Volume 32 (2014): Issue 1 (January 2014)

The mono and bi-layer TiO2 thin films have been prepared by sol-gel method on glass. X-Ray diffraction, Raman spectroscopy, atomic force microscopy, spectroscopic ellipsometry and m-lines spectroscopy techniques have been used to characterize the TiO2 films. The mono-layer film is found to be amorphous, while the bi-layer film shows the presence of anatase phase. The bi-layer film exhibits more homogeneous surface with less roughness. The thickness effect on the refractive index, extinction ceofficient, packing density and optical band gap is analysed. The waveguiding measurements of the bi-layer film exhibit single-guided TE0 and TM0 polarized modes from which we can measure the refractive index and the film thickness.

Bi4Ge3O12 single crystals were obtained using Czochralski growth method. Photoluminescence spectra were analyzed versus temperature from 12 to 295 K. Besides the previously observed emission bands at 610 and 820 nm, the new emission band at 475 nm was found by a careful temperature dependence measurement in the present study. The influence of basic and defect structure on the shape and position of the spectra versus temperature was discussed.

Pure and L-lysine added ammonium dihydrogen phosphate (ADP) crystals were grown in the 〈001〉 direction by Sankaranarayanan-Ramasamy (S-R) method. The grown crystals were characterized by X-Ray diffractometry (XRD), UV-Vis spectroscopy, Fourier Transform Infrared (FT-IR) and Vicker’s Microhardness analysis.

XRD spectrum of each of the grown crystals proved its crystallinity. The crystals showed good transparency in the entire visible region. FT-IR spectra of the specimens revealed the presence of functional groups in them. The hardness of the pure and L-lysine added ADP crystals were measured and that of the added one was found higher. Meanwhile, it was found that the ADP crystals (pure and L-lysine added) grown by S-R method had higher hardness compared to ADP crystal grown by conventional method.

We report here the structural and electrical properties of Zn0.95M0.05O ceramic varistors, M = Zn, Ni and Fe. The samples were tested for phase purity and structural morphology by using X-Ray diffraction XRD and scanning electron microscope SEM techniques. The current-voltage characteristics J-E were obtained by dc electrical measurements in the temperature range of 300–500 K. Addition of doping did not influence the hexagonal wurtzite structure of ZnO ceramics. Furthermore, the lattice parameters ratio c/a for hexagonal distortion and the length of the bond parallel to the c axis, u were nearly unaffected. The average grain size was decreased from 1.57 μm for ZnO to 1.19 μm for Ni sample and to 1.22 μm for Fe sample. The breakdown field EB was decreased as the temperature increased, in the following order: Fe > Zn > Ni. The nonlinear region was clearly observed for all samples as the temperature increased up to 400 K and completely disappeared with further increase of temperature up to 500 K. The values of nonlinear coefficient, a were between 1.16 and 42 for all samples, in the following order: Fe > Zn > Ni. Moreover, the electrical conductivity s was gradually increased as the temperature increased up to 500 K, in the following order: Ni > Zn > Fe. On the other hand, the activation energies were 0.194 eV, 0.136 and 0.223 eV for all samples, in the following order: Fe, Zn and Ni. These results have been discussed in terms of valence states, magnetic moment and thermo-ionic emission, which were produced by the doping, and controlling the potential barrier of ZnO.

A new thallium (I) coordination polymer [Tl(PsucH)]n (PsucH = phenylsuccinic acid) has been synthesized and characterized by single crystal X-Ray analysis, elemental analysis and IR spectroscopy. The single crystal X-Ray analysis shows that this polymer is 2-D along a axis. Flower-like nanostructure thallium (III) oxide, Tl2O3 has been prepared by direct thermal decomposition of thallium (I) coordination polymer. The nanostructure was characterized by scanning electron microscopy (SEM), X-Ray powder diffraction (XRD) and IR spectroscopy. The thermal stability of the Tl2O3 nanostructure was studied by thermal gravimetric analysis and differential thermal analysis (TGA /DTA) too.

