Thickness Of ZnS Layer Research Articles

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.

Optical properties upon ZnS film thickness in ZnS/ITO/glass multilayer films by ellipsometric and spectrophotometric investigations for solar cell and optoelectronic applications

ZnS film with various thicknesses (d ≈ 100–350 nm) deposited on the ITO coated glass substrate (ZnS/ITO/glass) by an electron beam evaporation process was examined structurally and optically. Different techniques were used to specify and analyze the optical characteristics of the film, such as spectroscopic ellipsometric (SE) and spectrophotometric (SP). The ZnS/ITO/glass films exhibit a wurtzite hexagonal type structure entrenched in the crystalline background of ITO film. XRD analysis revealed changes in structural and microstructural parameters, such as a decrease in lattice parameters, a reduction in microstrain, and a raise in crystallite size. The optical constants and the optical energy gap were extracted from SE by constructing an ellipsometric optical model, while the optical constants were calculated from SP by using Murmann's exact equations. It was seen that the overall behaviour of the refractive index n of the ZnS/ITO/glass films obtained from SE and SP increases with an increase in ZnS layer thickness, which is attributed to the increment of the size of the grain. It was additionally found that, the overall behaviour of the extinction coefficient k of the ZnS/ITO/glass films increases, when the thickness of the ZnS layer increments. Also, the direct optical transition was observed with energy band gap diminishes from 3.423 (d = 100 nm) eV to 3.287 eV (d = 350 nm) that is because of the rise in grain size, the decrease in microstrain, and reduction in lattice constants. Furthermore, it was found that the deposition of ZnS on ITO coated glass substrate increases the absorption compared with the ZnS/glass film and then reduces the transmittance and energy band gap. It was concluded that as the ZnS thickness increases, the optical constants of ZnS/ITO/glass films enhance. Finally, the overall behaviour of the optical constants within the experimental error range of the ZnS/ITO/glass films with different ZnS layer thicknesses obtained by SE was found to be consistent with that calculated from SP measurement. • Synthesis of various thicknesses (d ≈ 100–350 nm) of (ZnS/ITO/glass) via electron beam evaporation. • Investigation of the effects of film thickness on the optical and structural properties of (ZnS/ITO/glass). • The increase in ZnS thickness led to enhance the optical constants of ZnS/ITO/glass films.

Restricted charge recombination process in PbS quantum dot sensitized solar cells by different coating cycles of ZnS films

The relatively low power conversion efficiency (PCE) of quantum dot sensitized solar cells (QDSSCs) is attributed to charge recombination at the interfaces. Charge recombination process could be suppressed by coating the QD layer with a wide band gap semiconductor such as ZnS, which acts as a blocking layer between the QDs and hole transport material (HTM). In present study, to improve PCE of PbS quantum dot sensitized solar cells, ZnS passivation layer has been successfully fabricated on PbS (QDs) by simple successive ion layer adsorption and reaction (SILAR) method at room temperature and ambient pressure. The effect of ZnS layer thickness on the photovoltaic properties was investigated by changing the coating cycles (n). Experimental results showed that ZnS passivation layer improved the photovoltaic performances of PbS QDSSCs by hindering the charge recombination process. The solar cell containing of ZnS layer with n=6 showed higher (short-circuit current density (Jsc), fill factor (FF) and PCE of 11.11mA.cm-2, 60.37% and 3.96%, respectively. By increasing the number of coating cycles to an optimum value of 6, the solar cell efficiency improved. We explored the reasons for this improvement and demonstrated that it is caused by a lower charge recombination of photo-injected electrons with the holes of HTM. The effect of coating cycles has been investigated by UV–Vis spectra and current density–voltage analysis.

The Effects of ZnS Thickness on the Photocatalytic Performance of ZnO/ZnS Heterostructures

Well aligned ZnO/ZnS heterostructures with different thichness of ZnS layer have been synthesized on ITO substrates by a simple SILAR method. The morphology properties of as grown heterostructures were investigated by SEM and TEM images. From the SEM and TEM results, the thickness of ZnS layer increased with the increased SILAR period. When SILAR period was 10 times, the chickens of ZnS layer was about 24 nm. ZnO/ZnS(10) structure shows the highest photocatalytic activity. Although ZnO/ZnS heterostructures do not show very high photocatalytic activity, ZnO/ZnS heterostructures will attract increased attention due to its multifunction and low cost.

Optical Properties of Double-Shell Hollow ZnS–Ag2S Nanoparticles

The light emission properties of semiconductor nanoparticles are important for their applications in optical imaging, sensors, or lasers. ZnS nanoparticles are particularly useful for these applications, but the main hindrance for their widespread use are the low emission properties of pure ZnS nanoparticles. Formation of a core/shell structure is one way that has been used to improve the emission properties of pure ZnS in recent years. This study reports a unique synthesis route and the optical properties of double-shell ZnS–Ag2S hollow nanoparticles. Light emission properties of hollow Ag2S/ZnS are maximum (39%) compared to those of hollow ZnS/Ag2S (21%) or pure ZnS (14%) nanoparticles, and these properties highly depend on the external ZnS layer thickness.

