Bifunctional Hydrogen Production and Storage on 0D–1D Heterojunction of Cd0.5Zn0.5S@Halloysites

Development of efficient solar‐driven hydrogen (H₂) evolution and H₂ storage materials is challenging. Sulfide nanocatalysts show large potential for H₂ production, but suffer from the drawbacks of inefficient charge separation, serious photocorrosion, and easy agglomeration. Herein, a 0D–1D satellite‐core ethylenediaminetetraacetic acid (EDTA)‐bridged Cd_0.5Zn_0.5S@halloysite nanotubes tertiary structure is designed via facile in situ assembly, which settles all the above‐mentioned issues and achieves exceptional and stable photocatalytic H₂ evolution and storage. Significantly, EDTA grafted on halloysites as the hole (h⁺) traps steers the photogenerated h⁺ and electrons (e^?) from Cd_0.5Zn_0.5S separately to halloysites and outer surface Pt sites, achieving efficient directional separation between h⁺ and e^? and inhibiting the h⁺‐dominated photocorrosion occurring on Cd_0.5Zn_0.5S. Benefiting from these advantages, the hierarchy shows an unprecedented photocatalytic H₂ evolution rate of 25.67 mmol g^?1 h^?1 with a recording apparent quantum efficiency of 32.29% at λ = 420 nm, which is seven‐fold that of Cd_0.5Zn_0.5S. Meanwhile, an H₂ adsorption capacity of 0.042% is achieved with the room temperature of 25 °C and pressure of 2.65 MPa. This work provides a new perspective into designing hierarchical structure for H₂ evolution, and proposes an integration concept for H₂ evolution and storage.     

Heterojunction performance of dip coated n-Cd0.5Zn0.5S thin films on different metal sulfide substrates

In this work, n-type cadmium zinc sulfide (n-Cd_0.5Zn_0.5S) films were grown by a dip coating technique on different p-type metal sulfide substrates. The morphology, structure, and composition of the yielded materials have been con?rmed by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray analysis, respectively. Using the absorption measurements, the direct allowed band gap energies for Cd_0.5Zn_0.5S, PbS, CuS, CuInS₂, were found to be 2.93, 1.83, 1.98 and 2.5 eV at room temperature, respectively. The substrate dependence of the current density–voltage (J–V) characteristics of n-Cd_0.5Zn_0.5S/p-PbS, n-Cd_0.5Zn_0.5S/p-CuS, n-Cd_0.5Zn_0.5S/p-Cu_0.8In_1.2S₂, n-Cd_0.5Zn_0.5S/p-Cu_0.9In_1.1S₂, n-Cd_0.5Zn_0.5S/p-CuInS₂, n-Cd_0.5Zn_0.5S/p-Cu_1.1In_0.9S₂ and n-Cd_0.5Zn_0.5S/p-Cu_1.2In_0.8S₂ heterojunctions were measured at room temperature (～300 K). These characteristics showed a rectifying behavior consistent with a potential barrier formed at the interface for all the studied devices. The forward current density–voltage characteristics under low voltage bias were explained on the basis of thermionic emission mechanism. Heterojunction parameters such as ideality factor, n, series resistance, R_S and barrier height, Φ_b were obtained from J–V measurements using Cheung's method. The heterojunctions show non-ideal J–V behavior with an ideality factor greater than unity. Analysis of the experimental data under reverse voltage bias suggests that Schottky effect is the dominant mechanism. The dark capacitance–voltage characteristics of the heterojunctions were studied at 1 MHz. High value of built-in potential of 0.58 V was obtained for n-Cd_0.5Zn_0.5S/p-Cu_0.9In_1.1S₂ heterojunction as compared to the other studied heterojunctions. The photovoltaic characteristics were analyzed for the heterojunctions under illumination of 100 mW/cm².     

