Photo-quenched of the luminiscence signal in Co(II)-doped alumina prepared by the sol-gel method

Co(II)-doped alumina monoliths prepared by the sol-gel method were laser irradiated producing fluorescence. The intensity of this defect-induced fluorescence was exponentially reduced with the irradiation time to practically disappear. The rate the fluorescence intensity decays was modeled as a double exponential function of the irradiation time; the characteristic times associated with the decays are in the range of seconds. The suppression of the luminescence was associated with the local heating produced by the highly focused laser beam in a small area (≈ 2 μm in diameter) on the sample. This heating process reduces physical (grain boundaries and surface states) and chemical (oxygen vacancies) defects present in the sol-gel samples. Some residual fluorescence still remains after long periods of illumination. The characteristic times for alumina samples are compared with those obtained for other metal oxides prepared also by the sol-gel method.     

Preparation of alumina gels by a non-hydrolytic sol-gel processing method

Monolithic alumina gels were prepared by a novel non-hydrolytic sol-gel route based on the condensation reaction between aluminum alkoxides Al(OR)₃ and aluminum halides AlX₃, through the formation of alkyl halide RX(X = Br, Cl; R = iso-propyl, sec- or ter-butyl), around 100°C. Samples were then calcined and were found to be amorphous up to about 750°C; they kept a high specific surface area to about 900°C. This delayed crystallization is correlated with the large number of five-coordinate aluminum sites measured in dried gels by ²⁷Al NMR spectroscopy.     

Preparation of alumina fibers by sol-gel method

The shape of particles present in the alumina sols prepared from inorganic salts was examined by transmission electron microscopic observation and related to the rheological property and fiber drawing behavior of the sols. It was found that fibers could be drawn in the viscosity range of 1–100 Pa·s from the sols in which long-shaped particles were found, while no fibers could be drawn from the sols containing round particles. It was also found that non-spinnable sols showed relatively large structural viscosity, whereas spinnable sols showed Newtonian flow or very little structural viscosity.     

Effect of La doping on microstructure of SnO2 nanopowders prepared by co-precipitation method

A series of La-doped SnO₂ nanopowders with various dopant concentrations were prepared by chemical co-precipitation technique, and the nanopowders prepared were characterized by differential scanning calorimeter (DSC), thermo-gravimetric (TG), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The results show that La doping can obviously prevent the growth of nanosized SnO₂ crystallites. When the La concentration reaches and surpasses 5 at.%, SnO₂ crystallite size reaches a minimum value and remains almost constant. With the increase of La concentration, La tends to dissolve in the bulk phase of SnO₂ to form solid solution below 10 at.% addition and then starts to disperse onto the surface of the solid solution as a monolayer above 10 at.%. The effect of La doping on hindering crystallite growth can be attributed to the solute drag and lattice distortion resulting from La dissolving in the bulk phase of SnO₂ to form solid solution, rather than the monolayer of La on the surfaces of the SnO₂ powders.     

r-GRIN glass rods prepared by a sol-gel method

Preparation of radial gradient refractive index (r-GRIN) glass rods has been undertaken by a sol-gel process using metal alkoxides. Two binary systems, Si(OCH₃)₄---Ge(OC₂H₅)₄ and Si(OCH₃)₄−Ti(O−n-C₄H₉)₄ have been investigated. It has been shown that immersion of rod-shaped wet gels in neutral or acidic water gives rise to leaching of the dopants (germanium and titanium components). Since this leaching is controlled predominantly by diffusion, the dopants remaining in the gels are expected to form concentration gradients. Optical measurements of the glass rods obtained after drying and sintering of the leached gels have shown that the concentration gradients are retained in the glass rods and they give r-GRIN profiles.     

PbS microcrystals with a magic‐square‐like structure prepared by a simple hydrothermal method

PbS microcrystals with a magic‐square‐shaped structure were successfully fabricated via a simple hydrothermal route, employing (CH₃COO)₂Pb and Na₂S₂O₃ as the lead and sulfur source without the assistance of any surfactant or template. S₂O₃^2‐ ions acted not only a supplier of S^2‐ ions but also a coordinating reagent. The formation of the above morphology was the direct result of the coordination between thiosulfate ions and lead ions. Researches indicated that the different synthetic approach could influence the morphology of the final product. A possible formation mechanism was suggested. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of pure ZnO thin films prepared by a direct photochemical method

In this paper, amorphous ZnO thin films were obtained by direct UV irradiation of β-diketonate Zn(II) precursor complexes spin-coated on Si(1 0 0) and fused silica substrates. ZnO films were characterized by means of XPS, X-ray diffraction (XRD) and Atomic Force Microscopy (AFM). These analyses revealed that as-deposited films are amorphous and have a rougher surface than thermally treated films. Optical characterization of the films showed that these are highly transparent in the visible spectrum with an average transmittance of up to 95% over 400 nm, and an optical band-gap energy of 3.21 eV for an as-deposited film, and 3.27 eV for a film annealed at 800 °C. Low resistivity values were obtained for the ZnO films (1.0 × 10⁻² Ω cm) as determined by Van der Pauw four-point probe method.     

