Types Of Heterostructures Research Articles

Impurity affected transport properties of quantum well heterostructures with electronic and high-κ dielectric quantum screening

The effect of electronic and high-κ dielectric quantum screening (ES and DS) on the impurity-limited electron transport properties of quantum well/high-κ dielectric barrier type heterostructures with two-dimensional electron gas (2DEG) is studied theoretically. Characteristic of these heterosystems the 2D compound forms of screened impurity potential are employed for the first time. In the framework of 2D Debye-Hückel potential form an electron momentum relaxation time (τ) expression depending on the impurity 2D screening radius is obtained analytically. A numerical analysis of τ is carried out for the realistic HfO/InSb/HfO2QW heterostructure taking account both the finite mismatch of the energy bands at the heterointerface and the energy band non-parabolicity of InSb. The contributions of screened potential compound 2D forms to τ are established depending on QW width. A significant suppression of the scattering rate τ−1 (by an order of magnitude) is received with accounting of ES + DS combined effect.

Optically Active Defect Engineering via Plasma Treatment in a MIS‐Type 2D Heterostructure

AbstractAt the interface of 2D heterostructures, the presence of defects and their manipulation play a crucial role in the interfacial charge transfer behavior, further influencing the device functionality and performance. In this study, the impact of deliberately introduced photo‐active defects in the h‐BN layer on the interfacial charge transfer and photoresponse performance of a metal‐insulator‐semiconductor type heterostructure device is explored. The formation and concentration of defects are qualitatively controlled using an inductive coupled plasma treatment method, as evidenced by enhanced h‐BN defect emission and more efficient optically induced doping of graphene at the graphene/h‐BN interface. Besides, the use of the h‐BN layer between graphene and WS2 not only suppresses charge carriers in the dark state, but also promotes the separation of photo‐generated electron‐hole pairs and interfacial charge transfer due to the existence of defect levels, leading to orders of magnitude improvement in the light on/off ratio and self‐driving performance of the heterostructure photodetector. This strategy of controlling defect states in the insulating layer provides a new approach to optimize the charge transfer processes at the 2D interfaces, so as to expand its potential applications in the fields of electronic and optoelectronic devices.

Van der Waals heterostructures of AlAs and InSe: Stacking-dependent Raman spectra and electric field dependence of electronic properties

In the present work, the electronic and vibrational properties of a van der Waals type heterostructure, composed of single layers of AlAs and InSe, are investigated using density functional theory (DFT)-based first-principles calculations. Vibrational analyses reveal that dynamically stable single layers of AlAs and InSe form van der Waals type heterostructure which is shown to exhibit stacking-dependent Raman spectra by means of the frequency shifts. According to our findings, a type-II band alignment with a direct band gap of 1.84 eV is found in the ground state stacking of AlAs/InSe vertical heterostructure, in contrast to the indirect band gap behaviors of each individual layer. Moreover, the application of an external vertical electric field shows that the both band alignment type and the electronic behavior of the heterostructure can be tuned. The heterostructure is found to exhibit direct to indirect band gap transition under negative electric field as well as a transition from type-II to type-I heterojunction under negative fields up to 0.3 V/Å. The stronger fields along the same direction results in overlapping of valence states of each layer and lead to a non-linear change of the energy band gap. Overall, the predicted van der Waals type heterobilayer of InSe and AlAs with stacking-dependent vibrational features and well-controlled electronic properties under external field is shown to be potential candidate for optical and optoelectronic applications.

Vapor-Phase-Deposited Ag/Ir and Ag/Au Film Heterostructures for Implant Materials: Cytotoxic, Antibacterial and Histological Studies.