Electrical properties of anisotype heterojunctions n-CdZnO/p-CdTe

Anisotype surface-barrier n-Cd_0.5Zn_0.5O/p-CdTe heterojunctions are fabricated by the high-frequency sputtering of a Cd_0.5Zn_0.5O alloy film onto a freshly cleaved single-crystal CdTe surface. The main electrical properties of the heterojunctions are studied and the dominant mechanisms of charge transport are established, namely, the multistage tunnel-recombination mechanism under forward bias, Frenkel-Pool emission, and tunneling under forward bias. The influence of the surface electrically active states at the heterojunction interface is analyzed and their surface concentration is evaluated: N _ss ?? 10¹⁴ cm^?2.     

Preparation and properties of CuO/ZnxCd1−xS photocatalysts

CuO/Zn_0.384Cd_0.616S was prepared by an impregnation method, and its structure and optical properties were characterized using X-ray diffraction, scanning electron microscopy, ultraviolet–visible diffuse-reflectance spectroscopy and X-ray photoelectron spectroscopy and their photocatalytic activity were evaluated based on photocatalytic degradation of methyl orange (MO) solution under visible light. The effects on photocatalytic degradation of the catalyst amount, MO concentration and pH were investigated. And the mechanism for enhancing the photocatalytic activity was also discussed. The results indicated that 0.5 wt% CuO/Zn_0.384Cd_0.616S showed the highest photocatalytic activity among the prepared samples. The mechanism for the degradation of MO occurring on the CuO/Zn_0.384Cd_0.616S surface differs from that on Zn_xCd_1−xS surfaces. The catalytic reaction under visible-light irradiation followed pseudo-first-order kinetics.     

Design of 2D Layered Catalyst by Coherent Heteroepitaxial Conversion for Robust Hydrogen Generation

The structural engineering of 2D layered materials is emerging as a powerful strategy to design catalysts for high-performance hydrogen evolution reaction (HER). However, the ultimate test of this technology under typical operating settings lies in the reduced performance and the shortened lifespan of these catalysts. Here, a novel approach is proposed to design efficient and robust HER catalysts through out-of-plane deformation of 2D heterojunction using metal-organic chemical vapor deposition. High-yield, single-crystalline WTe₂ nanobelts are used as an epitaxial template for their coherent conversion to WS₂. During the conversion process, the WTe₂/WS₂ heterostructure containing both lateral and vertical junctions are achieved by coherent heteroepitaxial stacking despite differences in symmetry. The lattice coherency drives out-of-plane deformation of heteroepitaxially grown WS₂. The increase in the effective surface area and decrease in the electron-transfer resistance across the 2D heterojunctions in turn enhances the HER performance as well as the long-term durability of these electrocatalysts.     

Synthesis,characterization and dielectric properties of Polyaniline@Ni0.5Zn0.5Fe2O4 composite nanofibers

Polyaniline@Ni_0.5Zn_0.5Fe₂O₄ (PANI@NiZn) composite nanofibers were prepared by in situ polymerization of aniline in the presence of NiZn ferrite nanoparticles. The composites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), UV–vis and FTIR spectra. Their magnetic and dielectric properties were found that the PANI@NiZn nanocomposite nanofibers possess adjusted magnetic properties by change NiZn content. The PANI@NiZn composite nanofibers also have high dielectric constant and exhibit two dielectric relax regions at room temperature. The high-frequency dielectric relaxtion at about 3.5 MHz may be contribute to the interfacial polarization occuring at the interface of NiZn nanoparticle and PANI polymer. This will reach a better understanding of the mechanism in polymer/inorganic nanocomposites.     

