Synthesis of organic ligand passivated zinc selenide nanorods via wet chemical route

Zinc selenide (ZnSe) nanorods have been synthesized by simple and inexpensive wet chemical method using N-Methylaniline as a capping agent. The morphologies and structure of ZnSe nanorods have been characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The SEM and TEM reveal the formation of nanorods. XRD shows the cubic structure with the lattice constant of 5.633 Å. Strong “blue shift” absorption is observed from UV-visible spectrophotometry. The enhanced luminescence property is measured from photoluminescence spectrophotometry. The presence of N-Methylaniline in the ZnSe nanorods is confirmed by the Fourier transformed infrared spectrum.     

Synthesis of alpha-alumina nanoribbons: characterization and their morphological evolution

Single crystalline α-alumina nanoribbons were synthesized by reacting aluminum with silicon monoxide at high temperature. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and high-resolution transmission electron microscope (HRTEM). The intense peaks of XRD pattern indicate that the prepared nanoribbons have a high degree of crystallinity. In the present work, silicon monoxide was used as an oxidant and precursor, which served to control the reaction rate. An interesting morphological evolution that nanoribbons resulted from nanosaws was described, and these novel nanosaws were also carefully characterized.     

Effects of multiple organic ligands on size uniformity and optical properties of ZnSe quantum dots

The effects of multi-ligands on the formation and optical transitions of ZnSe quantum dots have been investigated. The dots are synthesized using 3-mercapto-1,2-propanediol and polyvinylpyrrolidone ligands, and have been characterized by X-ray diffraction, transmission electron microscopy (TEM), UV–visible absorption spectroscopy, photoluminescence spectroscopy, and Fourier transform infrared spectroscopy. TEM reveals high monodispersion with an average size of 4 nm. Polymer-stabilized, organic ligand-passivated ZnSe quantum dots exhibit strong UV emission at 326 nm and strong quantum confinement in the UV–visible absorption spectrum. Uniform size and suppressed surface trap emission are observed when the polymer ligand is used. The possible growth mechanism is discussed.     

溶剂热法合成ZnSe纳米材料

以乙酸锌为锌源, Na₂SeO₃•5H₂O或Se粉为硒源, 采用溶剂热法在乙醇胺(EA)溶剂中一步合成晶型和形貌可控的闪锌矿和纤锌矿结构的ZnSe纳米材料。利用X射线衍射(XRD)、能量色散X射线谱 (EDS)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对产物的晶型、成分和形貌进行了表征。结果表明, Se源的选取直接决定了ZnSe纳米材料的晶型和形貌: 以Na₂SeO₃•5H₂O为源, 产物为立方相闪锌矿结构的ZnSe纳米颗粒, 直径30 nm左右; 以Se粉为源, 产物为六方相纤锌矿结构的ZnSe纳米片, 厚度约50 nm。进一步的研究表明, 具有合适配位能力的乙醇胺溶剂和Se源对ZnSe纳米结构的合成起重要作用。通过紫外-可见光谱(UV-Vis)和室温光致发光光谱(PL)表征了产物的光学性质。     

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.     

Lattice expansion in ZnSe quantum dots

Solid ZnSe quantum dots (QDs) have been prepared via chemical route. The QDs have been characterized by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Photoluminescence (PL) and Ultraviolet-Visible Spectroscopy (Uv-Vis). The QD sizes were found to vary from 2.5 to 9.5 nm. The XRD measurement reveals an increase in the interplanar spacing in QDs as compared to their bulk counterpart. This observation is further supported by Rietveld analysis which establishes the formation of single phase zinc blende ZnSe QDs and confirms 3.9% lattice expansion. Calculations based upon the thermodynamical theory yield 8.7% concentration of vacancies due to the lattice expansion. We observe various peaks in the PL spectra which may arise either due to the QD size variations or the defects due to the vacancies.     

