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Breakdown and Langmuir Electrical Characteristics of Glow Discharge Plasma in DC Reactive Dual-Magnetron Sputtering System
Abstract
In this work, the breakdown and Langmuir characteristics of dc glow discharge plasma employing dual-magnetron assembly were studied. The electrical characteristics of this system are optimized to use it for reactive sputtering applications. The plasma was generated by electric discharge of argon gas at pressures ranging from 0.1 to 0.8 mbar. Also, a mixture of argon and oxygen was used to generate plasma since oxygen is used as the reactive gas. First, the Paschen's curves for both cases (argon only and argon/oxygen mixture) were plotted as the variation of breakdown voltage with the product of gas pressure (p) and inter-electrode distance (d) (i.e., p.d). The minima of these curves were ranging in 145-208V for different inter-electrode distances. The minima were also determined for the glow discharge of oxygen only to be ranging in 185-320V. In case of argon/oxygen mixture, the minima were ranging in 100-208V. The resistance of the gaseous medium was determined from the I-V characteristics and the argon showed higher resistance when compared to oxygen and argon/oxygen mixture. The plasma parameters, mainly electron and ion temperatures and densities, were determined from the Langmuir probe measurements for argon only and argon/oxygen mixture. Electron and ion temperatures in argon/oxygen mixture were higher than those in only argon. The densities showed contradictive behaviors as the electron density was lower in argon/oxygen mixture, while the ion density was higher in the same mixture.
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In this work, high-quality nanostructured silicon nitride films were prepared by reactive direct current magnetron sputtering technique. The properties of the prepared structures were determined by the ratios of gases (argon and nitrogen) in the discharge gas mixture. This parameter was effectively seen important to control the structural characteristics of the prepared nanostructures, especially surface roughness and particle size. The prepared nanostructures were successfully tested for gas-sensing applications and they exhibited reasonably high sensitivity for their resistance changes to gas concentration with increasing temperature (up to 96% at 350 °C). This work can be good attempt to use silicon nitride nanostructures in such important application.
In this work, a gas sensor is fabricated from polycrystalline nickel cobaltite nano films deposited on transparent substrates by closed-field unbalanced dual-magnetrons (CFUBDM) co-sputtering technique. Two targets of nickel and cobalt are mounted on the cathode of discharge system and co-sputtered by direct current (DC) argon discharge plasma in presence of oxygen as a reactive gas. The total gas pressure is 0.5 mbar and the mixing ratio of Ar:O2 gases is 5:1. The characterization measurements performed on the prepared films show that their transmittance increases with the incident wavelength, the polycrystalline structure includes 5 crystallographic planes, the average particle size is about 35 nm, the electrical conductivity is linearly increasing with increasing temperature, and the activation energy is about 0.41 eV. These films show high sensitivity to ethanol vapor.
In this work, highly-pure silicon oxide nanostructures were prepared by a closed-field unbalanced magnetron plasma sputtering technique. These nanostructures were characterized by Fourier-transform infrared spectroscopy, UV-visible spectroscopy, x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy and atomic force microscopy in order to determine the optimum preparation conditions. Minimum particle size of 20 nm was determined for the samples prepared at an inter-electrode distance of 4 cm, Ar:O2 gas mixing ratio of 70:30, total gas pressure of 0.08 torr, discharge voltage of 2.5 kV, discharge current of 35 mA, anode temperature of 27 ∘C (room temperature) and cathode temperature of about 40 ∘C. These conditions are optimized to control the structural characteristics of such nanostructures and hence to satisfy certain requirements and purposes in spectroscopic and photonic applications of SiO2 nanostructures.
