ZnS Layer Research Articles

Band Gap Engineering Improves Three-Photon Luminescence of Quantum Dots for Deep Brain Imaging.

Three-photon fluorescence microscopy (3PFM) has emerged as a promising tool in monitoring the structures and functions of the brain. Compared to the various imaging technologies, 3PFM enables a deep-penetrating depth attributed to tighter excitation confinement and suppressed photon scattering. However, the shortage of three-photon probes with a large absorption cross section (σ3) substantially limits its uses. Herein, CdSe/CdS/ZnS quantum dots (QDs) with enhanced 3PF performance were synthesized via the band gap engineering strategy. The introduction of a CdS interlayer with optimized thickness between the emitting CdSe core and the ZnS shell significantly enhanced the 3P absorption cross section of QDs, which originated from the intrinsic piezoelectric polarization effect and the change of the core/shell structure from type-I to quasi-type-II. In addition, the outer ZnS layer compensated the poor electronic passivation of CdS, providing a high level of passivation for the improvement of quantum yield as well as the 3P action cross section of QDs. Under the excitation of a 1600 nm femtosecond laser, PEGylated CdSe/CdS/ZnS QDs were used for in vivo 3PFM imaging of cerebral vessels with high resolution. A tiny capillary with a diameter of 0.8 μm could be resolved at the imaging depth of 1550 μm in a mouse brain with an opened skull. A penetration depth of 850 μm beneath the skull was also achieved using a mouse model with an intact skull.

Improved Luminous Efficiency of AgInS2 Quantum Dots and Zeolitic Imidazolate Framework-70 Composite for White Light Emitting Diode Applications.

The application of multiple quantum dots (QDs) in the field of white light emitting diodes (WLEDs) is still an important challenge due to their low luminous efficiency and quenching phenomenon. In this paper, we prepared AgInS2 QDs/zeolitic imidazolate framework-70 (AIS/ZIF-70) composite by a microwave hydrothermal method. Owing to the high porosity and stability of ZIF-70, it could effectively prevent quenching issues due to the aggregation of QDs. Since the ZIF-70 and QDs were chemically bonded, the formation of the ZnS layer could effectively passivate the surface defect and thus the quantum yield reached 21.49 % in aqueous solution. The luminous efficiency (LE) of the assembled AIS/ZIF-based WLED was reinforced by 6.8 times with a molar ratio of AgIn/Zn=18, i. e. at 5.26 % molar fraction of ZIF-70. Moreover, the color rendering index (CRI) and correlated color temperature (CCT) of AIS/ZIF-based WLED were 84.3 and 3631 K, respectively, indicating its potential application in solid-state lighting.

Enhanced light absorption in a MoS2-based photonic crystal

We investigate theoretically the absorbance, reflectance and transmittance in a MoS2-based photonic crystal. The proposed design of the photonic crystal consists of a monolayer of MoS2 which is sandwiched between ZnS and SiO2 layers. We obtain that, absorbance and transmittance as well as absorbance can be adjusted easily by the number of photonic crystal periods. Also, the absorbance can be effectively enhanced with the number of periods. Furthermore, for different incident wavelengths the absorbance, reflectance and transmittance demonstrate an oscillatory behavior as the thickness of the ZnS layer changes. As the period increases, the coefficient of absorbance increases for wavelengths within the ultraviolet and visible regions, contrary to the reflectance and transmittance coefficients, and reaches the maximum value (100%). While, for the infrared wavelengths, the absorbance coefficient first increases and then reaches a relatively small constant value (15%). Our proposed structure can be useful for optical and optoelectronic devices.

