Synthesis and characterization of Cu2ZnSnSe4 nanocrystals prepared by one pot route

Quaternary compound Cu₂ZnSnSe₄ (CZTSe) is one of the most promising absorber layer materials for thin film solar cells. In present work, the CZTSe nanocrystals were successfully synthesized via one pot route, and the influences of reaction temperature on the structural, compositional, morphological and optical properties of as‐synthesized CZTSe nanocrystals were investigated in detail via X‐ray powder diffraction (XRD), energy dispersive X‐ray spectrometry (EDS), transmission electron microscopy (TEM) and UV‐Vis spectrophotometry, respectively. The characterization results of as‐synthesized nanocrystals, under optimal synthesis condition (250 °C, 1 h), indicated that the nanocrystals was monodispersed with polycrystalline, the size was in the range of 10–15 nm, and the band gap energy was around 1.44 eV which is very closed to the best band gap energy for the solar cell. All results suggested that the as‐synthesized CZTSe nanocrystals were good light absorber layer material for thin film solar cell.     

Synthesis and characterization of magnetite nanocrystals

Nanocrystals of magnetite (Fe₃O₄) were prepared by sol‐gel technique. The prepared nanocrystals were characterized for phase by powder X‐ray diffraction (XRD) of the samples annealed at successively higher temperature. The magnetite phase was formed during the annealing of the synthesized powder at 400 °C for a few hours. The Fourier transform infrared spectroscopy (FTIR) was performed to analyze the functional groups in the material. The energy dispersive X‐ray diffraction (EDAX) was performed for chemical composition analysis. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques were used to analyze the morphology of nanocrystals and for estimating their average size. The results confirm the formation of Fe₃O₄nanocrystals of the sizes ∼20–50 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of spindle‐shaped α‐FeOOH and α‐Fe2O3 nanocrystals

Spindle‐shaped α‐FeOOH nanocrystals were facilely synthesized using a poly (vinyl pyrrolidone) (PVP)‐assisted route under hydrothermal conditions. The chemical compositions and morphol‐ogies of the as‐prepared samples were characterized in detail by X‐ray power diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscope (TEM). The experimental results reveal that these spindle‐shaped α‐FeOOH nanocrystals have self‐organized into assemblies with hierarchical nanostructures. The crucial roles of PVP in the hydrothermal synthesis of hierarchical α‐FeOOH nanostructures were discussed. The possible formation mechanism was also suggested. Moreover, the spindle‐shaped α‐Fe₂O₃ nanocrystals could be easily obtained after calcining the α‐FeOOH prepared by the PVP‐assisted hydrothermal process. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal synthesis of nano‐crystalline BaMoO4 under mild conditions using simple additive

Large‐scale high‐quality BaMoO₄ nanocrystals have been synthesized in aqueous solutions under mild conditions with citrate as a simple additive. The crystals have bone‐like, spindle‐like and wheatear‐like morphologies assembled from nanoparticles, nanofibers and have been characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. The results showed that experimental parameters had great influences on the shape evolution of products. The adjustment of these parameters such as room temperature stirring time, reaction temperature and reaction time of hydrothermal reaction, can lead to obvious morphology changes of products, and the growth mechanism has been proposed. Room‐temperature photoluminescence indicated that the as‐prepared BaMoO₄ nanocrystals had a strong blue emission peak at 481.5 nm. This facile route could be employed to synthesize more promising nanomaterials with interesting self‐assembly structures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Surfactant‐assisted synthesis of novel star‐like PbWO4 hierarchical architectures

Large‐scale star‐like PbWO₄ hierarchical architectures were controllably synthesized by a facile surfactant‐assisted technology under mild conditions in the presence of a mixed solvent of ethylene glycol and water. The morphology, structure, and phase composition of PbWO₄ architectures were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FE‐SEM), field emission transmission electron microscopy (FE‐TEM), and nitrogen adsorption‐desorption isotherms. The possible formation mechanism of the star‐like PbWO₄ architectures (initial nucleating stage and a subsequent self‐assembly stage) was proposed based on the observations from a time‐dependent morphology evolution process, which may pave the way to shape‐controlled synthesis of inorganic nanocrystals with the complex structures. This route provides a facile strategy to fabricate complex hierarchical PbWO₄ structures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation mechanisms of tripod and tetrapod CdTe0.67Se0.33 nanocrystals