One‐Step Preparation of Coaxial CdS–ZnS and Cd1–xZnxS–ZnS Nanowires

Preparation of coaxial (core–shell) CdS–ZnS and Cd_1–xZn_xS–ZnS nanowires has been achieved via a one‐step metal–organic chemical vapor deposition (MOCVD) process with co‐fed single‐source precursors of CdS and ZnS. Single‐source precursors of CdS and ZnS of sufficient reactivity difference were prepared and paired up to form coaxial nanostructures in a one‐step process. The sequential growth of ZnS on CdS nanowires was also conducted to demonstrate the necessity and advantages of the precursor co‐feeding practice for the formation of well‐defined coaxial nanostructures. The coaxial nanostructure was characterized and confirmed by high‐resolution transmission electron microscopy and corresponding energy dispersive X‐ray spectrometry analyses. The photoluminescence efficiencies of the resulting coaxial CdS–ZnS and Cd_1–xZn_xS–ZnS nanowires were significantly enhanced compared to those of the plain CdS and plain Cd_1–xZn_xS nanowires, respectively, owing to the effective passivation of the surface electronic states of the core materials by the ZnS shell.     

Cd0.8Zn0.2S 薄膜的结构和光学性质

采用真空共蒸发法在玻璃衬底上制备了Cd1-xZnxS薄膜,并用XRD、XRF以及光学透射谱对刚沉积薄膜的结构、组分和光学性质进行了表征。刚沉积的薄膜为六方结构,沿(002) 择优取向。XRF测试结果表明石英振荡法监控的薄膜组分与XRF 获得的结果非常好地吻合。由Cd0.8Zn0.2S薄膜的光学透射谱,通过Swanepoel 原理与Wemple- DiDomenico 单振子模型,推导出薄膜的光学参量,如折射率、单振子能量、色散能、吸收系数、光学能隙等。     

Tunable properties of cadmium substituted ZnS nanocrystals

Tailored Zn_1−xCd_xS (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles, synthesized by co-precipitation method under ultrasonic irradiation, were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), UV–Vis and photoluminescence (PL) spectroscopy measurements. According to the XRD results, substitution of Zn²⁺ by Cd²⁺ ion leads to an increase in the lattice parameters and the average size of zinc blended nanoparticles are in the range of 3–4 nm. Transmission electron microscopy image revealed the formation of nano-sized particles with dimension of 5 nm confirming that the samples are quantum dots. The shift observed in the absorption edges by increasing Cd²⁺ ion substitution is ascribed by the alloying effect but the enhancement of band gap energy compared to that of the corresponding bulk value is attributed to the nanometric grain size and quantum confinement effects. The position and intensity of PL emission peaks are tuned with Cd²⁺/Zn²⁺ ion content.     

Photoelectrochemical (PEC) studies on Cd0.5Fe0.5Se nanocrystalline thin films deposited by a spray pyrolysis technique

Recently, nanostructured thin films have attracted the attention of researchers from several disciplines, due to their outstanding electronic and optical properties and potential applications in various optoelectronic devices. The ternary Cd_0.5Fe_0.5Se nanocrystalline thin films were deposited by a spray pyrolysis method onto glass, aluminium, copper and stainless steel substrates. The structural and morphological properties were studied by X-ray diffraction and scanning electron microscopy analysis. The XRD study revealed that, Cd_0.5Fe_0.5Se films are nanocrystalline in nature with hexagonal lattice. The optical absorption study showed that, the semiconductor Cd_0.5Fe_0.5Se thin film deposited on glass exhibits direct band gap energy of the order of 1.95 eV. The PEC study revealed that, Cd_0.5Fe_0.5Se thin films deposited on aluminium substrate exhibited maximum fill factor (FF) and efficiency (η) as compared to the films deposited on stainless steel and copper substrates.     