A simple route to triethanolamine (TEA) and cysteine capped ZnSe nanoparticles

Water soluble triethanolamine (TEA) and cysteine capped ZnSe nanoparticles have been synthesized via simple solution based route. The method involves the reduction of selenium followed by the addition of the metal salt and capping group. The pH and metal salts were varied to study their effect on the optical properties and morphology of the particles. The as-synthesised ZnSe nanoparticles properties were studied by UV-Vis, photoluminescence, FTIR spectroscopy, powder X-ray diffraction, transmission electron microscopy (TEM) and high resolution TEM.     

A new hydrothermal route to nano- and microstructures of trigonal selenium exhibiting diverse morphologies

High purity single crystalline trigonal selenium (t-Se) with different morphologies (wires, rods, flowerlike, and hollow spheres) have been synthesized under hydrothermal conditions through simple one-step at lower temperature (120 °C) using in situ generated sulphurous acid as a new reducing agent. It is noted that the experimental parameters such as reaction duration, temperature and surfactants have an effective and important influence on the formation of different morphologies. The phase analysis, purity, morphology and optical properties of the as obtained products have been characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis spectroscopy, respectively. A possible reaction scheme as well as growth mechanism has been proposed for the formation of t-Se nanowires.     

Chemical synthesis of the high-pressure cubic-spinel phase of ZnIn2S4

Chemical reactions conducted in solution are known to generate solid precursors containing molecular units that help in the formation of high-temperature phases. The structural units are created by controlling the molecular environments in solution, and as a result, phases that normally form and are stable at high temperatures can be synthesized at low or moderately elevated temperatures. However, the application of chemical approaches for synthesizing phases that normally form at high pressure are relatively unknown. In this work, a simple room-temperature aqueous chemical precipitation route has been used to synthesize the high-pressure cubic spinel modification of ZnIn2S4. A solution coordination model (SCM) has been proposed to explain the formation of the high-pressure phase. The crystallinity, phase purity and phase transformation characteristics of the cubic phase have been studied using X-ray diffraction (XRD) including Rietveld refinement, transmission electron microscopy (TEM), and Auger electron microscopy (AEM). Results of these studies are discussed in the light of a proposed solution coordination model (SCM). © 1998 Kluwer Academic Publishers     

Phase transformation and thermal stability of ZnSe QDs due to annealing: emergence of ZnO

In the present study ZnSe quantum dots (QDs) were synthesized by chemical co-precipitation method using mercaptoethanol as the capping agent. These nanostructures were characterized for structure and surface morphology by using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectrometry respectively. The average size of ZnSe quantum dots from XRD and HRTEM is found to be 4–5 nm having cubic crystalline phase. Effect of annealing temperature, which were determined as phase transformation temperatures (299 and 426 °C) using differential scanning calorimetry has been investigated for structural and thermal stability of QDs. The XRD of annealed samples at temperatures 325 and 442 °C (slightly higher than the temperatures corresponding to two crystallization peaks in the DSC scan) have been carried out to find structural changes corresponding to these annealing temperatures. Sample annealed at 325 °C showed no change in the phase except improvement in intensity of peaks (crystallinity) whereas sample annealed at 442 °C showed transitions from cubic phase of ZnSe to ZnO and orthorhombic phases of ZnSeO₄, ZnSeO₃. Emergence of ZnO peaks in the XRD pattern of annealed samples have been further verified by Raman spectroscopy of the annealed samples. Besides this crystallization kinetics of ZnSe quantum dots has been employed to determine activation energies of these transitions due to oxidation by employing Kissinger, Augis Bennett and Ozawa’s models. Higher activation energy of crystallization corresponding to first crystallization peak shows that the cubic phase is more thermally stable.     