Laser induced structure changes in amorphous Co70Fe3Mn3.5Mo1.5B11Si11 alloy have been studied by means of X-ray diffraction and magnetic properties measurements. Both three types of structural relaxations and a starting stage of crystallization process are considered as main characteristics of structure transformation upon laser treatment. Results of investigation of this amorphous alloy at different parameters of laser irradiation have shown that this alloy becomes partly crystalline after irradiation with laser pulse fluence of about 1.8 J/mm2 and pulse duration τ = 2 × 10−5 sec. Increasing of laser pulse fluence above 2.0 J/mm2 leads to the destruction of ribbon, due to intensive evaporation.

The synthesis of CoFe2O4 nanoparticles has been achieved by a simple thermal decomposition method from an inorganic precursor, cobalt ferrous cinnamate hydrazinate (CoFe2(cin)3(N2H4)3) which was obtained by a novel precipitation method from the corresponding metal salts, cinnamic acid and hydrazine hydrate. The precursor was characterized by hydrazine and metal analyses, infrared spectral analysis and thermo gravimetric analysis. Under appropriate annealing, CoFe2(cin)3(N2H4)3 yielded CoFe2O4 nanoparticles, which were characterized for their size and structure using X-Ray diffraction (XRD), high resolution transmission electron microscopic (HRTEM), selected area electron diffraction (SAED) and scanning electron microscopic (SEM) techniques.

Inclusion complexation of 2-aminopyrimidines with β-cyclodextrin was studied in the solid state by infrared spectroscopy (IR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The aminopyrimidine-β-CD complexes were also investigated in a solution by nuclear magnetic resonance spectral techniques (1H-NMR and 13C-NMR). Qualitative modifications in the position and number of peaks or bands obtained from spectral methods as well as thermal analysis indicated the inclusion.

Alumina and scandia doped zirconia was prepared through a soft chemistry synthesis route and sintered at 1873 K. X-ray diffraction patterns indicate a pure cubic phase for the composition of 0.88ZrO2-0.112Sc2O3-0.008Al2O3. Thin films were fabricated on Al2O3 〈0001〉 substrates using pulsed laser deposition technique. Dense films of 0.941 μm thickness were obtained at 873 and 1023 K substrate temperatures at an oxygen partial pressure of 15 Pa. The ionic conductivity of both thin film and sintered pellet was measured using ac impedance spectroscopy in air. The conductivity values are higher for thin films compared to that of sintered pellets.

Organic chemical hazardous gases pose a significant threat to human life and the environment. An urgent need exists for the development of reliable chemical sensors that would be able to identify these hazardous gases. In a recent study, conductive carbon nanotubes were mixed with six polymers with various chemical adsorption properties to produce a composite thin film for the fabrication of a chemical sensor array. A silicon wafer was used as a microelectrode substrate for a resistance sensor fabricated using a typical semiconductor manufacturing process. This sensor array was then used to identify hazardous chemical gases at various temperatures. Results for two hazardous gases, ammonia (NH3) and chloroform (CHCl3), tested with the six polymers at different temperatures, indicated that the variation in sensitivity/resistance increased when the temperature increased. It was found that the MWNTs-PVP and MWNTs-PMVEMA sensing films had high sensitivity, excellent selectivity, and favorable reproducibility in detecting the two chemical agent vapors. In addition, we derived the solubility parameter (Δδ) to demonstrate the sensitivity of the polymers to ammonia (NH3). The results showed that smaller solubility parameter corresponds to a stronger interaction between NH3 gas and polymers, and increased sensitivity. Additionally, we used the statistical methods of principal component analysis to identify the interaction of hazardous gases with the MWNTs-polymer sensor.

The 0.5(BiGd0.05Fe0.95O3)-0.5(PbZrO3) composite was synthesized by means of a high temperature solid-state reaction technique using high purity ingredients. Preliminary X-ray structural analysis confirms the formation of the composite. The dielectric constant and loss tangent have been studied. The impedance parameters have been measured using an impedance analyzer in a wide range of frequency (102–106 Hz) at different temperatures. The Nyquist plot suggests the contribution of bulk effect only and the bulk resistance decreases with a rise in temperature. Electrical impedance confirms the presence of grain effect and hopping mechanism in the electrical transport of the material. The dc conductivity increases with a rise of temperature. The frequency variation of ac conductivity shows that the compound obeys Jonscher’s universal power law and from Jonscher’s power law fit confirms the Small Polaron (SP) tunneling effect. Temperature dependence of dc and ac conductivity indicates that electrical conduction in the material is a thermally activated process.

