Preparation and characterization of monodispersed PbSe nanocubes

Monodispersed PbSe nanocubes were synthesized through a simple hydrothermal method by using Pb²⁺‐EDTA complex and Na₂SeSO₃. Composition and morphology of the samples were characterized by means of XRD, TEM and SEM. The gradually releasing of Pb²⁺ from Pb²⁺‐EDTA complex, and the adopting of PVP can adjust the growth rate in <100> and <111> directions of PbSe. Both Pb²⁺‐EDTA complex and PVP played important roles in the crystal growth of the monodispersed PbSe nanocubes. In addition, UV‐vis and photoluminescence properties were characterized. E_g of the PbSe nanocubes is 1.5 eV approximately, which is much larger than that of bulk PbSe. Under PL excitation at 406 nm, a red emission peak at 696 nm is observed, showing that the synthesized PbSe is luminescent nanomaterials. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and characterization of PbSe and PbSe/PbS core–shell colloidal nanocrystals

A new colloidal procedure, for the synthesis of PbSe and PbSe/PbS core–shell semiconductor nanocrystals (NCs), is reported. The synthesis includes the reaction between tributyl-phosphine selenium and lead 2-ethyl-hexanoate, under inert gas at room temperature. High-resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectroscopy (EDS), absorption and photoluminescence (PL) spectroscopy were used to characterize the samples. The EDS and HRTEM confirmed the existence of rock-salt cubic structures of the PbSe. Furthermore, the HRTEM showed the formation of PbSe/PbS core–shell structures, with epitaxial shell layer with thickness varying between 1 and 4 ML. The absorption spectra of these materials exhibited distinct transitions, related to the e1–h1, e2–h2 and e2–h3 and e2–h1 transitions. These bands are blue shifted with decrease in the NCs diameter. However, the e1–h1 is slightly red shifted with increase in the PbS shell thickness. The last effect can be due to an electronic mixing of the PbSe and PbS conduction states. The PL measurements showed a substantial increase of the exciton emission in the core–shell structures, arising by an efficient chemical passivation of the PbSe core.     

Preparation and characterization of silver trimolybdate

Fibrillar crystals of silver trimolybdate have been obtained. The composition and structural characterization of the compound were determined by chemical analysis and derivatographic, proton magnetic resonance and X-ray diffractometric studies.     

Preparation and characterization of telluride glasses

Chalcogenide bulk glasses Ge₂₀Se_80?xTe_x for x ∈ (0, 10) have been prepared by systematic replacement of Se by Te. Selected glasses have been doped with Er and Pr, and all systems have been characterized by transmission spectroscopy, measurements of dc electrical conductivity and low-temperature photoluminescence. Absorption coefficient has been derived from measured transmittance and estimated reflectance. Both absorption and low-temperature photoluminescence spectra reveal shifts of absorption edge and/or dominant luminescence band to longer wavelength due to Te → Se substitution. Arrhenius plots of dc electrical conductivity, in the temperature range 300–450 K, are characterized by activation energies roughly equal to the half of the optical gap. Arrhenius plots for temperatures below 300 K yield much lower activation energies. The dominant low-temperature luminescence band centered at about half the band gap energy starts to quench above 200 K and a new band appears at 900 nm. The band at 900 nm, due to band to band transitions, overwhelms the spectra at room temperature. Systems doped with Er exhibit a strong luminescence due to ⁴I_13/2 → I_15/2 transition of Er³⁺ ion at 1539 nm, and Pr doped samples exhibit a relatively weak luminescence peak at 1590 nm, which we tentatively assign to ³F₃ → ³H₄ transition of Pr³⁺ ion.     

Preparation and characterization of magnetic PVC nanocomposites

A new method was developed in order to achieve an excellent dispersion of magnetite onto a polymer matrix. For that a ferrofluid was prepared containing nanometric size (15 nm) magnetite and di-octyl phthalate (PVC plasticizer), this ferrofluid was dispersed in a polyvinyl chloride (PVC) plastisol and magnetic PVC films were made by static casting from plastisols and ferrofluids based on magnetite. Flexible films were characterized by vibration sample magnetometry, and stress-strain testing; rheometry was used to characterize the ferrofluid and the (PVC) plastisols containing ferrofluid (inverse ferrofluid). The effect of magnetite content on the magnetic and mechanical properties of the films was studied and showed an increase on magnetization values with magnetic loading and a variation in the stress-strain with magnetic loading as function of magnetic load content. It was found that the inverse ferrofluid showed a Bingham fluid behavior.     