Using gas-phase deposition (Physical Vapor Deposition (PVD) and Metal Organic Chemical Vapor Deposition (MOCVD)) methods, modern implant samples (Ti alloy and CFR-PEEK polymer, 30% carbon fiber) were functionalized with film heterostructures consisting of an iridium or gold sublayer, on the surface of which an antibacterial component (silver) was deposited: Ag/Ir(Au)/Ti(CFR-PEEK). The biocidal effect of the heterostructures was investigated, the effect of the surface relief of the carrier and the metal sublayer on antibacterial activity was established, and the dynamics of silver dissolution was evaluated. It has been shown that the activity of Ag/Ir heterostructures was due to high Ag+ release rates, which led to rapid (2-4 h) inhibition of P. aeruginosa growth. In the case of Ag/Au type heterostructures, the inhibition of the growth of P. aeruginosa and S. aureus occurred more slowly (from 6 h), and the antibacterial activity appeared to be due to the contribution of two agents (Ag+ and Au+ ions). It was found, according to the in vitro cytotoxicity study, that heterostructures did not exhibit toxic effects (cell viability > 95-98%). An in vivo biocompatibility assessment based on the results of a morphohistological study showed that after implantation for a period of 30 days, the samples were characterized by the presence of a thin fibrous capsule without volume thickening and signs of inflammation.

Innovations in p-n type heterostructure composite materials (La2O3/CeO2) for environmental contamination remediation: synthesis, characterization, and performance assessment

Innovations in p-n type heterostructure composite materials (La2O3/CeO2) for environmental contamination remediation: synthesis, characterization, and performance assessment

Оптические свойства ван-дер-ваальсовых гетероструктур на основе 2D-монослоев борофена, нитрида галлия и оксида цинка

In this paper, we consider two new atomic models of van der Waals vertical heterostructures of metal-semiconductor type based on a 2D buckled triangular borophene with metallic conductivity and graphene-like 2D monolayers of gallium nitride GaN and zinc oxide ZnO, which are semiconductors. Using the density functional theory, the equilibrium configurations of supercells of the borophene/GaN and borophene/ZnO heterostructures are found and their thermodynamic stability at room temperature is shown. Within the framework of the nonstationary first-order perturbation theory, the optical characteristics (complex permittivity and absorption coefficient) are calculated in the electromagnetic radiation wavelength range of 0.2–2 μm. The presence of anisotropy in the optical properties of the borophene/GaN and borophene/ZnO heterostructures is established when the direction of light polarization is chosen. This is due to different manifestations of the optical properties of the constituent monolayers of the heterostructure. When light is polarized in the direction of the zigzag edge of the GaN/ZnO (along the X axis), the optical properties of GaN and ZnO semiconductor monolayers are predominantly manifested. When light is polarized in the direction of the zigzag edge of the borophene monolayer (along the Y axis), the optical properties of borophene manifest themselves. A synergistic effect has been found from the combination of borophene and ZnO monolayers in the composition of the borophene/ZnO vertical heterostructure, which manifests itself in the form of a section of the increasing plot of the real and imaginary parts of the complex permittivity in the infrared region for both directions of light polarization. It is shown that the difference in the values of the absorption coefficient of the borophene/GaN heterostructure between the UV and visible ranges can reach ~ 7 times, between the UV and near IR ranges - ~ 14 times, and for the borophene/ZnO heterostructure this difference can be up to ~ 6 times and up to ~18 times, respectively. It is predicted that borophene/GaN and borophene/ZnO heterostructures can be used to create UV radiation detectors.

Misfit-generated structural and optical anisotropies of the natural MoS2−PbS van der Waals heterostructure merelaniite

Significant efforts developing ${\mathrm{MoS}}_{2}\text{\ensuremath{-}}\mathrm{PbS}$-based heterostructure devices with several different architectures show promise for photosensor, solar cell, and chemical sensor applications. Merelaniite $({\mathrm{Mo}}_{4}{\mathrm{Pb}}_{4}{\mathrm{VSbS}}_{15})$ is a newly discovered natural van der Waals heterostructure of the cylindrite type, composed predominantly of heavily modulated pseudotetragonal PbS layers and pseudohexagonal ${\mathrm{MoS}}_{2}$ layers with large misfit-induced anisotropy. For an incommensurate modulated structure, the refined structural model from single-crystal x-ray diffraction analysis is in reasonable agreement with the results obtained by high-resolution scanning transmission electron microscopy, especially in light of the fact that that the two isolated single-crystal domains used for the x-ray and electron diffraction experiments were extracted from two different whiskers and subjected to different sample preparation methods. The effects of the misfit-induced structural anisotropy are studied using angle-resolved polarized Raman spectroscopy. The intensities of 12 Raman modes are studied as a function of incident polarization angle relative to merelaniite's whisker axis, and show maximal intensity with the polarization direction perpendicular to the whisker axis. Polarization-dependent anisotropic third-harmonic generation from ultrathin mechanically exfoliated flakes reveals the anisotropy of the third-order nonlinear susceptibility tensor. Merelaniite demonstrates an expanded structure-chemistry space for engineering stable layered materials for potential device applications.