Micromorphological studies on the ZnSe single crystals grown by chemical vapour transport technique

Single crystals of ZnSe have been grown by chemical vapour transport technique. Microscopic observation of crystal surfaces has been carried out using optical microscope and scanning electron microscope (SEM). Different micromorphological patterns such as microsteps, spirals and kinks were observed on the surface of the grown crystals in different growth conditions. Present studies show that the formation of these microstructures on the surface of the grown crystals depends on the growth parameters such as undercooling and stability of the growth interface. The morphology and lattice parameters of the grown crystals have also been determined by X-ray analysis.     

Facile hydrothermal synthesis of graphene-ZnSe electro-catalytic electrodes for dye sensitized solar cells

A ZnSe-graphene nanocomposites was prepared using by a facile hydrothermal method followed fabrication serials film counterelectrode (CEs) by the doctor-blade method. Transmission electron microscopy (TEM) results show that ZnSe nanoparticles are uniformly implanted on the graphene film. The improved performance compared to the pristine ZnSe is attributed to the increased number of active catalytic sites of ZnSe/rGO and highly conducting path of graphene. The comprehensive ZnSe/rGO synthesis process is a simple and scalable process which can easily adapt for large scale electro-catalytic film fabrication for several other electro-chemical energy harvesting and storage applications.     

Electron density distribution and bonding in ZnSe and PbSe using maximum entropy method (MEM)

The study of electronic structure of materials and bonding is an important part of material characterization. The maximum entropy method (MEM) is a powerful tool for deriving accurate electron density distribution in crystalline materials using experimental data. In this paper, the attention is focused on producing electron density distribution of ZnSe and PbSe using JCPDS X-ray powder diffraction data. The covalent/ ionic nature of the bonding and the interaction between the atoms are clearly revealed by the MEM maps. The mid bond electron densities between atoms in these systems are found to be 0.544 e/ų and 0–261 e/ų, respectively for ZnSe and PbSe. The bonding in these two systems has been studied using two-dimensional MEM electron density maps on the (100) and (110) planes, and the one-dimensional electron density profiles along [100], [110] and [111] directions. The thermal parameters of the individual atoms have also been reported in this work. The algorithm of the MEM procedure has been presented.     

Solution-based route to semiconductor film: Well-aligned ZnSe nanobelt arrays

Large-scale, well-aligned, and oriented semiconductor ZnSe nanobelt arrays have been achieved via the thermal treatment of belt-like precursor (ZnSe·ethylenediamine), which has been synthesized by a simple template-free solvothermal route. ZnSe nanobelts grow perpendicularly on zinc substrate, with thickness of about 50 nm, widths of several hundreds of nanometers, and lengths of up to several micrometers. The as-obtained products have been characterized by scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray, and photoluminescence spectrometer. The cooperative action of the mixed solvents is responsible for the formation of the morphology of the resulting ZnSe nanobelt arrays. Room-temperature photoluminescence measurement indicates that the as-obtained ZnSe nanobelt arrays have a strong emission peak centered at 578 nm and two weak emission peaks centered at 420 and 433 nm. The strong emission from the unique well-aligned ZnSe nanostructures reveals their potential as building blocks for optoelectronics devices.     

Synthesis of nanocrystallite by mechanical alloying and in situ observation of their combustion phase transformation in Al3Ti

Elemental powders of stoichiometric Al₃Ti were mechanically alloyed (MA) in order to investigate the phase formation during the milling process. Furthermore the stability of MA powders were studied under transmission electron microscopy (TEM). The results indicate that a supersaturated Al(Ti) solid solution with nanocrystalline size has been formed after mechanical alloying for 360 ks in consuming the elemental powders of Al and Ti and no further phase transformation can be detected upon longer milling. The MA powders are unstable being irradiated by electron beams under the TEM observation, exothermically forming various intermetallic compounds. The combustion phase transformation processes and products are depending on the time of mechanical alloying. The structural changes and phase transformations during both mechanical alloying process and annealing process were also characterized by using X-ray diffraction measuring.     