CdTe_0.67Se_0.33 nanocrystals were synthesized using a typical organic route. Two major morphologies are observed from transmission electron microscopy (TEM) images, one being a tripod, and the other being a tripod‐like with a black dot in the center of the nanocrystal. The nanocrystals have two distinct geometrical shapes, one being a tripod, and the other being a tetrapod. High‐resolution TEM (HRTEM) examinations show that the tetrapod nanocrystals consist of a zinc‐blende nucleus and four wurtzite arms connected through a common facet, whereas the tripod nanocrystals result from the coalescence of three zinc‐blende nanorods. These results are helpful to interpret the growth process of other II–VI semiconductor NCs.     

Additive induced morphology changes of nano‐crystalline SrWO4

Large‐scale high‐quality SrWO₄ nanocrystals have been synthesized in aqueous solutions under mild hydrothermal conditions with citrate as a simple additive. The crystals undergo an interesting 0‐D to 1‐D and to 0‐D morphology changes and have been characterized by X‐ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The results showed that the experimental parameters had great influences on the shape evolution of products. The adjustment of these parameters such as the addition of the citrate and hydrothermal reaction conditions, can lead to obvious morphology changes of products, and the growth mechanism has been proposed. Room‐temperature photoluminescence indicated that the as‐prepared SrWO₄ nanocrystals had strong emission peaks at about 434 and 506 nm, respectively. This facile route could be employed to synthesize more promising nanomaterials with interesting self‐assembly structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Monodisperse CeO2 sub‐micro spherical aggregates with controllable building blocks

Monodisperse CeO₂ spherical aggregates with diameters ranging from 200 to 300 nm have been successfully synthesized through a facile hydrothermal method. The structure and morphology of the samples were characterized by powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and field‐emission scanning electron microscopy (FE‐SEM). The building blocks (primary nanocrystals) of the spherical aggregates could be effectively tuned by adding different amount of urea. Furthermore, N₂ adsorption/desorption experiment displays a gradual increase of BET surface areas of spherical aggregates with increasing the amount of urea. Finally, the formation mechanism of CeO₂ spherical aggregates was preliminarily discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of shuttle‐like Sb2S3 nanorod‐bundles via a solvothermal approach under alkaline condition

Uniform shuttle‐like Sb₂S₃ nanorod‐bundles were synthesized via a polyvinylpyrrolidone (PVP) assisted solvothermal approach under alkaline condition, using antimony chloride (SbCl₃) and thiourea (CH₄N₂S, Tu) as the starting materials in ethanol. The phase structure, composition and morphology of the product were characterized by means of X‐ray diffraction (XRD), energy dispersive X‐ray spectrometry (EDS), transmission electron microscopy (TEM), and high‐resolution transmission electron microscopy (HRTEM). XRD and EDS results confirm that the synthesized Sb₂S₃ nanorod‐bundles have an orthorhombic structure and an atomic ratio of 3:2 for S:Sb. TEM and HRTEM results show that the shuttle‐like Sb₂S₃ bundles are composed of nanorods with a size distribution of 20‐40 nm and growing along c‐axis. Furthermore, experiments under different reaction conditions were carried out and the mechanism for the growth of nanorod‐bundles was discussed (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Catanionic surfactants assisted synthesis of dilead pentaoxochromate nanorods

Single‐crystalline dilead pentaoxochromate (Pb₂CrO₅) with nanorod‐shape has been synthesized by adjusting the pH value of the catanionic reverse micelles formed by a cationic surfactant CTAB (hexadecyltrimethylammonium bromide) and an anionic surfactant SDS (sodium dodecyl sulfonate), followed by a hydrothermal process. The results show that reaction parameters play important roles in the formation of the single‐crystalline Pb₂CrO₅. The reaction parameters include the kinds of the surfactants, the molar ratio (r) between the mixed cationic and anionic surfactants, reaction time and temperature. The as‐synthesized products are characterized by transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM) and powder X‐ray diffraction (XRD). (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Self‐template hydrothermal synthesis ZnS microspheres