In this work, novel design of closed-field unbalanced dual magnetrons system was employed in a DC reactive sputtering system to prepare silicon nitride nanostructures. Two types of silicon wafers (n-and p-type) were sputtered in presence of nitrogen gas to deposit nanostructured silicon nitride thin films on glass substrates. The prepared nanostructured were polycrystalline with six dominant crystal planes: (101), (110), (200), (232), (301) and (321). The surface roughness of the sample prepared at inter-electrode distance of 4cm was higher than other samples prepared at smaller or larger distances and the average and R.M.S roughness were 0.777 and 1.03 nm, respectively. The nanoparticles of minimum size of 30nm were formed and recognized as individual accumulated particles. Two bands of significant absorption were observed around 960 and 1086 cm-1 , those are attributed to the SiN -Si vibration mode in Si 3 N 4 molecule. An absorption peak was observed at 389nm, which is attributed to the quantum size effect of nanostructures. The refractive index of the prepared Si 3 N 4 samples was determined to be 1.38-2.1 and the energy band gap was ranging in 5.1-5.2 eV. The energy band gap was found to increase with decreasing thickness of the prepared film. The wide energy band gap of Si 3 N 4 nanostructures makes them good candidate, as similar as AlN, BN and GaN, for power electronics and optoelectronics operating at high temperatures.
In this work, the spatial distribution of the magnetic field between two magnetrons in a closed-field unbalanced dual magnetron system was studied. The magnetic field was measured as a function of the position along the circumference of the circular surface of one magnetron. As well, the variation of magnetic field intensity along the vertical distance separating the two magnetrons was determined. A strategy was proposed for the measurement of the variation of magnetic field intensity at 4 cm away from the electrode surface along four axes. The spatial distribution of the magnetic field intensity over the magnetron surface at 4cm was determined and analyzed.
In this work, experimental results on Langmuir probe diagnostics of low-pressure glow discharge plasma using argon-nitrogen mixtures are presented. The effect of variation in working pressure on the current-voltage characteristics of Langmuir probe diagnostics in unmagnetized glow-discharge plasma was introduced. The current-voltage characteristics of Langmuir probe diagnostics in glow-discharge plasma were studied at working pressure of 0.7mbar and three different cases (no magnetron, using one magnetron at the cathode, and using dual magnetrons). Similarly, the current-voltage characteristics of Langmuir probe in glow-discharge plasma at three different positions of the Langmuir probe inside plasma volume were presented. The variation of electron temperature and density in plasma with working gas pressure at the center point between the electrodes when dual magnetrons were used was determined. As well, the effect of mixing nitrogen with argon on the Langmuir probe characteristics at total working pressure of 0.7mbar and inter-electrode distance of 4cm was studied.
In this work, the current-voltage characteristics of dc plasma discharges were studied. The current-voltage characteristics of argon gas discharge at different inter-electrode distances and working pressure of 0.7mbar without magnetrons were introduced. Then the variation of discharge current with inter-electrode distance at certain discharge voltages without using magnetron was determined. The current-voltage characteristics of discharge plasma at inter-electrode distance of 4cm without magnetron, with only one magnetron and with dual magnetrons were also determined. The variation of discharge current with inter-electrode distance at certain discharge voltage (400V) for the cases without magnetron, using one magnetron and dual magnetrons were studied. Finally, the discharge current-voltage characteristics for different argon/nitrogen mixtures at total gas pressure of 0.7mbar and inter-electrode distance of 4cm were presented.
In this article, the key mechanisms of glow discharge in low-pressure gas mixtures were presented and discussed. The particle motions – mainly collisions – in discharge plasma those considered in most applications of plasma were presented. The regions of glow discharge were identified and their main characteristics were highlighted. These mechanisms were supported by experimental results obtained from a homemade dc plasma sputtering system. The experimental parameters, such as inter-electrode distance, using magnetrons and adding nitrogen to the gas mixture, and their effects on the Paschen's curve of glow discharge were introduced.
In this study, the parameters affecting the Langmuir characteristics of a closed-field unbalanced magnetron plasma sputtering system were studied. These parameters include the effect of variation in working pressure on the current-voltage characteristics of Langmuir probe diagnostics in unmagnetized glow-discharge plasma. Also, the current-voltage characteristics of Langmuir probe diagnostics in glow-discharge plasma at working pressure of 0.7mbar and three different cases (no magnetron, using one magnetron at the cathode, and using dual magnetrons) were introduced. The current-voltage characteristics of Langmuir probe in glow-discharge plasma at three different positions of the Langmuir probe inside plasma volume were determined. The variation of electron temperature and density in plasma with working gas pressure was determined at the center point between the electrodes when dual magnetrons were used. Finally, the effect of mixing nitrogen with argon on the Langmuir probe characteristics at total working pressure of 0.7mbar and inter-electrode distance of 4cm was introduced.