Improved stability and luminescent efficiency of AgInSe2 nanocrystals by shelling with ZnS

In this paper, AgInSe2 (AISe) core and AgInSe2/ZnS (AISe/ZnS) core/shell nanocrystals (NCs) were synthesised by a one-pot method in an organic solvent. Firstly, the synthesis of AIS core NCs with different sizes was performed by hot-injection of Se precursor into the Ag and In complexes at different temperatures from 100 °C to 180 °C for a reaction time of 20 min Then, the ZnS was grown on the surface of AISe NCs at 150 °C for 60 min to produce the AISe/ZnS core/shell structures. The as-synthesised AISe core and AISe/ZnS core/shell NCs were characterised by using x-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and optical spectroscopies (UV–vis absorption and photoluminescence (PL)). After shelling ZnS layer, AISe/ZnS core/shell NCs become more stable (12 months) in ambient air and emit strong luminescence with a high quantum yield (QY) of 40% in the range from 610 nm to 762 nm by varying the reaction temperature of AISe core synthesis from 100 °C to 180 °C. The observed increase of QY and blue-shift in photoluminescence spectra after coating ZnS on surface AISe core NCs are rationalised by the formation of the alloyed structure and passivation of surface states. With their outstanding luminescent properties, AISe core and AISe/ZnS core/shell NCs are very promising in designing emitters for solid-state lighting sources in the greenhouse and in-door farming and bio-related devices.

Self-Powered UV Photodetectors Based on Heterojunctions Composed of ZnO Nanorods Coated with Thin Films of ZnS and CuI

A simple, inexpensive solution process is used to deposit γ-CuI thin films, and many aspects of the films, such as morphology, crystalline phase, and its optical and electrical properties on annealing are studied. All of the grown films exhibited p-type conductivity and an average transmittance of 70 to 80% in the visible region. The film annealed at 200 °C is observed to be relatively smooth with root-mean-square roughness of 13.25 nm. CuI films annealed at 200 °C displayed a hole mobility of 0.53 cm2/Vs and a hole concentration of 8.36 × 1018 cm–3. Additionally, the potential of γ-CuI as a p-type material for photodetection is explored by fabricating transparent hybrid ultraviolet (UV) photodetectors based on p-CuI/n-ZnO nanorods and p-CuI/n-ZnS/ZnO nanostructures. The high-resolution transmission electron microscopy (HRTEM) image showed that the ZnO nanorods grew as a single crystal along the [001] direction and smaller CuI attached on their surface. A simple sulfurization procedure has created a poly-nanocrystalline ZnS shell layer over the ZnO nanorods. Crucial photodetector parameters such as responsivity, external quantum efficiency, and detectivity are analyzed with different illumination intensities and incident wavelengths. Under self-powered conditions, upon illumination with 372 nm and intensity of 0.25 mW/cm2, the p-CuI/n-ZnO nanorod showed significant responsivity of 25.11 mA/W and detectivity of 4.59 × 1013 Jones. Insertion of the ZnS layer between the ZnO and CuI has enhanced these parameters to 43.85 mA/W and 3.84 × 1014 Jones, respectively. This research underlines the potential of p-type CuI as a transparent, high-performance optoelectronic material.

Unraveling the structure-activity-selectivity relationships in furfuryl alcohol photoreforming to H2 and hydrofuroin over ZnxIn2S3+x photocatalysts

ZnxIn2S3+x has emerged as a promising candidate for alcohol photoreforming based on C-H activation and C-C coupling. However, the underlying structure-activity-selectivity relationships remain unclear. Here we report on ZnxIn2S3+x with varying Zn:In:S ratios for visible-light-driven furfuryl alcohol reforming into H2 and hydrofuroin, a jet fuel precursor, via C-H activation and C-C coupling. S-• radicals are directly identified as the catalytically active sites responsible for C-H activation in furfuryl alcohol, promoting selectivity toward H2 and hydrofuroin. The optimum ZnxIn2S3+x activity derives from a trade-off between enhanced carrier dynamics and diminished visible light absorption as the x value in ZnxIn2S3+x increases. Further, a higher Zn-S:In-S layer ratio prolongs the S-• lifetime in the Zn-S layer, promoting C-H activation and delivering a higher C-C coupling product selectivity. The findings represent a step toward further establishing sulfide-based photocatalysts for sustainable H2 production via organic photoreforming.

