Advanced Materials Research Vols. 931-932

Abstract: Photoresist used in the fabrication of Microelectrochemical Systems (MEMS) has traditionally been processed using conventional curing technology. This type of curing is often time intensive and results in non-uniform products. A uniform bake of the layer is not always possible due to the mechanisms of heat transfer conventional curing offers, leading to poor pattern resolution, formation of micro-cracks and severe outgassing occurring as a consequence. The Variable Frequency Microwave (VFM) Technique was successfully utilised in this study as an alternative method for the processing of negative tone SU8 photoresist. The VFM method was compared to the conventional processing method, which utilises a Hotplate, and a hybrid method utilizing both Hotplate and the VFM and found that an increase on the degree of cure was observed using the VFM at similar processing temperatures which means that SU8 curing at lower temperatures or rapid curing is possible. The increase in cure rates can be attributed to a combination of heat transfer and the unique capability of microwave to couple with the sample. Optical studies of the microstructures fabricated suggest that films that have a degree of cure of <60% resulted in poor quality microstructures. The VFM was found to achieve satisfactory microstructures at most of the temperatures tested as compared to the other two methods tested.

Abstract: Bio-based biodegradable Poly (lactic acid) (PLA) suffers limitations such as brittleness and slow crystallization. This study aims to resolve the brittle nature of PLA by blending with Poly (butylene succinate) (PBS), a more ductile biodegradable polymer with superior toughness and flexural properties. In this research, a series of PLA/PBS blends was prepared at the blend ratios of 100/0, 80/20, 60/40, 40/60, 20/80 and 0/100. FTIR showed that there was no change in the functional groups of the PLA/PBS blends. Thermal stability assessed by TGA revealed that PBS degraded at higher temperature than that of PLA; the decomposition temperature (T_d) at 10% weight loss of PLA and PBS were 330.8 and 356.4°C respectively. The T_d of all the blends increased gradually with the addition of PBS. The flexural properties in terms of the flexural strength and the flexural modulus of the blends reduced significantly with PBS content. The PLA/PBS specimens with greater PBS content were softened and flexed more easily, thereby requiring a much lower flexural strength. The flexural modulus of the 80/20 and 60/40 blends dropped from 3.5 GPa for neat PLA to 3.2 GPa and 2.1 GPa while the flexural strength also declined from 105.3 MPa to 90.9 MPa and 69.1 MPa respectively. The toughness of all the blends was greater than that of neat PLA; in particular the 60/40 blend exhibited superior impact strength of 48.7 J/m compared with 30.9 J/m of the neat PLA. The microscopic images of all the blends showed two distinct phases; the 60/40 blend consisted of well dispersed small particles of the tough PBS, resulting in greater absorption of energy upon impact.

Abstract: This research aims to study the influences of carvacrol essential oil on the tensile properties and antimicrobial activity of food packages prepared from poly (butylene succinate) (PBS). Overall, the tensile strength and tensile modulus of the PBS film decreased with the addition of carvacrol beyond 4wt%. PBS elongated to a greater extent when carvacrol was employed; the elongation reached its maximum level at 19% when carvacrol was added at 10wt%. The water vapor permeation (WVP) and oxygen permeation (OP) of PBS/carvacrol films tended to increase with increasing carvacrol content due to the vaporization of some carvacrol. Carvacrol was found to effectively inhibit microorganism growth; its antimicrobial activity against S.arious growth was evident when 4wt% of carvacrol was compounded with PBS while that against E.coli growth was found only when 10wt% of carvacrol was employed.

Abstract: The effect of Sr doped La_4-xSr_xNi₃O_10±δ (x = 0, 0.05, 0.1, 0.2 and 0.3) has been investigated as an intermediate temperature SOFC cathode material. The Ruddlesden-Popper (RP) compositions of n = 3 were successfully synthesized via citrate gel method. The single phase of sintered La_4-xSr_xNi₃O_10±δ (x = 0, 0.05, 0.1 and 0.2) powders was confirmed as an orthorhombic structure. However, this structure changes to more symmetry with an increasing amount of Sr dopant. With x = 0.3, the phases of La_1.7Sr_0.3NiO₄ as n = 1 RP and NiO appear without n = 3 RP. La_3.95Sr_0.05Ni₃O_10±δ shows the highest electrical conductivity with a value of 140 S/cm at room temperature. Nevertheless, the electrical conductivity of La_4-xSr_xNi₃O_10±δ decreases and further decreases with increasing amount of Sr. The conductivity values at 200°C of La_4-xSr_xNi₃O_10±δ (x =0, 0.05 and 0.1) are 89, 113 and 101 S/cm, respectively. For x = 0.3, the conductivity decreases lower than x 0.1 with its value of 36 S/cm because of the low conductivity phase of n = 1 RP.

Abstract: In this work, n-CdS/p-CuFeO₂ heterojunction diode was fabricated by thermal evaporating CdS thin films on 1 mm thick-CuFeO₂ ceramic substrate with substrate temperature kept at 373 K during evaporation process. The forward current-voltage characteristics of n-CdS/p-CuFeO₂ heterojunction in a temperature range of 100-300 K were investigated to determine the electrical parameters and conduction mechanism. It was found that, at forward bias below 0.5 V, the conduction mechanism of the diode is dominated by thermionic emission (TE) mechanism. At bias voltage above 0.5 V, the current transport is due to space charge limited current (SCLC) controlled by an exponential trap distribution in the band gap of CdS. The temperature dependence of the saturation current and ideality factor are well described by tunneling enhanced recombination at junction interface with activation and characteristic tunneling energy values as about 1.79 eV and E₀₀ = 86 meV, respectively. The value of interface state density (N_ss) evaluated from capacitance spectroscopy increases from 2.09x10¹¹ eV^-1cm^-2 (at 300 K) to 2.70x10¹¹ eV^-1cm^-2 (at 363 K). Free carrier concentration of 5.80x10¹³ cm^-3 at room temperature was estimated from capacitance-voltage measurements at 50 kHz.

