Advanced Materials Research Vol. 802

Abstract: A simple synthesis route to high-quality ZnO nanorod is reported, utilizing ZnO thin films grown by Filtered Pulse Cathodic Vacuum Arc (FPCVA) deposition as seed layers and continuous growth by hydrothermal method. Depending upon the FPCVA deposited conditions, implanted voltages, thickness and annealing temperature of ZnO seed layer, the surface morphology of the ZnO nanorod on ZnO film was noticeably different. The average diameters of the nanorod on Al substrates varied from about 131.99 ± 23.87 to 418.17 ±75.50 nm. The grown ZnO nanorod showed a high crystallinity with energy gap of 3.37 eV and low defect density confirmed by UV/VIS Spectrometer and photoluminescence spectrum (PL). Large-area growth, quasi-aligned and high quality indicates that the ZnO nanorods produced have potential application in field emission and optoelectronic devices.

Abstract: The objective of this work is to provide the process for making BaTiO3-based ceramics by adding bismuth oxide (Bi2O3) into the system. The attention is also focused on synthesis conditions, where sintering temperature exhibits a pronounced effect on phase formation, density, microstructure and dielectric properties of BaTiO3 ceramics doped with different contents of Bi2O3 nanoparticles. The phases of BaTiO3-based ceramics have been prepared by solid state reaction using different Bi2O3 amount and characterized by X-ray diffractometry, Archimedes’s method, scanning electron microscopy and dielectric spectroscopy. The results show that single phase of BaTiO3 with no evidence of secondary phase forms in all samples. Abnormal grain growth was found in pure BaTiO3 ceramic with 37.30 µm of average grain size. After added Bi2O3 nanoparticles into system, the grain size significantly decreases and the sintering temperature of BaTiO3-based ceramics efficiently reduces without degrading the dielectric characteristics.

Abstract: Manganese zinc pyrophosphate (Mn_(2-x)Zn_xP₂O₇ when x = 0.0, 0.5, 1.0, 1.5 and 2.0) ceramics were fabricated by conventionally mixing oxide using the normal sintering method. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman spectroscopy and scanning electron microscopy (SEM). The XRD results indicated that synthesized Mn_(2-x)Zn_xP₂O₇ systems have a pure monoclinic phase without the presence of phase impurities. The lattice parameters and crystalline sizes analyzed from XRD data were changed depending on the amount of added Zn²⁺ ion concentration in the Mn₂P₂O₇ structure. The FT-IR and Raman results showed the fundamental vibrations of P₂O₇^4-ion and Mn-O or Zn-O, which confirmed the Mn_(2-x)Zn_xP₂O₇ formation. In addition, dielectric stability of temperature and frequency was observed in the composition, x = 1.0, with a dielectric constant value of 11.5 at 1 MHz.

Abstract: This study aims to investigate the effect of the Sn²⁺-substituted into the CuFeO₂ delafossite on thermoelectric properties in the Sn content of x = 0.03, 0.05. The CuFe_1−xSn_xO₂ samples were synthesized by solid state reaction. The crystal structure was characterized by XRD, TGA, XPS and the thermoelectric properties were measured in the range of 300 to 960 K. The Seebeck coefficient display positive sign in all temperature range and the XPS show the stable Sn⁺² state as confirming the Sn-doped CuFeO₂ playing p-type conductor. The Sn²⁺-substituted supports the mixed valency Fe³⁺/Fe⁴⁺ state in transition octahedral oxide of FeO₆ layer enhancing Seebeck coefficient. The high Seebeck are appeared in content of x=0.03 which are 280 to 340 µV/K in the range of 300 to 800 K. The experimental Seebeck corresponds to the prediction formula at high temperature. Totally, the maximum Power Factor is 2.30×10⁻⁴ W/mK² occurring in the CuFe_0.95Sn_0.05O₂ at 860 K which is higher than that value of the undoped-CuFeO₂ in 4 times. These support that the Sn-substituted CuFeO₂ delafossite enhancing thermoelectric properties.

Abstract: Multiferroics, which display simultaneous ferrimagnetic and ferroelectric properties, have been interesting recently because of their potentially significant applications in multifunctional devices such as magnetic resonance, drug delivery, high-density data storage, ferrofluid technology, etc. Composites combining BaTiO₃ with Co_0.5Ni_0.5Fe₂O₄ have influenced the interest of many researchers, due to their outstanding and distinguished character called magnetoelectric (ME). In this work, ferrimagnetic-ferroelectric composites of BaTiO₃ nanopowder and Co_0.5Ni_0.5Fe₂O₄ nanopowders were prepared by a conventional mixed oxide method. The multiferroic ceramics were compounded with the formula, (1-x)BaTiO₃-(x)Co_0.5Ni_0.5Fe₂O₄, in which x = 0, 0.05, 0.10, 0.20 and 0.35. All of the compositions were analyzed by an X-ray diffractometer (XRD) in order to reveal the phase of perovskite and spinal structure. Scanning electron microscopy (SEM) was used to examine the variation of morphology and grain size of the composited ceramics. The magnetism of all the ceramics was measured using a vibrating sample magnetometer (VSM). The results showed that microstructure and the amount of ferrite are related strongly with magnetization.

