Wan Mahmood

Putra University, Malaysia, Klang, Selangor, Malaysia

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Publications (16)12.08 Total impact

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    10/2012: pages 403-418; , ISBN: 978-953-51-0797-2
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    ABSTRACT: Porous silicon (PSi) layers were formed on a p-type Si wafer. Six samples were anodised electrically with a 30 mA/cm 2 fixed current density for different etching times. The samples were coated with a 50–60 nm gold layer and annealed at different temperatures under Ar flow. The morphology of the layers, before and after annealing, formed by this method was investigated by scanning electron microscopy (SEM). Photoacoustic spectroscopy (PAS) measurements were carried out to measure the thermal diffusivity (TD) of the PSi and Au/PSi samples. For the Au/PSi samples, the thermal diffusivity was measured before and after annealing to study the effect of annealing. Also to study the aging effect, a comparison was made between freshly annealed samples and samples 30 days after annealing.
    Materials 01/2012; · 2.25 Impact Factor
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    ABSTRACT: Porous silicon (PSi) layers were formed on n-type silicon (Si) wafers using electrochemical etching method. The effects of etching time and current density were investigated. Three sets of samples were prepared at different current densities: 10, 20, and 30 mA/cm 2 and six etching times: 10, 20, 30, 40, 50, and 60 min. The thickness and porosity of the layers were measured using the gravimetric method. The surface morphology was studied by Field Emission Scanning Electron Microscope (FESEM). The optical and thermal properties of porous silicon on silicon substrates were investigated by employing photoluminescence (PL) and photoacoustic spectroscopy (PAS). Thermal results showed that the thermal diffusivity (TD) of samples decrease with increasing the porosity. The band gap of the samples were obtained from photoluminescence (PL) and photoacoustic absorption spectra. These results showed that the band gap of porous silicon samples increase with increasing porosity.
    International journal of electrochemical science 01/2012; 7:8266-8275. · 3.73 Impact Factor
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    ABSTRACT: The porous silicon (PSi) layers were formed on p-type silicon (Si) wafer. The six samples were anodised electrically with 30 mA/cm 2 fixed current density for different etching times. The structural, optical, and thermal properties of porous silicon on silicon substrates were investigated by photoluminescence (PL), photoacoustic spectroscopy (PAS), and UV-Vis-NIR spectrophotometer. The thickness and porosity of the layers were measured using the gravimetric method. The band gap of the samples was measured through the photoluminescence (PL) peak and absorption spectra, then they were compared. It shows that band gap value increases by raising the porosity. Photoacoustic spectroscopy (PAS) was carried out for measuring the thermal diffusivity (TD) of the samples.
    Advances in Optical Technologies 01/2012; 9.
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    ABSTRACT: Nonlinear refractive index and nonlinear absorption of Ag nano-fluid prepared by γ-radiation method were investigated using a single beam Z-scan technique. Under a CW laser beam excitation operated at 532 nm with the power output of 40 mW, the Ag nano-fluid shows a large thermal-induced nonlinear refractive index and nonlinearity absorption. We measured the nonlinear refraction coefficient of silver nano-fluid for concentrations, 1.170 x 10 -3 and 5.297 x 10 -3 M. respectively. We found the nonlinear refractive index is in the order of 10 -8 cm 2 /W with the negative sign indicates the self-defocusing phenomenon. However for the Ag nano-fluid sample with 1.170 x 10 -3 M, the result shows that the nano-fluid sample has only a nonlinear refractive index property.
    Australian Journal of Basic and Applied Sciences. 01/2011; 5:587-591.
