Band Configuration Research Articles

High temperature (300 °C) ALD grown Al2O3 on hydrogen terminated diamond: Band offset and electrical properties of the MOSFETs

Hydrogen-terminated diamond (H-diamond) metal-oxide-semiconductor field effect transistors (MOSFETs) were fabricated on a polycrystalline diamond substrate. The device has a gate length of 2 μm and uses Al2O3 grown by atomic layer deposition at 300 °C as a gate dielectric and passivation layer. The Al2O3/H-diamond interfacial band configuration was investigated by X-ray photoelectron spectroscopy, and a large valence band offset (3.28 eV) that is very suitable for p-channel H-diamond FETs was observed. Meanwhile, the measured O/Al ratio hints that there are Oi or VAl defects in the Al2O3 dielectric, which can work as an acceptorlike transfer doping material on a H-diamond surface. The device delivers the maximum saturation drain current of over 200 mA/mm, which is the highest for 2-μm H-diamond MOSFETs with the gate dielectric or passivation layer grown at 300 °C or higher temperature. The ultrahigh on/off ratio of 1010 and ultralow gate leakage current of below 10−12 A have been achieved. The high device performance is ascribed to the ultrahigh carrier density, good interface characteristics, and device processes. In addition, the transient drain current response of the device can follow the gate voltage switching on/off pulse at a frequency from 100 kHz to 1 MHz, which indicates the potential of the H-diamond FETs in power switch applications.

Isopropanol-assisted synthesis of highly stable MAPbBr3/p-g-C3N4 intergrowth composite photocatalysts and their interfacial charge carrier dynamics.

Two phase photocatalysts can be intergrown with each other, resulting in superior photocatalytic properties. Herein, methylamine lead bromide (MAPbBr3) wrapped/entrapped protonated graphitic carbon nitride (p-g-C3N4) intergrowth microcrystals were fabricated by mixing a pervoskite precursor with p-g-C3N4 colloidal sol. A highly stable isopropanol (IPA) solvent based photocatalytic system for dye degradation was demonstrated. The composite with an optimal p-g-C3N4 mass percentage of 3.3 wt% (denoted as MAPbBr3/p-g-C3N4-1.0 mg) exhibited the highest photocatalytic degradation of malachite green (99.8%) within 10 min under visible light, which was 5.3-fold and 16-fold greater than that exhibited by its constituents separately. The strong chemical interaction and fundamental photophysical processes in MAPbBr3/p-g-C3N4 were systematically evaluated by spectroscopic and electrochemical techniques, confirming the effective separation of photogenerated electron–hole pairs and faster interfacial charge transfer behavior. Furthermore, active superoxide radicals (O2˙−) played a vital role in the catalytic reaction, because of the significant photoinduced electron transfer rate (ket) in the inverted type-I core/shell MAPbBr3/p-g-C3N4 band configuration structure. In addition, MAPbBr3/p-g-C3N4 has good cycling stability for 10 cycles and versatility for other cationic (RhB) and anionic (MO) dye pollutants, indicating the great potential for solar energy conversion into chemical energy.

A core@dual-shell nanorod array with a cascading band configuration for enhanced photocatalytic properties and anti-photocorrosion

ZnO–CdS–NiOx core@dual-shell nanorod arrays with cascade electron and hole transfer between them for high-performance photocatalytic H2 production.

Microphone position and noise exposure assessment of building façades

The prevention or reduction of the exposure of the population to environmental noise is the fundamental objective of the European Noise Directive (END). To this end, strategic noise maps are considered as the basic tool and on-site measurements play an important role in its successful implementation. In this regard, the ISO 1996 standards are the reference for the measurement and assessment of environmental noise, but their application may be complex in many cases. It is therefore necessary to find urban scenarios in which the effects of the placement of the measuring equipment with respect to the façade on noise exposure levels can be analysed.In this study, an educational building was selected for an analysis of the differences in the weekly sound level from road traffic between a microphone flush-mounted on a plate at the façade and another placed between 0.5 and 2.0 m from it. The recommendations in Annex B of ISO 1996-2 were followed in the placement of the microphones. A broadband analysis shows that similar results were found for the four distances analysed, but that variations of up to 0.6 dBA above the reference value arose. An analogous study using frequency octave bands shows differences higher than 2 dB between the measured configurations for bands under 250 Hz. Based on the distance range given in ISO 1996-2 for the position of a microphone in front of a reflecting surface, the results suggest that the most appropriate option for accurately assessing the sound level incident on the façade of buildings is to place the microphone at a distance of 2 m if the guidelines of the ISO 1996-2 standard can be met.