Vapor phase equilibria in the Cd1−xZnxTe alloy system

Cd_1−xZn_xTe compounds of different compositions have been prepared at temperatures ranging from 400 to 1000°C by annealing elemental Te in sealed quartz ampoules, in an atmosphere comprising vapors of Cd and Zn whose partial pressures were varied by varying the composition of the binary Cd_1−yZn_y alloys which provided the Cd and Zn vapors in these annealing experiments. The chemical compositions of the resulting Cd_1−xZn_xTe compounds have been analyzed using electron probe microanalytical techniques. Results indicate that presence of a 0.5%Zn along with Cd in a closed or semi-closed system may prove to be beneficial in preventing decomposition and/or formation of a metal/non metal phase during annealing of Cd_0.96Zn_0.04 Te substrates. Using the thermodynamic data in the literature for the binary Cd_1−yZn_y alloys and with the assumption that the activities of the Cd and Zn components are weakly dependent on temperature, the partial pressures of Cd and Zn in equilibrium with the Cd_1−xZn_xTe compounds at various temperatures have been evaluated.     

Effects of ammonia concentration on property of Cd1−xZnxS films by chemical bath deposition

Cd_1−xZn_xS thin films were grown on soda–lime glass substrates by chemical-bath deposition (CBD) at 80 °C with stirring. All the samples were annealed at 200 °C for 60 min in the air. The crystal structure, surface morphology, thickness and optical properties of the films were studied with transmission electron microscopy (TEM), X-ray diffraction (XRD), scanning electron microscopy (SEM), step height measurement instrument and spectrophotometer respectively. The results revealed that Cd_1−xZn_xS thin films had cubic crystal structure and the intensity of the diffraction peak increased gradually as ammonia concentration rose and the grain size varied from 5.1 to 8.3 nm. All of Cd_1−xZn_xS thin films had a granular surface with some smaller pores and the average granule sizes increased from 92 to 163 nm with an increase in ammonia concentration. The Cd_1−xZn_xS thin films had the highest transmittance with ammonia concentration of 0.5 M L⁻¹, whose thickness was 50 nm and band gap was 2.62 eV.     

Enhanced ammonia sensing characteristics of tungsten oxide decorated polyaniline hybrid nanocomposites

Polyaniline (PAni)-tungsten oxide (WO₃) hybrid nanocomposites sensor have been lucratively synthesized by in-situ chemical oxidative polymerization method by entrapping tungsten oxide nanoparticles (10–50%) in the polyaniline matrix on precleaned glass substrate. The structural, morphological and surface composition elucidation of PAni-WO₃ hybrid nanocomposites were explored by X-ray diffraction (XRD) technique, field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The existence of WO₃ in PAni matrix and interaction between them was confirmed using XRD and Raman spectroscopy. The incorporation of WO₃ nanoparticles into the PAni matrix introduces porosity which enhanced gas sensing properties. The TEM image of PAni-WO₃ hybrid nanocomposite film exploded the average diameter of WO₃ nanoparticles ranging from 40 to 50 nm. Chemical composition of PAni-WO₃ hybrid nanocomposites was characterized by using X-ray photoelectron spectroscopy (XPS). In order to investigate the gas sensing parameter of PAni-WO₃ hybrid nanocomposite, hybrid nanocomposite film was exposed to different oxidizing gases (Cl₂, NO₂) and reducing gases (NH₃, H₂S, CH₃OH, C₂H₅OH) in range 5–100 ppm concentration of gas. It was observed that the sensors of PAni-WO₃ hybrid nanocomposites showed better sensitivity, selectivity, stability and reproducibility compared to pure PAni and pure WO₃. PAni-WO₃ (50%) hybrid nanocomposite sensor operating at room temperature reveals maximum response of 158% towards 100 ppm of NH₃ gas and also capable to respond very little concentration of 5 ppm NH₃ gas with reasonable response of 24%. The gas sensing mechanism of the nanocomposites in presence of air and with target NH₃ gas atmosphere was discussed in detail with the help of energy band diagram. The interaction of NH₃ and NO₂ gas with PAni-WO₃ hybrid nanocomposite sensor was investigated by employing an impedance spectroscopy also.     