Indium tin oxide (ITO) films were deposited on soda-lime glass substrates by the spray pyrolysis method using a spray solution of InCl3·3H2O as a precursor, SnCl4·5H2O as a dopant and acetylacetone (AcAcH) as a chelating agent. The effect of the addition of AcAcH to the spray solution on the surface morphology of the ITO film was investigated. The surface quality of the film prepared from the spray solution with AcAcH was better than that without AcAcH. The ITO film with the thickness of 230 nm, using the spray solution with AcAcH, exhibited the lowest resistivity of 4.75 × 10−4 Ω·cm and higher optical transmittance of 85 %, respectively.

TiO2 powders were prepared through the hydrolysis of titanium isopropoxide followed by calcination at temperatures of 200 °C to 600 °C. The obtained powders were characterized by N2 adsorption-desorption and X-ray powder diffraction. The results confirmed strong dependence between specific surface area of the TiO2 powders and both the conditions of the hydrolysis process and the calcination temperature. While calcination temperature strongly affected crystallinity of the product, no significant influence of the hydrolysis conditions on this parameter was observed. TiO2 powders prepared at various conditions were examined as catalysts for photodegradation of Acid Red 18 in water. Photoactivities of the prepared powders were influenced by both the amount of water used to hydrolyze the TiO2 precursor and the temperature of calcination process. TiO2 samples calcined at 500 °C appeared to be the most active and the photocatalytic activities of the prepared materials increased along with the amount of water used for the hydrolysis process.

Investigations of bilayer and trilayer Al2O3/SiO2 and Al2O3/HfO2/SiO2 antireflective coatings are presented in this paper. The oxide films were deposited on a heated quartz glass by e-gun evaporation in a vacuum of 5 × 10−3 [Pa] in the presence of oxygen. Depositions were performed at three different temperatures of the substrates: 100 °C, 200 °C and 300 °C. The coatings were deposited onto optical quartz glass (Corning HPFS). The thickness and deposition rate were controlled with Inficon XTC/2 thickness measuring system. Deposition rate was equal to 0.6 nm/s for Al2O3, 0.6 nm − 0.8 nm/s for HfO2 and 0.6 nm/s for SiO2. Simulations leading to optimization of the thin film thickness and the experimental results of optical measurements, which were carried out during and after the deposition process, have been presented. The optical thickness values, obtained from the measurements performed during the deposition process were as follows: 78 nm/78 nm for Al2O3/SiO2 and 78 nm/156 nm/78 nm for Al2O3/HfO2/SiO2. The results were then checked by ellipsometric technique. Reflectance of the films depended on the substrate temperature during the deposition process. Starting from 240 nm to the beginning of visible region, the average reflectance of the trilayer system was below 1 % and for the bilayer, minima of the reflectance were equal to 1.6 %, 1.15 % and 0.8 % for deposition temperatures of 100 °C, 200 °C and 300 °C, respectively.

Rare earth Eu3+-doped MgNb2O6 red-emitting phosphor was prepared by solid-state reaction. Structure and photoluminescence properties of the samples were characterized by X-ray diffraction (XRD), scan electron microscopy (SEM) and fluorescence spectrophotometer. Meanwhile, the effect of the co-activator Bi3+ on the PL of the MgNb2O6:Eu3+ phosphor was studied. The results showed that the pure phase of MgNb2O6 could be available after firing at 1200 °C. The Mg1−x Nb2O6:Eux3+ phosphors could be effectively excited by the UV irradiation (273 nm) and emit red light at 615 nm due to the forced electric dipole 5 D 0 → 7 F 2 transitions on Eu3+, which indicated that Eu3+ occupied the non-inversion symmetry sites in the MgNb2O6 host lattice. So, the addition of the co-activator Bi3+ not only increased the excitation band of the MgNb2O6:Eu3+ phosphor at about 330 nm, but also strengthened the PL intensity at 615 nm. Therefore, MgNb2O6:Eu3+, Bi3+ might find application to InGaN chip-based white light emitting diodes.