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    ABSTRACT: An investigation on the HXR emitted from APF plasma focus device operated with different volumetric ratios of nitrogen-neon (N2:Ne) admixture working gas at different voltage-pressure limits is presented. The optimum pressures obtained at the applied voltages of 12, and 13kV were 3.5torr for percentage of (50:50) of (N2:Ne) admixture and 3torr for percentages of (75:25) and (90:10) in admixture and also for pure N2, while at the voltage of 11kV, the optimum pressures were 3torr for percentage of (50:50) and 2.5torr for percentages of (75:25), (90:10), and pure N2. At each applied voltages of 11, 12, and 13kV, with increasing percentage of N2 in the (N2:Ne) admixture, the intensity of HXR was found to increase where the low intensity was for percentage of (50:50) of (N2:Ne) and the higher intensity was for pure N2. The results illustrate that the voltage and the composition of working gas are effective parameters in the HXR emission from a plasma focus device. KeywordsPlasma focus–APF–HXR–X-ray–Plastic scintillator-PMT–Pinhole camera
    Journal of Fusion Energy 01/2011; 30(5):388-393. · 1.00 Impact Factor
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    ABSTRACT: Copper corrosion is one of the important parameters used for evaluating the quality of biodiesel. In this work, a polypyrrole–chitosan sensing layer was utilized for the detection of Cu 2þ in biodiesel using the surface plasmon resonance technique. With the sensitivity of this sensor being about 0.1 ppm, different corrosion levels could be recognized in samples that were classified as class 1a according to the standard copper strip test.
    Optical Review 01/2011; · 0.70 Impact Factor
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    ABSTRACT: Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Electrical conductivity and shielding effectiveness (SE) of conductive polymer composite of polypyrrole-chitosan (PPy-CHI) have been studied. It was shown that chitosan can improve electrical and thermal properties of polypyrrole. The applicability of PPy-CHI composite films to the electromagnetic wave shielding in the microwave frequency range from 8 to 12 GHz were investigated. The SE of the composite films had a strong dependence on chitosan content. The SE of the composite films was obtained by Simon formalism. Comparison of the experimental and theoretical values revealed good correspondence of the shielding of the composite films at high conductivity and frequency.
    Journal of Macromolecular Science Part A 01/2010; 47:71-75. · 0.81 Impact Factor
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    ABSTRACT: Thin films of copper selenide (CuSe) were physically deposited layer-by-layer up to 5 layers using thermal evaporation technique onto a glass substrate. Various film properties, including the thickness, structure, morphology, surface roughness, average grain size and electrical conductivity are studied and discussed. These properties are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), ellipsometer and 4 point probe at room temperature. The dependence of electrical conductivity, surface roughness, and average grain size on number of layers deposited is discussed. KeywordsCuSe thin films–electrical conductivity–surface roughness–film thickness–grain size
    Central European Journal of Physics 01/2009; 7(2):379-384. · 0.91 Impact Factor
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    ABSTRACT: The polypyrrole-chitosan (PPy-CHI) composite films formed by electrochemical polymerization were studied by electrical and mechanical techniques. The electromagnetic interference shielding effectiveness (EMI SE) at the frequencies range from 8-12 GHz was also studied. It is shown by electrical conductivity measurement and DMA (dynamic mechanical analysis) that the enhanced conductivity and mechanical properties of the prepared films are due to the presence of CHI in the composite film. Most of the composite films had more than 98% shielding of electromagnetic energy. The EMI SE shown through reflection and absorption increased with the increase in conductivity and relative shielding efficiency by reflection and absorption can be easily controlled by the electrical conductivity.
    Solid State Science and Technology. 01/2009; 17:12-21.
  • Mat Yunus, W. Mahmood
    Applied Optics 01/1992; 31. · 1.69 Impact Factor
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    ABSTRACT: An effort has been made to produce polypyrrole-carboxymethylcelllulose (PPY-CMC) conducting polymer composite film on Indium Tin Oxide (ITO) glass electrode from an aqueous solution containing pyrrole monomer, p-toluenesulfonate electrolyte and carboxymethylcellulose (CMC) insulating polymer. The conductivity of the prepared composite film was found to increase with the increase in CMC concentration in pyrrole solution. The optical microscopic study showed the influence of CMC concentration in the pyrrole solution on the morphological changes of the prepared film. The dynamic mechanical analysis (DMA) on the prepared PPY-CMC film revealed the higher plastic property of the PPY-CMC composite film due to the addition of CMC in the polypyrrole structure. The electromagnetic interference (EMI) shielding effectiveness of PPY-CMC film in the frequency range of 8-12 GHz showed a high shielding effectiveness above 41 db, which supported its probable use in various electromagnetic interference shielding applications.