Influence of substrate type on the structural,optical and electrical properties of CdxZn1−xS MSM thin films prepared by Spray Pyrolysis method

0.25 μm Cd_xZn_1−xS thin films were deposited on Si and glass substrates by using a chemical Spray Pyrolysis technique (CSP). Measurements of the absorption spectrum of the film were carried out. The values of band gaps (E_g) are calculated from the absorption spectrum. X-ray diffraction (XRD) of the Cd_xZn_1−xS thin films on Si and glass substrates was carried out. The full width at half-maximum (FWHM)) of diffraction peak was calculated to be about 0.640, which showed that it is a polycrystalline thin film. A Cd_xZn_1−xS Metal–Semiconductor–Metal (MSM) photodetector with nickel (Ni) contact electrodes was then fabricated. The electrical property of the Ni/Cd_xZn_1−xS/Si and Ni/Cd_xZn_1−xS/glass detectors was investigated using the current–voltage (I–V) measurements. The barrier heights ϕ_Β of Ni/Cd_xZn_1−xS/Ni MSM on Si and glass substrates were 0.551 eV and 0.593 eV, respectively with an applied bias voltage of 3 V.     

Near-IR comparative characterization of optical second-order nonlinearities in Te-based semiconductors

We have systematically characterized the second harmonic generation efficiency of Te-based binary and ternary II–VI compounds in the near-IR spectral region, namely at=1.5 m and=1.9 m. A phase mismatched technique has been employed, as a translation into the spectral domain of the Maker fringes method. By using sub-picosecond optical pulses, reliable results for the value of non second-order linear coefficientd and of chromatic dispersion have been obtained. We have performed a comparative evaluation of nonlinear wavelength conversion efficiency of Te-based semiconductors and GaAs. The ternary alloys Cd_0.5Zn_0.5Te and Cd_0.78Mn_0.22Te can be considered as the best performing basic materials for optical wavelength converters working in the third communication window, since they possess at the same time a highd coefficient, good transparency, and low chromatic dispersion.     

Composition‐ and Shape‐Controlled Synthesis and Optical Properties of ZnxCd1–xS Alloyed Nanocrystals

Composition‐tunable Zn_xCd_1–xS alloyed nanocrystals have been synthesized by a new approach consisting of thermolyzing a mixture of cadmium ethylxanthate (Cd(exan)₂) and zinc ethylxanthate (Zn(exan)₂) precursors in hot, coordinating solvents at relatively low temperatures (180–210 °C). The composition of the alloyed nanocrystals was accurately adjusted by controlling the molar ratio of Cd(exan)₂ to Zn(exan)₂ in the mixed reactants. The alloyed Zn_xCd_1–xS nanocrystals prepared in HDA/TOP (HDA: hexadecylamine; TOP: trioctylphosphine) solution exhibit composition‐dependent shape and phase structures as well as composition‐dependent optical properties. The shape of the Zn_xCd_1–xS nanocrystals changed from dot to single‐armed rod then to multi‐armed rod with a decrease of Zn content in the ternary nanoparticles. The alloying nature of the Zn_xCd_1–xS nanocrystals was consistently confirmed by the results of high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), and UV‐vis absorption and photoluminescence (PL) spectroscopy. Further, the shape‐controlled synthesis of the ternary alloyed nanocrystals was realized by selecting appropriate solvents. Uniform nanodots in the whole composition range were obtained from TOPO/TOP solution, (TOPO: trioctylphosphine oxide) and uniform nanorods in the whole composition range were prepared from HDA/OA solution (OA: octylamine). The effect of the reaction conditions, such as solvent, reaction temperature, and reaction time, on the PL spectra of the alloyed Zn_xCd_1–xS nanocrystals was also systematically studied, and the reaction conditions were optimized for improving the PL properties of the nanocrystals.     