The electronic structures of Hg-doped anatase TiO2 with different O vacancy concentrations were calculated using the first-principles based on the density functional theory. The calculated results show that the forbidden band widths of Hgdoped anatase TiO2 widened along with the increase of O vacancy concentration, which is responsible for the blue shift in the absorption edges. It can be deduced from the present study that the Hg-doped TiO2 samples prepared in the experimental research contain a certain quantity of O vacancies.

The present study illustrates the characteristics and co-precipitation method for synthesis of tin oxide nanoparticles. The tin oxide nanoparticles were produced using tin chloride, Triton X-100 and ammonia precipitators. Structure, size and surface morphology of the tin oxide was studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results show sphere shaped tin oxide nanoparticles without chlorine contamination. The crystallite size determined by the Scherrer formula is about 23 nm. Lattice parameters calculated by Nelson-Riley equation show high quality of crystallization.

Indium tin oxide (ITO) films were deposited on glass substrates by dip-coating and thermal pyrolysis methods. Sn (IV) is often used in the spray method as a precursor salt, but in this research we have employed a new procedure that uses Sn (II) and In(NO3)3 for preparation of transparent conductive thin films. Then, colloidal Ag was deposited on the ITO layers in order to compare the two synthesis methods, and the structural and electrical properties of the resultant films were investigated by FESEM, XRD, and four-terminal resistometry. The obtained films are polycrystalline with a preferred orientation of (200). The XRD patterns of the films indicate that in both films, the Sn phase is crystallized separately from In2O3. The presence of a Sn peak and the overall low intensity of XRD peaks suggest relative crystallization of ITO structure. For this reason, Ag films were deposited by dip coating method using a colloidal sol. By analyzing the XRD patterns of Ag-ITO films after eliminating the Sn peak, the increased intensity of the peaks confirmed the relatively good crystallization of the ITO films. The results show that the films with a sheet resistance as low as 2 × 10−2 Ω·cm, which is beneficial for solar cells, were achieved.

Silver colloidal nanoparticles were prepared according to the chemical reduction method in which the ascorbic acid was used as a reducing agent and sodium citrate as a stabilizing agent. The absorption spectra of all prepared samples obtained using the UV-Vis spectrophotometer showed a surface plasmon peak at a wavelength of about 420 nm. The size of the silver nanoparticles was controlled by changing the pH values of the reaction system. At high pH, smaller size silver nanoparticles were obtained compared to low pH values. This difference can be attributed to the difference in the reduction rate of the precursor. In addition to the inverse proportionality between the size and the pH value it is clear that increasing the pH value enables us to obtain spherical nanoparticles while at low pH, rods and triangular particle shapes were formed. Poor balance between nucleation and growth processes could be the cause of this result.

The first-principles calculations have been performed to study the influence of boron on the adsorption of Ti and C on different TiC surfaces. It is found that boron can be adsorbed on both TiC (001) and (111) surfaces. When boron is present and carbon supply is high during the preparation of TiC, boron can bond with carbon atoms to form B-C clusters on (001) surface, but the formation of them is less favorable than that of Ti-C clusters. However, under the low carbon-supply condition, both B-B and Ti-Ti clusters can be formed, and, once being formed, B-B clusters are more stable than the Ti-Ti ones. On Ti-terminated (111) surfaces, boron adatoms are more likely to be moved to form B-B clusters. The study of the diffusion of the adatoms on the surfaces demonstrates that boron adatoms can be more easily migrated on (111) surfaces, which further confirms the above results.

Ag — 8 wt. % ZnO composites were synthesized by ball milling, heat treating and hot pressing of silver and zinc oxide powder mixtures. The crystalline size and microstrain of the milled powders before and after heat treatment were determined by Debye-Scherrer andWilliamson-Hall methods. It was shown that heat treatment resulted in decrease of microstrain and increase in the crystallite size of the milled powders. The effect of uniaxial pressure magnitude and duration of hot pressing at 550 °C on the final density of the powder compacts were investigated. The results showed that both plastic flow and atomic diffusion mechanisms affected densification of the composite powders during the hot pressing process. However, the latter one had more effective role on the density of the hot-pressed samples. The synthesized composites showed homogenous microstructure with relatively high density and hardness.