Papers by Keyword: RF Power

Abstract: Thin films of tungsten oxide were deposited on glass substrates by the radio frequency (RF) reactive sputtering from a high purity tungsten metal target (99.9%) with a diameter of 10 cm. The reactive sputtering was carried out in an argon-oxygen gas mixture containing 20% of O₂ and 80% of Ar. The used RF power is 200 W while fixing the deposition time at 120 min. Finally, the prepared films were annealed at different temperatures (350 °C, 400 °C, 450 °C, 500°C and 550 °C) for 1 hour under air and under vacuum. X-ray diffractograms showed that the deposited thin films crystallized in Hexagonal/Monoclinic WO₃ phase. It was found that the crystallite size varies with the annealing temperature and the lattice parameters is a= 7.3064Å, b = 7.5292Å, c = 7.6875Å and a=b= 7.3242Å, c= 7.6624 Å, for h-WO₃ and m-WO₃ structures, respectively. Scanning Electron Microscopy (SEM), Raman spectra confirmed the formation of WO₃ thin films. In addition, optical transmittance data revealed that the optical bandgap of the films decreases with increasing the annealing temperature. Electrical measurements revealed that annealing in air results in more resistive samples, which should be taken into account in future investigations, especially as buffer layers for efficient photovoltaic solar cells. Keywords: Vacuum, Tungsten oxide, Raman spectroscopy, RF Sputtering method, RF Power, Annealing temperature.

Abstract: Silicon-rich silicon nitride thin films have been grown by plasma enhanced chemical vapor deposition (PECVD) at 13.56MHZ on glass and N-type monocrystalline silicon substrate using high purity NH3,N2 and SiH4 as reactant gas sources by changing of radio-frequency (RF) power and deposition pressure. The samples were characterized by the ultraviolet-visible (UV-UIS) light transmittance spectra, Fourier transform infrared absorption spectroscopy (FTIR) and an X-ray (XRD) diffraction, respectively. The results showed that both the RF power and deposition pressure increase promote the deposition rates. However, the increase of rf power leads to the decrease of optical band gap, the increase of refractive index, and the increase of deposition pressure leads to the widening of optical band gap. The increase of rf power leads to the increase of the silicon atoms in the thin films and the transition of the films to the silicon-rich state. As the deposition pressure increase, the probability of N atoms entering the films increase and the thin films change to a nitrogen-rich state. At a certain pressure, when the rf power is changed, the average grain size in the films decrease by XRD analysis. Based on the above analysis, both the deposition pressure and rf power have an important effect on the microstructure, and optical properties of the thin films. By properly adjusting these two parameters, the silicon-rich silicon nitride films with good density can be obtained.

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.

Abstract: Nanocomposites of ZnO/TiO₂ were fabricated by two methods. Firstly, deposition of TiO₂ nanoparticles by Radio Frequency (RF) magnetron sputtering. Secondly, growths of ZnO nanostructures on the TiO₂ nanoparticles by solution-immersion method with aqueous solution of Zinc nitrate hexahydrate as precursor solution and stabilizer hexamethylenetetramine (HMTA) in water as solvent. The optical properties of ZnO/TiO₂ nanocomposites were examined by Ultraviolet-Visible (UV-Vis) spectroscopy, Raman spectroscopy and Photoluminescence (PL) spectroscopy. UV-vis spectra of ZnO/TiO₂ nanocomposites display high absorption in the UV region and high transparency in the visible region. There is improvement in UV absorption for ZnO/TiO₂ nanocomposites compared to pure TiO₂ due to imperfect alignment of ZnO nanostructures. Raman analysis shows the presence of wurtzite hexagonal ZnO in all the films and presence of anatase structure of TiO₂ in the film deposited at 200 W. PL spectra of the films show the emissions in the UV and visible regions. Intensity of PL emission in UV region (λ< 400 nm) is maximum for film deposited at 200 W and minimum for film deposited at 300 W resulting from the change in the surface state density. A broad peak from ~ 600-700 nm also was found for all the films.

