Narrow Results

We present an investigation of the electronic properties and optical constants of zinc-blende ZnS_xSe_1-x semiconducting alloys at normal and under hydrostatic pressure up to 20 kbar. For this purpose, we used an empirical pseudopotential method within the virtual crystal approximation. The effects of alloy composition are taken into consideration in the calculation, which improves significantly the bandgap bowing parameters with respect to the experiment. Results regarding the composition and pressure dependences of energy bandgaps, electron valence and conduction charge distributions, optical high-frequency dielectric constant and its linear pressure coefficient are presented and discussed. The information derived from the present study may be useful for the development of opto-electronic devices that operate in the blue/green spectral range.

Ground state properties of zinc-blende structures ZnS and ZnSe are investigated from first principles using plane wave basis, projector augmented wave method and local orbital-dependent potential, as well as a basis set of Gaussian-type functions with hybrid functionals for the approximation of exchange-correlation energy. The results of DFT calculations with the LDA, LDA+U, GGA, GGA+U, BLYP, B3P86, P3PW, BH-HP, KMLYP and B3LYP approximations are compared. It is shown that the hybrid functional B3LYP provides an accurate quantitative description of the structural, electronic and vibrational properties of ZnS and ZnSe in comparison with experimental data.

Polyvinyl alcohol (PVA) has been used as a matrix to synthesize ZnS/PVA nanocomposite film on glass substrate by chemical method. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Scanning electron microscopy (SEM) has been used for structural, morphological and compositional characterization. Optical properties have been studied by UV-Visible spectrophotometry and photoluminescence (PL) spectroscopy. Changing pH value from 4.8 to 0.8 decreases the particle size and correspondingly increases the band gap. The PL emission intensity also increases by decreasing the pH values.

Deposition of zinc sulfide (ZnS) thin films on Si (1 0 0) and glass substrates has been performed using RF magnetron sputtering method. Film structure has been analyzed by X-ray Diffraction (XRD), while the scanning electron microscope (SEM) images have been used to explore the film morphology. FTIR and Raman spectroscopies have been used to confirm the film composition. The stoichiometry has been verified by Energy dispersive X-ray spectroscopy (EDX) technique. The XRD patterns have indicated that the films possess a polycrystalline nanocrystallite cubic structure. The optical properties of the grown films were characterized by optical transmittance measurements (UV–Vis). The deduced energy bandgaps of the films show an increase from 3.75 eV to 3.88 eV with the power source changes from 90 W to 125 W. Furthermore, Z-scan technique (CW diode laser $\lambda =635$ nm) was employed to estimate the nonlinear optical absorption of the prepared ZnS films.

The phase transition of zinc sulfide (ZnS) from Zinc-blende (ZB) to a rocksalt (RS) structure and the elastic, thermodynamic properties of the two structures under high temperature and pressure are investigated by first-principles study based on the pseudo-potential plane-wave density functional theory (DFT) combined with the quasi-harmonic Debye model. The lattice constant $a_0$, bulk modulus $B$ and the pressure derivative of bulk modulus $B$’ of the two structures are calculated. The results are in good agreement with experimental results and the other theoretical data. From the energy–volume curve, enthalpy equal principle and mechanical stability criterion, the transition pressures from the ZB to the RS structure are 16.83, 16.96 and 16.61 GPa, respectively. The three results and the experimental values 14.7–18.1, 16 GPa are very close to each other. Then the elastic properties are also calculated under the pressure ranging from 0 to 30 GPa. Finally, through the quasi-harmonic Debye model, the thermodynamic properties dependence of temperature and pressure in the ranges between 0–1600 K and 0–30 GPa are obtained successfully.

Log Q versus log I_ph characteristics and laser enhanced mobility in the case of ZnS have been studied using a XeCl laser. The comparison of results in this case with multiphoton photoconductivity of other materials indicates two photon excitation from a lower valance band, wherefrom one-photon excitation is forbidden but two-photon excitation is allowed. Since the band-gap of ZnS is smaller than the photon energy of the XeCl laser, the result seems to be interesting.