Two-Dimensional Mixed Lead/Bismuth Oxychloride Based Materials As Anodes for Sodium-Ion Batteries

The continuous pursuit on building low cost and sustainable batteries to efficiently harvest renewable energy from intermittent sources is ever expanding. The research on Na-ion technology has gained significant interest due to inexpensive and broad availability of precursor materials. Until now, various Na-ion anodes including carbonaceous materials such hard carbon, alloy-based materials such as Bi, Pb, Sb and Sn based systems and conversion materials have been explored1. Along this line, the recent chase on two dimensional (2D) materials such as chalcogenides, MXenes and van der Waals types oxyhalide heterostructures, have become more intense due to their excellent electrical and structural properties 2. Among them, 2D Sillén-type metal oxyhalide heterostructures (MOX), due to their unique layered structure consisting of anionic sheets interleaved with cationic layers have gain particular interest as electrode materials. BiOCl is one such candidate with fluorite-like layers, [Bi2O2]2+ intergrown with halide Cl– anions, have been studied as anode in rechargeable batteries. However, its application is mainly challenged by rapid capacity decay originating from particle pulverization and unstable solid electrolyte interphase (SEI).In this work, 2D layered mixed lead bismuth oxychloride nanosheets (BiOCl4 and PbBiO2Cl 3) were synthesized by new rapid room temperature chemical precipitation route. In former anode, the electrolyte engineering approach has been used to enhance the cycling stability of BiOCl and at the same time, its electrochemical (de)sodiation mechanism is also clarified through in-operando XRD studies, which reveals the reversible formation of Bi ↔ NaBi ↔ cubic-Na3Bi phases. On the other hand, the later anode, i.e., 2D-PbBiO2Cl was further investigated with the combined in-operando XRD and ex-situ TEM, XPS studies, which reveal a distinct (de)sodiation process of the 2D-PbBiO2Cl in comparison with reported Na-(Pb/Bi) phase diagram. This 2D heterostructure demonstrated stable sodium storage performance (~250 mAh g–1 for 250 cycles at 100 mA g–1). Henceforth, the detailed understanding of formation process of these two structures (BiOCl and PbBiO2Cl) at room temperature using material characterizations and electrochemical studies combined with operando findings will be discussed to comprehend the reversible storage mechanism of 2D-MOX type heterostructures as anodes in SIBs.

Fe2O3/MoO3@NG Heterostructure Enables High Pseudocapacitance and Fast Electrochemical Reaction Kinetics for Lithium-Ion Batteries.

Transition metal oxides (TMOs) hold great potential for lithium-ion batteries (LIBs) on account of the high theoretical capacity. Unfortunately, the unfavorable volume expansion and low intrinsic electronic conductivity of TMOs lead to irreversible structural degradation, disordered particle agglomeration, and sluggish electrochemical reaction kinetics, which result in perishing rate capability and long-term stability. This work reports an Fe2O3/MoO3@NG heterostructure composite for LIBs through the uniform growth of Fe2O3/MoO3 heterostructure quantum dots (HQDs) on the N-doped rGO (NG). Due to the synergistic effects of the "couple tree"-type heterostructures constructed by Fe2O3 and MoO3 with NG, Fe2O3/MoO3@NG delivers a prominent rate performance (322 mA h g-1 at 20 A g-1, 5.0 times higher than that of Fe2O3@NG) and long-term cycle stability (433.5 mA h g-1 after 1700 cycles at 10 A g-1). Theoretical calculations elucidate that the strong covalent Fe-O-Mo, Mo-N, and Fe-N bonds weaken the diffusion energy barrier and promote the Li+-ion reaction to Fe2O3/MoO3@NG, thereby facilitating the structural stability, pseudocapacitance contribution, and electrochemical reaction kinetics. This work may provide a feasible strategy to promote the practical application of TMO-based LIBs.

