Papers by Author: M. Horprathum

Abstract: Spectroscopic Ellipsometry (SE) was used to analyse the effect of plasma treatment on aluminium oxide thin films. The aluminium oxide thin films were fabricated by reactive DC magnetron sputtering at different operating pressures. The as-deposited thin films were plasma treated at different ambient Ar and O₂ conditions. The prepared samples were investigated for physical microstructures with scanning electron microscopy (SEM) and optical characteristics with ellipsometry. The ellipsometric spectra of the prepared samples were measured in the range of 250 to 1650 nm with the incidence angle of 70 degree. Based on the optical model with the Tauc-Lorentz function, the thickness and the refractive index of the films were determined and discussed. The results showed that the thickness and the refractive index of the aluminium oxide thin films were greatly affected after the plasma treatments. In comparison, the results of those prepared at different operating pressures were also discussed. The SE results were confirmed with those from SEM.

Abstract: This study investigates tantalum oxide (Ta₂O₅) nanorods prepared by the dc magnetron sputtering with the glancing angle deposition (GLAD) technique. Silicon (100) wafer and glass slides were used as the substrates. The effect of the glancing angle varying from 73-87°, on the structural and optical properties were investigated by field-emission scanning electron microscopy (FE-SEM), atomic force microscope (AFM) and spectrophotometry. The results show that the deposition rate and diameter of Ta₂O₅ nanorod films were decreased with the increase in the glancing angle. At the highest glancing angle of 87°, the prepared Ta₂O₅ nanorod yielded the highest porosity from the vertically aligned columnar structure, and were must suitable for many functional applications.

Abstract: Recent studies demonstrated that, titanium oxide (TiO₂) thin films, which kill bacteria and viruses under mild UV illumination, offers numerous potential applications. In this work, the TiO₂ thin films were successfully deposited by DC reactive magnetron sputtering technique. The high-purity Ti target was sputtered on BK7 glasses and silicon (100) wafer substrates. The annealing treatment at various temperatures was next performed on the obtained samples. Their crystalline structure, film morphology and optical properties, as well as anti-bacterial activities, were investigated. The structure and morphology of films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM). The optical property was determined by UV-Vis spectrophotometer. After the post-annealing in air at higher than 200 °C, all the films showed crystallized mixture of anatase and rutile phase. The antibacterial properties of the TiO₂ thin films were discussed.

Abstract: Titanium dioxide (TiO₂) films were prepared by thermal oxidation from Ti films. The Ti films were deposited on glass and silicon (100) wafer substrate by dc magnetron sputtering and subsequent with thermal oxidation process. The crystal structure and morphology of TiO₂ films were estimated by using X-ray diffractometry (XRD) and field-emission scanning electron microscopy (FE-SEM), respectively. The optical property of TiO₂ films was determined by UV-Visible spectrophotometer. The influences of annealing temperature between 200 to 500°C in air for 1 hour on the structure and optical properties of TiO₂ films were investigated. The increasing of annealing temperature was directly affected the phase transition from Ti to TiO₂. The optical and structural properties of TiO₂ films are the best exhibited with increasing the annealing temperature at 500 °C.

Abstract: In this study, silver-doped titanium dioxide (Ag-TiO₂) thin films were prepared co-sputtering technique in order to promote photo-induced antibacterial applications. The high-purity Ag (99.995%) and Ti (99.995%) were simultaneously co-sputtering on BK7 glass and silicon (100) wafers substrate. The structure, morphology, surface roughness and optical properties were characterized by grazing-incidence X-ray diffraction (GIXRD), field-emission scanning electron microscopy (FE-SEM) and UV-Vis spectrophotometer, respectively. The results showed that the as-deposited Ag-TiO₂ thin films had high transparency in the visible range. The antibacterial activity was studied in the presence and in the absence of UV irradiation against Escherichia coli as a model for Gram-negative bacteria. The results indicated that, in comparison to conventional TiO₂ films, the Ag-TiO₂ thin films exhibited excellent antibacterial properties under the UV illumination.

