Z.A. Talib

Measuring Gaussian laser beam diameter using piezoelectric detection

A simple method is described to measure a Gaussian laser beam diameter using piezoelectric detection. Scanning the beam with a single-edge razor blade and monitoring the transmitted beam with a PZT detector, an accuracy of within 10% was obtained for the He-Ne laser beam.

Synthesis and Physical Characterization of Carbon Nanotubes Coated by Conducting Polypyrrole

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.

Structure, Magnetoresistance and Magnetism of La0.67(Sr1−xBax)0.33MnO3 Perovskite

The effect of Ba‐substitution at Sr site on the structure, magnetoresistance and magnetic properties of La0.67(Sr1−xBax)0.33MnO3 samples with x = 0.00, 0.25, 0.50, 0.75 and 1.00 has been investigated. Single phase samples were obtained by a conventional solid state reaction method with rhombohedral (x = 0.00) and orthorombic (x = 1.00) structure. The grain size increases with Ba content. Low field magnetoresistance phenomenon at low temperature can be observed for all samples. However it vanishes at 300 K for x = 0.75 and 1.00. The variation of MR% value is small ranging between 16 to 18% at 100 K in an applied field of 1 T. All samples show a single magnetic transition from the ferromagnetic (FM) state to the paramagnetic (PM) state as the temperature increases. Curie temperature, Tc decrease with increasing Ba concentration.

Optical Characterization of Zinc Selenide Compound Prepared through Hydrothermal Method

ZnSe which show a potential application in electronic devices such as photovoltaic devices, light emitting devices and photodetector have been synthesized through a hydrothermal method using ZnCl2 and Se powder as the source. In a typical synthesis, Zn2+ and Se2- ion have been prepared separately and charged into a Teflon-lined stainless steel autoclave. The hydrothermal reaction was conducted at 180 °C for 32 hours. Structural properties of ZnSe are studied by X-ray diffraction (XRD) while the optical properties of ZnSe compound are characterized through ultraviolet–visible spectroscopy (UV-Vis). From the XRD result, pure ZnSe with main XRD peak at 2θ = 27.29°, 45.30°, 53.62°, 65.88°, 72.68° has been observed. The result have been supported by the optical results where absoprtion peak at 460 nm with optical band gap energy (Eg) at 2.5 eV.

Density Functional Study of Electronic and Optical Properties of Ternary Mixed Chalcogenides Topological Insulators

This paper presented a theoretical study of structural, electronic, and optical properties of the ternary mixed chalcogenides Topological Insulators with a formula M2X2Y (M = Bi, X = Te and Y= Se, S) using density functional theory (DFT) within the local density approximation (LDA). From the calculation, we have evaluated the bulk modulus and its corresponding pressure derivatives of these compounds. The linear photon-energy dependent of dielectric functions, some optical properties such as reflectivity, refraction index, conductivity function, and energy-loss spectra, have also been obtained and analyzed within the electronic band structures and density of states of these compounds.

Lattice Strain Effect in Structural, Magnetoresistance and Electrical Properties of La0.67Sr0.33MnO3 Bulk and Thin Film System

Polycrystalline La0.67Sr0.33MnO3 (LSMO) powder prepared via conventional solid state reaction was pressed into pellet form. The pellets became target to growth thin films on corning glass (LSMO-C), fused silica (LSMO-FS) and MgO (100) (LSMO-M) substrate via pulsed laser deposition (PLD) method. XRD results showed that all samples were hexagonal structure with R-3C space group. Thin films showed relatively smaller crystallite size compared to bulk samples. From Rietveld Refinement analysis, all thin films experienced lattice strain when deposited on different substrate. LSMO compound deposited in different substrate induced structure distortion and lattice strain. Compression along c-axis occurred when the lattice strain increased thus shifted the metal-insulator transition temperature to lower temperature and increased its resistivity.

Structural, Electrical Properties and Magnetoresistive Effect in the (La1-xDyx)0.67Sr0.33MnO3 Compound

The significant influences of substituting low concentration Dy at La- site for La0.667Sr0.333MnO3 perovskites compounds in structural, electrical and magnetoresistance properties have been studied. The polycrystalline samples (La1-xDyx)0.667Sr0.333MnO3 with x= 0.00, 0.02 and 0.10 were synthesized via conventional solid-state reaction in bulk. This work measured their resistivity properties with (below 1 Tesla) and without the presence of magnetic field (0 Tesla) as a function of temperature, microstructure and particle distribution and structural distortion using four point probe resistivity technique, X- ray diffractometer (XRD) and Atomic Force Microscope (AFM). The resistivity in applied magnetic field or so-called magnetoresistance ratio is defined as MR% = (Ro – RH)/RH x 100 was measured at 90K, 100K, 150K, 200K, 250K, 270K and 300K. The highest MR% values for x=0.00, 0.02 and 0.10 are 15.3%, 15.5% and 20.6% at 1 Tesla respectively. The metal- insulator transition temperature, TMIT correspond to >300K, 298K and 230K of sample with x= 0.00, 0.02 and 0.10 respectively were observed from resistivitytemperature (R-T) curve.