Advanced Materials Research Vol. 979

Abstract: Tantalum oxide (Ta₂O₅) thin films were prepared, at different deposition time, by a DC reactive magnetron sputtering. During the deposition, a high-quality tantalum target was sputtered under argon and oxygen ambience on to silicon (100) and glass substrates. The prepared thin films were systematically characterized for both physical and optical properties based on spectroscopic ellipsometry (SE), and consequently confirmed by several methods. With the SE physical models, we could determine the thin film thickness as well as their inhomogeneity. The films thickness results were directly confirmed by field-emission scanning electron microscopy (FE-SEM) used to observe cross-sections, and surface profiler used to measure the physical thickness of the films. With the SE optical models, we applied both the Cauchy and Tauc-Lorentz dispersions in order to obtain the optical constants, to be directly compared with those from the Swanepoel method (SM). Our result showed that from the SE analyses, the SE physical model was obtained as the multi-layer configurations. The obtained Ta₂O₅ thin film thickness was closely related with the measured result from the FE-SEM cross-sectional micrographs and the surface profiler. For the optical characteristic, the double layer physical model was best optimized with the Tauc Lorentz dispersion model for the most accurate results. In comparison, the SM technique also demonstrated a capability to determine both the film thickness and its refractive index only from some samples. Therefore, this study proved that the SE technique successfully and accurately determine both the physical and optical properties of the Ta₂O₅ thin films.

Abstract: Tungsten trioxide (WO₃) thin films were prepared by a DC reactive magnetron sputtering technique. The thin film fabrication process used tungsten (99.995%) as the sputtering target, the mixture of argon and oxygen as sputtering and reactive gases, and silicon (100) and glass slides as the substrates. The effects of annealing temperature in the range of 200-400°C on physical and optical properties of the WO₃ thin films were investigated. The nanostructures and morphologies of these films were characterized by grazing-incident X-ray diffraction (GIXRD) and field-emission scanning electron microscopy (FE-SEM). The optical properties were analyzed by variable-angle spectroscopic ellipsometry (VASE) and spectrophotometer. From the XRD results, the as-deposited and annealed WO₃ thin films up to 300°C were all amorphous. Only the WO₃ thin film annealed at 400°C exhibited a polycrystalline monoclinic phase. The FE-SEM cross-sections and surface topologies demonstrated nearly identical thin-film thickness and physical grain sizes. The SE analyses showed that the thin films were all homogeneous dense layers with additional surface roughness. With the annealing treatment, the thin film thickness was slightly decreased. The SE physical model was best optimized with the Cauchy optical model. The results showed that the refractive index at 550 nm was increased from 2.17 to 2.23 with the increased annealing temperature. The results from the spectrophotometer confirmed that the optical spectra for the WO₃ thin films were decreased. This study demonstrated that, the thin film annealed at 400°C exhibited the slightly lower transparency, which corresponded to the results from the GIXRD and SE analyses.

Abstract: This work investigated the decoration of the gold (Au) nanoparticles (NPs) on the TiO₂ thin films for the applications in ethanol gas sensors. The Au-decorated TiO₂ thin films (Au-TiO₂) were prepared by the DC magnetron sputtering on the silicon (100) wafers and alumina substrates, interdigitated with Au electrodes. The distribution and size of Au nanoparticles were controlled by varying the sputtering time. Morphologies and element composition of the Au-TiO₂ films were examined by field-emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX) respectively. The FE-SEM micrographs when the sputtering time was increased, the average size of the Au NPs was also increased. On the other hand, the distribution of the Au NPs was decreased. The change in size and distribution of the Au NPs consequently improved the response of ethanol gas sensors. The prepared Au-TiO₂ was tested, in comparison with TiO₂ reference films, as the ethanol sensors at 250-350^oC in 50-1,000 ppm gas concentration. The results showed that the TiO₂ thin film with Au-decorated at 6 sec sputtering time yielded the highest response of 514 at 350^oC operating temperature and 1,000 ppm gas concentration.

Abstract: Three-dimensional (3D)-hybrid surface-enhanced Raman scattering (SERS) substrates have been achieved via simultaneous assembled silver nanoparticles (AgNPs) onto the anodic aluminum oxide (AAO) templates. The AAO templates were prepared from the UHV aluminum foil in 0.3 M oxalic acid using the two-step anodization process at 0°C. The effect of applied voltage ranging from 30 to 50 V on the porous diameter and the inter-porous distance of the AAO templates was investigated and observed with filed-emission scanning electron microscope (FE-SEM). The results showed that the porous distance and the inter-porous distance were linearly increased with the increase in the voltage potentials. To investigate the pore-size effect on the SERS activities, the AgNPs were deposited on the AAO nanoporous templates. The SERS activities of these nanostructures were demonstrated with the methylene blue (MB) as the probing molecules.