Highly deformed bands in Nd nuclei: New results and consistent interpretation within the cranked Nilsson-Strutinsky formalism

Three new highly-deformed (HD) bands are identified in Nd136 and the highly deformed band of Nd137 is extended at higher spin by four transitions, revealing a band crossing associated with the occupation of the second νi13/2 intruder orbital. Extended cranked Nilsson-Strutinsky calculations are performed for all HD bands observed in Nd134, Nd136, and Nd137, achieving for the first time a consistent interpretation of all HD bands in the Nd nuclei. The new interpretation has significant consequences, like the change of parity of the yrast HD bands of Nd134 and Nd136, and the involvement of two negative-parity neutron intruder orbitals in the configurations of most HD bands. The present experimental results and their theoretical interpretation represent an important step forward in the understanding of the second-minimum excitations in the Nd nuclei.

Construction of two-dimensionally relative p-n heterojunction for efficient photocatalytic redox reactions under visible light

Precisely modulating the interfacial contact of heterojunction photocatalysts and regulating the spatial transfer of photoexcited charge carriers are the core factors to promote the photocatalytic efficiency for energy and environmental applications. Herein, novel 2D/2D relative p-n heterojunction CdS/g-C3N4 with Z-scheme (or S-scheme) was fabricated by in-situ growing ultrasmall 2D CdS nanoflakes on the surface of 2D g-C3N4 nanosheets. The optimized 2D/2D heterojunction structure with proper band configuration and suitable heterojunction interface can improve photoexcited charge carriers separation spatially and transfer to the ideal reaction sites. Therefore, 2D/2D CdS/g-C3N4 composites show high photocatalytic reduction (H2 evolution) and oxidation (selective oxidation of 5-hydroxymethylfurfural into 2,5-diformylfuran) activities, which are about 26.8 times and 3.51 times higher than individual g-C3N4 and are about 4.4 times and 2.39 times higher than individual CdS, respectively. The mechanisms including direction and inner impetus of the photoexcited charge separation and transfer in the composite photocatalyst are proposed and verified by experimental and computational analyses. This investigation highlights the promising scope to intelligently regulate the spatial separation and transfer of photoexcited charge carriers and rationally construct new relative p-n junction or Z-scheme photocatalysts for energy and environmental applications.

Influence of wire configuration on resistance to fragment distraction of tension bands placed in a greater trochanteric osteotomy model.

To determine the influence of wiring configurations on initial tension and resistance to tensile loads in tension band constructs without the contributions of Kirschner-wire stabilization. Experimental study. A solid brass femur model manufactured on the basis of computed tomography of a normal right femur of a 30-kg dog modified by transection of the greater trochanter and placement of two pins that did not cross the simulated osteotomy. Four tension band configurations were applied to the metal trochanteric osteotomy model: figure-of-eight with one twist (OT), figure-of-eight with two twists (TT), dual interlocking single loop, and double loop (DL). Configurations were tested under both monotonic loading (n = 8 per configuration) and incremental cyclic loading (n = 8 per configuration). Initial tension after tying, residual tension remaining after each cycle, and failure load at 2 mm of displacement (considered equivalent to clinical failure) were compared between configurations. The initial tension and the load to 2 mm of displacement were lower for OT wires compared with TT wires. The DL was the strongest and most stable configuration, generating 2.3 to 3.5 times greater initial tension, maintaining a greater percentage of residual tension under incremental cyclic loads, and resisting 2.0 to 2.4 times greater load before failure at 2 mm. Failure load was highly correlated with initial tension. Wire configurations reaching greater initial tension, such as the DL, allowed constructs to resist higher tensile loads. Wire configurations allowing higher initial tension may be warranted when tension bands are expected to sustain high tensile loads.

Comparative analysis of index and chemometric techniques-based assessment of leaf area index (LAI) in wheat through field spectroradiometer, Landsat-8, Sentinel-2 and Hyperion bands

Successful retrieval of leaf area index (LAI) from hyperspectral remote sensing relies on the proper selection of indices or multivariate models. The objectives of the research work were to identify best vegetation index and multivariate model based on canopy reflectance and LAI measured at different growth stages of wheat. Comparison of existing indices revealed optimized soil-adjusted vegetation index (OSAVI) as the best index based on R2 of calibration, validation and root mean square error of validation. Proposed ratio index (RI; R670, R845) and normalized difference index (NDI; R670, R845) provided comparable performance with the existing vegetation indices (R2 = 0.65 and 0.62 for RI and NDI, respectively, during validation). Among the multivariate models, partial least squares regression (PLSR) model with Hyperion band configuration performed the best during validation (R2 = 0.80 and RMSE = 0.58 m2 m−2). Our results manifested the opportunities for developing biophysical products based on satellite sensors.

