Polycrystalline ZnS Research Articles

Investigation on the Machinability of Polycrystalline ZnS by Micro-Laser-Assisted Diamond Cutting.

Polycrystalline ZnS is a typical infrared optical material. It is widely used in advanced optical systems due to its excellent optical properties. The machining accuracy of polycrystalline ZnS optical elements must satisfy the requirements of high-performance system development. However, the soft and brittle nature of the material poses a challenge for high-quality and efficient machining. In recent years, in situ laser-assisted diamond cutting has been proven to be an effective method for ultra-precision cutting of brittle materials. In this study, the mechanism of in situ laser-assisted cutting on ultra-precision cutting machinability enhancement of ZnS was investigated. Firstly, the physical properties of ZnS were characterized by high-temperature nanoindentation experiments. The result revealed an increase in ductile machinability of ZnS due to plastic deformation and a decrease in microhardness and Young's modulus at high temperatures. It provided a fundamental theory for the ductile-brittle transition of ZnS. Subsequently, a series of diamond-cutting experiments were carried out to study the removal mechanism of ZnS during in situ laser-assisted cutting. It was found that the mass damage initiation depth groove generated by in situ laser-assisted cutting increased by 57.99% compared to the groove generated by ordinary cutting. It was found that micron-sized pits were suppressed under in situ laser-assisted cutting. The main damage form of HIP-ZnS was changed from flake spalling and pits to radial cleavage cracks. Additionally, the laser can suppress the removal mode difference of different grain crystallographic and ensure the ductile region processing. Finally, planning cutting experiments were carried out to verify that a smooth and uniform surface with Sa of 3.607 nm was achieved at a laser power of 20 W, which was 73.58% better than normal cutting. The main components of roughness were grain boundary steps and submicron pit. This study provides a promising method for ultra-precision cutting of ZnS.

Synthesis of micro- and nano-sized zinc sulfide crystallites by the method of self-propagating high-temperature synthesis

The paper presents the results that demonstrate how ZnS crystallites of different sizes can be obtained by the method of self-propagating high-temperature synthesis (SHS). The SHS is possible due to an exothermic reactions occurring in mixtures of Zn and S powders, due to a large amount of heat released (enthalpy of formation being 202 kJ/mol). Pressed powders of Zn and S are placed in a stoichiometric ratio into a reactor filled with Ar or N under a pressure of P>0.5 MPa. After initiated by ignition, the chemical reaction propagates through the mixture to produce a sample in the form of an ingot. ZnS crystallites with a characteristic size of ~ 30 μm are obtained in the traditional solid-state reaction of the SHS. Аfter the passage of the combustion wave, the reaction of the components continues in parallel with crystallization processes, which causes the formation of an active medium where self-organization processes occur. Sometimes, abnormally large ("giant") crystallites with length ~ 1 mm, thickness 0.1-0.2 mm, and regularly-shaped spatial structures are observed. The size of synthesized zinc sulfide crystallites can be changed with a dispersant, NH4Cl. When 5 wt.% of the dispersant is introduced, the monolithic sample is polycrystalline ZnS with a characteristic grain size of ~ 40 μm, and when 7 wt.% is introduced, the grain size decreases to 20 μm. As the concentration of the dispersant is increased to 10 wt. %, the synthesized material becomes loose, the characteristic grain size decreasing to 5-10 μm. At concentrations greater than 10 wt. %, powder-like ZnS is formed. The SHS method makes it possible to obtain meso- and nano-sized ZnS, with grain sizes of order 50 – 100 nm and 2 – 50 nm, respectively, in two ways. The first one consists in the condensation of the substance’s vapor in a rarefied inert atmosphere. When, during the SPS, the pressure of the inert gas changes in the interval from 40 to 400 Pa, a part of the reactants in the form of steam escapes from the ampoule into the reactor bulk. When the steam particles collide with the inert gas atoms, they quickly lose their kinetic energy to form particles with sizes of 2 to 100 nm. To form particles of the required size, it is necessary to adjust the pressure of the inert gas in the reactor. The second method for obtaining nanoparticles by the SBC is based on the use of an inert diluent, which prevents the growth of the forming particles. The main requirement for the diluent material is its inertness to both the reagents in the charge and the synthesized material. The effect of changing the pressure of the inert gas on the size of the obtained nanoparticles manifests itself both directly and indirectly—through the size of the condensation zone. As the gas pressure increases, its density increases, heat removal increases, the rate of crystallization center formation in the gas phase decreases, but the rate of crystal growth increases. As a result, so does the size of the resulting particles. The shape of nanoparticles obtained by this method depends on their size. Nanoparticles of size <20 nm have a shape close to spherical, which is a result changing the relative fraction of the surface energy in the total energy of a nanoparticle as its size decreases. Larger-size particles are faceted.