Abstract: Optimization of titanium dioxide (TiO2) nanostructures deposited on glass substrate by Radio Frequency (RF) magnetron sputtering has been studied. The aim of this paper is to determine which parameter of RF powers influence the optimization of TiO2 nanostructures. The surface morphology and topology, roughness properties and cross-sectional of TiO2 nanostructures were observed by Atomic Force Microscope (AFM). The particle size of TiO2 nanostructures were observed by Field Emission Scanning Electrons Microscope (FESEM) and the UV-vis transmission spectra were recorded using UV-vis spectroscopy. The lowest surface roughness has the smallest average TiO2 size particle with indirect optical band gap of 3.39 eV for optimum TiO2 nanostructures deposited at varies RF power.

Abstract: Zinc Oxide (ZnO) thin films were deposited onto SiO₂/Si substrates using radio frequency (RF) magnetron sputtering method as an Ammonia (NH₃) sensor. The dependence of RF power (50~300 Watt) on the structural properties and sensitivity of NH₃ sensor were investigated. XRD analysis shows that regardless of the RF power, all samples display the preferred orientation on the (002) plane. The results show that the ZnO deposited at 200 Watt display the highest sensitivity value which is 44%.

Abstract: In recent years, hydrogenated nanocrystalline silicon (nc-Si:H) film has received much attention due to its potential application in various optoelectronic devices. In the present work, nanocrystalline silicon (nc-Si) films were fabricated from SiH4 diluted with H2 in very high frequency (40.68 MHz) plasma enhanced chemical vapor deposition system. The influence of radio frequency (rf) power on the structural properties of nanocrystalline silicon films has been studied. Raman spectra show that the crystallinity of the nc-Si films can be increased by promoting the rf power. But over high rf power leads to the structural deterioration of nc-Si:H film. AFM images manifest that, with the increase of deposition time, the grain size becomes larger accompanied by the decrease of the number density.

Abstract: ZnO thin films were deposited on Teflon substrates by RF magnetron sputtering at different substrate temperature and different RF power. In this work, we investigated the dependence of the deposition rate and also the ZnO physical and electrical properties on the substrate temperature and RF power. It is observed that the deposition rate increased as the temperature and RF power increased. FE-SEM images confirmed that microstructure of the thin films consists of nanoparticles. XRD data confirmed that the ZnO thin films at various RF power and substrate temperature have (002) structure.

Abstract: Nanocrystalline silicon (nc-Si) thin films were deposited on glass and polytetrafluoroethylene (PTFE, teflon) substrates using Radio frequency (RF) magnetron sputtering. The effect of RF power and deposition temperature on the physical and structural properties of nc-Si on the glass and Teflon substrate was studied. The thin films properties were examined by Raman spectroscopy and field emission scanning electron microscopy (FESEM). We found that the thickness of thin films increased with increased RF power and deposition temperature. Raman spectroscopy results it showed that, with increasing RF power and deposition temperature can cause the changing of crystallinity on both glass and Teflon substrate.

Abstract: The effect of RF power on the formation and morphology evolution of ZnO nanostructured thin films deposited by magnetron sputtering are presented. This project focused on electrical, optical and structural properties of ZnO thin films. The effect of variation of RF power at 50 watt-250 watt at 200 °C on glass substrate of the ZnO thin films was investigated. The thin films were examined for electrical properties and optical properties using two point probe current-voltage (I-V) measurement (Keithley 2400) and UV-Vis-NIR spectrophotometer (JASCO 670) respectively. The structural properties were characterized using field emission scanning electron microscope (FESEM) (JEOL JSM 7600F) and atomic force microscope (AFM) (Park System XE-100). The IV measurement indicated that at RF power 200 watt the conductivity of ZnO thin film show the highest. All films show high UV absorption properties using UV-VIS spectrophotometer (JASCO 670). The root means square (rms) roughness for ZnO thin film were about 4 nm measured using AFM. The image form FESEM observed that transformation of structure size started to change as the RF power increase.