Functional Materials and Devices

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Authors: Muti Mohamed Norani, Tan Yee Chech, Abdul Kadir Masrom
Abstract: Strong and versatile carbon nanotubes are finding new applications in improving conventional polymer-based fibers. Nanotube-reinforced composites could ultimately provide the foundation for a new class of strong and lightweight fibers with properties such as electrical and thermal conductivity unavailable in current fibers. A recent research has discovered that the best type of nanotube for polymer composite reinforcement is the small diameter multiwalled nanotubes (MWNTs). Here, a catalytic technique has been developed to produce narrow diameter bulk multiwalled carbon nanotubes of less than 38 nm. Structural characterizations including scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), thermo gravimetric analysis (TGA) and Raman spectroscopy conducted on CNTs grown on three different catalysts, namely iron, cobalt and nickel have indicated that the catalyst used affects their sizes and crystallinity. Results showed that the smallest CNTs could be obtained by catalytic growth on Ni catalyst. The study has proven that with the skillful use of catalyst, a range of narrow sized nanotubes could be produced, providing the material needed to investigate the optimum diameter for the best mechanical reinforcement of polymer composites.
Authors: N. Al-Jufairi
Abstract: Sol-gel processing route has been used for the production of thin films from titanium isopropoxide (TIP). The surface properties and statistics results have been characterized by AFM; the coating process has been examined using SEM and optical microscope. The structure phase of TiO2 has been analyzed by XRD; the composition of TiO2 has been estimated through EDS; the thickness of film has been measured by polarized microscope in an interferometric technique. The coating films are always crystallined in the anatase structure with circular particles in nanometer size.
Authors: Tarriq Munir, Azlan Abdul Aziz, Mat Johar Abdullah, Naser Mahmoud Ahmed
Abstract: We focus in this paper the temperature variation effects on the current – voltage ( I-V) characteristics of n-GaN schottky diode. The diode was doped with carrier concentration 1*1013cm-3 and Pt electrode was used. The simulated current were obtained at temperatures from 50K to 500K and voltage up to 2Volt. We use the Srh (Schokley read hall), Cvt (Lombardi Model), Auger (Auger), Fermi (Fermi Dirac), Impact, Bgn (Bandgap Narrowing), Complete ioniz model to get the schottky rectifying current – voltage (I-V) characteristics.. We find that by increasing the temperature from 50K to 500K, the forward schottky rectifying current decreases from 2.7187 Amp to 0.383 Amp. while the forward turn – on voltage decreases. In reverse bias at low temperature the current is high and we increase the temperature the current decreases. The breakdown voltage decreases at higher temperature.
Authors: W.S. Wan Nik, S.G. Eng Giap, H.H. Masjuki, H.B. Senin
Abstract: Tribological aspects of bio-oils have to be investigated before they are used as industrial fluids. In this paper rheological (fluid deformation under shear) properties of four bio-oils are presented. A Couette type viscometer was used to evaluate flow behavior of the oils at seven discrete temperatures. Commercial coconut, canola, sunflower and corn oil were used in this study. For all the oil samples, viscosities were affected by the change of shear rate and temperature. Two rheological models, temperature dependence and shear rate dependence, were used in the study. The original power law gives contradict picture of flow curves and flow parameters. Thus, modified power law model was proposed. The modified model was fitted to experimental data to obtain the flow behavior index. Arrhenius type equation was fitted to experimental data to obtain the activation energy due to different temperatures and shear rates. Evaluation of rheological properties by modified power law model indicates that these bio-oils belong to the pseudo-plastic group.
Authors: Lajos Daróczi, C. Hegedűs, V. Kökényesi, Dezső L. Beke
Abstract: Metal-ceramic systems play very important role in the prosthetic dentistry. The most widely used metallic alloys are the Ni-Cr, Co-Cr, Au-based alloys and Ti. The bonding strength between the metal base and the ceramic covering layer can be very different in different systems and is strongly affected by the firing conditions as well. For the further improvement of the bonding properties the detailed knowledge of the microstructure of the metal–ceramic interlayer is essential. In this work our results, obtained by scanning and transmission electron microscopy on systems of commercial alloys and corresponding porcelains will be reviewed.