Influence of Al3+, Ga3+, and In3+ substitution on the structural, microstructural and dielectric characteristics of ZnS nanoparticles

Trivalent metal cations modified polycrystalline ZnS nanoparticles, Zn0.95X0.05S (X = Al3+, Ga3+, & In3+) NPs, were synthesized using co-precipitation technique and their physicochemical investigations were carried out. Structural analysis revealed that all the compositions display cubic crystallinity having Fm3‾m space group as evident from Rietveld refinement technique. The average crystallite size evaluated using Williamson-Hall plot was found to be 4.75 nm, 5.17 nm, and 5.76 nm for Zn0.95Al0.05S NPs, Zn0.95Ga0.05S NPs, and Zn0.95In0.05S NPs respectively. Microstructural studies depicted the nanoscale formation of nanoparticles with uniform grain distribution where the average grain size was observed between 38.2 nm and 45.4 nm. FT-IR spectra analysis confirmed the formation of Zn0.95Al0.05S, Zn0.95Ga0.05S, and Zn0.95In0.05S NPs with high frequency stretching vibrations about 465 cm−1 and 654 cm−1, belonging to the weak and strong edge of elemental regions. The value of the dielectric constant in the lower frequency region was found to be maximum (27.2) for Zn0.95In0.05S NPs and least (17.8) for Zn0.95Al0.05S NPs. It was observed that ac conductivity increases sharply with the increasing frequency of the applied electric field. The measured values of ac conductivity at 1 kHz for Zn0.95Al0.05S NPs, Zn0.95Ga0.05S NPs, and Zn0.95In0.05S NPs were found to be 5.06 × 10−7 Ω−1cm−1, 1.24 × 10−6 Ω−1cm−1, and 1.28 × 10−6 Ω−1cm−1, respectively.

Mesoscale modeling of light transmission modulation in ceramics

We present a modeling approach for simulating and predicting spatially resolved properties of polycrystalline ceramics with coupled optical, elastic and dielectric degrees of freedom. This approach is implemented in the Ferret application, built upon the Multiphysics Object Oriented Simulation Environment (MOOSE) finite-element framework, that allows for the determination of the dependency of optical properties on polycrystalline grain orientation, size, and shape, as well as the action of externally applied electric fields and mechanical distortions. For the evaluation of optical transmission through a polycrystal we adopt a modification of the wave-retardation theory, originally developed by Raman and Viswanathan in 1955. The coupled model produces excellent agreement with experimental results obtained for polycrystalline Al2O3, Ce-doped Y3Al5O12, and ZnS which are used as test cases in this investigation, to evaluate both the visible and infrared parts of the electro-magnetic spectrum. Simulations of the optical properties modulation under different applied mechanical and electrical boundary conditions predict large changes to transmission, including switching from full transparency to opacity in some instances. The results of this investigation highlight a remarkable promise of functional nano- and micro-ceramics for a wide range of advanced engineering applications, including broad spectrum windows with high frequency transparency modulation, and multifunctional metamaterials by design.

Self-starting mode-locked Cr:ZnS laser using single-walled carbon nanotubes with resonant absorption at 2.4 μm.

