Hexagonal ZnSe Research Articles

Investigating the effects of varying sulfur concentration on ZnSxSe1-x (0 ≤ x ≤ 1.0) thin films prepared by photo-assisted chemical bath method

Zinc sulfur-selenide (ZnSxSe1-x) (0 ≤ x ≤ 1.0) thin films were grown on glass substrates using photo-assisted chemical bath deposition technique and the deposited samples were annealed in an open-air furnace at 250 ℃ for 3 h. X-ray diffraction analysis revealed a phase transition from hexagonal ZnSe to cubic ZnS as x changes from 0 to 1.0. Raman scattering showed two longitudinal optical modes due to ZnSe structure. The effects of S and Se ions variation is observed by the change in surface morphology from nanoflakes to spherical particles as x increased. The presence of the expected elementary composition was confirmed by the energy dispersive x-ray spectroscopy. The bandgap of the films was found to increase from 2.68 to 3.50 eV with a corresponding decrease in crystallite size (11.9 – 7.1 nm) as x varied from 0 to 1.0. Photoluminescence excitation and emission showed defect emission peaks ascribed to intrinsic and extrinsic deep level defects such as Zn2+ or S2- ions vacancies and interstitials. The emission colours were tuned from red to yellowish-green with increased x values as confirmed from Commission Internationale de L’Eclairage analysis. The tunability of the ZnSxSe1-x structural, optical and morphological properties makes it a good candidate for optoelectronic applications.

Growth and characterization of Fe2+:ZnSe single crystals for tunable mid-infrared lasers

Iron-doped ZnSe (Fe:ZnSe) single crystals were grown by the traveling heater method with the accelerated crucible rotation technique (ACRT) using SnSe as a solvent. The as-grown Fe:ZnSe single crystals were characterized by XRD, Raman, XPS, IR transmission imaging microscope, and the X-ray rocking curve. The results show two kinds of inclusions existing in Fe:ZnSe crystals, i.e. solvent SnSe inclusions, and hexagonal ZnSe inclusions with a wurtzite structure. The inclusions with sizes ranging from 30 to 150 μm were homogeneous distributed with a total concentration of only 2.68 × 102 cm−2. The full width at half-maximum (FWHM) of X-ray rocking curve on (220) diffraction planes was 38 arcsec and the average infrared transmittance exceeded 70%. Furthermore, it was confirmed that the iron ions were successfully incorporated into ZnSe lattice without degrading the crystalline quality, and the bivalence was dominant for iron atoms in Fe:ZnSe crystals, meaning that they are suitable for developing mid-infrared (3–5 μm) gain medium applications.

Electronic, magnetic and optical properties of monolayer (ML) hexagonal ZnSe on vacancy defects at Zn sites from DFT-1/2 approach

In this work, we have investigated the electronic, magnetic and optical properties of hexagonal monolayer ZnSe compound via atomic vacancy defects by using DFT-1/2 approximation. Our calculations revealed that monolayer ZnSe is a direct band semiconductor with the transition along Γ−Γ symmetry. The measured value of electronic band gap is ~2.68 eV in very good agreement with the experimental results. The optical spectra of hexagonal ZnSe is measured along the x- and z-axis as a function of wave length (λ). The absorption coefficient is highly anisotropic with majority of optical response lies along x-axis. The maximum absorption intensity is ~6.5 × 104cm−1 in violet-blue range of UV–Vis spectra. Our results of optical spectra comprehended the experimental results.

Phase transformation on zinc selenide thin films deposited by photo-assisted chemical bath method: The effect of annealing temperature

Zinc selenide (ZnSe) thin films have been deposited on glass substrates via photo-assisted chemical bath deposition technique. The films were annealed at different temperatures 100, 150, 200, 250, 300, 350 and 400 °C in air for 2 h and were characterized using different techniques. The glancing incidence X-ray diffraction (GIXRD) showed that the as-deposited sample and films annealed from 100 to 200 °C contained secondary peaks due to combine effects of ZnSe and unreacted Zn and Se. The films annealed at 250 and 300 °C showed pure hexagonal ZnSe phase while those annealed at 350 and 400 °C changed to hexagonal ZnO. The estimated crystallite sizes were found to decrease in size with increased annealing temperature. The change in phase was also observed in Raman spectroscopy, scanning electron microscopy and UV–visible spectroscopy. Atomic force micrographs showed decrease in surface roughness with an increase in the annealing temperature. Energy band gap increased with annealing temperature. Three emission bands due to band-edge and defect levels were observed in the photoluminescence spectroscopy. The lifetime decay did not show any ordered dependence on the annealing temperature. The sample annealed at 250 °C was considered because its parameters such as the diffraction angle, lattice constants and energy band gap were closest to the bulk ZnSe. The Commision Internationale de L'Eclairage showed blue emission color with color purity between 56 and 97%. The films especially 250 °C sample was recommended for lighting applications.

