Advanced Materials Research Vol. 1133

Abstract: Thermoluminescence (TL) characteristics for various cross-sections of 6 mole% of tailor-made Ge-doped cylindrical optical fibers were determined. The general TL characteristic i.e., dose rate dependence, energy dependence, dose response and reproducibility of the samples have been investigated. The samples were irradiated using electron beam (Linac) and been exposed to dose ranging from 1 to 4 Gy. The cylindrical optical fibers provide highly linear dose response within the clinical relevant dose range, independence of radiation energy over the range of energies investigated, independence of dose rate and excellent reproducibility. This research shows that germanium doped silica fibers have high potential of dosimetric properties and suitable as TL-mode detectors in instances of radiotherapy (clinical dosimetry).

Abstract: Rare earth Gd-doped ZnO thin films were prepared by a simple sol-gel spin coating method in order to search for a new functional diluted magnetic semiconductor for potential application in spintronics. The thin films were deposited onto glass substrates with zinc acetate dehydrate, monoethanolamine and 2-methoxyethanol as a starting material, stabilizer and solvent, respectively. The dopant percentage was increased up to 8%. Optical investigation showed that the crystallinity of the thin films was changing due to the increase of the Gd concentrations and optical band gap energy (E_g) value was estimated to be around 3.12 ~ 3.28 eV using Tauc's model. The crystallite size determined from XRD spectra and the results was found that the value is in the range of 14.42 ~ 21.98 nm.

Abstract: Eu (tta)₃phen and Tb (4DBBA)₃TPPO were synthesized as red and green phosphor for generating white light under the excitation of UV LED. The phosphor materials were doped into hybrid sol-gel (VTES:TEOS) matrix with different ratio of 1:8, 1:16, 1:25, 1:30, 1:40 and 1:50. The samples were fabricated as thick films by drop-casting and heat treated at 60°C overnight. Photoluminescence spectra were measured using spectrafluorometer system. Measurement of color properties such as color rendering index (CRI), color temperature and Commission Internationale de L’Eclairge coordinates were recorded by exciting the samples using a 380nm UV LED and focused the generated light into an integrating sphere. Based on the results, the mix ratio of 1:40 produce the nearest coordinate within the white color region with color temperature around 4100K to 4200K.

Abstract: Thin films of undoped and gadolinium-doped zinc oxide (Gd-doped ZnO) with different Gd concentration (1-8 at. %) were deposited onto a glass substrate by sol–gel spin-coating technique. X-ray diffraction (XRD, Bruker D8 Advance) studies confirmed the nature of the films as polycrystalline, with typical hexagonal wurtzite structure. The film also showed variation in crystallite size and change in relative intensities, upon different Gd concentrations. Besides, the influence of Gd concentration on the optical transmittance of ZnO films was studied using ultraviolet-visible spectrophotometer (UV-Vis, Shimadzu UV 1800) in the wavelength range 300-800 nm. The optical transmittance of all films is higher than ~95% in the visible region, and doped films become more transparent. The electrical resistance was measured by two point probe (Keithley-2400). The resistance decrease with increasing Gd concentration up to 2 at.% and it increased for further increase Gd concentrations.

Abstract: Local structures around gadolinium atoms in rare-earth (RE)-doped InGaGdN thin films were studied by means of fluorescence extended X-ray absorption fine structure (EXAFS) measured at the Gd L_III-edges. The samples were doped with Gd in-situ during growth by plasma-assisted molecular beam epitaxy (PAMBE). Gd L_III-edge EXAFS signal from the GaGdN, GdN and Gd foil were also measured as reference. The X-ray absorption near edge structure (XANES) spectra around Gd L_III absorption edge of InGaGdN samples observed at room temperature indicated the enhancement of intensities with the increase of Gd composition. Further EXAFS analysis inferred that the Gd atoms in InGaN were surrounded by similar atomic shells as in the case of GaGdN with the evidence indicating majority of Gd atoms substituted into Ga sites of InGaGdN. A slight elongation of bond length for the 2nd nearest-neighbor (Gd–Ga) of sample with higher Gd concentration was also observed.