We develop a mode-locked Cr:ZnS polycrystalline laser using single-walled carbon nanotubes (SWCNTs) that have resonant absorption at the wavelength of 2.4μm. The laser generates ultrashort pulses of 49fs duration, a 2.4μm center wavelength, and a 9.2THz (176nm) spectral span at a repetition rate of 76MHz. We also confirm self-starting of the mode-locked operation. SWCNTs, if appropriately controlled in terms of their diameters, prove to be useful as ultrafast saturable absorbers in the mid-infrared region.

Preparation, composition, and mechanical properties of CVD polycrystalline ZnS

Polycrystalline ZnS samples with a slight composition fluctuation are grown by chemical vapor deposition (CVD) method, and their optical and mechanical properties and microstructure were investigated in detail. The CVD samples present a maximum transmittance of ∼73% in the 7–10 μm region. By changing the sulfur content, a maximum Knoop hardness of 2.375 GPa was found in the Zn50.06S49.94 sample, while Zn46.84S53.16 presents a high flexural strength of 133.8 MPa. The microstructural origin of this abnormal changing of mechanical properties was discussed according to the results of micrographs, XRD patterns and Raman spectra. The results suggest that beside the main phase of zincblende, a small amount of wurtzite is existed. This composited microstructure is responsible for the higher hardness and strength of CVD ZnS.

Even and odd harmonics-enhanced supercontinuum generation in zinc-blende semiconductors

We report on even and odd harmonics-enhanced supercontinuum generation in polycrystalline ZnS and ZnSe samples, as pumped by femtosecond mid-infrared pulses. We demonstrate that efficient generation of multiple harmonics takes place due to random quasi-phase matching, which is an intrinsic property of polycrystalline structure that supports multiple simultaneous three-wave mixing processes over a broad wavelength range. More specifically, using sub-μJ, 60 fs, 3.6 μm input pulses, we measured multi-octave supercontinuum spectra spanning the 0.4–5 μm and 0.5–5 μm wavelength ranges in ZnS and ZnSe samples of few mm thickness, respectively. Even and odd harmonics up to the 10th order in ZnS and up to the 8th order in ZnSe were recorded with the input pulses at 4.6 μm. In contrast, filamentation in ZnTe single crystal is shown to produce only a moderate spectral broadening, which is accompanied by the generation of just second and third harmonics, highlighting the advantages of the polycrystalline structure of zinc-blende semiconductors to generate ultrabroadband radiation.

Two Stages of Impact Fracture of Polycrystalline ZnS and ZnSe Compounds

Mechanoluminescence (ML) in ductile solids is caused by the motion of charged dislocations in the deformable material. Interatomic bond ruptures followed by electronic structure reconfiguration are the main source of ML in brittle bodies. We studied ML in ceramics composed of mixed ionic/covalent ZnS and ZnSe compounds, which are generated during impact loading higher than the limit deformation. Depending on synthesis method and thermal treatment, the resulting ceramics had different size and geometry of grains and intergrain boundary structure, which presumably may have a significant effect on the dislocation glide. In both materials, the time sweeps of ML pulses have two well-resolved peaks. The position of the peaks along the time axis is substantially dependent on the size of ceramic-forming grains and, to a smaller extent, on the barrier properties of intergrain boundaries. The first peak is associated with plastic deformation preceding disintegration of the crystal structure. The second peak emerges upon crack nucleation as interatomic bonds are ruptured and the material is undergoing local deformation in tips of propagating cracks. The distributions of ML pulse amplitudes (the dependences between the number of pulses and their amplitude) calculated for both peaks individually follow the power law, which demonstrates that the electronic processes having different excitation mechanisms (dislocation motion vs bond rupture) are correlated.

Temperature-dependent optical constants of highly transparent solids determined by the combined double optical pathlength transmission-ellipsometry method.