Development and Characterization of Multilayered Cu/HA/ZnS + PEEK Coating System by Hybrid Technology

In this study, multilayered Cu/HA/ZnS + PEEK coatings were fabricated using hybrid technology on Zr–2.5Nb alloy substrates. The use of electrophoretic deposition (EPD) and heat treatment allowed the 1st base composite ZnS + PEEK layer and the 2nd hydroxyapatite (HA) top layer to be obtained. The EPD kinetics of both layers was studied. Heating at a temperature of 450 °C and slow cooling resulted in densification and sulfonation of PEEK. It also led to an increase in the adhesion of HA particles on the surface of the PEEK + ZnS layer and to the settlement of HA particles deep into the 1st layer. The effect of substrate preparation on the adhesion strength of coatings was investigated. The ZnS + PEEK layer exhibited high adhesion to the chemically treated zirconium alloy. Furthermore, the first layer was characterized by a high scratch resistance. The selective distribution of Cu on the top of the coating was obtained by shadow-masked pulsed laser deposition (PLD). The multilayered coatings exhibited high roughness and mild hydrophobicity. This study showed the possibility of obtaining a multilayered coating system with a controlled distribution of bioactive components (HA) and antimicrobial components (Cu) on its surface using a hybrid method that combined EPD, heat treatment, and PLD.

Analytical model for studying the role of ZnS-doped CdS on the performance of CZTSSe solar cells

This study focuses on thin-film structures made of ITO, CdS, ZnS, CZTSSe, and Mo (i.e., ITO/CdS:ZnS/CZTSSe/Mo) for solar cell applications. The effect of ZnS content on the performance of this cell has been theoretically investigated. The optical losses caused by reflection at various interfaces and absorption in ITO and CdS:ZnS layers have been calculated using the current structure's experimental data. The losses due to charge carrier recombination at the front and back surfaces of the CZTSSe absorber have been calculated using the absorber layer and depletion region parameters. It was discovered that increasing the ZnS content causes more photons to enter the absorber layer, causing the short-circuit current density to increase. Under consideration of optical and recombination losses, a maximum efficiency of about 13.75%, a fill factor of 81.6%, and an open-circuit voltage of 808 mV were obtained for ZnS-content = 0.5.

Stabilizing zinc anodes for long-lifespan zinc–nickel battery through the in-situ construction of zincophilic interface layer

Zinc–nickel batteries are identified as one of the ideal next-generation energy storage technologies because of the advantages of high safety, low cost, and excellent rate performance. However, the limited reversibility of zinc electrode caused by dendrites growth, shape change and side reactions results in poor shelf life and cycling life. To overcome these limitations, a dense and uniform ZnS coating layer is in-situ constructed on ZnO surface to improve the stability of ZnO anode. Charge migration and redistribution occur at the interface of ZnO and ZnS, and an electric field is built, which promotes the charge transfer, enabling the anode with improved reversibility and reactivity. In addition, the ZnS layer protects active zinc from bulk electrolyte, inhibiting side reactions. Moreover, the zincophilic ZnS film regulates the Zn(OH)42− ions concentration gradient and harmonizes the ions migration, mitigating the shape change and dendrites growth. These features endow the ZnO@ZnS350 electrode with stable stripping/plating cycling behavior during 1000 h at 17 mA cm−2. Furthermore, the assembled zinc–nickel battery displayed an improved storage life and a significantly extended cycling life of higher than 790 h even at a high current of 10 A (∼138 mA cm−2) and higher than 690 h at 20 A (∼276 mA cm−2), which was largely longer than that based on ZnO electrodes, demonstrating great promise in practical applications.

Fabrication and characterization of ZnS and ZnSe absorber layers for UV-selective transparent photovoltaics

We have fabricated ZnS, ZnSe and mixed Zn(S,Se) thin film layers for application as solar cell absorbers in ultraviolet (UV)-selective solar cells. We fabricated the thin film layers using a two-step process involving evaporation of the Zn layer followed by an anneal in an H2S and/or H2Se containing atmosphere. A study of the annealing conditions was performed to minimize hole formation in the thin film layer. A mixed Sulfur and Selenium containing layer was also developed in order to reach a 3 eV band gap, such that the layer absorbs all the UV light and leaves the visible light passing through. Next, we tried to increase the conductivity of the layer by adding extrinsic doping elements. Cu was found to increase the conductivity by more than three orders of magnitude, while leaving the transparency of the layer mostly unchanged. Finally, solar cell devices were fabricated using transparent back and front contacts and a NiO buffer layer. We could measure a very small photocurrent of about 100 μA/cm2 and an open circuit voltage of about 500 mV under AM1.5 G illumination.

