised by larger mean and variance, and less skewness and kurtosis, compared to the distributions for the myocardium. This work demonstrates that a polarisation-holographic Mueller matrix method can be applied to the assessment of the 3D morphology of biological tissues, with applications in disease diagnosis.

Effect of geometric and magnetic boundary conditions on magnetic islands in 3D force-free ideal MHD equilibria

Three-dimensional boundary features and magnetic perturbations affect the magnetic topology of the force-free ideal MHD equilibria formed within a given volume. The use of the PSI-Tet 3D finite-element equilibrium code reveals the existence of magnetic islands inside such equilibria within boundaries with three-dimensional features in configurations that directly depend on the natures of those features. The nature and limits of the influence of such features are explored, as is the influence of flux boundary conditions to qualitatively identify the structure of magnetic islands in Taylor state equilibria with three-dimensional boundary conditions.

Structure and Diversity of the Demersal Fish Assemblages off Psara Island (Central Aegean Sea) Caught by Experimental Bottom Trawling

Data with high spatial resolution on the structure and diversity of marine assemblages are valuable for fisheries management and conservation planning but are seldom available. This study provides fisheries-independent, baseline information on the structure and diversity of the demersal fish assemblages of the continental shelf and upper slope off the island of Psara (Central Aegean Sea). Experimental bottom trawl hauls were conducted during 2009–2010, using identically designed trawls. All the fish in the catches were identified onboard, enumerated, and weighted to the nearest g. Species abundance and biomass were transformed to CPUE. Forty-seven taxa were identified in the catches. For 18 of the species caught no other fisheries-independent information on their abundances and distributions is available for the wider area. Among the Elasmobranchii species collected, Squalus acanthias, Dipturus oxyrinchus, and Raja clavata are species of conservation concern. Species composition was generally more similar to that reported for assemblages of the Cretan Sea and the South Aegean Sea than for assemblages of the North Aegean. The assemblages were structured with depth, a pattern that may be driven in part by the differences in benthic habitat between depth zones. No trends by depth in total numerical abundance and species diversity were identified, whereas the bathymetric change in taxonomic diversity was attributed to the depth distributions of certain species-rich orders and families. The frequency distribution of the trophic level of the species followed the broad-scale pattern that applies in the Mediterranean Sea.

Evolution of interfacial structure of the joints between a tungsten-copper composite and austenitic stainless steel

Joining of CuW70 composite and 0Cr18Ni9 stainless steel was successfully achieved at temperatures 1150 °C with durations from 15 to 90 min after adding a pure copper intermediate layer. Microstructure, phase composition and elemental distribution at the interfacial region were studied. The optimum joining interface with a dense microstructure was obtained at a joining temperature of 1150 °C with a duration of 60 min. Interdiffusion of atoms occurred at the interface between the tungsten-copper composite and stainless steel, resulting in formation of various compounds such as W0.6Cu0.4, Cu3.8Ni and Fe0.946Ni0.054. An iron chromium-rich layer was formed at the interface near the tungsten-copper composite side, and an island structure containing Cr, Cu, and Ni was formed near the stainless steel side.

Effect of DNA modifications on the transition between canonical and non-canonical DNA structures in CpG islands during senescence.

Patterns and levels of DNA modifications play important roles in senescence. Two major epigenetic modifications of DNA, 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC), target CpG sites. Importantly, CpG concentrated regions, known as CpG islands, contain GC-rich sequences, which have the potential to fold into non-canonical DNA structures such as i-motifs and G-quadruplexes. In this study, we investigated the effect of 5mC and 5hmC modifications on the transition between a duplex, and i-motif and G-quadruplexes. To examine the transition, we firstly investigated the stability and structure of the i-motif and G-quadruplexes, considering the molecular environment in senescent cells. Analyses of their stability showed that the modifications did not drastically affect the stability. However, noteworthily, the modification can weaken the (de)stabilisation effect on G-quadruplexes caused by cosolute(s) and cations. Circular dichroism analyses indicated that the surrounding environments, including the molecular crowding and the type of cations such as K+ and Na+, regulate the topology of G-quadruplexes, while neither 5mC nor 5hmC had a drastic effect. On the other hand, the modifications changed the transition between duplexes and quadruplexes. Unmodified DNA preferred to fold into quadruplexes, whereas DNA with 5mC and 5hmC preferred to fold into duplexes in the absence of PEG200; on the other hand, DNA with or without modifications tended to fold into i-motifs under crowded conditions. Furthermore, an investigation of quadruplexes forming sequences in CpG islands, which are hyper- or hypomethylated during senescence, followed by gene ontology enrichment analysis for each gene group classified by the presence of quadruplexes, showed a difference in function between genes with and without quadruplexes in the CpG region. These results indicate that it is important to consider the effects of patterns and levels of DNA modifications on the transition between canonical and non-canonical DNA structures to understand gene regulation by epigenetic modification during senescence.

Topological engineering of two-dimensional ionic liquid islands for high structural stability and CO2 adsorption selectivity.