The optical constants of five highly transparent substrates (polycrystalline BaF2, CaF2, MgF2, ZnSe, and ZnS) were experimentally determined based on a combined technique using both the double optical pathlength transmission method and the ellipsometry method within temperature range 20°C-350°C in the ultraviolet-infrared region (0.2-20μm). The results show that the refractive index spectra of polycrystalline BaF2, CaF2, and MgF2 are similar, but differ from that of polycrystalline ZnSe and ZnS. The thermo-optic coefficient of these highly transparent substrates increases with increasing temperature. The absorption indices show a significant temperature-dependent behavior, which increases with increasing temperature from 20°C to 350°C over the transparent region. For the sake of application, the fitted formulas of the refractive index of the five highly transparent substrates as a function of wavelength and temperature are presented.

Vertically Aligned ZnO@ZnS Nanorod Chip with Improved Photocatalytic Activity for Antibiotics Degradation

The photocatalytic degradation for environmentally hazardous substances has been widely explored with the use of various photocatalysts and techniques. It still remains a challenge to achieve efficient degradation and removal of residual antibiotics in the water environment. Here, we report an improved photocatalytic activity chip for degradation of antibiotic tetracycline hydrochloride by perpendicular ZnS-coated ZnO nanorod arrays (ZnO@ZnS NAs). The enhanced photocatalytic activity contributed to the polycrystalline ZnS shell’s effective inhibition of the recombination of photogenerated electron–hole pairs. Meanwhile, vertically aligned ZnO@ZnS nanorod arrays can increase the light harvesting ability by enhancing scattering of light among ZnO@ZnS NAs. On the basis of these findings, an improved photocatalytic activity ZnO@ZnS NA chip has been fabricated by growth of ZnO NAs on a piece of silicon wafer and further sulfurization. More importantly, ZnO@ZnS NA chips have been utilized to construct a ladderlike device, purifying antibiotics wastewater in one step, to effectively degrade tetracycline hydrochloride with enhanced photocatalytic efficiency in flowing contaminated water. In addition, the ZnO@ZnS NA device exhibited excellent recyclability in multiple repeated cycles. The ZnO@ZnS NA chip provided a convenient and fast strategy for removal of antibiotics and pharmaceutical residues in wastewater.

Optical and structural analysis of ZnS core-shell type nanowires

ZnS core-shell type nanowires were grown by the hot filament chemical vapor deposition technique using ZnS powders as solid source and molecular hydrogen as reactant gas. The growth temperature was varied ranging from 200 to 400 °C. X-ray diffraction patterns and micro-Raman spectra show that the grown material is formed by hexagonal and cubic crystalline ZnS combined phases. Micrographs revealed the formation of nanostructures with a pyramidal morphology ending with long tips. The tip endings measurement gives 600 nm-length and 20 nm-diameter. High resolution images indicate the formation of the core-shell type nanostructures with metallic zinc core and polycrystalline ZnS shell. The photoluminescence spectra of the nanowires are caused by native defects, elemental sulfur species on the surface and structural defects in the nanostructures.

Design of the ZnS/Ge/GaSe pn interfaces as plasmonic, photovoltaic and microwave band stop filters

Abstract In the current work, we report and discuss the features of the design of a ZnS (300 nm)/Ge (300 nm)/GaSe (300 nm) thin film device. The device is characterized by the X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy (EDS), optical spectroscopy, microwave power spectroscopy and light power dependent photoconductivity. While the X-ray diffraction technique revealed a polycrystalline ZnS coated with two amorphous layers of Ge and GaSe, the hot probe tests revealed the formation of pn interface. The optical spectra which were employed to reveal the conduction and valence band offsets at the ZnS/Ge and Ge/GaSe interface indicated information about the dielectric dispersion at the interface. The dielectric spectra of the ZnS/Ge/GaSe heterojunction which was modeled assuming the domination of surface plasmon interactions through the films revealed a pronounced increase in the drift mobility of free carriers in the three layers compared to the single and double layers. In the scope of the fitting parameters, a wave trap that exhibit filtering properties at notch frequency of 2.30 GHz was designed and tested. The ac signals power spectrum absorption reached ∼ 99%. In addition, the photocurrent analysis on the ZnS/Ge/GaSe interface has shown it is suitability for photovoltaic and photosensing applications.