Impact of the ZnS layer position in a stacked precursor film on the properties of CZTS films grown on flexible molybdenum substrates

In the present study, CZTS thin films were prepared by annealing and reaction of Cu–Sn–ZnS precursor layers. First, sputter deposition was carried out on flexible molybdenum (Mo) foil to form Mo-foil/CuSn/ZnS/Cu, Mo-foil/CuSn/Cu/ZnS and Mo-foil/ZnS/CuSn/Cu stacked precursor structures. Annealing process was performed in sulfur atmosphere using Rapid Thermal Processing (RTP) method to obtain kesterite CZTS phase in the reacted layers. All prepared precursors and CZTS thin films displayed Cu-poor and Zn-rich chemical composition, as targeted. XRD patterns of CZTS samples showed that the kesterite phase was obtained in all samples regardless of the stacking order of the precursor films. However, the full width at half maximum (FWHM) values of the (112) preferential peaks extracted from the XRD patterns, and the corresponding structural parameters (crystallite size and microstrain), indicated that the Mo-foil/ZnS/CuSn/Cu precursor structure yielded more promising crystalline quality. The occurrence of kesterite phase in all samples and existence of low amount of CTS phase were verified by Raman spectroscopy measurements. The CZTS sample prepared employing the Mo-foil/ZnS/CuSn/Cu precursor film structure presented more prominent, homogenous and compact surface microstructure as observed in SEM images. Optical band gap values were found to be in the range of 1.44–1.50 eV. The room temperature photoluminescence (PL) measurements showed that the transitions from the conduction band to intrinsic defect levels dominated the spectra instead of the band-to-band transitions. Electrical characterization of the films showed that Mo-foil/CuSn/ZnS/Cu and Mo-foil/ZnS/CuSn/Cu precursor films yielded lower electrical resistivity and higher carrier concentration due to better crystalline quality. Overall, it was seen that the CZTS thin films produced using the Mo-foil/ZnS/CuSn/Cu stacked precursor layers displayed better properties in terms of crystalline quality, surface microstructure, and optical and electrical properties, which are favorable for photovoltaic applications.

Hierarchical ZnS layers-coated Ti3+-TiO2 nanostructures for boosted visible-light photocatalytic norfloxacin degradation

Self-doped Ti3+-TiO2 and amorphous ZnS layers-coated Ti3+-TiO2 nanostructures were successfully fabricated for via a calcination-ultrasonic synthesis strategy for organic pollutant degradation under visible-light illumination. The experimental results revealed that the synthesized Ti3+-TiO2 clusters displayed efficient visible-light absorption and photocatalytic performance. It was also found that amorphous ZnS layers were formed on the coral-like Ti3+-TiO2 clusters via an ultrasonic synthesis method, and the strongly combined interfaces greatly boosted the charge separation between ZnS layers and self-doped Ti3+-TiO2 clusters. The synthesized Ti3+-TiO2@ZnS-15% heterojunction presented the highest photocatalytic activity with a rate constant of 0.03197 min−1, approximately 9.87 times of commercial TiO2. In addition, the prepared Ti3+-TiO2@ZnS composites also exhibited highly boosted photocatalytic performance towards ciprofloxacin and tetracycline degradation under visible-light illumination compared with those of commercial TiO2, Ti3+-TiO2, and ZnS samples. Finally, the norfloxacin degradation pathways and visible-light photocatalytic mechanism over nanostructured Ti3+-TiO2@ZnS heterojunctions were suggested.