In this paper, the preparation and optical properties of sphere-like ZnS nanocrystals are reported. Pure and uniform cubic-phase sphere-like ZnS nanocrystals with grain sizes of 30–40 nm were synthesized by thermolysis of a new precursor complex (enH₂)_0.5[Zn(en)₃](SCN)₃ (en = ethylenediamine) in nitrogen stream at 800°C. The as-synthesized products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), respectively. The XRD analysis reveals the phase of ZnS with cubic zinc blende. UV-Vis and photoluminescence spectra (PL) were utilized to investigate the optical properties of sphere-like ZnS nanocrystals. By testing on UV-Vis spectra, it is concluded that the limiting wavelength of the ZnS nanocrystals is 320 nm and the band gap is 3.88 eV. In room temperature PL spectra, one strong emission peak centered at 322 nm is discovered, which could be attributed to the band to band transitions. The above-mentioned results showed that the thermolysis method is preferable for synthesizing high-quality sphere-like ZnS nanocrystals. The synthesized precursor could be used as morphological templates to prepare nanostructure inorganic compounds.

In this study, zinc sulfide (ZnS)/titanium oxide(TiO₂) nanoparticles were prepared by a two-step facile hydrothermal method and then annealing at $400^{\circ }\mathrm{\text{C}}$ for 30 min. Also, the transient absorption measurement and photocatalytic activity of ZnS/TiO₂ before and after annealing were investigated. The characterization technique such as the scanning electron microscopy (SEM) and X-ray diffraction (XRD) and UV–Visible spectroscopy have been employed to study the surface morphology and structural details. The SEM image shows the change in the surface morphology due to annealing. The change of the crystal structure of ZnS–TiO₂ is revealed by XRD spectra. The femtosecond transient absorption measurement showed moderate decay over several hundred picoseconds for annealed ZnS/TiO₂. Moreover, improved photocatalytic activity of annealed ZnS/TiO₂ nanoparticles in visible light has been observed.

Deposition of Zinc sulfide (ZnS) thin films on Si (100) and glass substrates has been performed using electron beam evaporation (EBE) method without annealing. Film structure has been analyzed by XRD, while SEM and AFM have been used to explore the films morphology. Raman spectroscopy has been used to confirm film composition. The stoichiometry has been verified by EDX and XPS techniques. XRD patterns indicated that the films possess a polycrystalline cubic structure with orientations along (111) and (220) planes. The crystallinity has been better with film thickness in the 350–1700 nm range while the RMS roughness increases. Optical properties of the grown films were characterized by optical transmittance measurements (UV–Vis). The deduced energy band gap of the films shows a clear reduction from 3.45 eV to 3.36 eV with increasing film thickness. The evolution of refractive index, extinction coefficient, and dielectric constants with thickness has been investigated from transmittance spectra in the 500–1000 nm wavelength range.

In recent years, increasing attention has been paid to Mie resonance-based dielectric metamaterials. Here, we report a ZnS nanoparticles-based dielectric metamaterials. The permittivity of ground state and excited state of ZnS were calculated by Materials Studio, and the obtained permittivity was used to simulate the light transmission characteristics of ZnS nanoparticles-based Mie metamaterials. ZnS nanoparticles were prepared by solid reaction process, which were dispersed into alcohol solution to get Mie resonance-based metamaterials. The transmission characteristics were measured by UV–Vis spectrophotometer. There is resonance peak both in simulation and experiment and the different electromagnetic response in ground state and excited state indicates that tunable Mie resonance-based metamaterials were fabricated. This work demonstrates the feasibility of fabrication of tunable dielectric metamaterials at optics frequencies which can be used as sensors with chemical methods.

An improved chemical bath deposition (CBD) technique has been provided to prepare zinc sulfide (ZnS) thin films on glass substrates deposited at 80–82°C using a mixed aqueous solution of zinc sulfate, ammonium sulfate, thiourea, hydrazine hydrate, and ammonia at the alkaline conditions. Both the traditional magnetic agitation and the substrates vibration by hand frequently were done simultaneously during the deposition. The substrates vibration reduced the formation and residence of gas bubbles on the glass substrates during growth and resulted in growth of clean ZnS thin films with high quality. Ammonia and hydrazine hydrate were used as complexing agents. It is found that hydrazine hydrate played an important role in growth of ZnS films. The structure and microstructure of ZnS films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV-vis spectroscopic methods. The XRD showed a hexagonal structure. The formed ZnS films exhibited good optical properties with high transmittance in the visible region and the band gap value was estimated to be 3.5–3.70 eV.