Preparation and characterization of monolithic alumina aerogels

Alumina aerogels were prepared by a sol-gel method combined with the ethanol supercritical drying technique using aluminum tri-sec butoxide and nitric acid as the precursor and catalyzer respectively. This method affords high-surface-area alumina aerogel monoliths without the use of complexing agents. The structure and morphology of the aerogels were investigated by TEM, XRD, FTIR and BET techniques. The results confirmed that the as-prepared alumina aerogel possessed a network microstructure made up of pseudoboehmite fibers and a surface area of 690 m²/g. It was transformed to γ-Al₂O₃ after heat treatment at 800 °C without a significant loss in surface area. DMA analysis and hotdisk thermal analysis were performed to characterize the mechanical and thermal properties of the samples. The results indicated that the alumina aerogel was robust and exhibited excellent thermal insulating properties. The elastic modulus was up to 11.4 MPa after drying, which is the one of the highest modulus of alumina aerogels ever reported. The thermal conductivities at 30 °C and 400 °C were 0.028 W/mK and 0.065 W/mK respectively.     

Sm-substitution effects on structural and transport properties of PbSe

Polycrystalline single phase of Pb_1−xSm_xSe (x = 0.00–0.09) samples were prepared by the solid state reaction. XRD and SEM/EDAX methods were used for structural and chemical characterization of the obtained materials. The investigated samples were also characterized by the measurements of the samarium concentration dependence of the electrical conductivity and Seebeck coefficient. The power factor shows that these materials have the potential for high temperature applications with promising thermoelectric performance.     

Preparation and characterization of superconducting MgB2 rods

Superconducting Cu/Fe/MgB₂ and Steel/Cu/MgB₂ rods were prepared through the ex‐situ modified PIT technique with explosive consolidation method. The phase composition, microstructural features were investigated by X‐ray diffraction and scanning electron microscope. The AC susceptibility for a core samples was measured by the AC susceptometry. Measurements of the magnetization hysteresis loops were also carried out. It is found that no impurity phase was formed in MgB₂ rods. In addition, it was found that grains in both Cu/Fe/MgB₂ and Steel/Cu/MgB₂ rods are densely packed. The magnetic measurements show that the critical temperature of Cu/Fe/MgB₂ and Steel/Cu/MgB₂ rods is 37.7 K and 37.6 K, respectively. The high critical current density of 9.22 × 10⁵ A/cm² (4.1 K, 0.2 T) was obtained for Steel/Cu/MgB₂ rod. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and characterization of ordered mesoporous silica membrane

Hexagonal mesoporous silica (MCM-41) membranes were prepared at air-water interface by means of an interfacial silica-surfactant self-assembly process. The free-standing and oriented mesoporous silica membranes with pore size ≈2.9-3.8 nm were synthesized at room temperature in acidic media and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) observations. Small-angle X-ray diffraction (SAXRD) patterns of membranes clearly indicated that as-synthesized membranes were typical of MCM-41 materials with a periodic hexagonal structure with the channels parallel to the surface. SEM images showed that the as-synthesized membrane was continuous and crack-free. In this paper, some novel findings are reported.     

Preparation and characterization of ZnO nanofibers by electrospinning

Electrospun ZnO nanofibers were obtained by calcinating PVA/Zinc Acetate composite fibers at various temperatures. Atomic Force Microscopy (AFM) revealed that the ZnO fibers have diameters in the range of 100‐200 nm. The fibers were characterized by FT‐ IR, TGA‐DTA, and XRD studies. The XRD results showed that the crystal structure and the morphology of the fibers were largely dependent on the calcination temperature (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and characterization of hcp Co-coated Fe nanoparticles

A relatively simple method was described for coating and modifying iron nanoparticles with a hexagonal close-packed (hcp) cobalt layer. It was realized by depositing cobalt onto the poly(N-vinyl-2-pyrrolidone) (PVP) modified iron particles in ethanol solution. XRD, XPS and HRTEM were used to characterize the product. The Co layers, grown as the exclusive hcp phase, were ascribed to the inducement of the body-centered cubic (bcc) iron cores. Thus-prepared hcp Co-coated Fe particles displayed a much enhanced coercivity and decreased saturation magnetization (M_S) compared with that of the uncoated sample.     

Optical properties of novel PbS and PbSe quantum-dot-doped alumino-alkali-silicate glasses

Lead sulfide PbS and lead selenide PbSe quantum dots (QDs) were synthesized in novel alumino-alkali-silicate glass. The synthesis of the nanocrystals was stabilized by introduction of two alkaline components. The presence of crystalline phase was confirmed by X-ray diffraction analysis, transmission electron microscopy and optical spectroscopy. For PbS (PbSe) QD-doped glass, the position of the 1S–1S excitonic absorption peak can be managed in the spectral range of 1.5–2.1 μm (for PbS) or 1.8–2.2 μm (for PbSe) by appropriate heat‐treatment mode. The corresponding QD average diameter was found to be 5.8–9.7 nm (for PbS) and 7.5–9.5 nm (for PbSe). The influence of the secondary heat-treatment at the temperatures of 490–525 °C on the PbS QD growth in the glass matrix initially treated at 480 °C was studied in details. The photoluminescence of the PbS-QD-doped glass was observed, it was referred to the radiative recombination of the excitons from the 1S–1S state. The possibility to obtaining narrow 1S–1S absorption lines at the wavelengths longer than 2 μm is discussed.     