Facile solid-state synthesis for producing molybdenum and tungsten co-doped monoclinic BiVO4 as the photocatalyst for photoelectrochemical water oxidation

BiVO4 has been widely applied as photocatalysts for water oxidation, owing to preferable band configuration and small band gap for absorbing wide range of light. Synthesizing BiVO4 is usually based on wet routes, which are more complex and require extra steps for separating photocatalysts from solutions. A novel solid-state synthesis is firstly proposed in this study to efficiently synthesize BiVO4 by simply mixing bismuth and vanadium salts without other mediums and directly annealing the mixture at 450°C. Heteroatom-doping of BiVO4 is also achieved by annealing the mixture of W and Mo salts along with bismuth and vanadium precursors to increase the carrier concentration and accelerating the charge transfer. The W and Mo co-doped BiVO4 electrode with the W:Mo ratio of 1:1 shows the highest photocurrent density of 0.21 mA/cm2 at 1.23 V versus reversible hydrogen electrode and the smallest onset potential of 0.686 V versus reversible hydrogen electrode under air mass 1.5 solar illumination. This study successfully realizes the efficient fabrication of BiVO4 and the incorporation of W and Mo dopants using the solid-state synthesis. Applying this manner cannot only reduce the synthesis time but also provide more precise control of the element composition. Further developments of the co-catalyst/photocatalyst system are expected to be realized by applying this novel solid-state synthesis.

Development of a 2D digital Coincidence Doppler Broadening Spectrometer

A 2D digital spectrometer for coincidence measurement of Doppler broadening of positron annihilation radiation is developed and tested. The spectrometer is based on a 14-bit waveform digitizer which gives the possibility of fast and direct sampling of the preamplifier signals of the HPGe detectors and preserves the information required by the physics of Doppler broadening spectroscopy. Some features of the digital spectrometer are compared with its analog counterpart. Superior energy resolution, better peak symmetry, effective elimination of ballistic deficit and better stabilization of peak position are the advantages of the digital spectrometer. The performance of the digital spectrometer to support the CDBS experiment is tested by investigation on the electronic structure of some elements at 1st series of transition metals. The results show that the spectrometer is sensitive enough to distinguish the electronic structure of 3d metals differing a little in their valance band configuration.

Fast and slow interface traps in transparent NiO gated AlGaN/GaN heterostructure field-effect transistors

In the present study, the reliability of transparent NiO gated AlGaN/GaN heterostructure field-effect transistors have been investigated. Compared with the TiN Schottky gated device, the p-NiO electrode can suppress the gate leakage and shift the threshold voltage positively. Pulse-mode and temperature-dependent current-voltage measurements demonstrate that both kinds of devices present good stability. The frequency-dependent conductance measurement confirms that only fast trap is detected for the TiN gated device while both fast and slow traps for the NiO gated one. The slow trap is ascribed to the hole trapping in the type-II staggered band configuration between NiO and AlGaN/GaN, which is also confirmed from the obvious threshold voltage instability in high frequency loop scan curves.

Ensemble-based topological entropy calculation (E-tec).

Topological entropy measures the number of distinguishable orbits in a dynamical system, thereby quantifying the complexity of chaotic dynamics. One approach to computing topological entropy in a two-dimensional space is to analyze the collective motion of an ensemble of system trajectories taking into account how trajectories "braid" around one another. In this spirit, we introduce the Ensemble-based Topological Entropy Calculation, or E-tec, a method to derive a lower-bound on topological entropy of two-dimensional systems by considering the evolution of a "rubber band" (piece-wise linear curve) wrapped around the data points and evolving with their trajectories. The topological entropy is bounded below by the exponential growth rate of this band. We use tools from computational geometry to track the evolution of the rubber band as data points strike and deform it. Because we maintain information about the configuration of trajectories with respect to one another, updating the band configuration is performed locally, which allows E-tec to be more computationally efficient than some competing methods. In this work, we validate and illustrate many features of E-tec on a chaotic lid-driven cavity flow. In particular, we demonstrate convergence of E-tec's approximation with respect to both the number of trajectories (ensemble size) and the duration of trajectories in time.

Dynamic interaction of multiple shear bands

A mechanical model for waves impinging different configurations of multiple shear bands already formed in a ductile material, allows to analyze the ways in which dynamic interactions promote failure. It is shown that the presence of more than one shear band may lead to resonance and correspondent growth of a shear band or, conversely, to its annihilation. At the same time, multiple scattering may bring about focusing or, conversely, shielding from waves. The proposed mechanical modelling, represents the only way to analyze the fine micromechanisms governing material collapse, and discloses the complex interplay between dynamics and shear band growth or arrest.