Authors: Tarriq Munir, Azlan Abdul Aziz, Mat Johar Abdullah, Naser Mahmoud Ahmed
Abstract: We focus on the epi layer carrier concentration variation effects to improve the current – voltage (I-V) characteristics of an n-GaN schottky diode. The carrier concentration of 1×10 15cm-3, 1×1016 cm−3, 1×1017 cm−3 were employed. The simulated current was obtained by forward biasing the device of up to 2Volt at room temperature using Pt electrode. The study was conducted by using Atlas/Blaze using various models such as Consrh (Concentration Dependent Shockley Read Hall), Cvt (Lombardi Model), Fermi (Fermi Dirac), Bgn (Bandgap Narrowing), Conmob (Concentration Dependent Mobility), Auger (Auger). We found that as the concentration increases the value of forward current also increase linearly when biased at maximum of 2 volts. The reverse bias characteristics at the same concentration of the simulated diode up to 100Volt were also determined. We found that at low carrier concentration the reverse leakage current is minimum and breakdown voltage is maximum. As the carrier concentration increases there is a linear relationship between reverse leakage current and epi layer doping carrier concentration. By analyzing the forward and reverse characteristics we conclude that in forward bias for low carrier concentration the diode shows schottky rectifying behavior while for higher carrier concentration the diode shows ohmic behavior. For higher carrier concentration there is a linear relationship between carrier concentration (n) and forward current. The reverse leakage current is minimum approaching an ideal value at n≤1×1015cm-3 and breakdown voltage is maximum at these values of concentration. Increasing the concentration from n≤1×1015cm-3 the value of reverse leakage current is approaching to the maximum value as a result breakdown voltage decreases. We conclude that for n-GaN schottky diode the ideal schottky rectifying behavior of I-V characteristics is obtained at carrier concentration of n≤ 1×1015cm-3 for the simulated diodes at different carrier concentration.
Authors: N. Al-Jufairi
Abstract: TiO2 coating films of 50-200nm thickness were prepared by the sol-gel technique using hydrolysis of titanium isopropoxide (TIP) in an attempt to study structure and surface properties of anatase at ambient temperature. The anatase phase is exhibited by the XRD peak at 2θ'=25o with orientation in (101), the crystal parameters of XRD for TiO2 thin films (50-200 nm), were varied depending on the thickness of film and substrate type. An annealing temperature and annealing time had an effect on the film surface quality and exhibit porosity and aggregates in the films. The surface of TiO2 thin film showed cluster particles through SEM and the shrinkage rate on the film increased as a result of heat treatment during annealing process. The film was uniform and homogeneous under AFM investigate. EDS have determined the stochiometric ratio of TiO2 film.
Authors: Nadeer Aljaroudi, Taiju Tsuboi
Abstract: Photoluminescence (PL) measurements have been made for a spin-coated thin film of phosphorescent tris(2-phenylpyridine) iridium [Ir(ppy)3] doped in N,N’-bis (3-methylphenyl)-N, N’-bis(phenyl)-benzidine (TPD) host material in the temperature range from 10 K to room temperature. When temperature is increased from 10 K to 300 K, the PL intensity of Ir(ppy)3 increases from 10 K and decreases above about 200 K. Theoretical calculations are undertaken for the temperature dependence using (1) a three-level model where three zero-field splitting substates are generated in the triplet state of Ir(ppy)3 and (2) endothermic energy transfer from the TPD host to the Ir(ppy)3 guest, and (3) energy diffusion from the excited TPD to the neighboring unexcited TPD. A good agreement was obtained between the measured and calculated temperature dependences of the PL intensity.
Authors: N. Zainal, Abu Hassan Haslan, Hassan Zainuriah, M. Roslan Hashim, Naser Mahmoud Ahmed
Abstract: The performance of InGaN quantum well based Light Emitting Diodes; (LEDs) had been numerically investigated by using standard industrial software, Silvaco. In this work, we found that InGaN single quantum well (SQW) LEDs gives better performance than InGaN triple quantum wells LEDs. The simulation results suggest that the inhomogeneity of electron and hole distributions in quantum wells active region plays an important role in the LEDs performance. The threshold current per μm also increases as the number of quantum well is increased.

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