Preparation and characterization of amorphous cadmium–selenium ribbons

Chalcogenide glasses based on the cadmium–selenium system, with the selenium composition varying from 0 to 7.5 wt% have been prepared using melt-quenching method i.e., single-roller quenching technique. The X-ray diffraction (XRD) and selected area electron diffraction (SAD) patterns of the CdSe ribbons indicate that the ribbons are amorphous. The transmission electron microscopy (TEM) studies carried out on these ribbons reveal that the constituents are inhomogeneously distributed in these ribbons. The temperature dependence of the electrical resistivity, ρ and thermoelectric power (TEP) of these ribbons has been studied in the temperature range 30–350 °C. The sudden jump in the values of electrical resistivity at a specific temperature for each case in these ribbons has been correlated with the phase transition i.e., the onset of crystallization in these materials during heating. The crystallization temperature, T_c has been found to be a function of Se content of these ribbons. The phase change in these ribbons as a result of heating does not seem to affect the variation of TEP with temperature. However, the slope of TEP versus temperature curves depends on Se content in these ribbons. The differential scanning calorimetry (DSC) of these ribbons indicates that the supercooled region in these ribbons extends from 50 to 70 °C. The composition CdSe ribbon with 0.5 wt% Se has the highest value of T_c and glass forming ability, K_g = 0.7.     

Preparation and characterization of a novel solid titania precursor

Titania (TiO₂) is an important metal-oxide semiconductor and has a broad range of industrial applications in areas including pigment, photocatalysts, solar cells, ceramics, inorganic membranes, sensors, nonlinear optics and environmental purification, etc. Titania is often prepared using titania precursors. Here we report preparation of a novel solid titania precursor using a simple synthetic method, with a general chemical formula of TiSO₄(AcAc)_2−n(OH)_n · mH₂O (n < 2 and m < 2), that possesses high stability against hydrolysis and can be very conveniently employed for preparation of fine titania particles with no need of any solvent. Well dispersed TiO₂ nanoparticles with an average size of about 20 nm are prepared by directly annealing the solid titania precursor at 600 °C for 2 h. Characterization of the new solid titania precursor is carried out using transmission electron microscopy (TEM), thermogravimetry (TGA), Fourier transform infrared spectrometer (FT-IR) and X-ray diffractometer (XRD).     

Preparation and characterization of electrodeposited indium selenide thin films

Indium Selenide (InSe) thin films were deposited from a mixture of Indium chloride and selenium dioxide in aqueous solution by electrodeposition technique on Indium Tin oxide coated glass substrates. The effects of the parameters during deposition such as current density, deposition potential versus saturated calomel electrode, pH value and concentration of source material were studied. X‐ray diffraction studies were carried out on the films to analyze the microstructure using an x‐ray diffractometer and were examined by RAMAN spectroscopy. The Raman peak position did not change much with chemical concentrations. Raman scattering due to the (LO) phonon was observed at 211 cm^–1. Optical absorption studies were performed with a double beam ultra violet‐visible –NIR spectrophotometer in the wavelength 300–1100 nm. The surface morphology of the layer was examined using a scanning electron micrograph. The composition of the films was studied using an Energy Dispersive Analysis by X‐Rays (EDAX).     

Preparation of amorphous carbon tetrachloride and characterization by neutron diffraction

A 5 g sample of carbon tetrachloride (CCl₄) deposited from the vapour on to a cadmium substrate at 5 K is shown to be amorphous by the absence of Bragg peaks in its neutron diffraction spectrum. Simple analysis shows that the range of correlations in amorphous CCl₄ extends only to next-nearest neighbours.     

Preparation and characterization of amorphous silica nanowires from natural chrysotile

By chemical dispersing and acid leaching, silica nanowires have been prepared from the natural mineral, chrysotile. X-ray fluorescence analysis (XRF), thermogravimetric analysis and differential thermogravimetric analysis (TGA–DTA), powder X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the silica nanowires. The results indicate that the chemical composition of the silica nanowires is SiO_1.8 · 0.6H₂O, and although the silica is amorphous, its structure is regular to some extent. The structural unit of the silica nanowires is the [SiO₄] tetrahedron and six-member silicon–oxygen ring with the tetrahedral positioned alternately up and down in the six-member ring. The silica nanowires are well-dispersed and have cylindrical morphology and smooth surface, with lengths over 10 μm and diameters of 30–60 nm.     

Preparation and characterization of Si sheets by renewed SSP technique

Silicon sheets from powder (SSP) ribbons have been prepared by modified SSP technique using electronic-grade (9N purity) silicon powder. The surface morphology, crystallographic quality, composition and electric properties of the SSP ribbons were investigated by surface profiler, X-ray diffraction (XRD), scanning electron microscopy (SEM), metallurgical microscope, Auger electron spectroscopy (AES) and four-point probe apparatus, respectively. The results show that the SSP ribbon made from electronic-grade silicon powder is a suitable candidate for the substrates of crystalline silicon thin film (CSiTF) solar cells, which could meet the primary requirements of CSiTF solar cell process on the substrates, including surface smoothness, crystallographic quality, purity and electric conductivity, etc.