Abstract: According to the growing interest in development of high-sensitivity surface-enhanced Raman scattering (SERS) substrates, this study focused on the fabrication of silver nanorods (AgNRs) based on the DC magnetron sputtering, with the glancing-angle deposition (GLAD) technique. The influence of incident angles on the film morphologies and SERS activities of the deposited films were investigated by field-emission scanning electron microscopy (FE-SEM) and Raman spectroscopy. With methylene blue as the test agent, the vertical aligned silver nanorods proved highly potential in highly sensitive SERS detections. The pesticidal cypermethrin were also used as the probe molecules to investigate for future practical applications. This work showed that the increase in the incident angle during the deposition helped promote the porosity of the AgNRs. The SERS signals were significantly enhanced from the vertically aligned silver nanorods grown at 85o incident deposition angle and 20 rpm substrate rotational speed.

Abstract: Transparent conductive oxides (TCOs) with indium tin oxide (ITO) thin films were deposited without substrate heating and post-deposition anneal using ion-beam assisted evaporation technique on glass and silicon substrates. The oxygen ion with emitting current produced using End-Hall ion source for bombardment of growing surface to improve ITO films structure. In this study, we investigate the effect of an ion flux to ITO films in terms of structural, optical and electrical properties. The emitting current can be varied from 0.5 to 2.0 A with the oxygen flow rate 7 sccm. The total film thickness and deposition rate are 200 nm and 0.2 nm/s, respectively. The structural properties of thin films were characterized by X-ray diffraction (XRD) to discover the preferred orientation with phase of crystalline and scanning electron microscopy (SEM) to examine the surface morphology in cross-section view. To determine the transmission spectra of the films, UV-visible spectrometer is introduced. Moreover, the films were also measured to investigate resistivity, carrier concentration, mobility and sheet resistance by Hall-effect measurements and four-point probe. It has been found that the ITO films with lowest electrical resistivity for the emitting current of 1 A about 5.57x10^-4 Ω.cm and slightly increases with increase of the emitting current. The mobility and carrier concentration rapidly decreases with increase the emitting current from 1.0 A to 2.0 A.

Abstract: Plaster is a material which is widely used in Thailand. However, some variations of plaster that contain powdered silica or asbestos may present health hazards if inhaled. Asbestos is a known irritant when inhaled in powder form can cause cancer, especially in people who smoke, and inhalation can also cause asbestosis. Therefore, finding a way to recycle plaster waste has received attention. This study investigated the composition and phase of major plaster waste from ornament factory in Thailand by X-rays Fluorescence spectrometer (XRF) and X-Rays Diffractometer (XRD). The main compositions of new plaster and plaster waste by an XRF spectroscopy were SiO₂, SO₃ and CaO, they accounted for about 99.6 wt% of the total. The main phase of new plaster was found to be SiO₂, CaSO₄, CaO, S and Ca₂Si form. The main phase of plaster waste was found to be SiO₂ and CaSO₄ form. These results indicated that plaster waste may be used as substitute or additive for silica source in other industry.

Abstract: In this work, subbitumious fly ash in Thailand was sintered at different temperatures and analyzed for their compositions and crystal structures. Glasses were prepared from B₂O₃ mixed with subbitumious fly ash and additive Na₂O in various concentrations. The results have shown that SiO₂, Al₂O₃ and Fe₂O₃ are the major compositions of the fly ash. The crystal structures of fly ash at sintering temperature below to 800 0C are mullite and quartz with the occurrence of hematite phase at 1,000 0C. The density, reflective index and hardness values were found to increase with the increasing of Na₂O concentration. The absorption spectra corresponded to the color of the glass (yellow to brown). The higher the Na₂O concentration is, the lighter the color of the glasses. The results from this work demonstrated the possibility of glass production from subbitumious fly ash and utilization of industrial waste in Thailand.

Abstract: The borosilicate glass samples doped with NiO have been fabricated by conventional glass making process and changed the composition of chemicals. Rice husk ash (RHA) was used as a SiO₂ source for prepare the glass samples. The physical and optical properties, viz., glass density, molar volume, refractive index and absorption spectra have been studied. The results show the density increased with increasing of NiO amount due to the difference of atomic weight of Si and Ni. The molar volume obtained from the density of glass, depends on changed rates of density and atomic weight. Those values increased when the amount of NiO increase due to the increasing in bond length between atoms. Moreover, the refractive index increased with increasing concentration of NiO.

Abstract: This research studied the effect of dysprosium on the physical, optical and luminescence properties of the bismuth borosilicate glass in compositions 40Bi₂O₃ : 20SiO₂ : (40-x)B₂O₃ : xDy₂O₃ (where x = 0.0, 0.5, 1.0, 1.5, 2.0 and 2.5 mol%). The glass systems have been prepared at 1100 °C by melt quenching technique. The results showed that the density and molar volume of glass samples are between 4.6477 ± 0.0020 to 5.0047 ± 0.0041 g/cm³ and 45.6608 to 48.6797 cm³/mol, respectively. The values of density and molar volume of these glasses were not depend on the Dy₂O₃ concentration. The optical absorption spectra of glass samples in the UV-Vis-NIR region shows absorption bands at 794, 906, 1094, 1276 and 1690 nm, respectively. The photoluminescence spectra show emission bands at 482 (blue), 576 (green), 663 (yellow) and 756 (red) nm under 453 nm excitation wavelength. The emission spectrum at 576 nm has shown a strongest intensity.