Preparation of ZnSe powder by vapor reaction during combustion synthesis

Abstract ZnSe powders have been prepared by vapor reaction during combustion synthesis. The powders contain both cubic and hexagonal ZnSe, where the fraction of the hexagonal phase increases with increasing distance from the evaporation source. The powders consist of spherical particles and rod-like crystals with sizes from submicron to a few microns. In UV–Vis region, the ZnSe powders have two absorption edges at 450–500 nm and 650–700 nm, likely connected with intrinsic band-gap transition and defect energy levels. From the optical absorption data, the band-gap of the ZnSe powders is estimated to be 2.4–2.5 eV. Under an UV or blue excitation, the ZnSe powders show very weak near-band-edge emission but strong defect-induced red emission. It appears that the ZnSe powders synthesized by vapor reaction clearly differ from the bulk ZnSe sample by melt solidification in both phase composition and optical properties.

ZnSe Nanowires and Partially Hollow Nanotubes Synthesized by Femtosecond Laser Ablation in Liquid

Hexagonal ZnSe nanowires were synthesized by the self-assembly of nanoparticles prepared by femtosecond laser ablation in deionized water. With introduction of air, partially hollow ZnSe nanotubes were also obtained. The nature of the ZnSe nanowires was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectrometry mapping (EDS-Mapping), and X-ray diffraction (XRD). Possible self-assembly and hydrolysis mechanisms for the formation of nanowires and partially hollow nanotubes were discussed.

Rapid Formation of Ternary CdZnSe2 Chalcogenide Thin Film by Microwave Assisted Chemical Bath Deposition

SummaryNanostructured ternary cadmium zinc selenide (CZS) thin films have been deposited by a rapid and reliable Microwave assisted chemical bath deposition (MA‐CBD) method by using ethylenediaminetetraacetic acid (EDTA) and triethanolamine (TEA) as complexing agents. Optical, structural, morphological, compositional and electrical properties of CZS thin films have been investigated as a function of different complexing agents. Band gap energy of CZS thin films obtained for EDTA and TEA was 2.03 and 1.75 eV respectively. X‐ray diffraction (XRD) studies revealed that films were nanocrystalline in nature with mixed phase structure, in which cubic phase of CdSe dominant over hexagonal ZnSe. The scanning electron microscopy (SEM) images show porous surface morphology with distinct grains over the substrate surface. The EDS spectra show presence of Cd, Zn and Se elements. Thermoelectric power (TEP) measurement shows films were n‐type semiconducting in nature. Synthesized thin films shows potential for solar cell application.

Bis((dialkylamino)alkylselenolato)metal complexes as precursors for microwave-assisted synthesis of semiconductor metal selenide nanoparticles of zinc and cadmium in the ionic liquid [BMIm][ BF4

Based on (dimethylamino)ethyldiselenide, (diethylamino)ethyldiselenide and (dimethylamino)propyldiselenide six different bis(dialkylamino)alkylselenolates with zinc and cadmium were decomposed by microwave irradiation in the ionic liquid (IL) 1-butyl-3-methyl-imidazolium tetrafluoridoborate ([BMIm][BF4]) to give the respective metal selenide nanoparticles. In comparison to common methods like the hot injection method attention was paid how variations of the ligand system and different decomposition times affect the nanoparticle synthesis with respect to size, shape, crystallinity and crystal phase. The decomposition of the single-source zinc and cadmium precursors in the fluorous IL led mostly to spherical, crystalline and only slightly agglomerated nanoparticles. No formation of ZnF2 or CdF2 was observed which is different from the known dual-source synthesis. In case of the zinc precursors, hexagonal and cubic ZnSe with a particle diameter between 4–7 nm were obtained, whereas in case of the cadmium precursors hexagonal CdSe with an average particle diameter of 10–19 nm were prepared. An increase in decomposition time from 5 to 15 min at 250 °C mostly led to similar results concerning the particle size and crystal phase which is different from the hot injection method, thereby suggesting that the IL has a decisive role for nanocrystal growth and stabilization. No further stabilizing agents were necessary to reproducibly prepare ZnSe or CdSe particles with an average diameter below 10 or 20 nm, respectively. All dispersions of the metal selenide nanoparticles in [BMIm][BF4] were characterized by high resolution transmission electron microscopy (HR-TEM), energy dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (PXRD).