Study of structural,optical and electrical parameters of ZnSe powder and thin films

Nanocrystalline ZnSe powder and thin film forms have been synthesized via chemical bath deposition technique. The ZnSe thin films are deposited onto ultrasonically clean glass substrates in an aqueous alkaline medium using sodium selenosulphate as Se^2? ion source. The ZnSe powder and thin film are characterized by structural, optical and electrical properties. It is confirmed from X-ray diffraction study that cubic phase is present in ZnSe thin film form with (111) as preferred orientation and hexagonal phase is present in ZnSe powder form with (100) as preferred orientation. Optical absorption measurement indicates the existence of direct allowed optical transition with a wide energy gap and blue shift in the fundamental edge has been observed in both cases. The optical band gap of ZnSe powder is greater than the thin film. The electrical conductivity (both dark and photoconductivity) measurements are also carried out in different temperature range and variation in activation energy has been calculated.     

Microwave-assisted synthesis of barium tungstate nanosheets and nanobelts by using polymer PVP micelle as templates

Single-crystal BaWO₄ nanosheets and nanobelts have been successfully synthesized by using polymer PVP micelle as templates in a reflux system under microwave irradiation. Our result shows that the concentration of PVP aqueous solutions played an important role in the formation of BaWO₄ crystal with different morphologies. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and electron diffraction (ED).     

Controlled synthesis and characterization of ZnSe quantum dots

Adopting improved metal-organic "Green method," Colloidal ZnSe quantum dots were synthesized by using cheap and low toxic zinc oxide (ZnO) in an organic solvent system of 1-hexadecylamine (HDA), lauric acid (LA) and tri-n-octylphosphine (TOP). The effects of HDA dosage, injection temperature, growth temperature and time on the microstructure and optical properties of ZnSe were studied by means of X-Ray diffraction(XRD), transmission electron microscopy (TEM), spectrofluorometers and ultraviolet spectrophotometer, respectively. The results showed that ZnSe quantum dots with the best range of the size evolution were obtained under the condition of injection at 280 degrees C and growth at 240 degrees C by choosing the optimal parameters of ZnO:HDA:LA= 1:2.1:5.2 and TOPSe = 1 mol/L. Its size became larger and the emission peak shifted obviously to red with increasing the growth time. Meanwhile, the obtained ZnSe was of the wurtzite structure, had good uniformity and fluorescent characteristics.     

Synthesis and characterization of carbon spheres prepared by chemical vapour deposition

Carbon spheres, with uniform diameters of about 1 μm, have been achieved via Chemical vapour deposition (CVD). The fabricated materials have been fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray analysis (EDX). The results show that the spheres are 95% carbon. The formation mechanism of carbon spheres has also been discussed.     

The synthesis and photocatalytic activity of ZnSe microspheres

This paper reports the synthesis of semiconductor ZnSe microspheres composed of nanoparticles via a solvothermal route between the organic molecule selenophene (C(4)H(4) Se) and ZnCl(2) without adding any surfactant. The ZnSe microspheres were characterized by x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), specific surface area measurement, and photoluminescence (PL) spectra. A strong and broad blue PL emission at 443 nm in wavelength (～2.79 eV in photon energy) is attributed to the near-band-edge (NBE) emission of ZnSe, while the 530 nm peak is a defect-related (DL) emission. The photocatalytic activity of the as-prepared ZnSe microspheres was evaluated by photodegradation of methyl orange (MO) dye under ultraviolet (UV) light and visible light irradiation. The degradations of MO reach 94% or 95.1%, close to 100%, in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 7 or 10 h under UV irradiation, respectively. Meanwhile the degradations of MO reach 94.3% or 60.6% in the presence of the as-synthesized ZnSe microspheres or commercial ZnSe powder after 12 h, respectively. The degradation rate of ZnSe microspheres is twice that of ZnSe commercial powder under UV light irradiation, and three times under visible light irradiation. The degradation process of MO dye on ZnSe microspheres under UV or visible light is also discussed.