Temperature-Based Selective Detection of Hydrogen Sulfide and Ethanol with MoS2/WO3 Composite.

A sensitive and temperature-based selective sensor toward hydrogen sulfide and ethanol using MoS2/WO3 composite as a sensing surface was developed in this work. The MoS2/WO3 nanocomposite was successfully obtained using a facile two-step method. Structural analysis revealed the successful formation of the composite. Further, the n-type semiconducting nature as revealed in the initial gas-sensing measurements was also confirmed via Mott–Schottky plots. The composite-based sensor showed preferential detection of ethanol (260 °C) and hydrogen sulfide (320 °C) by simply modulating the temperature of the sensor device. The device also displayed repeatability and long-term stability at respective operating temperatures. Improved sensitivity and selectivity are ascribed to synergistic effects arising from the formation of n–n type heterostructures. The present work indicates the potential use of composite-based heterojunctions to tune the sensing parameters and provide new possibilities to enhance the applications of MoS2 and metal-oxide semiconductor-based composites.

LED-driven photocatalysis of toluene, trichloroethylene and formaldehyde by cuprous oxide modified titanate nanotube arrays

In this study, cuprous oxide modified titanate nanotube arrays photocatalyst (Cu2O/TNAs), a p-n type hetero-structure, was successfully synthesized by square wave voltammetry electrodeposition method (SWVE) with copper (II) acetate monohydrate as precursor. Cu2O/TNAs photocatalysts were characterized by SEM, XRD, XPS, and UV–vis DRS to investigate the physical and chemical properties such as surface structure, light absorption, and element composition. Results of characterization indicated that the Cu2O nanoparticles (Cu2O NPs) were firmly deposited on the surface of TNAs without significant morphological change. The enhanced photocatalytic (PC) performance of as-synthesized materials was exemplified by the test of photocurrent, which revealing that the average photocurrent density of Cu2O/TNAs (0.95 μA cm−2) was 1.38 times higher than TNAs (0.69 μA cm−2) under 24.2 mW cm−2 LED irradiation. Three VOCs (volatile organic compounds), namely, Toluene, Formaldehyde and Trichloroethylene can be completely removed in the Cu2O/TNAs PC process with rate constants (kobs) of 2.08 × 10−2, 3.11 × 10−2, and 6.58 × 10−2 min−1, respectively, with the effort of the synergism of the photo-generated holes and hydroxyl radicals. Detail mechanism of hetero-junction Cu2O/TNAs composite PC system was proposed to clarify the redox reaction.

The ZnO–Au-Titanium oxide nanotubes (TiNTs) composites photocatalysts for CO2 reduction application

The presence of gold nanoparticles (Au) on the zinc oxide (Zn)-titanium oxide nanotubus (TiNTs) composites to form the Z-scheme type photocatalysts has been investigated for photocatalytic reduction of CO2 to methanol. In this study, the commercial titanium dioxide powder (P-25) was first treated under a strong basic environment and applied a hydrotherrmal method to systhsize TiNTs, and calcined to use as a support. Then, various ratios of ZnO and TiNTs from 0.1 to 0.5 were also prepared by hydrothermal method to form TiNTs-ZnO-X (TZ-X, X is equal to the ZnO/TiNTs weight ratio) composites, and 1 to 5 wt % of Au were impregnated on the TiNTs-ZnO support to form the ZnO–Au-TiNTs composite photocatalysts.The catalysts will be characterized by x-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible spectroscopy (UV–Vis) and photoluminescence spectroscopy (PL) techniques to determine the structures and morphology of the ZnO–Au-TiNTs composites. The catalytic results have revealed that the TZ-0.20–2 wt% Au catalyst has the best photocatalysis activity with a 7777.1μmole/(g-cat) (hr) CH3OH production yield.The formation of the ZnO–Au-TiNTs Z-scheme type heterostructure results in an efficient electron transfer pathway and electron-hole separation inside the composite catalyst which lead to a highly efficient CO2 reduction and excellent improvement in methanol yield.

TiO2@Cu2O n-n Type Heterostructures for Photochemistry.