Synthesis and characterization of ZnS nanotubes assisted by ethylene glycol

This paper is focusing on the synthesis and characterization of poly-crystalline ZnS nanotubes. The ZnS@ZnO core/shell nanorods were formed by replacing O2− ions with S2− ions released by hydrolyzed thioacetamide assisted by ethylene glycol; then, ZnS@ZnO core/shell nanorods were etched with potassium hydroxide solution to remove the ZnO core. Elaborate characterizations were carried out to show the fine crystalline structure. The key factor of preparing poly-crystalline ZnS nanotubes is the control over the replacement process of O2− ions by S2− ions with the assistance of ethylene glycol to inherit the morphology of ZnO nanorods.

Charge state and energy transfer investigation of iron-chromium co-doped ZnS polycrystalline prepared by step-temperature diffusion for mid-infrared laser applications

The spectroscopic characterization and energy transfer mechanism of iron-chromium co-doped ZnS polycrystalline (Cr,Fe:ZnS) were reported with dimension of 10 mm × 10 mm × 1.5 mm produced by step-temperature thermal diffusion method. The infrared absorption is characterized by two absorption broad-bands centered at 1.67 μm and 2.9 μm which can be attributed to the spin-allowed transition 5T2↔5E within the 3 d4 shell of Cr2+ and Fe2+ ions. The valences of iron and chromium in ZnS were analyzed by X-ray photoelectron spectroscopy. Photoluminescence spectrum shows a relatively strong broad emission band centered at 4 μm with a width of 800 nm (FWHM) under 1.56 μm excitation at room temperature and reveals an effective Cr2+→Fe2+ energy transfer process. The measured photoluminescence decay was about 5 μs at room temperature. All the results indicate that Cr,Fe:ZnS could be used as the gain medium operating at 3.5–4.5 μm via Cr2+→Fe2+ energy transfer using a more convenient laser pump source in the near IR region.

One-Step Synthesis of Single-Wall Carbon Nanotube-ZnS Core-Shell Nanocables.

Nanocables with a single-wall carbon nanotube (SWCNT) core and a ZnS shell were directly synthesized in one step through a thermal reaction method by using carbon, Zn, and FeS powder as starting materials. The as-fabricated nanocables were studied using scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The nanocables have diameters of ~50 nm, lengths of several micrometers, and shell thickness of ~20 nm. TEM analysis revealed that the shell is polycrystalline wurtzite-type ZnS with good crystallinity, and the core of the nanocables is one to several SWCNTs. Raman results showed that the diameters of SWCNTs core are mainly distributed at 1.28 and 1.16 nm, with high quality and metallic character. A growth mechanism is proposed to explain the formation of the nanocables. This simple method may be applied to other SWCNTs-metal sulfide nanocables, which may have potential applications in photocatalysts, photocurrent, and other optical-electrical devices.

Room-temperature laser on a ZnS:Fe2+ polycrystal with a pulse radiation energy of 0.6 J

A laser on polycrystalline ZnS:Fe2+ samples pumped at room temperature by a pulsed electrodischarge HF laser was investigated. Samples of zinc sulphide grown by the method of chemical vapour deposition (CVD) were doped with iron ions from two sides by the diffusion method. The doping of the crystals was performed using the process of hot isostatic pressing (HIP treatment) at an argon pressure of 100 MPa and a temperature of 1265 °С. A longer duration of HIP treatment resulted in a greater depth of sample doping and higher slope efficiency of the laser. For a crystal subjected to HIP treatment for 151 h, a generation energy 660 mJ was obtained. The values of the slope and total efficiency of the energy absorbed in an active element were, respectively, ηslope = 36% and ηabs ≈ 26%. Based on the results obtained, and data from earlier published works, a conclusion has been made that to enhance the generation characteristics of a ZnS:Fe2+ laser it is necessary to increase the temperature of the HIP treatment of CVD ZnS.