Optical properties of flower‐like CdS prepared by a hydrothermal method with SDBS as surfactant

In this article, flower‐like CdS structures have been prepared by a hydrothermal method with SDBS as surfactant. The influences of different experimental conditions on the morphologies, UV‐Vis and fluorescence properties of CdS have been investigated. The performances of CdS have been analyzed by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet‐visible (UV–Vis) and room‐temperature photoluminescence (PL). The XRD result indicates that the flower‐like CdS structures are of hexagonal phase. The FESEM results indicate that the main role of SDBS is to make the CdS crystals assemble together to form the flower‐like structures. The UV–Vis results show CdS has a strong absorption in the ultraviolet region and visible‐light region. The PL results show CdS has two emission peaks, respectively at 461 nm and 553 nm. The growth mechanism for the formation of flower‐like CdS structures is also described.     

Characteristics of sputtered amorphous carbon films prepared by a closed-field unbalanced magnetron sputtering method

We discuss the tribological performance of sputtered amorphous carbon (a-C) films deposited by closed-field unbalanced magnetron (CFUBM) sputtering with a graphite target using a mixture of helium (He) and argon (Ar) as sputtering gases. We investigated the effects of the graphite target power density on the micro-structural and physical properties. In the Raman spectra, the G-peak position moved to the higher wavenumbers. The I_D/I_G ratio increased with the increase of target power density in the fixed DC bias voltage. This was the result of the structural change in the a-C film that resulted with the increase in sp² bonding fraction. Also, the maximum hardness of the a-C film was 23 GPa, the friction coefficient was 0.1, and the critical load was 25.9 N on the Si wafer. In addition, the compressive residual stress of the film increased a little with increasing target power density. Consequently, the various properties of a-C films, with an increase of the target power density, were associated with the increase of cross-linked sp² bonding fraction and the cluster size. The tribological properties of a-C film showed clear dependence on the energy of ion bombardment with the increase of plasma density during film growth.     

Insights into effects of annealing on microstructure from SnO2 thin films prepared by pulsed delivery

Tin dioxide thin films were prepared by pulsed laser deposition techniques on clean glass substrates, and the thin films were then annealed for 30 min from 50 to 550 °C with a step of 50 °C, respectively. The influence of the annealing temperature on the microstructural and morphological properties of the tin dioxide thin films was investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and selected area electron diffraction. The experimental results showed that the amorphous microstructure almost transformed into a polycrystalline tin dioxide phase exhibiting a preferred orientation related to the (1 1 0), (1 0 1) and (2 1 1) crystal planes with increased temperatures. The thin film annealed at 200 °C demonstrated the best crystalline properties, viz. optimum growth conditions. However, the thin film annealed at 100 °C revealed the minimum average root-mean-square roughness of 20.6 nm with average grain size of 26.6 nm. These findings indicate that the annealing temperature is very important parameter to determining the thin film quality, which involves the phase formation, microstructure and preferred orientation of the thin films.     

Amorphous phase separation and crystallization in a lithium silicate glass prepared by the sol-gel method

A 10Li₂O---90SiO₂ (mol%) gel-glass has been prepared by using tetramethyl orthosilicate and lithium iso-propoxide as starting materials. The phase separation and crystallization behaviour was compared with the corresponding conventionally melted glass using DTA, X-ray diffraction and TEM. The same crystallization phase was found in both the gel glass and melted glass upon heating above 650°C. However, the rate of crystallization in the gel-glass was higher than in the melted glass. TEM revealed amorphous phase separation in the gel glass and melted glass. However, the morphologies were different, an interconnected microstructure being observed in the gel glass and a droplet structure in the melted glass. These differences can be partly attributed to differences in OH content. Other potential influencing factors are also considered. After 650°C for 2 h lithium disilicate crystals were observed in the volume of the gel glass by TEM. As the crystals grew they absorbed Li₂O from the surrounding lithia-rich amorphous phase so that silica-rich (lithia depleted) diffusion zones formed around them.     

Effect of deposition pressure on microstructure and properties of hydrogenated carbon nitride films prepared by DC-RF-PECVD

Hydrogenated carbon nitride (a-CN:H films) were deposited on n-type (1 0 0) silicon substrates making use of dual direct current radio frequency plasma enhanced chemical vapor deposition (DC-RF-PECVD), at working pressure of 2–20 Pa, using a mixed gas of CH₄ and N₂ as the source gas. The growth rate, composition, bonding structure of the deposited films were characterized by means of XPS and FTIR, and the mechanical properties of the deposited films were investigated by nano-indentation test. It was found that the parameters for the DC-RF-PECVD process had significant effects on the growth rate, structure and properties of the deposited films. The growth rate of the deposited films increased at first with increasing deposition pressure, then saturated with further increase of the deposition pressure. The N/C ratio inside the deposited films increased with increasing working pressure except that it was as much as 0.50 at a working pressure of 5.0 Pa. The nano-hardness of the films decreased with increasing deposition pressure. CN radicals were remarkably formed in the deposited films at higher pressures, and their contents are related to the nitrogen concentrations in the deposited films.     