Zinc sulfide (ZnS) microspheres were synthesized by a self‐template hydrothermal route using thiourea as sulphur source. The formation of these hollow spheres was mainly attributed to the oriented aggregation of ZnS nanocystals around the gas‐liquid interface between gas (H₂S, NH₃, or CO₂) and water followed by an Ostwald ripening process. The gas bubbles of H₂S, NH₃, or CO₂ produced during the reaction might play a soft‐template to form ZnS hollow microspheres. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), electron diffraction (ED), and photoluminescence (PL). The crystal structure of prepared ZnS microspheres is hexagonal phase polycrystalline. The average microspheres diameter is 1.5 ‐ 6 µm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Solvothermal synthesis and structural characterization of unfilled and Yb‐filled cobalt antimony skutterudite

Unfilled and ytterbium (Yb)‐filled cobalt antimony (CoSb₃) nanoparticles were synthesized via solvothermal route using sodium borohydride (NaBH₄) as a reducing agent. The effect of various amounts of sodium borohydride on the formation of as‐synthesized CoSb₃ nanoparticles with pure phase was investigated. It is found that a sufficient amount of NaBH₄ was required in order to form pure phase CoSb₃. In addition, the effect of annealing time and temperature on the phase transformation of the as‐prepared non‐pure phase CoSb₃ sample was also investigated. It is found that annealing at 500 °C for 5 h would eliminate those non‐CoSb₃ phases and result in pure cubic skutterudite phase CoSb₃. Structural characterization of the as‐prepared unfilled and Yb‐filled nanoparticles was carried out with transmission electron microscopy (TEM) which revealed the formation of highly crystalline cubic phase of skutterudite Yb‐filled CoSb₃. Laser induced breakdown spectroscopy (LIBS) confirmed the presence of ytterbium in the Yb‐filled CoSb₃ samples.     

Structural and morphological studies on Mn substituted ZnO nanometer‐sized crystals

Mn substituted ZnO nanocrystals synthesized by a co‐precipitation method. X‐ray diffraction (XRD) studies confirms the presence of wurtzite (hexagonal) crystal structure similar to un doped ZnO, suggesting that doped Mn ions go at the regular Zn sites. The lattice parameters a and c are increasing with increasing Mn content. The unit cell volume increases with increasing Mn concentration, indicating the homogeneous substitution of Mn²⁺ for the Zn²⁺. The lattice distortion parameter (ε_v) is evaluated from XRD data and found that it enhances as Mn content increases. Transmission electron microscopy photographs show that the size of the ZnO crystals is in the range of 20‐50 nm. The SAED pattern confirms the hexagonal and crystalline nature of the samples which are in agreement with X‐ray analysis. The chemical groups of the samples have been identified by FTIR studies (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of semiconductor metal sulfide nanocrystals using microemulsion technique

The semiconductor nanocrystals ZnS, PbS, CdS and CuS were synthesized via microemulsion technique involving metal acetate, reducing agent (Na₂S) and Triton X‐100 as surfactant. Nanocrystals were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM) and dynamic light scattering (DLS). The average size of ZnS, PbS, CdS and CuS nanocrystals were found to be 5.6 nm, 13.3 nm, 11.4 nm and 6.2 nm, respectively. Different parameters like surfactant (Triton X‐100) concentration, water‐to‐surfactant ratio (ω), precursor concentration [zinc acetate, (Zn(AC)₂], reducing agent concentration [sodium sulphide, (Na₂S)] were optimized to synthesize ZnS quantum dots.     

Facile morphology‐controlled hydrothermal synthesis of flower‐like self‐organized ZnO architectures

Flower‐like self‐organized crystalline ZnO architectures were obtained through a facile and controlled hydrothermal process. As‐synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high‐resolution transmission electron microscopy (HRTEM), X‐ray diffraction (XRD), electron diffraction and UV‐Vis spectroscopy. XRD and electron diffraction results confirmed the obtained materials are pure wurtzite ZnO. The effects of different ratios of starting materials and solvent on the morphologies of ZnO hydrothermal products were also evaluated by SEM observations. It is suggested that the use of water, rather than ethanol as the solvent, as well as employing a precursor of Zn(Ac)₂ and 2NaOH (v/v) in hydrothermal reactions are responsible for the generation of specific flower‐like self‐assembled ZnO structures. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of nanocrystalline lithium niobate powders at low temperature