A TiO2@Cu2O semiconductor heterostructure with better photochemical response compared to TiO2 was obtained using an electrochemical deposition method of Cu2O on the surface of TiO2 nanotubes. The choice of 1D nanotubes was motivated by the possibility of achieving fast charge transfer, which is considered best suited for photochemical applications. The morphology and structural properties of the obtained heterojunction were determined using standard methods —SEM and Raman spectroscopy. Analysis of photoelectrochemical properties showed that TiO2@Cu2O heterostructures exhibit better properties resulting from an interaction with sunlight than TiO2. A close relationship between the morphology of the heterostructures and their photoproperties was also demonstrated. Investigations representing a combination of photoelectrochemical cells for hydrogen production and photocatalysis—photoelectrocatalysis—were also carried out and confirmed the observations on the photoproperties of heterostructures. Analysis of the Mott–Schottky plots as well as photoelectrochemical measurements (Iph-V, Iph-t) showed that TiO2 as well as, unusually, Cu2O exhibit n-type conductivity. On this basis, a new energy diagram of the TiO2@Cu2O system was proposed. It was found that TiO2@Cu2O n-n type heterostructure prevents the processes of photocorrosion of copper(I) oxide contained in a TiO2-based heterostructure.

Metal Oxide Nanoheterostructures for Gas Sensing

1. Introduction.Metal oxides such as SnO2, MoO3. TiO2, CuO, are well-known to exhibit significant changes in their electrical resistance upon admission of certain oxidizing or reducing chemical species which constitutes the base for their application as gas sensors. These materials can be synthesized in different forms ranging from bulk ceramics to thin films. Thin-film technology has contributed significantly to the development of reliable chemical sensors as it is easily controllable and results in reproducible parameters of deposited layers [1,2]. Moreover, it is compatible with interdigitated transducer IDT electrodes which facilitates film deposition and subsequent electrical contacts with the resistance measuring units [3]. Emerging nanotechnology has led to a revolution in sensing especially as far as different forms of nanomaterials have demonstrated better response, sensitivity and selectivity to different stimuli. Moreover, the nanostructured sensors can operate much faster due to better kinetics of responses at relatively low temperatures, i.e., close to room temperature. The aim of this contribution is to review the most recent work performed in the field of thin film resistive-type gas sensors with a special emphasis on the n-n and n- p nanostructures.2. ExperimentalThin films of different stoichiometry and crystal structures have been deposited by magnetron sputtering of Ti, Sn, and Cu targets in reactive Ar+O2 atmosphere with controlled composition. Characterization of films has been performed by X-ray diffraction XRD, X-ray reflectivity, XRR, X-ray photoelectron spectroscopy XPS, atomic force microscopy, AFM, scanning electron microscopy, SEM and optical spectrophotometry over uv and visible range of the light spectrum. Gas sensing measurements both in dc and ac modes have been carried out in a custom-made set-up capable of detecting changes in the electrical resistance under stabilized temperature and humidity level. Modular XM-MTS unit from Solartron Analytical has been used to detect the impedance spectra in reference atmosphere (air) and upon gas (NO2, H2) admission.3. ResultsExperimental results concerning thin film characterization will be presented and compared with the most representative data obtained by other authors. Fundamental properties of different n-type (TiO2, SnO2) and p-type (CuO) semiconductors will be discussed.Depending on the material being sputtered and the substrate on which a thin film is deposited one can observe a growth of different nanostructures. Typically, a columnar structure is obtained in the case of TiO2 while the amorphous films of SnO2 result in a smooth top SEM image composed of small, isolated grains. CuO thin films crystallize easily with relatively large, well-developed grains.Gas sensor responses are good and reproducible in the case of n-type semiconductors such as TiO2 and SnO2. CuO being a p-type semiconductor demonstrates much lower response which can be improved by forming TiO2/CuO n-p type hetero-structure.