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    ABSTRACT: The porous silicon layer was prepared on n-type Si wafers using electrochemical- etching method. The current density was varied from 16 mA/cm2 to 40 mA/cm2. The surface morphology measured using SEM confirms the formation of porous layer on the silicon substrate. The photoacoustic (PA) absorption band and optical band gap energy were determined from PA signal intensity spectra measured at three different modulation frequencies (i.e. 15 Hz, 23 Hz and 33 Hz). The absorption band and energy gap of porous silicon gradually shifted towards higher energy region as the increase of current density thus confirming the porosity dependence of band gap on sample porosity.
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    ABSTRACT: Photopyroelectric (PPE) spectroscopy is a useful tool for examining optical properties in semiconductor materials. The ceramic (ZnO - xTiO2) was sintered at 1270 o C for 1 and 3 hours to investigate the variations of energy band-gap with respect to mol % of dopant TiO2. The X-ray diffractrometry shows that the crystal structure of ZnO doped at low level remains to be of hexagonal type but has developed second phase, Zn2TiO4, at high level. Microstructure and compositional analysis of the selected areas are analyzed using SEM and EDAX. The maximum grain size obtained were 26.8, 52.4 µm at 0.4 mol % of TiO2 for 1 and 3 hours sintering time, respectively. The band-gap determined from the photopyroelectric spectrum has the value of 2.82 ± 0.01 eV for samples sintered for 1 and 3 hours at the doping level of 0.4 mol % of TiO2 and decreases with the increase of TiO2.
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    ABSTRACT: The carrier transport properties of Au/Si samples annealed at three temperatures (i.e. 100oC, 363 oC and 800oC) were investigated using open photoacoustic cell (OPC) technique. A gold film of 45 nm was deposited on the silicon substrate and annealed in air environment. We observed that Au8.1Si1.9 silicide and Au7Si(622) silicide were formed at both 363oC and 800oC annealing temperature. Obviously the Au8.1Si1.9 silicide was observed in all Au/p-Si system. The result indicates that the recombination process increases with the formation of Au7Si silicide. From the analysis of photoacoustic phase fitting and four point probe techniques, surface recombination velocity of gold silicide was found increase with the increasing annealing temperature. However, the band-to-band recombination lifetime decreased as annealing temperature increased. The I-V characteristic shows the Schottky curves for the annealing temperature of 363oC and 800oC. This behavior is due to the
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    ABSTRACT: In the present work, the effect of applied voltage and operating pressure on behaviour of X-rays emitted from nitrogen gas (N2) used in APF plasma focus facility is investigated. It was found that the optimum conditions for high emissions of SXR and HXR from the plasma focus (PF) are different. At four applied voltages of 10, 11, 12, and 13kV, the optimum pressures for SXR and HXR emissions of nitrogen gas (N2) were obtained. At lower voltages, 10, and 11kV optimum pressure for SXR emission was 3.5torr while for HXR emission was 2.5torr. At higher voltages, 12, and 13kV, the optimum pressures shift to higher values at 4 and 3torr for SXR and HXR emissions, respectively. Among the applied voltages, the least intensity of both SXR and HXR was at voltage 10kV and the most intensity was for 13kV which confirm with increasing voltage, the intensity of X-ray emission increases. Also the results obtained by images of pin-hole camera were in compatible with the results of detected signals by different filtered Pin-diodes and Scintillation detector. Our results illustrate that the voltage and the pressure are effective parameters in X-ray emission from the PF. KeywordsPlasma focus (PF)–APF–SXR–HXR–X-ray–PIN-diode–Plastic scintillator-PMT–Pin-hole camera
    Journal of Fusion Energy 30(5):413-420. · 1.00 Impact Factor