Abstract: The polycrystalline Na-doped CuAlO₂ ceramics were obtained by solid state reaction method. The mixture of high purity grade of CuO, Al₂O₃ and NaNO₃6H₂O powders was ground and then pressed by using uniaxial pressure. The obtained pellet was sintered in air at 1,423 K for 24 h. XRD patterns showed the crystal structure of the as-sintered Cu_1-xNa_xAlO₂ (0x0.05) belonging to rhombohedral, space groupalong with the CuO and CuAl₂O₄ phases. The minimum resistivity value around 4.48x10² Ωcm and maximum hole concentration around 2.04x10¹⁶ cm^-3 were observed for x=0.03 at room temperature. The properties of Seebeck coefficient and electrical resistivity were measured in the high temperature ranging 300 to 700 K. The results of electrical resistivity, Seebeck coefficient and power factor values decrease with increasing Na content. The calculated activation energy of conductivity (in the range of 160-250 meV) is larger than that of thermopower (in the range of 26-83 meV) which suggests that the conduction mechanism may be determined as a small polaron hopping type.

Abstract: Al₂O₃/ZrO₂ composites have been investigated as the bio-inert material. In the present work Al₂O₃/ZrO₂ Micro/Nano composites were prepared by colloidal method. The effects of the concentration of zirconium propoxide and the sintering temperature were studied on the distribution of ZrO₂ nano-grains in Al₂O₃ matrix and mechanical properties of composites. XRD patterns for all compositions showed a single phase of a-Al₂O₃, and the tetragonal and monoclinic ZrO₂ phases. Samples sintered at 1650°C demonstrated the high bulk density with value of 86-92% of theoretical density. ZrO₂ nano-grains were dispersed within Al₂O₃ grain and the grain boundary. The sample of the highest flexural strength of 710 MPa was synthesized using 100% Zr propoxide solution and sintered at 1650^o C. The flexural strength was found to increase with increasing the concentration of Zr propoxide and sintering temperature.

Abstract: The effect of ZrO₂ content on phase composition of CaO-ZrO₂-SiO₂ glass system was investigated in the present research. CaO, ZrO₂ and SiO₂ were used to made frits. It was found that glass samples of high ZrO₂ content contained wollastonite, pseudowollastonite and Ca₂ZrSi₄O₁₂ as the major components of crystalline phase and samples of low ZrO₂ content mainly included non-crystalline phase. The present results also confirmed that firing temperature and soaking time have influence on the phase transition of wollastonite. At high temperature, the wollastonite phase was changed to the pseudowollastonite phase which was verified by thermal analysis. Microstructure observations of glaze samples revealed the formation of crystals in different directions. The thermal expansion mismatch between glaze and body led to the development of microcracks.

Abstract: Solar-reflective green pigment was synthesized from the starting powder consisting of chromium oxide (Cr₂O₃), aluminum oxide (Al₂O₃), titanium dioxide (TiO₂), and vanadium oxide (V₂O₅) by high-speed, wet milling at the speed of 300 rpm for 2 h followed by calcination at 1150 or 1200 °C for 0.5-5 h. X-ray diffraction analysis revealed the presence of reduced chromium oxide, Cr₂O_2.4, which is the major component, and rutile TiO₂ phase of which its XRD peak intensities were intensified upon calcination as a result of phase transformation from amorphous portion in the starting TiO₂. Microstructural analysis revealed significant particle growth after calcination at 1200 °C for 5 h due to Ostwald ripening. Highest near-infrared reflectance of 70.1% was obtained from the product calcined at 1150 °C for 0.5 h. Higher calcination temperature and/or extended period of calcination time led to a reduced reflection which is ascribed to an increased of particle size of the synthesized pigment.

Abstract: Titanium nitride (TiN) thin films were deposited on to unheated silicon (100) and stainless steel substrates by home-made direct current (DC) reactive magnetron sputtering method at a deposition of 60 min in an Ar-N₂ gas mixture. The effects of sputtering power on structure and microstructure of these films have been studied. The films were analyzed by X-ray diffraction (XRD), Atomic Force Microscope (AFM) and Field-Emission Scanning Electron Microscope (FE-SEM). The films colors were influenced by sputtering parameter which altered from green purple to light gold and dark gold, respectively. By XRD, the polycrystalline structure of the as-deposited films was face center cubic (fcc) of TiN structure with (111), (200), (220), and (311), planes. The increasing of sputtering power transformed film from amorphous phase to crystal phase with crystal size were enhanced from 21.9 nm to 39.8 nm. The AFM scans revealed that sputtering power significantly affected surface morphologies and thicknesses of the TiN films. With increase in sputtering power, the roughness and films thickness were increased from 0.5 nm to 25.1 nm and 331 nm to 1113 μm, respectively. The microstructure combined with cross-section analysis FE-SEM revealed that the grain refinement with columnar structure were obtained for the film deposited at sputtering power of 270 W.