Ionic liquids (ILs) as green solvents and catalysts are highly attractive in the field of chemistry and chemical engineering. Their interfacial assembly structure and function are still far less well understood. Herein, we use coupling first-principles and molecular dynamics simulations to resolve the structure, properties, and function of ILs deposited on the graphite surface. Four different subunits driven by hydrogen bonds are identified first, and can assemble into close-packed and sparsely arranged annular 2D IL islands (2DIIs). Meanwhile, we found that the formation energy and HOMO–LUMO gap decrease exponentially as the island size increases via simulating a series of 2DIIs with different topological features. However, once the size is beyond the critical value, both the structural stability and electrical structure converge. Furthermore, the island edges are found to be dominant adsorption sites for CO2 and better than other pure metal surfaces, showing an ultrahigh adsorption selectivity (up to 99.7%) for CO2 compared with CH4, CO, or N2. Such quantitative structure–function relations of 2DIIs are meaningful for engineering ILs to efficiently promote their applications, such as the capture and conversion of CO2.

Urban climate and registration of thermal anomalies of territories using satellite imagery

This paper describes a simplified method of mapping of the ur-ban environment surface to obtain a map of the thermal anomalies distribu-tion and study the structure of the urban heat island. Those maps allow evaluating or planning the urban microclimate optimization methods and studying the effect of land cover type on the site temperature. The article discusses the processing of five satellite images for the summer and winter from 2002 to 2019. We propose a simpler and more automated processing of thermal images for Landsat 7 and Landsat 8. The stages of automatic atmospheric correction according to the DOS1 method and calculation of the emissivity with surface classification are considered. Image processing was carried out in the QGIS software package using the Semiautomatic Classification Plugin extension. As a result, thermal anomalies in Chelya-binsk were localized and a comparison of the thermal map for the specific region before and after urbanization was made.

Oil/water separation membranes with a fluorine island structure for stable high flux

Membranes with fluorine island structures consist of discrete low surface energy (LSE) domains at sub-microscale and consecutive hydrophilic domains. The former can effectively control oil fouling while the latter can provide high basic flux.

Туннельный ток между структурными элементами тонких графен/нанотрубных пленок

Based on the constructed atomistic models of graphene/nanotube films with different numbers of nanotubes in supercells, we carried out in silico studies of the regularities of the nonuniform density distribution, which determine the presence of an island structure in such films. As a result of quantum molecular dynamics modeling, it is found that thin tubes of subnanometer diameter are enveloped in graphene sheets, which makes them energetically stable and stable. We also studied tunneling contacts between individual film fragments that are not covalently bound, in particular, between graphene sheets with different topologies of contacting zigzag and armchair edges, depending on the distance between them, and between tubes of different chiralities, including (6,3), (4,4), (6,5), (12,6) and (16,0). It is found that the tunnel contacts of tubes with a semiconductor type of conductivity are characterized by the presence of voltage intervals with a negative differential resistance in the I – V characteristic. Such voltage intervals are not observed at all for tubes with a metallic character of conductivity. The new knowledge obtained is important for assessing the electrical conductivity of such films, two-thirds of which are semiconductor tubes.

External RMP effect on locked-mode-like instability in helical plasmas

The slowing-down mechanism of the locked-mode-like instabilities with and without an island structure is investigated through the effects of an external RMP (resonant magnetic perturbation) on the instabilities. For both instabilities, the slowing-down duration decreases with the increase in the external RMP, and the RMP dependence is consistent with the braking model of the j × B force due to the interaction between the instabilities and the external RMP. Moreover, the relationship between the amplitude and the frequency of both locked-mode-like instabilities during the slowing down is consistent with the force balance model between the j × B force due to the external RMP and a viscous force. These results suggest that the slowing down of both locked-mode-like instabilities with finite external RMP occurs due to the j × B force driven by the external RMP.

Atomically Resolved Structure of Monolayer Ceria Island on Pt(111)

Ceria supported on platinum substrate is one of the most extensively studied inverse model catalysts. Unraveling the atomic structure of the ceria film is of great importance in helping understand ...

Analytical Model and Optimization for SiC Floating Island Structure

Conventional power semiconductor devices suffer from a well-known performance limit. Floating Island (FI) structure can break the limit by inserting multiple oppositely doped islands into the drift layer and is suitable for silicon carbide (SiC) devices. In this article, the FI devices are classified into two distinct types according to the doping level of the islands, which are referred to as field-stop FI (FSFI) with highly doped island and fully depleted FI (FDFI) with medium-doped island. The theoretical limits for both types are revealed through 1-D modeling. The FDFI is found to be endowed with 12% lower specific ON-resistance than FSFI. To facilitate the comprehensive design of FDFI devices, 2-D analytical models for both conducting state and blocking state are established and verified by numeric simulation. By virtue of the 2-D models, charge balance effect of FDFI is illuminated, and parametric optimization for 2-, 4-, and 6-kV rated devices is performed. The optimal designs are presented and also simulated numerically. The results from models and numeric simulations show good agreement. The analytical models in this article are proved to be rather effective and can be helpful in revealing the mechanism of FI devices as well as in optimizing FI devices.