Abstract: We have investigated the suitability of 8% mole of tailor-made germanium (Ge)- doped silica (Si0₂) cylindrical fibers to use as the detector, to map dose that received by the patient during the treatment especially for X-ray radiation. The diameters of these cylindrical optical fibers are; 362μm, 483μm and 604μm with different in masses and have been supplied by Telekom Malaysia (TM) group. To study the thermoluminescence reponse of these fibers, X-ray source with 60 kVp, 80 kVp and 100 kVp were used to irradiate the samples. The dosage of X-ray source was measured by the calibrated ionization chamber. The potential of these (Ge) - doped silica (Si0₂) cylindrical fibers as an efficient thermoluminescence (TL) material was investigated comparing the thermoluminescence response of the fibers with standard TLD 100. In confronting the variation of the dopant concentration (Germanium) along the core of the optical fibers, the individual calibrations so called as Elemental Correction Coefficient (ECC) were carried out. The results showed that, the best annealing temperature and time (to erase the previous signal) for the samples are 400 °C for one hour. The TL Yield (measured in counts per second per unit mass of fiber) increases as the dose of X-ray beams increases from 0.08 Gy up until 2.8 Gy. The results were clearly indicated that the TL response of SiO₂ fibers were energy dependent. It can be concluded that, Ge-doped optical Silica (SiO₂) optical fibers is very suitable to use as TLD to measure dose in medical applications.

Abstract: The synthesized and characterization on the growth of copper oxide thin films on fluorine-doped tin oxide (FTO) coated glass with annealing and without annealing process has been studied by immersion techniques. Furthermore, ZnO layer has been used in order to improved the absorption spectrum of CuO films. The copper oxide films were analyzed on the morphological, structural, optical and electrical by field emission scanning electron microscopy (FESEM), X-ray diffractometer (XRD), UV-Vis spectroscopy (absorbance) and I-V characteristics instruments. The atomic force microscope (AFM) was used in order to characterize the surface imaging of copper oxide films and the thicknesses were measured using a surface profiler. The AFM studies revealed that the roughness of the CuO films increased after annealing was applied this is due to the formation of large clusters of grains from the merging of small clusters grains. The CuO films thicknesses also becomes two times higher than the CuO films without annealing process.

Abstract: Co₃O₄/SiO₂ nanocomposite was obtained via citrate-gel method. 22 nm in size Co₃O₄ particles in an amorphous SiO₂ matrix were obtained. Co₃O₄:SiO₂ wt. ratio was verified using EDX and found to be close to the 80 % nominal ratio. The UV-Vis measurements showed broad absorption bands at around 440 and 790 nm. The optical band gap values were 1.95 and 1.35 eV respectively, being close to those observed for pure Co₃O₄ nanoparticles. The electrochemical measurements in 5 M KOH solution were performed using a three-electrode type system. Co₃O₄/SiO₂ nanocomposite exhibited high specific capacitance reaching 758 F g^-1 at 2.5 mV s^-1. Very small solution and electrode-electrolyte interfacial charge transfer resistances were obtained when impedance spectra were analysed.

Abstract: Experimental work procedures on the anti-wear and friction properties were conducted to investigate the effect of nano-oil diluted with biodiesel fuel. In this work, an optimal composition (0.5 vol.%) of 70nm hBN nanoparticles was dispersed into SAE15W40 diesel engine oil by using sonication technique as a nano-oil. The homogenize nano-oil then was diluted by four difference percentages of B100 biodiesel fuel (5%, 10%, 15%, 20%). The anti-wear and friction tests were performed using four-ball tribometer according to the ASTM D-4172 standard. Result found that the addition of biodiesel fuel into homogenize nano-oil increases the coefficient of friction (COF) drastically by 25 ~ 96%, as compared with nano-oil and the wear rate also increase approximately by 9.68 ~ 19.50%.

Abstract: Lithium niobate nanostructured thin films were deposited on (100) N-type Si substrates. Spin coating technique was used employed the polymeric precursor method (Pechini process) . The prepared films were Annealing in static air and oxygen atmosphere was performed at 500 _C for 2 h. X-ray diffraction analysis and SEM properties was carried out for films prepared at different mol concentration (0.25,0.50,0.75,1.00) Mol%. The results show a good enhancement in both structural and surface morphology of the films with increasing the concentration