Papers by Keyword: Transmittance

Abstract: One dimensional ZnO nanorod has been extensively studied in sensor application due to its unique properties in direct energy band gap and high binding energy. In this report, ZnO nanorod arrays were synthesized via hydrothermal approach. Highly oriented (002) nanorods array with diameter of (22.42 ± 1.40) nm was successfully grown on the quartz surface. A low cost and room temperature optical based NO sensor was introduced. ZnO nanorods array show a high sensitivity upon the NO gas which is 20.1 % within 3 minutes. This newly established method can be potentially used in detection of other toxicity gas.

Abstract: The research of subsystems establishes the foundation to complex systems analysis with cascade structure. Analysing the diagrams of characteristics of confirmed system it has been determined that in case of approximate method the resonance frequencies cover with those which have been determined with exact method. However the values of the characteristic in other areas are different. The main aim of the paper is to study the dynamic characteristic of the discrete continuous mechatronic system determined by exact approximate, that means Galerkin's method for torsionally vibrating complex mechanical subsystems. The system composed from many subsystems having the same length and variable cross section, loaded by the focused moment was analysed. The main subject of deliberation was to determine the flexibility of the mechanic system with constant cross section using the exact and approximate Galerkin's method. Next the method comparison and the correction of approximate method where made. As far as the mechatronic system flexibility determinations concerned the Galerkin's method has been chosen. The analysis of subsystems of mechatronic and mechanic complex systems is however the introduction to the synthesis of torsionally vibrating mechatronic systems with assumed frequency spectrum.

Abstract: This paper reports on ITO/Ag and ITO/Ni thin transparent conductive electrodes (TCE) for optoelectronics device applications. The ITO/Ag and ITO/Ni bi-layer TCE were deposited on Si and glass substrates by thermal evaporator and radio frequency (RF) magnetron sputtering. Post-annealing was performed on the samples at 600°C in air. Electrical, optical and morphological characteristics were investigated by means of Hall Effect measurement system, UV-Vis spectrophotometer and atomic force microscope (AFM). The measured electrical resistivity of ITO/Ag (0.5 × 10^-4 Ωcm) is lower than ITO/Ni (1.2 × 10^-4 Ωcm) due to the high carrier concentration of ITO/Ag of 12.0 × 10²¹ cm^-3. Optical transmittance at visible ranges of ITO/Ag (70%) is higher than the ITO/Ni (44%). Higher surface roughness and smaller grain sizes of ITO/Ag as compared to the ITO/Ni are factors that contribute to the good quality of TCE characteristics.

Abstract: Zinc oxide (ZnO) thin films were prepared by sol-gel spin coating technique, which were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), NKD thin film analysis system and fluorescence spectrophotometer. The results show that ZnO thin films with the each layer thickness of 80 nm present obvious c-axis orientation. With the increase of coating layers, the c-axis orientation characteristic weakens. The reason is considered that the growth mode of ZnO thin films transforms from layer growth to island growth. For the ZnO thin film with 4 layers, it has a compact surface and a uniform particle size of approximately 50 nm, and the photoluminescence (PL) spectrum primarily consists of two PL emission bands, one is a strong and narrow ultraviolet (UV) emission band, another is a weak and broad luminescence emission band from 400 nm to 650 nm. The average transmittance in the visible range is beyond 90%. A optical band gap of 3.26 eV, slightly less than the intrinsic band gap width of 3.37 eV, is obtained by Tauc plotting method. The defects, such as Zn or O vacancies, grain boundaries, are considered to be the main factors causing this situation.

Abstract: Transparent conductive oxide (TCO) is one of the important components in dye-sensitized solar cells. The main requirements of TCO for dye-sensitized solar cells are having a low electrical resistance and a high light transmittance. This study focuses on the synthesis of fluorine-doped tin oxide including its optimization. The synthesis of fluorine-doped tin oxide has been conducted under spray pyrolysis technique in which a precursor solution of SnCl₂:F having concentration of 0.3, 0.5, 0.7, and 0.9 M. The spray pyrolysis was performed using a nebulizer with deposition time of 10 min. The glass substrate was heated at a temperature of 400, 450, and 500°C prior to deposition. The fluorine doped tin oxide was then measured the electrical resistivity for each area of ​​1 cm². Therefore, the mean and distribution of electrical resistivity of fluorine-doped tin oxide with an area of ​​10 x 10 cm then were predicted. In addition, the morphology and transmittance of fluorine-doped tin oxide are also examined. The optimization of the synthesis process of fluorine-doped tin oxide using spray pyrolysis was obtained at a concentration of 0.7 M with a sintering temperature of 400°C. The best fluorine-doped tin oxide has been also fabricated into the dye-sensitized solar cell and the performance has been studied.