Surface plasmon polaritons launched using a terahertz free-electron laser: propagation along a gold–ZnS–air interface and decoupling to free waves at the surface edge

In this paper, we experimentally study the propagation of surface plasmon polaritons (SPPs) along gold–ZnS–air interfaces and their diffraction at the surface edge. The SPPs were launched by the waveguide method using monochromatic radiation of the Novosibirsk Free-Electron Laser, operated at the wavelength 140 μm. SPP characteristics were studied via examination of the electromagnetic field of diffracted waves employing two terahertz sensors: a movable Golay cell and an optical system, consisting of a TPX lens and a 320×240 microbolometer focal plane array (MBFPA) recording images with a rate of 17  frames/s. The experimentally recorded intensity distribution of the diffracted wave in the direction normal to the surface differed from the evanescence wave distribution in the SPP, but their characteristic widths were practically the same and coincided with the theoretical calculations made within the Drude model [Phys. Rev. A87, 023828 (2013)]. Diffracted wave characteristics drastically changed when ZnS-layer thickness increased from 0 to 0.75 μm. The angular distributions grew from 0.16 to 3.6 deg, but the characteristic beam width decreased from 8 to 0.35 mm, which is promising for a number of applications. The propagation length of SPPs therewith decreased from 31 to 11 mm, which is 3 orders of magnitude less than the Drude theory predicts. Prospects for further studies are discussed.

Exciton Binding Energy under Electric Field in ZnTe1-xSx/ZnS Strained-Layer Superlattices

Conduction and valence band offsets in ZnTe1-xSx/ZnS strained-layer superlattices (SLSs) are calculated as a function of sulfur (S) concentration (x). The valence band offsets markedly decreases with increasing x because the energy difference between the band gaps ZnS and ZnTe1-xSx decreases with increasing x. Exciton binding energy in the ZnTe1-xSx/ZnS SLSs decreases with increasing ZnTe1-xSx and ZnS layer thickness. This system has two exciton systems under an applied electric field. The energy splitting of the exciton systems increases with increasing electric field strength.

Composite polymeric particles with ZnS shells

We report on a preparation of hybrid particles with polymeric cores and ZnS shells. Two types of monodisperse sterically stabilized polystyrene particles with hydroxyl-terminated PEG chains (PS/PEGMA) or β-diketone groups (PS/AAEM) on the surface have been prepared and characterized. Formation of ZnS layer on the surface of submicron particles has been studied by SEM and EDX. Deposition of ZnS on the surface of PS/PEGMA particles is not uniform and leads to formation of ‘raspberry’ morphology with rough surface. It has been found that presence of β-diketone groups on the particle surface leads to formation of well-defined ZnS layers. It has been assumed that such effect is due to the complexation of Zn cations by β-diketone groups leading to nucleation and growth of ZnS crystals on the polymer particle surface. Polymeric particles were completely covered with ZnS if the loaded amount of inorganic material was higher then 40wt%. The thickness of ZnS layer on the particle surface can be easily varied by changing the ZnS load (in present study maximal thickness of the ZnS shell was 70nm). It has been found that increase of the ultrasound power leads to considerable increase of the ZnS deposition on the particle surface without strong changes of the particle morphology. Hybrid particles have been investigated with XRD technique and their optical properties were studied by UV-spectroscopy. The colloidal stability of obtained particles was studied by separation analyser. Sedimentation experiments indicate that colloidal stability of obtained composite particles depends strongly on loaded ZnS amount and pH value of the aqueous medium. It has been found that highest sedimentation velocities (or maximum of instability) were determined by ZnS loads, which provide complete coverage of the particle surface. Increase of the ZnS layer thickness led to better stability of hybrid particles in aqueous medium.

Low-voltage driven ZnS:Mn MIS and MISIM thin film electroluminescent devices with Eu2O3 insulator layer

AC thin film electroluminescent devices of MIS and MISIM have been fabricated with a novel dielectric layer of Eu2O3 as an insulator. The threshold voltage for light emission is found to depend strongly on the frequency of excitation source in these devices. These devices are fabricated with an active layer of ZnS:Mn and a novel dielectric layer of Eu2O3 as an insulator. The observed frequency dependence of brightness-voltage characteristics has been explained on the basis of the loss characteristic of the insulator layer. Changes in the threshold voltage and brightness with variation in emitting or insulating film thickness have been investigated in metal-insulator-semiconductor (MIS) structures. It has been found that the decrease in brightness occurring with decreasing ZnS layer thickness can be compensated by an increase in brightness obtained by reducing the insulator thickness. The optimal condition for low threshold voltage and higher stability has been shown to occur when the active layer to insulator thickness ratio lies between one and two.

Temperature dependence of photoluminescence of ZnS-ZnSe superlattices

Undoped and In-doped ZnSe and ZnS-ZnSe SL films were prepared on GaAs (100) substrate by hot wall epitaxy and their photoluminescence was measured at temperatures ranging from 4.2 to 300 K. It was found that the photoluminescence associated with the band edge and with the D(In)-A pair shifted with temperature in a similar way to that of the band gap of the bulk. Photoluminescence associated with deep level defects is discussed in relation to strain and shallow levels. Moreover ZnS-ZnSe SLs with various thickness of ZnS layer (barrier layer) were prepared and the photon energies of their PL were analysed using the Kronig-Penney model to discuss band offsets Δ E c and Δ E v.

Green Electroluminescence in Low-Voltage-Driven Metal-Insulator-Semiconductor Structure Devices

Changes in emission waveforms and brightness with variations in emitting or insulating film thickness have been investigated in Metal-Insulator-Semiconductor (MIS) structure thin-film electroluminescent (TFEL) devices, such as Glass/In2O3/ZnS:TbF3/Sm2O3/Al. It is found that the decrease in brightness with decreasing ZnS layer thickness can be compensated by an increase in brightness obtained by reducing the insulator thickness, and the emission intensity ratio with regard to the applied voltage polarity (P(Al-)/P(Al+)) is proportional to the film thickness ratio of the emitter and the insulator (dZ/dI), in MIS-TFEL devices. Under the optimal condition dZ/dI=1∼2, when P(Al-)≃P(Al+), bright green electroluminescence of 400 fL and 830 fL with threshold voltages of 37 V and 57 V, respectively, are obtained under 5 kHz sinusoidal voltage excitation.