Synthesis of Er and Yb-doped cubic and hexagonal phase ZnSe nano-assembled microspheres and their photocatalytic activities

We O2− synthesized ZnSe as well as Er and Yb-doped ZnSe nano-assembled microspheres by a hydrothermal method with and without hydrazine. ZnSe microspheres with a cubic phase were obtained with hydrazine, while ZnSe microspheres showed mixed cubic and hexagonal phases when hydrazine was not used. Introduction of low levels of Yb and Er resulted in morphologies of plates and rods, respectively, and these morphologies were unchanged when higher doping concentrations were used. The synthesized ZnSe was characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction crystallography, thermogravimetric analysis, UV–visible absorption, and photoluminescence spectroscopy. Photodegradation of methyl orange by undoped, Er and Yb-doped ZnSe was tested under visible light. Photoluminescence spectroscopy using terephthalic acid confirmed that OH radicals were efficiently formed over the doped ZnSe nanostructures upon visible light irradiation.

Theoretical aspects of graphene-like group IV semiconductors

Silicene and germanene are the silicon and germanium counterparts of graphene, respectively. Recent experimental works have reported the growth of silicene on (111)Ag surfaces with different atomic configurations, depending on the growth temperature and surface coverage. We first theoretically study the structural and electronic properties of silicene on (111)Ag surfaces, focusing on the (4×4)silicene/Ag structure. Due to symmetry breaking in the silicene layer (nonequivalent number of top and bottom Si atoms), the corrugated silicene layer, with the Ag substrate removed, is predicted to be semiconducting, with a computed energy bandgap of about 0.3eV. However, the hybridization between the Si 3p orbitals and the Ag 5s orbital in the silicene/(111)Ag slab model leads to an overall metallic system, with a distribution of local electronic density of states, which is related to the slightly disordered structure of the silicene layer on the (111)Ag surface. We next study the interaction of silicene and germanene with different hexagonal non-metallic substrates, namely ZnS and ZnSe. On reconstructed (0001)ZnS or ZnSe surfaces, which should be more energetically stable for very thin layers, silicene and germanene are found to be semiconducting. Remarkably, the nature and magnitude of their energy bandgap can be controlled by an out-of-plane electric field, an important finding for the potential use of these materials in nanoelectronic devices.

The use of de-aggregating agents in ZnSe mechanochemical synthesis

Conventional mechanochemical synthesis of zinc selenide, ZnSe nanoparticles was performed in a planetary ball mill by high-energy milling of zinc (Zn) and selenium (Se) powders with the de-aggregating agents ZnCl2 and phthalic acid (aromatic dicarboxylic acid, C8H6O4). Physical–chemical and optical properties of the prepared ZnSe nanoparticles were studied and compared. The mechanochemically synthesized products were characterized by X-ray diffraction analysis (XRD) that confirmed the presence of cubic-Stilleite and hexagonal ZnSe phases after 18, 25, 30, 40, 45 and 50 min of milling with various amounts of the added de-aggregating agents. Size of crystallites calculated from XRD patterns was from 20 to 31 nm for cubic ZnSe prepared with ZnCl2. For ZnSe synthesized with phthalic acid the crystallite size ranged from 16 to 73 nm. Size, phase composition, morphology, and crystallinity of ZnSe nanoparticles were studied by transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Photoluminescence spectra (PL) at room temperature have shown a broad red emission bands, and the presence of de-aggregating agent has altered the intensity of the PL signal as well.

(Invited) Theoretical Study of Silicene and Germanene

The structural and electronic properties of silicene and germanene on metallic and non-metallic substrates are investigated theoretically, using first-principles simulations. We first study the interaction of silicene with Ag(111) surfaces, focusing on the (4x4) silicene/Ag structure. Due to symmetry breaking in the silicene layer (nonequivalent number of top and bottom Si atoms), silicene is predicted to be semiconducting, with a computed energy gap of about 0.3 eV. However, the charge transfer occurring at the silicene/Ag(111) interface leads to an overall metallic system. We next investigate the interaction of silicene and germanene with hexagonal non-metallic substrates, namely ZnS and ZnSe. On reconstructed (semiconducting) (0001)ZnS or ZnSe surfaces, silicene and germanene are found to be semiconducting. Remarkably, the nature (indirect or direct) and magnitude of their energy band gap can be controlled by an out-of-plane electric field.