A facile route to prepare lithium niobate (LiNbO₃) powders was proposed by an alternative solid‐state method. Stoichiometric Li₂C₂O₄ and ammonium niobium oxalate were mixed with small amounts of water and then dried at room temperature. It was demonstrated that Li[NbO(C₂O₄)₂]·n H₂O intermediate was produced by an ion‐exchange reaction. Pure LiNbO₃ powders were successfully synthesized by heating the intermediate at 500, 600 and 700 °C for 3 h. X‐ray diffraction (XRD), scanning electron microscopy (SEM), Fourier‐transform infrared (FTIR) spectroscopy, UV‐Vis diffuse reflectance (UV‐Vis) spectroscopy and thermogravimetric (TG) analysis were used to characterize the precursor compound and as‐prepared samples. XRD results reveal that all the products are identified as hexagonal structure with high relative crystallinity (>87%). The particle size is found to be about 40 nm for the mixture calcined at 500 °C according to XRD data, which is in good agreement with SEM data. The as‐prepared LiNbO₃ powders by this method are high quality according to FTIR spectra. (Li_0.996Nb_0.005)Nb_0.999O₃ phase was formed when the calcination temperature was raised to 800 °C. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zr‐doped CeO2 Hollow slightly‐truncated nano‐octahedrons: One‐pot synthesis,characterization and their application in catalysis of CO oxidation

Zirconium‐doped ceria hollow slightly‐truncated nano‐octahedrons (HTNOs) (Ce_1‐xZr_xO₂) were synthesized by a one‐pot, facile hydrothermal method. The morphology and crystalline structure were characterized with powder X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and the high resolution transmission electron microscopy (HRTEM). The composition and chemical valence on the surface of the as‐prepared Ce_1‐xZr_xO₂ powders were detected by X‐ray photoelectron spectroscopy (XPS) and energy dispersive spectrometry (EDS). The surface area and pore size distribution of as‐obtained Zr‐doped ceria HTNOs were measured by N₂ adsorption‐desorption measurement. Mechanisms for the growth of Zr‐doped ceria HTNOs are proposed as both oriented attachment and Ostwald ripening process and the formation of the hollow structure is strongly dependent on the addition of Zr⁴⁺ ions. Furthermore, the as‐obtained Zr‐doped ceria HTNOs revealed superior catalytic activity and thermal stability toward CO oxidation compared to pure ceria. It may provide a new path for the fabrication of inorganic hollow structures on introducing alien metal ions.     

Controllable synthesis of hierarchical strontium molybdate by sonochemical method

Large‐scale chrysanthemum‐like strontium molybdate (SrMoO₄) with hierarchical structure has been successfully synthesized via a facile and fast ultrasound irradiation approach at room temperature. By varying the experimental conditions, SrMoO₄ with different morphologies, such as spindles, peanuts, spheres, and rods, can be obtained. The products are characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected‐area electron diffraction (SAED). The influent parameters including concentration, pH value, and surfactants have been investigated. A possible growth mechanism is proposed and the shape evolution of the products is characterized. The as‐prepared chrysanthemum‐like SrMoO₄ particles are used as the precursor for electrorheological fluid and their electrorheological property is investigated.     

Kinetically controlled synthesis of hollow Cu2O nanocubes under solvothermal condition

Hollow Cu₂O nanocubes have been fabricated under solvothermal condition using N,N ‐dimethylformamide (DMF) as solvent at 120 °C for 12 h. The products were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X‐ray powder diffraction (XRD) and high‐resolution transmission electron microscopy (HRTEM). Series of experiment confirmed that the amount of water, the reaction time and temperature played important roles in the morphology evolution of hollow Cu₂O nanocubes. DMF is a relatively weak alkali solvent and could release a certain amount of OH^– under the given conditions. As the release speed of OH^– from DMF became substantially slow, the nucleation and growth of Cu₂O nanocubes turned into kinetically controlled process. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of strontium chloroborate whiskers

Single crystalline strontium chloroborate (Sr₂B₅O₉Cl) whiskers with uniform diameter have been synthesized by a facile route based on the calcination of precursor. The precursor was prepared by the sedimentation reaction between SrCl₂ and Na₂B₄O₇ aqueous solution. The products were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectrum (FT‐IR). An optimal synthesis temperature for preparing Sr₂B₅O₉Cl whiskers was obtained, and the possible formation process was also presented.