Binary Ni–P bulk amorphous glass prepared by electrodeposition method

Compact and uniform bulk Ni–P binary amorphous alloys (BAAs) with thickness of up to 1 mm were prepared using electrodeposition method. This is the first finding that amorphous alloy can be obtained up to ‘bulk’ size not by rapid solidification but by electrochemical method. By improving the electrodeposition techniques, selecting proper plating solution, electrodeposition is probably a new method for preparing bulk amorphous alloys. The formation mechanism of the bulk amorphous was discussed within the concept of ‘disorder solid’.     

Indium phosphide nanofibers prepared by electrospinning method: Synthesis and characterization

Nine sets of (3 × 3) InP nanofiber samples have been successfully prepared at three different voltages (20, 25, 30 kV) and at three separate heights (5, 7, 10 cm) by electrospinning with a constant precursor flow rate of 0.3 mLh⁻¹. The crystalline structure, thermal, morphologies and nanostructure, electrical, and optical properties of the samples are characterized by X‐ray powder diffractometer (XRD) and thermal gravity‐differential scanning calorimeter (TG‐DSC), scanning electron microscopy (SEM), by Four‐Point Probe Technique (FPPT,) and ultraviolet/visible spectrometry (UV/VIS), respectively. From these measurements, we have found the formation of stoichiometric nanostructured InP with zinc‐blende structure and having lattice parameter of a = 5.874 Å, weight loss of 64.59% and crystallization temperature of 500°C, average fiber diameter of 65.82 nm, the activation energies, E_a, of the samples, and band gap energy, E_g, of the nanofibers developed at constant applied voltage 30 kV. The band gap energies determined at different distances 5, 7, and 10 cm are found to be as 1.29, 1.37, and 1.30 eV, respectively.     

Microcrystalline germanium thin films prepared by the reactive RF sputtering method

We focus on thin film microcrystalline germanium (μc-Ge) as narrow gap semiconductor materials for high infrared sensitivity and consider applying it to thermo-photo-voltaic (TPV). The μc-Ge films were prepared on glass substrates by the reactive RF sputtering method with Ar and H₂ gas mixtures. We could successfully produce photosensitive μc-Ge films. Higher crystallinity structures do not always result in better carrier properties. Probably, the amorphous portions between crystalline grains have important roles to suppress the grain boundary defects. We applied the μc-Ge to i-layers of pin structure devices, and observed the photovoltaic effect for the first time.     

BaMoO4 thin films prepared by electrochemical method at room temperature

Highly crystallized BaMoO₄ films were prepared on molybdenum substrates in Ba(OH)₂ solutions by electrochemical method at room temperature. The deposition conditions (reaction temperature and current density) during electrochemical formation were researched. The films were characterized by using the X‐ray Diffraction (XRD), Scanning Electronic Microscopy (SEM) and X‐ray Photoelectron Spectroscopy (XPS) analyses. The XRD analyses show that the films are good crystalline with single scheelite‐type tetragonal structure; the SEM photographs show that the films are densely deposited with double tetragonal tapers in shape; and the XPS analyses reveal that the composition of the BaMoO₄ films (embodied Ba²⁺, Mo⁶⁺ and O^2‐) is in agreement with stoichiometry. The optimum electrochemical conditions for BaMoO₄ films formation are the lower reacting temperature (near room temperature) and the feasible current density (about 1mA/cm²)     

Properties and microstructure of silica glass incorporated with tributyl phosphate by sol–gel method

An organic phosphate species tributyl phosphate (TBP) was incorporated into sol–gel-derived glass matrix. TBP could be directly added to the hydrolyzed silica source from tetraethylorthosilicate (TEOS) and immobilized in silica glass matrix. TBP was stably immobilized in silica glass matrix even in the case where the weight ratio of TBP to silica was unity, and where the volume fraction of the glass sample occupied by TBP moiety was as large as 69%. The glass sample showed an appearance of hard glassy solid even at such a large fraction of TBP which is an organic solvent in the neat state at room temperature. The FT-IR spectrum showed that TBP was immobilized in silica glass in an intact state without chemical bonding with the siloxane network. The Vickers hardness was large enough even at higher weight ratios of TBP to silica to be measured as data indicating that the immobilized TBP molecules could play a promotive role in forming the siloxane bonding. The wide-angle X-ray scattering experiments revealed that the siloxane bonding was expanded by TBP molecules entrapped in the siloxane network. Furthermore, TBP molecules are dispersed in the siloxane network in the molecular scale.     

Optical studies on ZnO films prepared by sol‐gel method

A standard sol‐gel method was used to deposit ZnO thin films of suitable thickness on glass substrate.The optical characteristics of the visible to infrared range on thermal stress were critically observed. Morphological signature of the films was detected by X‐ray diffraction (XRD) and the crystallite size determined by Scherrer method from XRD data were consistent with grain size estimated from spectroscopic data through Meulenkamp equation. The optical band gap value from the transmission spectrum was found to corroborate with the existing works. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)