الفهرس 
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Abstract
Plasma characteristics of low-pressure direct current (DC) glow discharge were investigated for application in processing of materials surfaces. The main tasks of this thesis focus on two aspects: the first is a fundamental study of DC glow discharge plasma characteristics; and second is the application of this DC glow discharge plasma to the surface modification of a polymeric material. In this thesis, the experiments were performed to examine the effects of helium and argon addition, in different ratios and cathode material (copper, stainless steel, and aluminum) on both the electrical characteristics of DC N2 glow discharge plasma and the performance of polymer surface after treatment with such plasma. The DC glow discharge plasma characteristics were investigated by measuring: 1) discharge current-voltage (I-V) characteristics, 2) breakdown characteristics, and 3) Langmuir probe characteristics of the internal plasma parameters, electron energy distribution function (EEDF), electron temperature, electron number density and plasma potential. Results showed that, the effective plasma resistance, Reff, (the slope of the I-V plots) of N2 discharge is found to increase with the addition of He and fluctuating with Ar percentage. Moreover, the breakdown voltage increases by increasing He percentage in (N2-He) gas mixture, and decreases by increasing Ar percentage in (N2-Ar) gas mixture. Results of this research also showed that the electron temperature and density can be either raised or reduced effectively by mixing helium or argon while, the electron energy distribution function (EEDF) can be either shifted effectively to low or high energy values by mixing helium or argon in nitrogen discharge. It is clear that electrode materials can, to some extent, affect the discharge voltage and breakdown voltage for sustaining the discharges, due to the differences of the work functions of different electrode materials. The reminder of the investigation in this thesis is in particular, concern with the application of plasma treatment to modify the surface properties of polymethylmethacrylate (PMMA) polymer. PMMA is one of the most widely used polymers in many industrial applications. The effect of plasma treatment depends on internal and external parameters like type of plasma (DC, RF, microwave), the discharge treatment power, pressure, the reactor design, the electrode material, the working gas or gas mixture and the treatment time. In this work, the influence of the experimental parameters (working gas or gas mixture, electrode materials, and the sample treatment time) of DC glow discharge N2 plasma on the wettability and surface properties of PMMA polymeric surfaces has been investigated. The investigated properties of the polymer films are mainly restricted to the surface free energy (SFE) calculated through contact angle measurements, surface morphology of the films characterized by scanning electron microscopy (SEM), and lastly, the chemical composition characterized by Fourier transform infrared spectroscopy (FTIR). Results showed that a clear change in the surface energy of PMMA films due to plasma treatment was observed. The surface free energy, calculated from the contact angle measurements, revealed that its polar component was a dominant factor in improving the wettability. As a consequence of different electrode materials, the use of aluminum electrode results in relatively larger increase in the polar component of SFE of the polymer followed by those obtained using stainless steel and copper electrodes. Results also showed that plasma treatment can change chemical structure of polymer surface. It is clear that,