In this work, the structural properties of the zinc sulfide (ZnS) films have been investigated using X-ray diffraction (XRD) analysis which show an enhancement in the crystallite degree after doping with copper (Cu). Good matching between the ZnS and porous silicon (PS) structure was noted from the atomic force microscope (AFM) results. The reflectivity gave a clear observation of anti-reflected coating improvement for PS layer and more enhancements after the ZnS deposition. The optical properties show a blue shift in the bandgap for the ZnS deposited with higher substrate temperature and a red shift after doped with different elements. For ZnS/PS heterojunction, the electrical resistivity has been increased after PS layer formed and changed with the variation of the pore size and it was much higher after ZnS deposited on the PS. However, use of ZnS:Cu/PS photodetector showed much higher output current at the ultraviolet (UV) region compared to ZnS/PS. The ZnS:Cu/PS photodetector showed higher output current value than that of the ZnS/PS leading to improvement in the quantum efficiency of 42%.

In the present work, Zinc Sulphide (ZnS) thin films deposited by resistive heating technique on BK-7 glass substrate. Optical and structural characterizations of ZnS films have been carried out along with the post-deposition annealing at different temperatures. The thickness of the film is monitored by quartz crystal monitor and found to be 500nm. Fourier transform infrared (FTIR) spectroscopy provides the qualitative analysis of ZnS film before and after annealing at different temperatures. The optical investigation shows that the as-deposited and annealed ZnS film display the high optical transmittance of (64–68%) in the visible/near infrared region. The optical energy gaps of present as-deposited and annealed ZnS film vary in the range of 3.32–3.18eV with the change in annealing temperature.

We report an investigation of luminescent and tunable photonic crystal structures formed by the infiltration and inversion of opal templates with high index and luminescent materials. Protocols are reported for the deposition of these materials and the properties of the resulting structures investigated by conventional structural and optical measurements. The properties of multi-layered and backfilled structures are reported and demonstrate the potential to modulate and statically tune the luminescence from photonic crystals.

This paper reports on the preparation of high purity ZnS nanoparticles by a facile single step solvent-free route via thermal decomposition of zinc acetate dihydrate and thiourea in air atmosphere. The third-order optical nonlinearity of the prepared ZnS nanoparticles were measured by Z-scan technique using continuous wave 532-nm diode pumped Nd:YAG laser. From nonlinear optical (NLO) measurements, the prepared ZnS nanoparticles possess negative nonlinearity i.e., self-defocusing. Open aperture Z-scan measurement shows saturable absorption within the medium. These results show that the prepared ZnS nanoparticles are promising candidate for various potential applications in the field of nonlinear optics.

This study reports the third-order nonlinear optical (NLO) properties of hexamethylenetetramine (HMTA) stabilized pure and transition metals (Cu, Co and Mn) doped ZnS nanoparticles (NPs) and their electronic structures. The third-order NLO properties of pure and transition metals (Cu, Co and Mn) doped ZnS NPs were measured by $Z$-scan technique. From these measurements, the pure and doped ZnS samples exhibit negative nonlinearity i.e., self-defocusing. The open aperture $Z$-scan measurement shows saturated absorption within the medium. The prepared pure and doped ZnS samples exhibit nonlinear refractive index of the order of 10${}^{-8}$(cm²/W), nonlinear absorption (NLA) coefficient of the order of 10${}^{-4}$cm/W and nonlinear optical susceptibility of the order of 10${}^{-6}$esu. The electronic structures of these ZnS NPs were investigated using near edge X-ray absorption fine structure (NEXAFS) measurements at the C K-, N K- and Co L${}_{3,2}$-edges. The C K- and N K-edges XANES spectra reveal the appearance of several spectral features in the range 285–290eV and 390–430eV respectively. The Co L${}_{3,2}$-edge NEXAFS spectrum exhibits multiplet absorption lines similar to those of Co${}^{2+}$ ions coordinated in tetrahedral symmetry with four sulfur nearest neighbors. These results clearly demonstrate that divalent Co ions substitute Zn sites. From the Raman spectra, the appearance of multiple resonance Raman peaks indicates that the prepared ZnS samples have good optical quality.

