Correlation between growth orientation and growth temperature for bismuth tri‐iodide films

This paper reports the growth of bismuth tri‐iodide thick films intended for direct and digital X‐ray imaging. Films were grown by the vertical physical vapor deposition method, onto glass substrates 2″x 2″ in size, with gold previously deposited as rear electrode. The film thickness was up to 33 μm (±5 %). Optical microscopy and SEM were performed on the films and grain size resulted to be up to 40 μm. A strong correlation was found between the microcrystals growth orientation and the growth temperature. At low temperatures, microcrystals grow with their c axis parallel to the substrate, whereas at higher temperatures, they grow with their c axis perpendicular to the substrate. The higher the growth temperature, the lower the dark current of the film, and the higher the resistivity, which was from 10¹³ to 10¹⁵ Ωcm. A sensitivity to X‐rays of 6.9 nC/R.cm² was measured irradiating the films with X‐rays from a mamographer. Film properties were correlated with the growth temperature, with previous results for bismuth tri‐iodide films and monocrystals and with data for films of alternative materials such as lead and mercuric iodide. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth of bismuth tri‐iodide platelets by the physical vapor deposition method

The work reports the growth of single BI₃ crystals with platelets habit. Platelets were grown by physical vapor deposition (PVD) in a high vacuum atmosphere and with argon, polymer or iodine as additives. Crystals grew in the zone of maximum temperature gradient, perpendicular to the ampoule wall. Crystals grown with argon as additive show a very shining surface, have hexagonal (0 0 l) faces, sizes up to 20 x 10 mm² and thicknesses up to 100 μm. They were characterized by optical microscopy and scanning electron microscopy (SEM). Dendritic‐like structures were found to be their main surface defect. SEM indicates that they grow from the staking of hexagonal unities. Electrical properties of the crystals grown under different growth conditions were determined. Resistivities up to 2 x 10¹² Ωcm (the best reported value for monocrystals of this material) were obtained. X‐ray response was measured by irradiation of the platelets with a ²⁴¹Am source of 3.5 mR/h. A comparison of results according to the growth conditions was made. Properties of the crystals grown by this method are compared with the ones measured for others previously grown from the melt. Also, results for bismuth tri‐iodide platelets are compared with the ones obtained for mercuric and lead iodide platelets. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and structural properties of lead iodide thin films prepared by vacuum evaporation method

Thermally processed lead iodide (PbI₂) thin films were prepared by the vacuum evaporation method in a constant ambient. Measured thickness of the film was verified analytically from the optical transmittance data in a wavelength range between 300 and 1600 nm. From the Tauc relation for the non‐direct inter band transition, the optical band gap of the film was found to be 2.58 eV for film thickness 300 nm. X‐ray diffraction analysis confirmed that PbI₂ films are polycrystalline, having hexagonal structure. The low fluctuation in Urbach energy indicates that the grain size is quite small. The present findings are in agreement with the other results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal growth and luminescent properties of Eu activated strontium iodide crystals

SrI₂:Eu crystals with 1.5 inch diameter were grown by the vertical Bridgman method. The melting point of SrI₂ doped with 5 at % Eu grown feedstock was determined to be 526 °C by differential scanning calorimetry (DSC). XRD proved Pbca structure of SrI₂ when the SrI₂:Eu sample was packaged with polyethylene film in air. The luminescent properties of SrI₂:Eu crystals are presented. Under the excitation of UV light or X‐ray, the crystals exhibit a single luminescent peak centered at 435 nm. The decay time of SrI₂:5%Eu crystal excited by UV were fitted to be 1.9 μs. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impurity induced structural phase transformations in melt grown single crystals of lead iodide

Lead iodide is a wide‐band gap and highly resistive semiconductor considered to be a promising room temperature nuclear detector. The phenomenon of polytypism is posing interesting problems of phase transformations among its polytypic modifications and formation of polytypic admixture during growth due to native impurities. Transformations have also been observed even when the material is stored for few months that causes deterioration in functioning of the PbI₂ devices. Lead iodide has been purified and single crystals were grown using zone‐refining system. The observed phase transformations during growth and storage have been explained in the light of distortion of [PbI₆]^4‐ octahedron due to impurities present in the material and the known crystal structures of PbI₂. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of ZnO nanostructures composed of nanosheets with controllable morphologies

ZnO nanostructures composed of nanosheets have been synthesized by a facile low temperature reaction of Zn(OH)₂ and NaOH without the aid of any organic molecular templates. The influences of the reaction parameters, such as the concentrations of Zn(NO₃)₂, reaction temperatures, and reaction time on the morphologies of ZnO have been investigated. The thickness of ZnO nanosheets can be adjusted from 10–20 nm to 30–40 nm by altering the reaction temperatures from 80 °C to 180 °C. ZnO nanosheets are single crystals and the growth direction is perpendicular to [1100]. A possible gradual nucleation – rapid growth formation mechanism of ZnO nanosheets is proposed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and properties of nanocomposites prepared from ball milled 6061aluminium alloy with ZrO2 nanoparticles