Tuning the Band Structure of Zn-Doped SnS2 Nanosheet-Based Thin Films by Atomic Layer Deposition for Photoelectric Devices

Two-dimensional tin disulfide (SnS2) is attracting attention from researchers in various fields due to its physical, optical, and electrical properties. In addition, research suggests that SnS2 doped with various metals can be used in a wide range of applications. However, few studies of the doping process in tin sulfide thin films with various doping concentrations using atomic layer deposition (ALD) and the super-cycle method have been published. Here, we describe the deposition of pristine SnS2 using ALD and analyze crystallinity, chemistry, and optical and electrical properties of SnS2 doped with various concentrations of zinc by controlling the ratio of SnS2 and ZnS using super-cycle recipes. As the doping concentration increased, a cubic-phase ZnS layer was formed, and chemical binding energies increased, revealing an n-type doping effect. As the doping concentration increased, the transmittance of the thin film increased by up to 80.5%, and the optical band gap increased to 3.43 eV. In addition, the valence-band edge energy increased up to 2.02 eV, and n-type characteristics appeared as the doping concentration of zinc increased as determined by calculation of the electronic band structure. These zinc-doped nanoscale SnS2 materials have potential for optoelectronic applications.

Cover Feature: Heterointerface Engineering of ZnO/CdS Heterostructures through ZnS Layers for Photocatalytic Water Splitting (Chem. Eur. J. 69/2022)

Cover Feature: Heterointerface Engineering of ZnO/CdS Heterostructures through ZnS Layers for Photocatalytic Water Splitting (Chem. Eur. J. 69/2022)

Heterointerface Engineering of ZnO/CdS Heterostructures through ZnS Layers for Photocatalytic Water Splitting.

Solar-driven water splitting to produce clean and renewable hydrogen offers a green strategy to address the energy crisis and environmental pollution. Heterostructure catalysts are receiving increasing attention for photocatalytic hydrogen generation. ZnO/ZnS/CdS and ZnO/CdS heterostructures have been successfully designed and prepared according to two different strategies. By introducing a heterointerface layer of ZnS between ZnO and CdS, a Z scheme charge-transfer channel was promoted and achieved superior photocatalytic performance. A highest hydrogen generation rate of 156.7 μmol g-1 h-1 was achieved by precise control of the thickness of the heterointerface layer and of the CdS shell. These findings demonstrated that heterostructures are promising catalysts for solar-driven water splitting, and that heterointerface engineering is an effective way to improve the photocatalytic properties of heterostructures.

A Novel Strategy to Enhance the Photostability of InP/ZnSe/ZnS Quantum Dots with Zr Doping.

Plentiful research of InP semiconductor quantum dots (QDs) has been launched over the past few decades for their excellent photoluminescence properties and environmentally friendly characteristics in various applications. However, InP QDs show inferior photostability because they are extremely sensitive to the ambient environment. In this study, we propose a novel method to enhance the photostability of InP/ZnSe/ZnS QDs by doping zirconium into the ZnS layer. We certify that Zr can be oxidized to Zr oxides, which can prevent the QDs from suffering oxidation during light irradiation. The InP/ZnSe/ZnS:Zr QDs maintained 78% of the original photoluminescence quantum yields without significant photodegradation under the irradiation of LED light (450 nm, 3.0 W power intensity) for 14 h, while conventional InP/ZnSe/ZnS QDs dramatically decreased to 29%.

Optimizing the size and amount of CdS quantum dots for efficiency enhancement in CdS/N719 co-sensitized solar cells

Co-sensitization of TiO 2 photoanodes in solar cells with Ruthenium dye and quantum dots offer better photovoltaic performance compared to the sensitization by the dye only. In the present study, TiO 2 nanostructured photoanode was co-sensitized with CdS quantum dots and N719 dye. CdS quantum dots were deposited using successive ionic layer adsorption and reaction (SILAR). A suitable thin ZnS interfacial layer has been introduced between two sensitizers to prevent the corrosion of CdS quantum dots by the iodide-based liquid electrolyte. In order to get the highest efficiency, the number of SILAR cycles for CdS quantum dot deposition has been optimized. A power conversion efficiency of 6.79% with short-circuit current density of 15.55 mA cm −2 and open circuit voltage of 764.5 mV have been obtained for the co-sensitized solar cell made with TiO 2 /CdS/ZnS/N719 co-sensitized photoanode under the illumination of 100 mW cm −2 with AM 1.5 spectral filter. Efficiency and short-circuit current density of the solar cell have been enhanced by 11.31% and 6.58% respectively due to the co-sensitization. The optimized co-sensitized solar cell shows a higher incident photon to current conversion efficiency and a reduced electron recombination compared to the solar cell with dye-sensitized photoanode. Higher recombination resistance and longer electron lifetime of the solar cell with CdS/ZnS/N719 co-sensitized TiO 2 photoanode have contributed to the increased short circuit current and open circuit voltage leading to the enhanced efficiency of 6.79% which is among the highest for a co-sensitized dye sensitized solar cell . • TiO 2 photoanode was co-sensitized with CdS quantum dots and N719 dye. • ZnS layer was introduced between CdS and N719 to prevent the corrosion of CdS. • Number of CdS SILAR cycles was optimized to get the highest solar cell efficiency. • Solar cell efficiency of 6.79% was obtained for TiO 2 /CdS/ZnS/N719 photoanode. • New photoanode showed a high recombination resistance and long electron lifetime. • 6.79% is among the highest efficiencies reported for co-sensitized solar cells.