Investigation of monolayer and submonolayer films using X-ray photoelectron spectroscopy

A method of layer thickness determination by X-ray photoelectron spectroscopy (XPS) is analyzed. Angle-resolved XPS spectra measured for three samples (gold films of different thicknesses located on top of silicon substrates) have been interpreted by the straight line approximation (SLA) model. Two configurations of films were considered: (i) a flat surface of a semi-infinite layer (substrate) is covered with a flat homogeneous layer, (ii) coating constitutes an island (cluster) structure. It is shown that the simplest model of an island coating makes it possible to qualitatively explain the effect of decreasing of the effective average coating thickness observed in the angle-resolved XPS experiments.

A hybrid dewetting approach to generate highly sensitive plasmonic silver nanoparticles with a narrow size distribution

Laser dewetting is a simple and efficient method for transforming a metal thin film into nanoparticles. However, the particles obtained via laser dewetting typically exhibit a wide size distribution. This study shows that a combination of thermal and laser dewetting processes can be used to generate more uniform metal nanoparticles. A 10-nm-thick Ag film deposited on glass was irradiated by an Nd:YAG laser pulse to produce nanoparticles with sizes in the range of 35–145 nm. When the film was thermally annealed at 250 °C in an Ar atmosphere before laser irradiation, Ag nanoparticles with a much narrower size distribution were obtained (mean size = 48 nm and standard deviation = 10.5 nm), which was attributed to the island structure formed by the pre-annealing step. X-ray photoelectron spectroscopy confirmed the absence of particle oxidation. An important feature associated with this hybrid dewetting approach was that the obtained Ag nanoparticles showed a strong single plasmonic resonance peak owing to their narrow size distribution. As a plasmonic sensing platform, they exhibited much enhanced refractive index sensitivity and figure of merit than the particles produced via laser dewetting.

On the fractal structure of soil moisture fields

We study the spatial structure of soil moisture fields within savanna ecosystems, whose persistence is vital because it is the driver of the entire ecological structure and function. These include changes in the physical and biogeochemical conditions of the landscape, affecting vegetation state, soil composition, water fluxes, and solar radiation. We focus on computations of the probabilistic structure of islands of soil moisture, known empirically to be related to that of tree clusters, defined as crossing properties of simulated soil moisture fields. Rainfall is modelled via Cox-Isham space-time fields endowed with characteristic scales. Results show that clusters of soil moisture islands are characterized by robust scale-free structures in the region of a phase transition whose order parameter depends on mean soil moisture. Signatures of this fractal structure are well-defined power laws of size distributions of soil moisture clusters; their perimeters-vs-area relations; variance-vs- area of the fields. These characteristics allow for the estimation of the fractal dimension of the field, and its Hurst coefficient. From the general covariance equation of a fractal field, spatial simulations are possible because its mean and variance are known from the probabilistic structure of soil moisture at a point. Our results identify the statistics of hotspots of microbial activity deduced from proper moisture islands, unattainable otherwise, and thus may guide the design of field and remote observations. The critical order parameter characterizing the phase transition establishes where the fractal structure of soil moisture fields exists as a function of the climatic drivers, and the thresholds reflecting where vegetation survives in the field. An example of application of the phase transition diagram presented here is carried out with reference to the Nylsvley savanna in South Africa.

Control of amplitude death by coupling range in a network of fractional-order oscillators

We investigate the oscillating dynamics in a ring of network of nonlocally delay-coupled fractional-order Stuart-Landau oscillators. It is concluded that with the increasing of coupling range, the structures of death islands go from richness to simplistic, nevertheless, the area of amplitude death (AD) state is expanded along coupling delay and coupling strength directions. The increased coupling range can prompt the coupled systems with low frequency to occur AD. When system size varies, the area of death islands changes periodically, and the linear function relationship between periodic length and coupling range can be deduced. Thus, one can modulate the oscillating dynamics by adjusting the relationship between coupling range and system size. Furthermore, the results of numerical simulations are consistent with theoretical analysis.

Atomic layer deposition ZnO on porous Al2O3 nanofibers film

The paper presents the results of the formation and study of the morphological and structural characteristics of the mesoporous ZnO / Al2O3 nanofibers film (ZANF). The deposition of a ZnO layer on Al2O3 nanofibers film (ANF) ∼ 1 µm thick was carried out by the method of atomic layer deposition. The morphology of the mesoporous composite layer ZnO / Al2O3 (ZANF) has been studied by scanning and transmission electron microscopy. It is shown that in the process of atomic layer deposition, the ZnO layer grows according to the Stranski-Krastanov mechanism. A ZnO layer less than 5 nm thick gives an island structure in which Al2O3 nanofibers are uniformly coated with ZnO particles, an increase in the ZnO layer thickness to 15 nm demonstrates a continuous coating of Al2O3 nanofibers. The system has a core-shell structure. The resulting composite structures are promising for applications in photocatalysis and gas sensing.