Molecular beam epitaxial growth of HgCdTe on CdZnTe(311)B

A series of n-type, indium-doped Hg_1−xCd_xTe (x∼0.225) layers were grown on Cd_0.96Zn_0.04Te(311)B substrates by molecular beam epitaxy (MBE). The Cd_0.96Zn_0.04Te(311)B substrates (2 cm × 3 cm) were prepared in this laboratory by the horizontal Bridgman method using double-zone-refined 6N source materials. The Hg_1−xCd_xTe(311)B epitaxial films were examined by optical microscopy, defect etching, and Hall measurements. Preliminary results indicate that the n-type Hg_1−xCd_xTe(311)B and Hg_1−xCd_xTe(211)B films (x ∼ 0.225) grown by MBE have comparable morphological, structural, and electrical quality, with the best 77 K Hall mobility being 112,000 cm²/V·sec at carrier concentration of 1.9×10⁺¹⁵ cm⁻³.     

Dependence of the properties of Cd1−x ZnxTe crystals on the type of intrinsic point defect formed by oxygen

Coordinated investigations of cathodoluminescence spectra, microstructure, specific resistance and presence of oxygen in Cd_1−x Zn_xTe crystals are used to identify how the electrical properties and degree of perfection of the crystal lattice of these materials are affected by the form in which oxygen is present as an intrinsic point defect. It is found that oxygen, which is the main background impurity in Cd_1−x Zn_xTe, forms different types of point defects at different positions in the lattice, depending on the ratio [Cd]/[Zn]. The optimum composition for making detectors of ionizing radiation, for which the crystal resistance is highest, is Cd_0.77Zn_0.23Te. Fiz. Tekh. Poluprovodn. 33, 569–573 (May 1999)     

Selective Vertical and Horizontal Growth of 2D WS2 Revealed by In Situ Thermolysis using Transmission Electron Microscopy

Direct observation of the growth dynamics of 2D transition metal dichalcogenides (TMDs) is of key importance for understanding and controlling the growth modes and for tailoring these intriguing materials to desired orientations and layer thicknesses. Here, various stages and multiple growth modes in the formation of WS₂ layers on different substrates through thermolysis of a single solid-state (NH₄)₂WS₄ precursor are revealed using in situ transmission electron microscopy. Control over vertical and horizontal growth is achieved by varying the thickness of the drop-casted precursor from which WS₂ is grown during heating. First depositing platinum (Pt) and gold (Au) on the heating chips much enhance the growth process of WS₂ resulting in an increased length of vertical layers and in a self-limited thickness of horizontal layers. Interference patterns are formed by the mutual rotation of two WS₂ layers by various angles on metal deposited heating chips. This shows detailed insights into the growth dynamics of 2D WS₂ as a function of temperature, thereby establishing control over orientation and size. These findings also unveil the important role of metal substrates in the evolution of WS₂ structures, offering general and effective pathways for nano-engineering of 2D TMDs for a variety of applications.     

Large area depositon of Cd1-xZnxTe on GaAs and Si substrates by metalorganic chemical vapor deposition

Results of large-area (up to 1000 cm²/run) Cd_1-xZn_xTe heteroepitaxy on both GaAs and GaAs/Si substrates by metalorganic chemical vapor deposition (MOCVD) are presented. Cd_1-xZn_xTe (x = 0-0.1) films exhibited specular surface morphology, 1% thickness uniformity (standard deviation), and compositional uniformity (Δx) of ±0.002 over 100 mm diam substrates. For selected substrate orientations and deposition conditions, the only planar defects exhibited by (lll)B Cd_1-xZn_xTe/GaAs/Si films were lamella twins parallel to the CdTe/GaAs interface; these do not propagate through either the Cd_1-xZn_xTe layer or subsequently deposited liquid phase epitaxy (LPE) HgCdTe layer(s). Background Ga and As-impurity levels for Cd_1-xZn_xTe on GaAs/Si substrates were below the secondary ion mass spectroscopy detection limit. Preliminary results of HgCdTe liquid phase epitaxy using a Te-rich melt on Si-based substrates resulted in x-ray rocking curve linewidths as narrow as 72 arc-sec and etch-pit densities in the range 1 to 3 x 10⁶ cm².