Environmental Conditions Associated with Observed Snowband Structures within Northeast U.S. Winter Storms

AbstractNortheast U.S. winter storms commonly exhibit multiple meso-β-scale (L < 200 km) bands of enhanced radar reflectivity and precipitation. We use radar observations, upper-air soundings, and reanalyses from 108 cases of cool season (October–April) storms from 1996 to 2016 that occurred within the coastal corridor from Delaware to Maine to identify and assess various banding structures and environments. Banding can occur in several configurations among storms, and banding characteristics can differ at different times within the same storm. We classified 6-h storm periods as containing long (>200 km) single bands, single bands co-occurring with sets of mesoscale multibands, multibands only, and radar echoes without any bands using a combination of automated and manual methods. Use of radar reflectivity data at 0.5-dB precision and a variable rather than a fixed threshold showed that the occurrence of long single bands without any mesoscale multibands was rare, occurring in only 5 of 113 6-h periods. The most frequently occurring band configuration (55%) was concurrent single bands and multibands, which usually were present in the northwest quadrant of mature cyclones. Sets of multibands without a nearby single band usually occurred in the northeast quadrant of a cyclone poleward of weak midlevel forcing along a warm front. Overall, mesoscale single and multibands more commonly occurred after the cyclone occluded than in the developing stages. Multibands occurred in a wide range of frontogenesis and moist potential vorticity environments.

Carbon-Dot-Based Heterojunction for Engineering Band-Edge Position and Photocatalytic Performance.

A photocatalytic reaction is always governed by energy band configuration of the catalyst, but its modulation is challenging. Here, the adjustment of band-edge positions of Ag3 PO4 through fluorescent carbon dots is reported for the first time. Both Ag3 PO4 and carbon dots which keep the similar sizes constitute a heterojunction. Such heterostructure not only promotes visible light absorption, photogenerated charge separation, and transfer, but it also transforms photocatalytic activity of Ag3 PO4 from photooxidation to photoreduction due to the huge changes of band-edge positions. In addition, the heterojunction structure of carbon dots and Ag3 PO4 exhibits unique temperature-responsive photocatalytic activities and higher photocatalytic stability than the pure Ag3 PO4 . According to the contrast experiments and related characterizations, the possible mechanism of photocatalytic reaction is proposed. Therefore, this work offers an alternative route for adjusting energy band positions or tuning photocatalytic performance as well as for preparing novel carbon-dot-based heterostructure.

Automatic method to monitor floating macroalgae blooms based on multilayer perceptron: case study of Yellow Sea using GOCI images.

Timely and accurate information about floating macroalgae blooms (MAB), including their distribution, movement, and duration, is crucial in order for local government and residents to grasp the whole picture, and then plan effectively to restrain economic damage. Plenty of threshold-based index methods have been developed to detect surface algae pixels in various ocean color data with different manners; however, these methods cannot be used for every satellite sensor because of the spectral band configuration. Also, these traditional methods generally require other reliable indicators, and even visual inspection, in order to achieve an acceptable mapping of MAB that appears under diverse environmental conditions (cloud, aerosol, and sun glint). To overcome these drawbacks, a machine learning algorithm named Multi-Layer Perceptron (MLP) was used in this paper to establish a novel automatic method to monitor MAB continuously in the Yellow Sea, using Geostationary Ocean Color Imager (GOCI) imagery. The method consists of two MLP models, which consider both spectral and spatial features of Rayleigh-corrected reflectance (Rrc) maps. Accuracy assessment and performance comparison showed that the proposed method has the capability to provide prediction maps of MAB with high accuracy (F1-score approaching 90% or more), and with more robustness than the traditional methods. Most importantly, the model is practically adaptable for other ocean color instruments. This allows customized models to be built and used for monitoring MAB in any regional areas. With the development of machine learning models, long-term mapping of MAB in global ocean is conducive to promoting the associated studies.