Dislocation equilibrium positions in bilayer structures

The stability of an edge dislocation embedded in a two-dimensional structure composed of one layer of ZnS and one layer of Ge has been theoretically investigated from a Peach–Koëhler force-based analysis in the absence of misfit stress and layer bowing effects. The effect of thickness ratio between the two layers of heterogeneous elastic coefficients has been characterized on the different equilibrium positions of the dislocation through the study of the climbing component of the Peach–Koëhler force. It is found that the number (from 3 to 5) and nature (stable or unstable) of these equilibrium positions distributed in both layers vary significantly as a function of the thickness ratio.

Surface Cu+ modified ZnIn2S4 for promoted visible-light photocatalytic hydrogen evolution

Surface modification by metal ion has been considered a promising strategy to enhance the photocatalytic activity by extending optical response and improving charge separation and transportation. Here, univalent copper species were modified on ZnIn2S4 photocatalyst via an in-situ photodeposition method, exhibiting a much higher H2 evolution rate of 41.10 ± 3.43 mmol g−1 h−1 and an impressive apparent quantum efficiency (AQE) of 20.81% at 420 ± 15 nm. Our characterizations indicate that the surface modification by copper species can broaden light utilization as well as promote charge separation and transportation. Besides, the density functional theory (DFT) results further exhibit that the energy levels (LUMO and HOMO) for copper-surface modified ZnIn2S4 present spatial separation, locating on the Zn-S and In-S layers, respectively, which can suppress the recombination of electron and hole and thus achieves higher photocatalytic H2 evolution efficiency.

Photophysics and photovoltaic properties of Zn-alloyed Ag-In-S quantum dots sensitized solar cells

Quantum dots (QDs) have attracted attention for use in photovoltaic applications. However, till now, QDs sensitized liquid junction solar cells (QDSCs) are primary concentrated on binary QDs that contain toxic elements which limit their practical applications in regarding of environmental issues. Hence, the study of less-toxic ternary such as AgInS2 (AIS) and CuInS2 (CIS) or core/shell AIS/ZnS and CIS/ZnS QDs with high power conversion efficiency (PCE) is the most common way for commercial applications. Although significant improvement has been realized for AIS (CIS) QDSCs by overgrowth of wide bandgap ZnS to form quasi type-I core/shell structure for eliminating surface trapping defects where the PCE is comparable or even better than toxic QDs, simultaneously the shell could also cause impeding electron injection from QDs to metal oxide matrix (TiO2) and hole scavenge. For resolving this problem, diffusion of Zn2+ into QDs forming alloyed QDs is a better strategy to improve the conductivity and thus the PCE owing to alloyed QDs could not only reduce the density of trap defects but also regulate the bandgap and contribute to electron injection. Herein, the highly luminescent heavy-metal free and hydrophilic Ag-In-S-Zn alloyed QDs with broad light harvesting range to near infrared (NIR) were synthesized as effective sensitizer for constructing QDSCs, where the optimal PCE of 3.12% was achieved. Moreover, surface passivation by deposition of ZnS layer over the sensitized electrode was also primarily studied to decrease the QDs/electrolyte/TiO2 interface recombination and a champion PCE of 3.78% was obtained.