Ball milling of 6061 aluminum alloy and nanocrystalline ZrO₂ powder allowed to obtain homogeneous mixture of nanocrystalline aluminum solid solution of grain size near 50 nm and ZrO₂ particles. The ZrO₂ particles are partially transformed after milling from tetragonal to the monoclinic crystal structure. After hot pressing in vacuum at temperature of 380 °C bulk nanocomposites were obtained of porosity below 1% consisting of aluminum solid solution of the average grain size near 80 nm and nano‐size ZrO₂ particles. Partial recrystallization occurred after hot pressing particularly near particles boundaries, where elongated recrystallized grains free from ZrO₂ nanoparticles of thickness near 1 μm and length of a few μm were identified. Estimated fraction of recrystallized grains was below 10%. The compression strength approaching 1000 MPa was obtained in composites containing 20% ZrO₂ nanoparticles, what is more than reported for ultra and nano‐grain 6XXX aluminum alloys. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New Mesogenic Compounds Containing a Terminal-Substituted Benzoxazole Unit

A series of novel mesogenic 2-(4-alkoxyphenyl-1-yl)-benzoxazole derivatives bearing different substituents (H, NO₂, CH₃, Cl, coded as nPB-H, nPB-N, nPB-M, and nPB-C, respectively) at the 5-position were prepared and characterized. nPB-N, nPB-M, and nPB-C exhibited enantiotropic smectic mesophases with the mesophase ranges 3 °C–32 °C and 3 °C–82 °C on heating and cooling processes, whereas nPB-H showed no mesophases. The substituents with the stronger electron withdrawing effect let to the wider mesomorphic temperature domain. The nPB-M, nPB-C, and nPB-H displayed intense emission in CH₂Cl₂ solutions with λ_max peaks of the photoluminescence spectra at 350–355 nm when excited at their absorption maxima.     

Growth and characterization of KBi(WO4)2 single crystals

Potassium bismuth tungstate [KBi(WO₄)₂] single crystals with dimensions up to 20 mm × 15 mm × 15 mm have been successfully grown by using the top‐seeded solution growth technique and K₂W₂O₇ as solvent. Experiments show that this crystal is unstable in a strong acid or alkali environment and has a blue fluorescence emission. The density, hardness, melting point, absorption edge, transparency range, prominent Raman shift frequency are 7.57 g/cm³, 238 kg/mm², 800 °C, 380 nm, 400–5450 nm, 868 cm^–1 respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermodynamic feasibility study for chemical vapour deposition of some ternary crystals using iodine and hydrogen iodide

Thermodynamic feasibility of transition metal dichalcogenide (TMDC) single crystals of Cu Al S₂, Cu Al Se₂, Cu Al Te₂, Cu Ga S₂, Cu Ga Se₂, Cu Ga Te₂, Cu In S₂, Cu In Se₂, Cu In Te₂, Ag Ga S₂, Ag Ga Se₂, Ag Ga Te₂, Ag In Se₂, Ag In Te₂, using iodine and hydrogen iodide as transporting agents has been reported in this paper. Results give range of temperature for the iodide transport and prevention of starting material formation (elemental transport) in the growth zone. From the range of temperature for the growth of crystals, selected source zone and growth zone temperatures with a differential of 100 °C are also listed. Referring the data listed in the tables can grow good quality crystals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Synthesis and Crystal Structure of [BiI2(tpy)2][Bi2I7(tpy)]: A New Metal Halide Material

Abstract [BiI₂(tpy)₂][Bi₂I₇(tpy)] (1) (tpy = 2,2′:6′2′′-terpyridine), a new compound containing a discrete bismuth halide anion, has been synthesized solvothermally and characterized by single crystal X-ray diffraction. The solvothermal reaction between BiI₃, Zn(NO₃)₂ · 6H₂O, and 2,2′:6′2′′-terpyridine in an ethanol/water solvent mixture resulted in the title compound. The anion and cation of this compound both contain bismuth, iodide ligands, and the organic ligand. The anion is composed of two face-sharing bismuth polyhedra, one of which is coordinated in a tridentate fashion to a disordered tpy ligand; and the remaining coordination sites at each Bi center are occupied by iodide ligands. The cation of the compound is a distorted, eight-coordinate polyhedron with a bismuth center, two iodide ligands, and six nitrogen atoms from two, tridentate tpy ligands. [BiI₂(tpy)₂][Bi₂I₇(tpy)] crystallizes in the triclinic space group P with the following lattice parameters: a = 10.0744(5) ?, b = 16.6115(8) ?, c = 18.5333(9) ?, α = 102.6490(10)°, β = 101.0850(10)°, and γ = 93.9160(10)°. Index Abstract The title compound, [BiI₂(tpy)₂][Bi₂I₇(tpy)], was synthesized solvothermally by the reaction between BiI₃ and 2,2′:6′2′′-terpyridine. Single crystal X-ray diffraction analysis reveals that the molecular structure contains one anion and one cation, both of which contain bismuth, iodine, and the tpy ligand, a situation not typically observed in these types of compounds.      