Triple Planar Heterojunction of SnO2/WO3/BiVO4 with Enhanced Photoelectrochemical Performance under Front Illumination

The performance of a BiVO4 photoanode is limited by poor charge transport, especially under front side illumination. Heterojunction of different metal oxides with staggered band configuration is a promising route, as it facilitates charge separation/transport and thereby improves photoactivity. We report a ternary planar heterojunction photoanode with enhanced photoactivity under front side illumination. SnO2/WO3/BiVO4 films were fabricated through electron beam deposition and subsequent wet chemical method. Remarkably high external quantum efficiency of ~80% during back side and ~90% upon front side illumination at a wavelength of 400 nm has been witnessed for SnO2/WO3/BiVO4 at 1.23 V vs. reversible hydrogen electrode (RHE). The intimate contact between the heterojunction films enabled efficient charge separation at the interface and promoted electron transport. This work provides a new paradigm for designing triple heterojunction to improve photoactivity, particularly under front illumination, which would be beneficial for the development of tandem devices.

Tailoring morphology, enhancing magnetization and photocatalytic activity via Cr doping in Bi25FeO40

The Cr doped Bi25FeO40 (Bi25Fe1-xCrxO40, x = 0–0.5) powders were synthesized by a simple hydrothermal process. Effects of the Cr dopant on the crystalline structure, morphologies, optical properties and photocatalytic activities of Bi25FeO40 have been investigated. With the increase of Cr concentration, the shape of particles occurs to transformation from regular microcubes (x = 0) to microspheres (x = 0.3) owing to the lattice expansion. The Fe-O and Cr-O bonds can be coexistence and Fe3+ cation could be well replaced by the Cr3+ without any secondary phases for the Bi25Fe1-xCrxO40 (x ≤ 0.3). Due to the enhanced exchange interaction between Fe2p-O-Cr2p, the decreased optical band gaps and enhancement of magnetization were found. The photo-degradation efficiency for 120 min was significantly enhanced from 43.8% (pure Bi25FeO40) to 92.5% (Bi25Fe0.75Cr0.25O40), which is nearly 2.1-fold higher than that of undoped Bi25FeO40 powders, attributing to cooperative effects of the different morphologies and energy band configurations.

Characterizing the Top Coal Cavability with Hard Stone Band(s): Insights from Laboratory Physical Modeling

One of the most challenging problems in longwall top coal caving is the top coal cavability. Stone bands, which are usually found in thick coal seams, have shown adverse effects on top coal fragmentation and cavability. Understanding the characteristics of the stone band caving process is a primary step in evaluating top coal cavability in such conditions. In this study, a series of laboratory tests was implemented to find an appropriate construction material that can truly display the whole caving process of top coal. On this basis, two large-scale physical models comprising sand, gypsum, and mica complying with relevant similarity rules were constructed to investigate top coal cavability with hard stone band(s) according to two real cases. Based on observations from physical models, it is concluded that hard stone band(s) embedded in top coal usually produce poor fragmentation and cavability of the top coal, which is also affected by the strength, thickness, and location of the stone band(s). According to its relation with the caved goaf and the top coal beneath it, the rock beam consisting of the stone band and the above top coal can produce three profiles before it caves, to which suitable fragmenting and caving characteristics were carefully discussed. Summarizing the stone band beam into different profiles enables the characterization of top coal cavability for various configurations of stone bands in top coal. The results also verified that the fragment size of the top coal can be used as an integrated parameter that reflects all potential factors that impact top coal recovery to evaluate its cavability.

Cloud/shadow detection based on spectral indices for multi/hyperspectral optical remote sensing imagery

Cloud and cloud shadow detection is a necessary preprocessing step for optical remote sensing applications because of the huge negative influence cloud and cloud shadow can have on data analysis. However, most of the existing cloud/shadow detection methods are designed based on specific band configurations of certain sensors, and their working mechanisms are relatively complex and computationally complicated, which limits their application. In view of this, in this paper, a unified cloud/shadow detection algorithm based on spectral indices (CSD-SI) is proposed for most of the widely used multi/hyperspectral optical remote sensing sensors with both visible and infrared spectral channels. On the one hand, the cloud index (CI) and cloud shadow index (CSI) are proposed to indicate the potential clouds and cloud shadows based on their physical reflective characteristics. In addition, considering the spatial coexistence of cloud and cloud shadow, a spatial matching strategy is utilized to remove the pseudo cloud shadows. The effectiveness of the proposed CSD-SI algorithm is demonstrated on eight different types of widely used multi/hyperspectral optical sensors, with different spectral and spatial resolution levels. Overall, in the experiments undertaken in this study, CSD-SI achieved a mean overall accuracy of 98.52% for cloud, with a mean producer’s accuracy of 93.13% and a mean user’s accuracy of 98.13%. For cloud shadow, CSD-SI achieved a means producer’s accuracy of 84.33% and a mean user’s accuracy of 89.12%. The experimental results show that the proposed CSD-SI method based on spectral indices can obtain a comparable cloud/shadow detection performance to that of the other state-of-the-art methods.