Room-Temperature Synthesis and Stable Na-Ion Storage Performance of Two-Dimensional Mixed Lead-Bismuth Oxychloride Heterostructure

The endless pursuit on building low cost and sustainable batteries to effectively harvest renewable energy from intermittent sources is ever increasing. The research on Na-ion technology has gained significant interest due to inexpensive and broad availability of precursor materials. Until now, various Na-ion anodes have been explored including carbonaceous materials such hard carbon, alloy-based materials such as Bi, Pb, Sb and Sn based systems and conversion materials [1]. Along this line, the recent chase on two dimensional (2D) materials such as chalcogenides, MXenes and van der Waals types oxyhalide heterostructures, have become more intense due to their excellent electrical and structural properties [2]. Among them, 2D Sillén-type metal oxyhalide heterostructures (MOX), due to their unique layered structure consisting of anionic sheets interleaved with cationic layers have gain particular interest as electrode materials. BiOCl is one such candidate with fluorite-like layers, [Bi2O2]2+ intergrown with halide Cl– anions, have been studied as anode in rechargeable batteries. For instance, the 2D-(Bi1-xFex)OCl have increased insertion kinetics in Li-ion storage performances [3] in comparison with unsubstituted BiOCl, whereas 2D-(Bi1-xSbx)OCl heterostructures have shown synergetic effect of (Bi/Sb) alloys on with improved K-ion storage capacity [4]. However, in continuation, the further assessment of other mixed cationic Sillén heterostructures with the crystal structures of [BixM1-xO2]n+ (M = Na+/Ca2+/Pb2+/Fe3+/Sb3+; n = +1, +2 and +3) layers intergrown with single/double/triple halide anionic layers, remain unexplored. This is mainly challenged by their current synthesis strategies which demand high temperature, longer reaction durations, toxic chemicals, and complex reaction setup.In this work, 2D layered lead bismuth oxychloride (PbBiO2Cl) heterostructure nanosheets were synthesized by new rapid room temperature chemical precipitation route within ~45 mins. The stepwise reaction intermediates were harvested and investigated further with XRD and SEM mechanistic studies. The formation proceeds through topotactic ion exchange route from analogous PbBiO2NO3 intermediate. When employed as an anode material in Na half-cell configurations (as presented in Figure 1), this 2D heterostructure demonstrated stable sodium storage performance (~250 mAh g–1 for 250 cycles at 100 mA g–1). Surprisingly, the electrochemical profile of the 2D-PbBiO2Cl significantly differs from those of its individual counterparts Pb, Bi anodes. This was further investigated with the combined in-operando XRD and ex-situ TEM, XPS studies, which reveal a distinct (de)sodiation process of the 2D-PbBiO2Cl in comparison with reported Na-(Pb/Bi) phase diagram. Henceforth, the detailed understanding of formation process of 2D-PbBiO2Cl at room temperature using non-operando material characterizations and electrochemical studies combined with operando findings will be discussed to comprehend the reversible storage mechanism of 2D-PbBiO2Cl type heterostructures as anodes in SIBs.

Synthesis and comparative evaluation of optical and electrochemical properties of efficacious heterostructured-nanocatalysts of ZnSe with commercial and reduced titania

We report semiconductor-semiconductor (S-S) type heterostructures prepared by solvothermal method using ZnSe (Z), commercial titania (C-TiO2) and reduced titania (R-TiO2−x) as precursor materials. The synthesized Z-C-TiO2 and Z-R-TiO2−x heterostructures manifest remarkable electrocatalytic oxygen evolution reaction (OER) activity with onset over potential of only 320 mV (Tafel slope = 40 mV dec−1) and 325 mV (Tafel slope = 45 mV dec−1) respectively, with activity over 6 h of testing time in alkaline medium. This enhancement in the activities of engineered nanoscale materials can be attributed to the better coping of reaction intermediate through synergistic effect of two semiconducting materials. Owning to the reduced electron-hole recombination by versatile cascade band alignment of titania with ZnSe, these heterostructures also show superior photocatalytic activity for degradation of reactive blue-866 dye (RB-866) under visible light irradiation when compared to pure titania.