Growth and characterization of a PbI2 single crystal used for gamma ray detectors

Lead iodide (PbI₂) is an important material for room temperature radiation detectors. In this paper, we have grown PbI₂ single crystal through a special craft, from which γ‐ray detector has also been fabricated. X‐ray diffraction analysis indicates structure of the grown crystal is 2H with hexagonal space group P3m1. Infrared transmission measurement shows transmission rate of the grown crystal sample (10×10×1mm³) reaches 40% averagely in range of 400∼4000cm^‐1. Ultraviolet absorbing test indicates cut‐off wavelength of the sample is 547.6nm, corresponding band gap of 2.27eV. Room temperature detector fabricated from the grown crystal is sensitive to ²⁴¹Am 59.5KeV γ‐ray. Full width at half maximum (FWHM) of the obtained energy spectrum is 26.7KeV. All the results indicate the PbI₂ crystal grown through the special craft is of good characteristics and can be used for γ‐ray detector. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TiO2 nanoparticles synthesis for application in proton exchange membranes

In the present paper, suitable TiO₂ nanoparticles are successfully synthesized by sol‐gel method, in order to utilize the freshly prepared TiO₂ nanoparticles for proton exchange membrane (PEM) preparation. Titanium tetrachloride (TiCl₄) is used as precursor and ethanol as a solvent. The optimum and suitable TiO₂ nanoparticles were obtained by varying gelatinisation time (4–120 h), concentration of precursor (TiCl₄) in ethanol (2–15 vol%), and reaction temperature (15–35 °C). The morphology, size and purity of the nanoparticles are investigated by transmission electron microscope (TEM), dynamic light scattering (DLS) and X‐ray diffraction (XRD). Optimum results were found at 4 h of gelatinisation time, 10% precursor concentration and 25 °C temperature for preparation of TiO₂ nanoparticles. Thus prepared nanoparticles are found to be suitable for preparation of nanocomposite PEM, and consequently the prepared PEM indicates enhanced properties, such as, higher thermal stability (high glass transition temperature of 184.1 °C), excellent proton conductivity (0.0822 S cm⁻¹ at room temperature) and low methanol permeability (1.11 × 10⁻⁹ cm2 s⁻¹).     

Effects of annealing on the lattice parameter of polycrystalline CdS thin films

Cubic CdS (β‐CdS) polycrystalline thin films were prepared on glass substrates by chemical synthesis at 80 °C. Samples were subjected to thermal treatments (TT) in the range of temperatures (T) 180 – 500 °C during 30 hours in different ambients. Annealing in air and in H₂ produces in CdS larger lattice parameter enlargements (≤2.5 %) when T of TT increases up to T ≤ 500 °C. Whereas, annealing in Ar + S₂ and vacuum provokes intermediate (≤1.2 %) and smaller (≤0.9 %) maxima values of the lattice parameter increments, respectively. Energy band gap (E_g) as a function of T of TT and as a function of the lattice parameter has been also studied where it was observed that E_g behaves in very different manners depending on the ambient chosen for annealing. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A novel thermolysis method of colloidal protein precursors to prepare hydroxyapatite nanocrystals

A novel thermolysis method of colloidal protein precursors is introduced to prepare hydroxyapatite (HAP) nanocrystals. The colloidal protein precursors are sonochemically synthesized from saturated Ca(OH)₂ aqueous solution, Ca(H₂PO₄)₂ aqueous solution and bovine serum albumin (BSA) molecules. The colloidal protein precursors are amorphous and composed of 15‐90 nm near spherical calcium phosphate nanoparticles and BSA molecules. The particle size analysis shows the volume particle size distribution is from 9.0 nm to 222.6 nm and the volume‐averaged particle size is 45.8 nm. During the calcination procedure BSA molecules are burningly removed and the HAP nanocrystals can be obtained at 500 °C. The effects of BSA concentration on the properties of samples are discussed. Results show that BSA combustion can promote the transformation of crystalline HAP from amorphous material. Moreover, the increase of BSA concentration reduces the crystalline sizes of HAP crystals and the crystallinity of product. With BSA concentration of 5 g/L, the obtained HAP nanocrystals are mainly 25∼100 nm similar spherical nanoparticles besides some 40∼70 nm×75∼150 nm short rod‐like crystals. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile and one-pot synthesis of magnetic nanoparticles containing mesoporous carbon