ZnS nanofibers with lamellar mesostructure could be built up from in situ generated ZnS precursors via hydrothermal routes using neutral n-alkylamines as structure-directing template and ethylene diamine tetraacetic acid (EDTA) as stabilizer. The morphology and structure of the obtained products were thoroughly investigated via scanning electron microscope (SEM), energy dispersive analysis of X-rays (EDX), transmission electron microscope (TEM), X-ray powder diffraction (XRD) and thermal analyses. HRTEM and XRD results revealed that the so-produced nanofibers were lamellar mesostructure and its framework was built of crystalline wurtzite ZnS. It was also found that the distance between the layers was proportional to the chain length of the alkylamine. The UV-visible absorption spectrum showed that the nanofibers exhibited strong quantum-confined effect with a blue shift in the band gap. Finally, a probable mechanism for the assembly of the nanofibers was also proposed.

A new unsymmetrical phthalocyaninato zinc complex with typical amphiphilic nature, namely 2,3-di(4-hydroxyphenoxy)-9,10,16,17,24,25-hexakis($n$-octyloxy)phthalocyaninato zinc, Zn[Pc(OC₈H${}_{17}{)}_6$(OPhOH)₂], has been designed, synthesized, and characterized by a range of spectroscopic methods. The Langmuir monolayer of this amphiphilic complex has been used as not only an organic template but also as a good functional organic material to produce the monodispersed nanoparticles of Zn[Pc(OC₈H${}_{17}{)}_6$(OPhOH)₂]/ZnS nanocomposite. In addition, multilayer pure and hybrid films have also been obtained by depositing monolayers of the amphiphilic complex and Zn[Pc(OC₈H${}_{17}{)}_6$(OPhOH)₂]/ZnS nanocomposite, respectively, using the Langmuir–Shäfer (LS) method. Surface pressure-area isotherms, UV-vis spectroscopic, and XRD studies indicate that the molecules adopted a face-to-face configuration and edge-on orientation in both the multilayer pure LS and Zn[Pc(OC₈H${}_{17}{)}_6$(OPhOH)₂]/ZnS hybrid films. In particular, current–voltage (I–V) measurements reveal the superior conductivity of the Zn[Pc(OC₈H${}_{17}{)}_6$(OPhOH)₂]/ZnS hybrid film nanocomposites to that of the stand-alone films, and this is due to the existence of the densely packed molecular architecture in the film matrix and the large interfacial area between the two components. These characteristics remove the charge transporting bottleneck by creating an interpenetrating consistent thin film of hybrid materials. The result sheds lights on new ways for developing organic-inorganic hybrid nanostructures with good semiconducting properties.

ZnS:6.25%Br quantum dots (QDs) were fabricated by a low temperature solid phase way. The impacts of zinc vacancies ($V_{\mathrm{\text{Zn}}}$) and Br on the energetic and electronic properties of ZnS QDs were discussed by the first-principles calculations combined with the experimental results. Moreover, the cytotoxicity of ZnS:Br QDs and their influences on the growth of Aspergillusoryzae (A. oryzae) were researched. The theoretical results showed that ZnS:6.25%Br and ZnS:3.125%$V_{\mathrm{\text{Zn}}}$ were n-type and p-type semiconductor, respectively, while ZnS:6.25%Br,3.125%$V_{\mathrm{\text{Zn}}}$ was a neutral semiconductor. It was found that ZnS:6.25%Br QDs were not only nontoxic for HeLa cells but also promoted the growth of A. oryzae. This work will provide a new method for improving the growth of A. oryzae.

Optical analysis (UV-vis spectroscopy) of solution of ZnS nanoparticles prepared at room temperature by a chemical capping method using methacrylic acid (MAA) capping agent at concentration of 0.05, 0.2, 0.5 and 1.17 molar is investigated. The spectroscopy results indicate increasing of band gap of ZnS through increasing concentration of the methacrylic acid as capping agent in the solution. According to the relation of Effective Mass Approximation, it is concluded that the size of nanoparticles decreased with the increasing concentration of the capping agent in the tested solutions. The size of the particles is found to be in 1.77-2.05 nm range.