MOF-derived polyhedral NiMoO4@NiO p-p heterostructure as an effective bridge for regulating carriers enhanced sensitivity and selectivity to trimethylamine

Metal organic framework (MOF) has been considered as an ideal precursor to prepare the metal oxide semiconductor (MOS) composites. Herein, the polyhedral NiMoO4 decorated NiO p-p heterostructures are prepared using the MOF as a self-sacrificing template with an annealing process. Compared with the pure NiO, the 5 wt% NiMoO4 decorated NiO based sensor exhibits improved gas performance. It shows not only high response values of 150 and fast response/recovery speed (20 s/16 s) to 50 ppm TEA at a relatively low operating temperature of 220 °C, but also outstanding selectivity and stability, which indicates that the as-prepared polyhedral NiMoO4 decorated NiO heterostructures can be used as a promising material to detect TEA effectively. The gas-sensing mechanism of high selectivity and response to TEA for the NiMoO4 decorated NiO based sensor is closely related to the catalytic synergistic promotion effect of the NiO and NiMoO4 composite materials, the large specific surface area, and electronic sensitization by forming the p-p type heterostructures. This work also provides a new solution for designing well defined p-p heterojunctions in gas-sensing applications.

MOF-derived NiWO4@NiO p-p heterostructure for distinguish detection of TEA and xylene by temperature regulation

Accurate detection of outdoor air quality requires a large number of gas sensors to be used in various fields. Thus, it is greatly significance to develop multifunctional sensors. In this work, the NiWO4 decorated NiO p-p type heterostructure were successfully synthesized using the metal organic framework (MOF) as a self-sacrificing template with annealing process. The gas sensitive measurements reveal that the 12 wt% NiWO4 decorated NiO based sensor exhibits the higher response value (65) than that of the pure NiO sensor (2.5) to 50 ppm triethylamine (TEA) at 240 °C. The selectivity of the NiWO4 decorated NiO based sensors could be changed when the operating temperature over 260 °C, and the 12 wt% NiWO4 decorated NiO based sensor shows the higher response value (28) than that of the pure NiO sensor (2) to 50 ppm xylene at 270 °C, indicated that as-prepared the NiWO4 decorated NiO heterostructure can be as a promising material applied to fabricate the dual sensor to detect TEA and xylene with high sensitivity as well as distinguish by adjusting the temperature. The improved gas-sensing mechanisms of the NiWO4 decorated NiO based on sensor are discussed in detail.

Machine learning classification of binary semiconductor heterostructures

Heterostructures of two semiconductors are at the heart of semiconductor devices with tremendous technological importance. The prediction and designing of semiconductor heterostructures of a specific type is a difficult materials science problem, posing a challenge to experimental and computational investigations. In this study, we first establish that the prediction of heterostructure type can be made with good accuracy from the knowledge of the band structure of constituent semiconductors. Following this, we apply machine learning, built on features characterizing constituent semiconductors, on a known dataset of binary semiconductor heterostructures extended by a synthetic minority oversampling technique. A significant feature of engineering made it possible to train a classifier model predicting the heterostructure type with an accuracy of $89%$. Using the trained model, a large number (872 number) of unknown heterostructure semiconductor types involving elemental and binary semiconductors is theoretically predicted. Interestingly, the developed scheme is found to be extendable to heterojunctions of semiconductor quantum dots.

Visible Light Driven VO2/g‐C3N4 Z‐Scheme Composite Photocatalysts for Selective Oxidation of DL‐1‐Phenylethyl Alcohol under Vis‐LEDs Irradiation and Aerobic Oxidation

AbstractA novel VO2/g‐C3N4 Z‐Scheme type heterostructure composite photocatalyst was fabricated by the ultrasonic‐assisted method. The newly synthesized photocatalyst has been systematically and comprehensively characterized and analyzed. Through the selective oxidation of DL‐1‐Phenylethyl alcohol under Vis‐LED irradiation and aerobic oxidation, the photocatalytic performance of VO2/g‐C3N4 photocatalyst was investigated. The results showed that the prepared VO2/g‐C3N4 nanocomposites exhibited excellent photocatalytic oxidation performance. Among them, the highest turnover frequency (TOF) was 0.42 mmol (DL‐1‐Phenylethyl alcohol)⋅mmol−1 (catalyst)⋅h−1, which was 5 times higher than the TOF of the original g‐C3N4. The effects of different wavelengths of LED monochromatic light, the composite ratio of VO2 and g‐C3N4, the reaction time, and the different benzyl alcohol substrates were studied. Also, catalyst life test was completed. Furthermore, a persuasive mechanism of photocatalytic selective oxidation of DL‐1‐Phenylethyl alcohol on VO2/g‐C3N4 photocatalyst was proposed through EPR and radical trapping experiments.