Abstract: This study demonstrates an attempt to fabricate the 25 µm channel-length bottom-contact pentacene TFTs using thermal evaporation through shadow mask technique and to investigate crystal structure, morphology and electronic structure of the pentacene layer deposited at the same time on gold (Au) source-drain electrodes and Poly(methyl methacrylate) (PMMA) gate-dielectric of the TFTs. The pentacene layers with thicknesses of 50 nm were deposited at the evaporation rates of 0.1, 0.5, 1.0 and 1.5 nm/min at substrate temperatures of 60 °C. These conditions were employed with and without preheating at 80 °C before deposition. Preheating at 80 °C was found to improve quality of the pentacene film on the PMMA gate-dielectric. Using the deposition rate of 1 nm/min and the substrate temperature of 60 °C, best performance of TFTs were obtained. At this deposition condition, pentacene film work function was found to be higher on the Au source-drain electrodes than on the PMMA gate-dielectric.

Abstract: The working electrode of dye-sensitized solar cell was modified using composite material of TiO₂ particles/TiO₂ nanofibers/CNT by doctor blade method. Structural properties of pre-cursor materials and as-prepared working electrodes were well characterized by X-ray diffraction and scanning electron microscopy. The efficiency and relevant parameters of solar cells with modified electrodes were measured. The optimized weight ratios of 1 wt.% TiO₂ nanofibers derived from leucoxene and 0.01 wt.% CNT exhibited the highest improvement of DSSC efficiency with solar efficiency of 1.11% and fill factor of 0.32. The increase of current density may be originated from easier electron transfer that occurred in the device with modified TiO₂ particles/TiO₂ nanofibers/CNT composite.

Abstract: This research related to the development of ultra-small inner spiral ribbed copper tubes (ISRCT) which has the quality and the efficiency in transferring the high heat. So the demand of using ultra-small tubes in electrical appliances today is very high and will be greater in the future. The technology required must be the technology that can produce ultra-small ISRCT with various distinguishing features such as small size, high quality, high functionality and low cost of productions in order to fulfill the increasing demand. The conventional production method was suitable for large tubes which high draw ability, but unsuitable for the fabrication of long ultra-small tubes because it is difficult to manufacture the devices used as tools such as an ultra-small spiral ribbed mandrel and a floating plug. This research has proposed tube sinking drawing method and presented a comparison of seven parameters, including the drawing stress, wall thickness ratio, ribbed base width ratio, ribbed tip width ratio, ribbed height ratio, ribbed pitch ratio, and ribbed spiral angle ratio. The experiment was found that the tube sinking was possible for making the ultra-small ISRCT. The results showed the sum of a reduction in the right size in the case of ultra-small ISRCT. The most appropriate must not exceed 68.81% and will be reduced after draw formed to the 8^th.

Abstract: A homogeneous photoresist for IC or read-write data storage head fabrication requires a certain flowing of the resist film on the topography surface for at least few micrometers, thus defining certain minimal resist viscosity for the remaining solvent concentration for spraying technique. The high photoresist solvent evaporates during flight (between spray nozzle and substrate) prevents the droplets from sticking to the substrate and causes a rough surface. The limitation of very low photoresist viscosity for micro droplets spraying is a drawback of the technique. Because of very low viscosity of spray coating resist, nitrogen in spray coating system will act as 2 functions. First is for spread photoresist to be micro droplets. In the same time nitrogen can dry the small droplet before locating to substrate and perform obstacle for UV exposure. The unsatisfied resist was protected UV light during exposure cause pattern deformation. The study was investigated the particles which always found on finished photoresist surface spraying, and aimed to find the solution to decrease or eliminate dry droplet. EDX identified element of the obstacle particles is photoresist. They are dry resist ball about 1 – 6 um size. The selected chemicals for the investigation to dilute or dissolve the resist ball, IPA, acetone and mixing solution between 70% IPA and 30% acetone. Acetone is most effective. The proper time for dissolve dry resist ball with slight photoresist degradation is 40 s, very short because of high vapor pressure of acetone at room temperature. There is a trade-off between resist surface smoothness and reflow characteristics. Final resist thickness with the acetone vaporization condition will be achieved 7.5 um as expectation with less corner coverage problem. SEM and AFM images were confirmed that morphology after acetone vapor exposure was improved. Surface roughness was reduced for 3 times to 8 nm with acetone vaporization environment. The end of this study was include on corrosion characterization for magnetic CoFe alloys underlying photoresist to explore the method to determine photoresist type in future manufacturing which necessary to run the process with sensitive material. With AZ4999 spray photoresist protection indicated corrosion rate of CoFe films was reduced for 100 times compare to bare films.