Advanced Materials Research Vol. 364

Abstract: Zinc oxide (ZnO) nanostructures prepared by immersion method were successfully grown on gold-seeded silicon substrate using Zinc nitrate hexahydrate (Zn (NO₃)₂.6H₂O) as a precursor, separately stabilized with non-toxic urea (CH₄N₂O) and hexamethylene tetraamine (HMTA). The effect of changing the stabilizer of ZnO solution on the crystal structure, morphology and photoluminescence properties of the resultant ZnO is investigated. X-ray diffraction of the synthesized ZnO shows hexagonal zincite structure. The morphology of the ZnO was characterized using Field Emission Scanning Electron Microscope (FESEM). The growth of ZnO using urea as stabilizer shows clusters of ZnO nanoflower with serrated broad petals were interestingly formed. ZnO in HMTA showed growth of nanorods. The structures has high surface area, is a potential metal oxide nanostructures to be develop for optoelectronic devices and chemical sensors. The formation of ZnO nanostructures is found to be significantly affected by the stabilizer.

Abstract: This study describes the preparation of polypyrrole multiwall carbon nanotube (PPy/MWNT) composites by in situ chemical oxidative polymerization. Various ratios of functionalized MWNTs are dispersed in the water, and PPy are then synthesized via in-situ chemical oxidative polymerization on the surface of the carbon nanotubes. The morphology of the resulting complex nanotubes (MWNT-PPY) was characterized by field-emission scanning electron microscopy (FESEM). The conductivity of each composite showed a maximum in the temperature scale of 120 – 160 °C and then decreased dramatically with the increase of temperature. The resultant PPy/MWNT nanotubes enhanced electrical conductivity and thermal stability of nanocomposite compared to PPy which was strongly influenced by the feed ratio of pyrrole to MWNTs.

Abstract: Herein novel mesoporous silica film nanocomposites are successfully synthesized by using phosphorescent columnar assembly of an amphiphilic trinuclear gold (I) pyrazolate complex [Au₃Pz₃] as a functional template in the sol-gel synthesis. By controlling the molar ratios of silica source tetrabutylorthosilicate (TBOS) to [Au₃Pz₃] in an acidic aqueous alcohol solution from 60:1 to 20:1, highly ordered phosphorescent nanocomposites can be fabricated with hexagonal [Au₃Pz₃]/silica_hex and lamellar [Au₃Pz₃]/silica_lam silicates.

Abstract: Nanocrystalline PbS thin films were prepared using chemical bath deposition method on glass substrates, together with lead acetate as a source of lead ions (Pb²⁺) and thiourea as a source of sulfide ions (S^2-) with different molar concentrations. The structural properties of thin films were studied using X-ray diffraction.The patterns showed a polycrystalline structure, and the preferred orientation changed along (111) and (200) planes .The grain size of the thin films varied from 27 to 41 nm. The crystallites were under strain, which varied between 0.054 and 0.3. Scanning electron microscope images showed that all the films have uniform surface morphology over the entire glass substrate and that the films were of good quality.

Abstract: Nanocrystalline cadmium sulfide thin films are prepared using chemical bath deposition (CBD) technique in aqueous alkaline bath at 60 °C and their subsequent condensation on glass substrates. Effects of annealing on structural, morphological and optical properties are presented and discussed. The best annealing temperature for CBD grown CdS films is found to be 350 °C from optical properties. The optical and structural properties of CdS films are found to be sensitive to annealing temperature and are described in terms of XRD, SEM, transmission spectra and optical studies. The structural parameters such as crystallite size have been evaluated through XRD while SEM micrographs exhibit ordering of grains upon annealing. The transmission spectra shift towards higher wavelength upon annealing indicating increase in crystallinity. Annealing over 350 °C is found to degrade the external structure and optical properties of the film.