Abstract

Magnetic nanoparticles containing mesoporous carbon materials have been synthesized via an one-pot strategy associated with a direct carbonization process from resol, metal ion sources (Co(NO₃)₂·6H₂O, Ni(NO₃)₂·6H₂O) and triblock copolymer F127. The samples exhibited well-ordered 2-dimensional (2-D) hexagonal mesostructures with p6mm symmetry. The Brunauer-Emmet-Teller (BET) surface area and pore size 1.0wt%Co- and 1.0wt%Ni-FDU-15(700) with 1.0?wt% Co and 1.0?wt% Ni content were 700, 528 m²/g and 17.2, 36.4 Å, respectively, after carbonization at 700?°C. The saturation magnetization values of 1.0wt%Co- and 1.0wt%Ni-FDU-15(700) after carbonization at 700?°C were 1.3 and 1.0?emu/g, respectively.     

Structural and optical properties of CdO nanowires synthesized from Cd(OH)2 precursors by calcination

CdO nanowires were produced by calcination process using Cd(OH)₂nanowires as precursors. The Cd(OH)₂ nanowires were synthesized via arc discharge method submerged in de‐ionized water. Transmission electron microscopy (TEM) analysis of the as‐synthesized Cd(OH)₂ nanowires revealed that nanowire morphology was abundant form with the diameters range from 5 to 40 nm. In addition to the nanowire morphology, Cd(OH)₂ nanospheres and hexagonal shaped nanoparticles were also displayed. The Cd(OH)₂ nanostructures were used as precursors to produce CdO nanowires and calcinated in air at 400 °C for four hours. After calcination, the structural, morphological and optical properties of the as‐synthesized CdO nanowires were characterized by means of TEM, selected area electron diffraction (SAED), X‐ray diffraction (XRD) and UV‐vis spectroscopy. The XRD and SAED techniques showed that the as‐synthesized Cd(OH)₂ nanostructures could be transformed into CdO nanostructures after the calcination process. TEM results revealed that the as‐synthesized CdO nanowires were 5–30 nm in diameter and shorter than corresponding Cd(OH)₂ nanowires. In addition, the diameters of the spherical or irregular CdO nanoparticles ranged from 20 nm to 50 nm. UV‐vis spectroscopy analysis was showed that the direct gap of the CdO nanowires were found to be 2.60 eV which is slightly higher than the earlier reported values of the bulk CdO for direct band gaps (2.3 eV) due to quantum size effect. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Two routes of forming nanorods on the base of nanoparticles

With ZnS nanoparticles as raw materials, two kinds of nanorods were fabricated. When ZnS nanoparticles were dispersed in Zn(NO₃)₂ solution and were treated in a sealed autoclave at 150 °C for 24 h, ZnO nanorods formed. ZnS nanoparticles work as a source of monomers for the growth of ZnO nanorods. With increase of concentration of Zn(NO₃)₂ solution, the products present long nanorods, short nanorods, star structure and bulk particle sequentially. When ZnS nanoparticles were kept in a solution at room temperature, ZnS nanorods formed after 21 days. ZnS nanoparticles work as assembly parts. They fit together spontaneously and present ZnS nanorods with many parallel stripes along the lengthways surface. To check the generality of self-assembling, PdS and Y₂S₃ nanorods were also fabricated.     

Synthesis,structural and optical properties of well dispersed anatase TiO2 nanoparticles by non‐hydrothermal method

The formation of nanocrystalline TiO₂ particles has been investigated via a surfactant‐free synthetic non‐hydrothermal method. Titanium isopropoxide and toluene were used as the starting materials. At a low temperature of 250 °C for 6 h, the reaction mixture turned in to a white precipitate (TiO₂) as a result of the thermal decomposition of metal alkoxide. The obtained product was found to crystallize purely in the anatase phase with well defined morphology. The powder XRD study confirms that the average size of the particle is close to ∼15 nm. The TEM analysis indicates the sizes of the primary and secondary particles in the range between 8‐10 nm and 15‐20 nm respectively. The quantum size confinement of the crystallites is evident from the blue shift of the absorption edge in the UV‐Visible absorption spectrum. The luminescence property of the TiO₂ nanoparticles studied by the emission spectrum confirms the presence of defect levels caused by the oxygen vacancies. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)