Abstract: This research aims to calculate the transmittance to direct irradiance due to absorption by precipitable water vapor in the atmosphere of Thailand, estimation of the absorptance by water vapor in the atmosphere and calculate the precipitable water vapor in the atmosphere. The precipitable water vapor in the atmosphere was calculated from upper air checking data relative humidity and temperature. The data were collected at four meteorological monitoring station located in Chiang Mai, Ubon Ratchathani, Bangkok and Songkhla during the years 1991-2010. The figures for precipitable water vapor obtained from this investigation were used to formulate a mathematical model relating to the precipitable water from four stations with surface climatological data, relative humidity and temperature at the same stations. The result showed that the relationship has a relatively high level of reliability. The precipitable water vapor obtained from upper air nearly is equal to the value from the model. The difference in the Root Mean Square Error (RMSE) is equal to 0.250 cm. Then, the researcher used a model to calculate the amount of precipitable water vapor at 85 meteorology stations nationwide. The result showed that the precipitable water vapor was less in the dry (November to March) and relative high in the rainy season (April-October). The average per year was found to be 4.559 cm. When analyzing the solar radiation absorption by water vapor in the atmosphere, found that the absorption is more or less depending on the precipitable water vapor in the atmosphere, which has an average annual as 15.53 percent. The transmittance to direct irradiance due to absorption average per year was found to be 84.51 percent.

Abstract: TiO₂ thin films were deposited by ion beam assisted electron beam evaporation and annealed at 200, 300, 400 and 500 ¡æ in air for one hour. The crystal structures and morphology of the samples were analyzed by an X-ray diffractometer and an atomic force microscope. The transmittance spectra were recorded by a UV-visible spectrophotometer. The results show that both the as-deposited TiO₂ thin film and that one annealed at 200 ¡æ are amorphous. The sample annealed at 300 ¡æ crystallizes in pure brookite phase and is preferentially oriented along the (121) plane. When the annealing temperature rises up to 400 and 500 ¡æ, TiO₂ thin films turn into pure anatase phase. All the samples exhibit high transmittance in the visible region. With the increase of annealing temperature, the transmittance slightly declines and the optical bandgaps also slightly decreases.

Abstract: Thin films of gallium nitride (GaN) and related nitride materials were prepared, and their properties as transparent conducting electrodes were investigated. GaN thin films were directly grown on sapphire single crystal substrates by the molecular beam epitaxy. Heavy doping of germanium was employed to reduce resistivity of the films, with sufficient reduction found to be possible while maintaining their epitaxial growth state. Optical transmission spectra of the films in the short wavelength region were slightly deteriorated by the heavy doping; however, this was successfully improved by growing GaN films under metal-rich conditions to increase the electron mobility and suppress unwanted increase of the carrier densities. In addition, the optical transmission spectra in the short wavelength region was improved also by alloying GaN with aluminum nitride, though the resistivities of these films were relatively higher than those of the unmodified GaN films. The prepared nitride thin films exhibited sufficiently suitable properties as transparent conducting electrodes for use in applications such as full-spectrum nitride-based solar cells.

Abstract: In recent years, there are many techniques developed to synthesize zinc oxide (ZnO) films. However, among the synthesis methods available, sol-gel has the most advantageous which offers cost effective features. In the present work, ZnO films were prepared by solgel spin coating technique. The effects of solution ageing times which varies at 2h 15 min, 3h 30 min and 24h were investigated. The structural, morphological and optical properties were studied using an x-ray diffractometer (XRD, Bruker D8 Advance), atomic force microscope (AFM, Tenko XE-100) and ultra violet-visible spectrophotometer (UV-Vis, Shimadzu UV 1800), respectively. Based on the XRD measurement, it was revealed that ZnO films were polycrystalline with hexagonal wurtzite structure. The crystallite size is in the range of 34.4 ~ 28 nm which decreased with ageing time increment. On the other hand, the AFM analysis revealed that the surface roughness of the films increased due to the increment of ageing times. Optical transmittance spectra indicate that all films were transparent (>75%) in the visible range which slightly improved with increasing of ageing times. The optical band gap was estimated to be around 3.24 ~3.26 eV using Taucs plot. We revealed that the ageing time of ZnO sol influenced the material properties of ZnO films. Based on our finding we proposed that 24h ageing time is optimum for the fabrication of high quality ZnO films.

Abstract: Aluminium doped zinc oxide (AZO) is fast becoming an important thin film material for applications as transparent conducting oxide (TCO) in several thin film solar cells, smart windows and many devices using touch screen displays. This is due to its good electrical and optical characteristics as well as lower cost and good abundance. Although sputtering is the general method for industrial fabrication of this material, but film characteristics depend strongly on fabrication processes. Thus, optimal films are obtained by optimization of the deposition conditions. In this work, we investigated the effects of RF deposition power on AZO thin films. Samples of similar thicknesses were grown under similar conditions in an RF sputtering chamber at different RF powers. The samples were then characterized using FESEM, AFM, UV-Vis, XRD and Hall effect measurement tools. Results indicate that the surface morphology is slightly affected with larger grain sizes obtained at higher RF powers. Also the surface roughness, average transmittance, conductivity and deposition rate all increase with the RF power. The lowest as-deposited resistivity of 15.3x10^-3 Ω/cm was obtained, at the highest RF power of 100 W. This film also have the highest values of carrier concentration, mobility and figure of merit of 4.24x10²⁰ cm^-3, 0.96 cm²/V and 0.27x10^-3 Ω respectively. This work highlights the significance of RF power in the fabrication of good quality AZO thin films.