Abstract: 10 and 40 wt% Co/Multiwall Carbon Nanotubes (MWCNT) and 10 and 40 wt% Co/Santa Barbara Amorphous-15 (SBA-15) catalysts were prepared via incipient wetness impregnation method. It was characterized by Scanning Electron Microscopy, BET, X-ray Diffractometry (XRD), Transmission Electron Microscopy (TEM), Temperature-Programmed Reduction and H₂ Desorption. A 200 ml hastelloy autoclave reactor was implemented to see the performance of the catalysts. It was observed that the performance of 40 wt% Co/SBA-15 was higher that other catalysts in terms of production of longer chain paraffins.

Abstract: This research, deals with modification of sol gel process for the synthesis of porous TiO₂-PEG thin films with good structural integrity for environmental self-cleaning applications. Relatively, by adding the PEG with various molecular weights (300, 400, and 600) could influence the formation of TiO₂ films structure and adhesion. Moreover, the formation of porous TiO₂ associated with larger pores will accelerate the mass transfer of the treated contaminants in the larger pore channels. The advantages of the unique structures of as-prepared TiO₂₂ films in the application of environmental self-cleaning systems are extensively studied by characterizing the produced films using various advanced characterization tools. Adhesion of TiO₂ thin films become smooth and better surface with increasing the coating layers. The X-ray Diffraction spectrum of prepared coating shows present of anatase phase as major phase.

Abstract: In this study, difatty acyl urea (DFAU), synthesized from palm oil, and natural clay (sodium montmorillonite) were used to prepare organoclay (OMMT). The clay modification was carried out by stirring the clay particles in an aqueous solution of DFAU at which the clay layer thickness increased from 1.25 to 2.82. This OMMT was then used for nanocomposite production to improve the property balance of poly (lactic acid) (PLA) by solution casting process. The nanocomposite was characterized using various apparatuses. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) results confirmed the production of nanocomposite. PLA modified clay nanocomposite shows higher thermal stability and significant improvement of mechanical properties in comparison with pure PLA. The use of DFAU as a modifier will reduce the dependence on petroleum-based surfactant. In addition to its applications such as films and textile fibers, this nanocomposite represents a good candidate to produce disposable packaging because they have good mechanical, thermal properties, fabricability and processability.

Abstract: The influence of organic solvent on the electrical and optical behavior of poly [2-methoxy-5-(2-ethylhexyloxy-p-phenylene-vinylene)] (MEH-PPV): Titanium Dioxide (TiO₂) active layer has been investigated. The performance of the nanocomposite thin films varied depending on different type of solvent (chloroform, tetrahydrofuran (THF), toluene, xylene and 1,3-Dicholorobenzene) to dissolve MEH-PPPV at concentration of 20 mg/20ml. The solvent used to dissolve MEH-PPV has a dramatic effect on the polymer properties and characteristics due to different chain interaction, crystalline structure formation and surface morphology. The electrical properties of nanocomposited MEH-PPV: TiO₂ thin films were measured by solar simulator in dark and under AM 1.5, 100 mW/cm² white light illumination condition while the characterization of optical properties has been done using UV-VIS spectrophotometer to evaluate the absorbance as well as the transmittance. By comparing the nanocomposite thin films with the same weight MEH-PPV: TiO₂, it was found the thin film which used 1,3-Dicholorobenze as a solvent has the highest conductivity around 338.64x10³ S.m^-1. However for the optical properties, solvent of xylene gives the highest absorption coefficient at 8.4x10⁶ m^-1. The dispersion of nanocomposited MEH-PPV:TiO₂ and film formation reproducibility, these solvents showed that its affected film resistance and dispersion stability in the thin films.

Abstract: The structural and optical properties of porous GaN films on sapphire (0001) prepared by UV assisted electrochemical etching were reported in this study. SEM micrographs indicated that the shapes of the pores for both porous samples are nearly hexagonal. As compared to the as-grown GaN films, porous layers exhibit a substantial photoluminescence (PL) intensity enhancement with red-shifted band-edge PL peaks associated with the relaxation of compressive stress. The shift of E₂(high) to the lower frequency in Raman spectra of the porous GaN films further confirms such a stress relaxation.