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Abstract : Oriented Zinc Oxide Nanocrystalline Thin Films Grown from Sol-Gel Solution
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Abstract: Zinc oxide (ZnO) is a wide band gap (~3.37 eV) semiconductor. Thin film ZnO has many attractive applications in optoelectronics and sensors. Recently, nanostructured ZnO (e.g. ZnO quantum dot) has been demonstrated as a hyperbolic material; its dielectric function has opposite signs along different crystal axes within the mid-infrared, making it an interesting material for metamaterials and nanophotonics. Conventional sputtering deposition usually leads to the formation of polycrystalline ZnO films with randomly oriented grains and rough surface. This work demonstrated a solution-based process to grow ZnO thin films with highly oriented nanocrystals. Low-temperature plasmas were employed to modulate the microstructure and optical properties of the films. Such highly anisotropic nanostructured transparent semiconductor films may lead to interesting material properties in developing new optoelectronic devices. Keywords: Zinc oxide, sol-gel, oxygen plasma, crystal size. |
Abstract : Effect of Surface Modification on the Absorption and Luminescence Response in tris(8-Hydroxyquinoline) Gallium Films Achieved by Thermal Treatment
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Abstract: This work reports on the impact of surface modification on the optical absorption and luminescence response of vacuum deposited tris(8-hydroxyquinoline) gallium (Gaq3) films. This surface modification was achieved by means of thermal treatment under nitrogen gas in the temperature range from 85 oC to 255 oC. The results of field emission scanning electron microscopy (FESEM) and x-ray diffraction (XRD) technique ascertained the formation of amorphous nano-rods along the surface of Gaq3 films. Considerable improvement in the absorption and luminescence characteristics of Gaq3 films was observed upon surface modification, which has been resulted from this treatment process. Keywords: Gaq3, thermal treatment, FESEM, XRD, morphology. |
Abstract : Reactive Magnetron Sputtering of ZrO2/Al2O3 Coatings: Alumina Content and Structure Stability
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Abstract: Ternary zirconia-alumina coatings with different compositional ratios, ranging from pure zirconia to 50% alumina content, were deposited by reactive sputtering from two targets, Zr and Al, in argon-oxygen mixtures. The coating composition was controlled by the Zr/Al target power ratio provided by two pulsed-DC power supplies. The coatings were ~1 µm thick and they were deposited on floating potential substrates at a temperature of 650±3K. XRD indicated that the pure zirconia coatings possessed a monoclinic structure with a grain size of 35-40 nm. Adding alumina to the zirconia coating stabilized the cubic zirconia phase and decreased the grain size to 10-15 nm. The alumina phase in the coatings remained amorphous. The hardness of the nanocomposite structure increased from 11.6±0.5 GPa to 16.1±0.5 GPa for an alumina content of 17%. At higher alumina concentrations, the zirconia phase became amorphous and the hardness decreased to 10-11 GPa. Structure stability of the zirconia-alumina coatings was studied by measuring the coating structure and hardness after annealing at temperatures up to 1173 K. Pure zirconia (m-ZrO2) coatings had low structure stability; the hardness reached a maximum value of 18±1 GPa after annealing at a temperature of 773-873K; however, at higher annealing temperatures the hardness decreased, reaching a minimum value of 12.3±0.6 GPa after annealing at 1173K. The hardness of the nanocomposite ZrO2/Al2O3 coating with various compositions increased with annealing temperature. The hardness of a coating with an alumina content of 17% reached a high value of 19.2±0.5 GPa after annealing at 1073-1173 K. Measurements of post annealing XRD analyses indicated that the stabilization of the coating structure with c-ZrO2/a-Al2O3 phases is the reason for the higher structure stability. From the analyses of phase stability and hardness before and after annealing, we conclude that adding alumina to the zirconia phase promotes the formation of nanocomposite c-ZrO2/a-Al2O3 coatings with a markedly higher stability than single-phase m-ZrO2. Highlights: 1. ZrO2/Al2O3 nanocomposite coatings were deposited by co-sputtering from Zr and Al targets. 2. Adding alumina to the zirconia coating stabilized the cubic zirconia phase. 3. ZrO2-17% Al2O3 coatings had a grain size of 10-15 nm and a hardness of 16.1±0.5 GPa. 4. ZrO2/Al2O3 coatings maintained a high hardness after annealing at 1173K with a high value of 19 GPa for alumina content of 17%. 5. The ZrO2/Al2O3 nanocomposite coatings were crack-free after annealing at 1173K. Keywords: Stabilized Zirconia, Thin coatings, Magnetron sputtering, Hardness, thermal treatments. |
Abstract : Carbon Nanotubes (CNTs) for Prolonging the Life of Micropunch
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Abstract: Carbon nanotubes (CNTs) coated on the WC/Co micropunch with diameter in 150 μm for prolonging the life of micropunch was investigated. Carbon nanotubes were synthesized by homemade method. With scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the morphology and structure of CNTs had been expressed. After the punching test with Ti as substrate, the effect of CNTs for prolonging the life of micropunch on the wear loss and the surface morphology of micropunch had been studied by confocal laser, SEM, digital balance etc. Results show the wear of CNTs coated micropunch decreases obviously. Even in the severe wear period the wear loss is less than that of non-CNTs coated micropunch. Compared with the micropunch without CNTs coating, the promising results are due to the formation of a transfer film at the contact region by rubbing of the CNT forest, CNTs produced adheres to the micropunch surface avoiding direct contact during the punching period and providing lubricant properties to the interface by virtue of their graphitic nature. Also, the relevant mechanism was illustrated primarily. Keywords: Carbon nanotubes, micropunch, wear characteristic, WC/Co. |