ZnS semiconductor quantum dots production by an endophytic fungus Aspergillus flavus

The development of reliable and eco-friendly processes for the synthesis of metal sulphide quantum dots has been considered as a major challenge in the field of nanotechnology. In the present study, polycrystalline ZnS quantum dots were synthesized from an endophytic fungus Aspergillus flavus. It is noteworthy that apart from being rich sources of bioactive compounds, endophytic fungus also has the ability to mediate the synthesis of nanoparticles. TEM and DLS revealed the formation of spherical particles with an average diameter of about 18nm and 58.9nm, respectively. The ZnS quantum dots were further characterized using SEM, EDAX, XRD, UV–visible spectroscopy and FTIR. The obtained results confirmed the synthesis of polycrystalline ZnS quantum dots and these quantum dots are used for studying ROS activity. In addition this paper explains kinetics of metal sorption to study the role of biosorption in synthesis of quantum dots by applying Morris-Weber kinetic model. Since Aspergillus flavus is isolated from a medicinal plant Nothapodytes foetida, quantum dots synthesized from this fungus may have great potential in broad environmental and medical applications.

High-power resonantly pumped passively Q-switched Ho:GdVO4 laser

In this paper, a passively Q-switched Ho:GdVO4 laser resonantly pumped by a 1.94 μm Tm-fiber laser is demonstrated for the first time to the best of our knowledge. By using a Cr2+:ZnS polycrystalline as the saturable absorber, the output performance of the passively Q-switched Ho:GdVO4 laser was investigated. The maximum average output power of 8.4 W was achieved at the absorbed pump power of 32.6 W, the corresponding minimum pulse width was 43.2 ns, and the pulse repetition frequency was 126.7 kHz. In addition, the beam quality factors M 2 ~ 1.13 and M 2 ~ 1.10 were measured at the maximum output level.

Mid-infrared laser emission from Cr:ZnS channel waveguide fabricated by femtosecond laser helical writing.

The operation of a mid-infrared laser at 2244 nm in a Cr:ZnS polycrystalline channel waveguide fabricated using direct femtosecond laser writing with a helical movement technique is demonstrated. A maximum power output of 78 mW and an optical-to-optical slope efficiency of 8.6% are achieved. The compact waveguide structure with 2 mm length was obtained through direct femtosecond laser writing, which was moved on a helical trajectory along the laser medium axis and parallel to the writing direction.

High-energy room-temperature Fe2+:ZnS laser

Characteristics of a room temperature laser on polycrystalline ZnS:Fe2+ subjected to diffuse doping from two sides were investigated. The sample was pumped by a non-chain electrodischarge HF laser with the FWHM duration of the radiation pulse of ~140 ns. The diameter of the pumping radiation spot on the surface of the crystal was 3.8 mm. Further increases in the size of the pumping spot were limited by parasitic generation arising due to a high concentration of Fe ions in the near-surface layer of the sample at a relatively small depth of doping (short length of active medium). The generation energy of 25.5 mJ was obtained at a slope efficiency of 12% with respect to the energy incident on the sample. Characteristics of lasers on polycrystalline ZnS:Fe2+ and ZnSe:Fe2+ have been compared in equal pumping conditions. The slope efficiencies of ZnSe:Fe2+ and ZnS:Fe2+ lasers with respect to the absorbed energy were 34% and 20%, respectively. At equal pumping energy absorbed in the samples, the duration of the ZnSe:Fe2+ laser radiation pulse was longer than that of the ZnS:Fe2+ laser. Possibilities of increasing the efficiency of ZnS:Fe2+ laser operation at room temperature by improving the technology of sample manufacturing and reducing the duration of the pumping pulse are discussed in this letter.