| Microwave discharge is one of the typical methods for generating plasmas.Microwave plasma, which possess unique advantages such as electrodeless discharge,energy convergence and working stably in comparison to many other methods, has been widely employed in industrial field, especially in functional material preparation.Microwave plasma includes various discharging modes in wide gas pressure ranges from 10-2 Pa to 1 atm. Deposition rate is significantly enhanced for the denser active precursor species in plasma under higher gas pressure. Considerable attention has been attracted on plasma source technology and material synthesis by using microwave plasma in the study of low temperature plasma.In this thesis, a resonance cavity for generating microwave plasma under high pressure is built. The discharge characteristic of CH4/H2/Ar microwave cavity-resonance plasma and its application in function material fabrication are investigated. Moreover, research on the deposition of magnetic Co-N films using microwave electron cyclotron resonance ?ECR? plasma is carried out under low gas pressure.We start from the transfer equation of electromagnetic wave, and give the principles of microwave transmission in various types of waveguides. Dimensions of the apparatus components are calculated by meeting the requirement of transmission,cutoff and resonance of the 2.45 GHz microwave in certain modes. Concerning the microwave mode converting simultaneously, we establish the microwave resonance cavity with adjustable parameters in wide ranges. The discharge effect can be optimized under different gas pressures to achieve a stable microwave plasma more than 100 hours.Features of microwave CH4/H2/Ar plasma under relative high pressure in the resonance cavity are studied through the combined usage of optical emission spectroscopy ?OES? and mass spectroscopy. It is found that hydrocarbon species exhibit different CH4 gas flow dependences. The intensity of CH radical firstly rises then decreases, whereas 2-carbon species increases continuously. These observations are related to the changing degree of CH4 dissociation and the enhanced dimerization reactions. Ar addition has influence on the vapor ambient by the penning effect and lowering the electron temperature. The complex variation of hydrocarbon radicals in the plasma with rising gas pressure suggests the change of electron activation mechanism to thermally driven chemistry for the formation of excited reactive hydrocarbon species at high gas pressures. Higher power leads to the higher gas temperature, which is in favor of the thermally driven mechanism and the CH4 dissociation. Excessive total gas flow rate causes the reducing CH intensity, reflecting the negative influence on the adequate decomposition of CH4.The microwave plasma was also utilized to prepare diamond films in the resonance cavity. Self-supporting diamond films with high quality and thickness uniformity were synthesized on the Mo substrate with diameter of 20 mm when the CH4/H2 flow ratio was maintained at 2%. The deposition rate was nearly 3 ?m/h.However, the central part of the films was thinner than the edge area when the Mo substrates were replaced by larger ones with diameter of 40 mm. The thickness nonuniformity may be ascribe to the "edge effect" induced from the distortion of the electric field by the larger Mo substrates. Diamond films with poor quality were deposited at a high deposition rate of 5 ?m/h as the CH4/H2 flow ratio was raised to 4%, which is related to the decreasing CH particles and increasing 2-carbon species in the bulk plasma. No significant influence of pressure on deposition rate and film quality can be observed from 4 kPa to 8 kPa.The magnetic Co-N films were deposited by introducing an DC biased Co target in the microwave ECR plasma under low pressure using N2 and Ar as reaction gases.Crystal structures and magnetic properties of the Co-N films are tunable at various Co/N compositional ratios by controlling the relative concentration of Co and N active species and substrate temperature. The saturation magnetization Ms decays by increasing the N2/Ar gas flow ratio, while the coercive field Hc increases and particles size of films decreases slightly. This is attributed to the reducing Co4N phase in higher nitrogen-incorporated Co-N films, which results from the increasing concentration of N species in plasma vapor. Raising substrate temperature enhances the N content in the films, leading to the decreasing Co4N phase and saturation magnetization Ms.However, the coercivity H2 decreases as substrate was heated to 500?, revealing a reverse trend with substrate temperature. It might be related to the formation of much larger particles with the size of ?400 nm in the film obtained at high growth temperature. Film with higher saturation magnetization Ms and lower coercivity H2 was synthesized under increasing negative bias voltage of Co target due to the rising concentration of Co atoms in the vapor ambient. It contains more Co4N phase and enlarged particle with pebble shape. These studies provide support for the further research on controllable magnetic properties of Co-N films. |
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