Abstract: The TiO₂ thin films were prepared by a dc reactive magnetron sputtering technique from high purity Ti target on silicon (100) wafers and alumina substrates inter-digital with gold electrodes. The as-deposited films were annealed from 400°C up to 800°C with 100 °C steps for 1 hour in air ambience in order to promote microstructure, morphology and gas-sensing properties. The change in microstructure and morphology of the films were investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The enhancement in the gas-sensing properties was test by ethanol gas. The prepared thin films were exposed to ethanol gas at concentration 1,000 ppm in purify dry air carrier. The resistance was measured as a function of the ethanol concentration of the films at operated temperatures in the range of 250 - 350°C. The influence of annealing temperature at 500 °C of TiO₂ thin film has a highest sensitivity at 350 °C operated temperature.

Abstract: Tantalum oxide (Ta₂O₅) films at 400 nm thickness were prepared at room temperature by DC reactive magnetron sputtering. The effect of annealing temperature on film crystallinity, microstructure and optical properties were investigated. In order to indentify the crystalline structure and film morphology, X-ray diffraction (XRD) and field-emission scanning electron microscope (FE-SEM) measurements were performance. The optical properties were determined by UV-Vis spectrophotometer and spectroscopic ellipsometry (SE). The result showed that, with the annealing treatment at high temperature (700-900°C), the as-deposited films were crystallized to orthorhombic phase of tantalum pentaoxide (β-Ta₂O₅). In addition, the transmittance spectrum percentage indicated 87%, which corresponded to the obtained optical characteristic. The refractive index varied at 550 nm from 2.17 to 2.21 with increased of the annealing temperature.

Abstract: Tungsten oxide (WO₃) nanorods were prepared by a DC reactive magnetron sputtering with a glancing-angle deposition (GLAD) technique, which promoted high surface area, for electrochromic applications. During the deposition, a high-quality tungsten target was sputtered under oxygen ambience on to Si (100) and glass/ITO substrates. The variation of the deposition time, which affected the length, size and patterns of the nanorods, was investigated based on their electrochromic properties. For physical studies, the prepared nanorods were examined by X-ray diffraction and field-emission scanning electron microscopy, which demonstrated moderately ordered nanorods with amorphous phase. The results showed that the length and size of nanorod were increased, in nearly linear order, with increasing the deposition time. For optical characteristics of the prepared films, the UV-Vis spectrophotometry was use to determined their transmission spectra and optical contrasts from the colored and bleached state. The electrochromic properties were also determined from cyclic voltammetry. The results indicated that, because of the optimal relations between the nanostructural length and size, the WO₃ nanorods prepared at 75 minutes (approximately 422 nm) yielded the highest optical contrast and electrochromic functions.

Abstract: The ZnO nanorods were fabricated on top of the seeded gold layer by the aqueous solution method with the solution of zinc nitrate and hexamethylenetetramine (HTMA) at 90°C for 24 hours. The variety of the ZnO nanorods were prepared and investigated based on the precursor concentrations, in a range of 1 to 40 mM. The physical morphologies and crystal structures were characterized by field-emission scanning electron microscopy (FE-SEM) and X-ray diffractometry (XRD), respectively. The results showed that, with the small precursor concentrations, the lateral growth of the nanorods was highly significant when compared to their axial growth. The precursor concentration of 20 mM was best optimized for the preparation of the ZnO nanorod arrays with the hexagonal structures at the highest rod diameter and length. At the higher concentrations, although the nanorod size remained nearly constant, the length was however rapidly decreased. Further analyses also proved that, with the increased precursor concentrations, the number density of the ZnO nanorods was progressively increased along with the more complete hexagonal wurtzite structures.

Abstract: Titanium dioxide (TiO2) thin films, 80-170 nm thick were deposited on unheated silicon wafers (100) and glass slides with controlled operating pressure in UHV dc sputtering system with a pressure control gate valve. The dependence of hydrophilic property of the films on the total sputtering pressure of mixed Ar and O2 gases (1-10 mTorr) was investigated. We found that hydrophilic activity as well as the structural and optical properties of the films were strongly related to the pressure maintained during the deposition. The TiO2 film structure and surface morphology were studied by X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM) and spectroscopic ellipsometry (SE). The optical constants of the TiO2 films was determined by SE. XRD showed that the films deposited between 1 – 5 mTorr had both anatase and rutile phase, but the rutile component reduced as the pressure increased. Only anatase peaks were obtained for the films deposited at pressure >5 mTorr. The AFM surface roughness decreased from 4.0 to 1.8 nm as the pressure increased from 1 – 10 mTorr. The contact angle measurement was used to determine the hydrophilicity of the films after exposed to UV light. I