XRD, SEM and photoelectrochemical characterization of ZnSe electrodeposited on Cu and Cu–Sn substrates

XRD, SEM and photoelectrochemical examinations of deposits formed on the Cu substrate by electrochemical deposition in a water solution containing 0.2 mol dm −3 of ZnSO 4 and 0.002 mol dm −3 of H 2 SeO 3 were performed. Formation of Cu 2 Se x at potentials positive to that of electrochemical deposition of ZnSe was proved by the XRD technique. The formation of Cu 2 Se x continued even after deposition due to further diffusion of the deposited Se into Cu. A nano-crystalline ZnSe of cubic structure was electrodeposited at a potential of −0.62 V vs. Ag/AgCl electrode and XRD examination of deposits formed using cyclic potential scanning and pulse plating revealed the presence of hexagonal ZnSe along with the cubic one. A photoelectrochemical characterization proved that the electrodeposited ZnSe was a p-type semiconductor. A significant amount of Cu 2 Se x was formed during annealing of ZnSe electrodeposited on the Cu substrate although only traces of copper selenide were detected before the annealing. ZnSe, SnSe and a small quantity of Cu 2 Se x were detected by XRD after annealing of ZnSe electrodeposited on the Cu–Sn/Mo/glass substrate.

Synthesis and photocatalytic property of ZnSe flowerlike hierarchical structure

Spherical flowerlike hierarchical structure of ZnSe(en) 0.5 was synthesized via a solvothermal route in the NH 3·H 2O–ethylenediamine (en)–N 2H 4·H 2O system at 180 °C for 24 h. The hierarchical structure is assembled from lots of regular nanosheets. The ZnSe(en) 0.5 was further converted into pure hexagonal ZnSe by annealing in a flowing nitrogen gas at 500 °C for 1 h with morphology preserved. The formation mechanism of ZnSe was discussed. The UV–visible absorption spectrum and PL spectrum of the ZnSe spherical flowerlike hierarchical structure were measured. In addition, photocatalytic activity of the ZnSe flowerlike structure for the degradation of methyl orange under the irradiation of the simulated sunlight was investigated. The excellent catalytic activity for the degradation of methyl orange was found and the possible mechanism of the photocatalytic activity is also proposed.

Optimization of the structural, microstructural and optical properties of nanostructured Cr 2+:ZnSe films deposited by magnetron co-sputtering for mid-infrared applications

In order to obtain optimally adherent films having the highest mid-infrared photoluminescence efficiency, nanostructured Cr 2+:ZnSe films were deposited at room temperature on various substrates by magnetron radiofrequency co-sputtering of a SiO 2 target covered by a given number of ZnSe and Cr chips, at different Argon pressures and radiofrequency powers. The deposition parameter effect on the compositional, structural, microstructural and optical properties of the films has been investigated using X-ray reflectivity and diffraction, optical transmission spectroscopy, transmission electron microscopy, and photoluminescence studies. The corresponding films are composed by highly textured cubic and hexagonal ZnSe phases and exhibit strong tensile in-plane residual stresses. The evolution of the tensile residual stress and porosity values are consistent with the optical properties of the layers, and in particular the evolutions of both optical gap and refractive index. The room temperature mid-infrared (2–3 μm) photoluminescence measurements under direct excitation (1850 nm) revealed that chromium has been incorporated in the Cr 2+ active state, and the corresponding fluorescence efficiency for an optimized thin film is only two times smaller than the one of a Cr 2+:ZnSe reference bulk single crystal.

