Functional Materials and Devices

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Authors: M. Kamil Abd-Rahman, M. Nasir Taib, Ibrahim Azmi
Abstract: Fiber Bragg gratings (FBG) are extensively used in optical add-drop multiplexers/demultiplexers, optical cross-connect switches, optical sensors and many others in optical fiber telecommunication networks. In this study, FBG was employed as an optical sensor for pile monitoring on steel and concrete structures particularly in bridges and buildings. The measurement was conducted in accordance to PWD (Public Works Department) requirements and the test showed compatible results to the vibrating wire strain gauge (VWSG) used in pile monitoring by PWD. The FBG sensors mounted onto the mild steel rod as a device-under-test have provided high sensitivity, good accuracy and linearity.
Authors: Mitra Djamal, Darsikin, Togar Saragi, M. Barmawi
Abstract: This paper describes magnetic sensors that have been developed in the last three years. GMR thin film materials have been successfully developed using unpinned CoFe/Cu/CoFe sandwiches on Si(100) substrate using a home built dc-opposed-target magnetron sputtering (OTMS). The magnetization of the sandwich is measured using hysteresis loop instrument, the Vibrating Sample Magnetometer (VSM). It was found that the phase of GMR was formed, with the MR ratio 15.76%.
Authors: R. Abd-Shukor, S.Y. Yahya
Abstract: This paper reports on the effectiveness of magnetic nanoparticles as pinning center in the Bi-based superconductor tapes. Nanosize γ-Fe2O3 and ultrafine Fe3O4 have been employed to enhance the transport current density of Ag-sheathed-(Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor tapes prepared by the powder-in-tube technique. The transport critical current density, Jc of (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(γ-Fe2O3)0.01, sintered at the optimum temperature of 845 oC is 6490 A/cm2 when measured at 77 K. A further single intermediate rolling step increases Jc to 9560 A/cm2. Samples without γ-Fe2O3 prepared under the same condition showed a lower Jc with a maximum of 1560 A/cm2. Similar results are also obtained for ultrafine Fe3O4. Magnetic impurities generally suppress superconductivity. However, our study shows great promise of magnetic nanorod γ-Fe2O3 and ultrafine Fe3O4 as novel pinning centers in enhancing the transport critical density of Ag sheathed Bi-Sr-Ca-Cu-O superconductor tapes. This is in line with previous calculations on frozen flux superconductor with magnetic nanoparticle as pinning centers.
Authors: M.A.K.M. Hanafiah, S. Shafiei, Mohamad Kamal Harun, M.Z.A. Yahya
Authors: Rosiyah Yahya, A. Hassan, Z. Aiyub
Abstract: The structural studies of potassium hexatitanates prepared under both hydrothermal and solid state conditions were carried out. Fourier Transform Infra-red spectroscopy (FTIR) results revealed that potassium hexatitanate structure consisted of TiO6 octahedral units irrespective of the preparative conditions and particle size. X-ray diffraction (XRD) results showed that the only potassium hexatitanate phase was detectable and the structure is of the Wadsley-type consisting of chains of Ti-O octahedral sharing edges with tunnels in which the potassium ions are located. From scanning electron microscopy (SEM) results, the different preparative conditions resulted in different particle sizes and morphologies of the potassium hexatitanate formed.
Authors: Izdihar Ishak, Alias Daud
Abstract: A simple microwave heating system was designed for firing phosphor samples. An 800W magnetron operating at 2.45 GHz was used. The system is capable of reaching 1200oC in less than three minutes with the help of SiC succeptor. The synthesis technique prior to the microwave heating is described. The results indicate that the samples start to crystallize after 5 minutes. The X-Ray diffraction (XRD) data indicates that the sample is polycrystalline and acquires the host structure. The Photoluminescence (PL) and Photoluminescence Excitation (PLE) spectra for the powder phosphor prepared show similar results as those prepared using the conventional method. The Y2O3 powder samples doped with Eu show strong red emission at 630nm, the Tb doped samples show a strong green emission at 550nm and Tm doped samples shows blue emission at 460nm. The Scanning Electron microscope (SEM) picture taken show that the crystal size of the microwave irradiated samples was smaller in comparison to those prepared using the conventional method. This may be due to shorter heating time. These results indicate that the microwave heating technique is a reliable, fast and suitable technique to produce these powder phosphors. The characteristics of the phosphors are as good as those prepared using the conventional heating technique.
Authors: N.K. Ali, M. Roslan Hashim, Azlan Abdul Aziz
Abstract: Porous silicon layer microstructure is sensitive to many parameters which need to be controlled during etching. These include not only anodization time, current density and applied potential but also electrolyte composition. Careful control these parameters will yield excellent reproducibility from run to run. In this paper we outline the advances in porous silicon surface quality and uniformity by recent techniques that have made the production of uniformly sized silicon nanocrystallites possible. In this work we used the oxidant H2O2 in the wet etching bath, with a high etching current. The resulting technique greatly improves the uniformity of the porous surface, producing a very thin layer of porous silicon. This is a significant improvement to the previous method. The result of a combined study of FTIR spectra and photoluminescence show that both quantum confinement and surface passivation are responsible of blue shift of the luminescence peak.
Authors: A.S.A. Khiar, S.R. Majid, N.H. Idris, M.F. Hassan, R. Puteh, A.K. Arof
Abstract: Measurement of the ionic conductivity for the CA-NH4CF3SO3-DMC system was carried out at frequencies of 50 Hz to1 MHz and also at temperatures of 298 K to 313 K. The plot of log σ versus 1000/T shows a linear behavior suggesting that the samples obey the Arrhenius relationship. The electrical relaxation of the system was analyzed using the complex electric modulus M* of the sample with the highest ionic conductivity at various temperatures. The analysis of electrical modulus and dissipation factor (tan δ) shows that charge transport occurs through a hopping mechanism.
Authors: C.K. Tan, Azlan Abdul Aziz, F.K. Yam, C.W. Lim, Hassan Zainuriah, A.Y. Hudeish
Abstract: Pd Schottky diode exhibited stable rectifying behavior up to 500°C for 35 minutes in sequential annealing; with the Schottky barrier heights (SBHs), ΦB (I-V) of 0.6-0.7eV with the leakage current (LC) of 20 A at -5V. With the same range of SBHs, PdSi diodes were stable up to 500°C for 5 minutes with the LC of 0.182mA at -5V. The electrical characteristics obtained in this study are also compared with those obtained for Pd and PdSi Schottky diodes on p-GaN.
Authors: C.K. Tan, Azlan Abdul Aziz, Hassan Zainuriah, F.K. Yam, C.W. Lim, A.Y. Hudeish
Abstract: The barrier height of as-deposited Cr contacts was found to be ΦB= 0.87eV with the ideality of η=1.51 and remained almost unchanged after further annealing at 500 oC for 5 minutes. The barrier height of diodes were increased drastically after annealed at 600 oC where ΦB=1.01eV with η=1.69. Upon annealing at 700 oC for 5 minutes, the ΦB decreased to 0.61eV and the Cr diodes were degraded for higher temperature in this annealing duration. The ΦB remained in 0.80- 0.90eV respectively at 800 oC for 2 minutes and 900-1000 oC for 1 minute.

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