Hydrothermal growth control of ZnSe·N2H4 nanobelts

Uniform and well-defined inorganic–organic hybrid nanobelts of the hexagonal wurtzite ZnSe·N2H4 having an average width of 200 nm, a mean thickness of 25 nm, and a typical length of a few micrometres have been grown facilely in an aqueous solution, and characterized by measuring photoluminescence spectra and kinetic profiles as well as diffraction patterns and electron microscopic images. The length-to-width and width-to-thickness ratios of ZnSe·N2H4 nanobelts have been controlled well by adjusting [Se]-to-[ZnCl2] ratios as well as reaction time and temperature in hydrazine-hydrate-assisted hydrothermal reactions. A sufficient amount of the selenium precursor has been found to be essential for the one-dimensional growth of crystalline ZnSe·N2H4 nanobelts. Photoluminescence from ZnSe·N2H4 nanobelts shifts to the red by 16 nm and increases 3.5 times with the increase of the [Se]-to-[ZnCl2] ratio. The mean lifetime of photoluminescence kinetics having three decay components of 18 ps, 85 ps, and 1300 ps increases with the length-to-width ratios of ZnSe·N2H4 nanobelts.

Inorganic–organic hybrid semiconductor nanomaterials: (ZnSe)(N 2H 4) x(C 5H 5N) y

In this paper, inorganic–organic hybrid semiconductor (ZnSe)(N 2H 4) x (C 5H 5N) y nanosheets as well as (ZnSe)(C 5H 5N) y nanoparticles were first synthesized by a solvothermal method in a ternary solution and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectra, ultraviolet–visible (UV–vis) absorption spectra, thermogravimetric analysis (TGA), differential scanning calorimeter (DSC) and photoluminescence (PL) spectra. The results indicated that the morphology and composition of the products were largely influenced by the reaction temperature and the volume ratio of water. When the reaction temperature and the water content were lower, (ZnSe)(N 2H 4) x (C 5H 5N) y nanosheets were formed. As the reaction temperature or the content of water was high enough, (ZnSe)(C 5H 5N) y nanoparticles were formed. Pure hexagonal wurtzite ZnSe nanosheets or zinc blende ZnSe nanoparticles were obtained by extracting the corresponding hybrids. The bandgap absorption of ZnSe nanocrystals blue shifted in comparison with the bulk. The photoluminescent intensity of (ZnSe)(N 2H 4) x (C 5H 5N) y nanosheets was much stronger than that of (ZnSe)(C 5H 5N) y nanoparticles.

Synthesis, conversion and comparison of the photocatalytic and electrochemical properties of ZnSe·N2H4 and ZnSe microrods

AbstractNovel ZnSe·N2H4 complex microrods with ∼2 μm in length and 100∼200 nm in diameter were successfully prepared by the solvothermal method at 110°C for 10 h, employing ZnAc2·2H2O and Se powders as the reactants, N2H4·H2O as the reductant and medium. Experiments showed that the as‐obtained complex could be further converted into pure hexagonal ZnSe in an ethanol medium at 180 °C for 10 h, and the morphology hardly changed. The as‐prepared products were characterized by X‐ray powder diffraction (XRD), Energy dispersive spectrum (EDS), IR spectrum, Thermogravimetric (TG) analysis and Field emission scanning electron microscopy (SEM). Also, their photocatalytic degradation and electrochemical property were compared. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Vertically aligned and hexagonal crystal ZnSe nanoribbon arrays on Zn substrates

The vertically aligned and hexagonal ZnSe nanoribbon array can be easily obtained by heating ZnSe: 0.38 en precursors (en = ethylenediamine), while ZnSe precursor nanoribbon arrays are grown directly on Zn foils in en using the solvothermal method. The nanoribbons are mostly about 4 nm in thickness, 100–300 nm in width, and 2 μm in length. The characteristics observed using scanning electron microscopy and X-ray diffraction indicate that the ZnSe precursor as well as ZnSe nanoribbons are vertically aligned on almost the whole zinc foil surface and form a large-scale uniform array. Particularly, ZnSe precursor nanoribbons are hybrid materials of ZnSe and en, while ZnSe nanoribbons are in the from of hexagonal structures. Possible growth mechanisms of the ZnSe precursor nanoribbon arrays are also proposed.

One-step Preparation of ZnSe Nanorod Aggregates

Abstract ZnSe semiconductor aggregations were prepared via γ-ray irradiation method. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of the products clearly show that ZnSe possesses an aggregation structure, and these aggregations were found to form through the aggregation of ZnSe nanorods. The length and the diameter of the ZnSe nanorods are about 500–1000 and 30–60 nm, respectively. Electron diffraction patterns of an individual ZnSe nanorod and X-ray diffraction (XRD) analysis were used to examine the crystal structure of the products. The obtained product is pure-phase hexagonal system ZnSe. The composition of the products was analyzed by X-ray photoelectron spectroscopy (XPS). Effect of the pH value on product morphology was investigated.