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Diamond, due to its unique properties, has been studied for decades. Many diamond synthesis methods have been developed as well. As one of the synthesis methods, combustion flame chemical vapor deposition (CVD) is considered as the most flexible way. Combined with laser irradiation, laser-assisted combustion flame CVD can enhance the deposition process of diamond films. In this thesis work, efforts were made to explore the capability of a laser-assisted combustion flame CVD technique with krypton fluoride (KrF) excimer laser irradiation for improving diamond thin film quality and deposition rate. The research efforts mainly focus on following activities, including: 1) studying the influence of the gap distance between the inner flame and the substrates on crystallographic orientations, quality and deposition rate of the diamond film to determine the optimal parameters for the deposition; 2) conducting in-situ KrF excimer laser irradiation during the deposition process to increase the quality and the growth rate of the diamond film with the optimal deposition parameters, which includes excimer laser irradiation on the diamond film and on the combustion flame; 3) applying post-growth KrF excimer laser irradiation on diamond films, which is aiming to understand and verify the effect of KrF excimer laser irradiation on the diamond film during the deposition. A multi-torch combustion flame CVD was also developed for increasing the efficiency of depositing large-area diamond thin films.
Diamond thin films have been deposited on tungsten carbide (WC) by the laser-assisted combustion-flame CVD technique in open atmosphere. A KrF excimer laser was used in the process to: 1) achieve energy coupling into combustion flame; 2) influence species proportions in the combustion flame; 3) promote seeding and nucleation process during diamond film deposition; 4) increase the diamond thin film quality and deposition rate through non-diamond carbon removal. Observations from experimental results confirmed that excimer laser irradiation could promote seeding and nucleation of diamond, growth rate and diamond quality. Furthermore, by changing the gap distance, the crystallographic orientations of diamond films can be controlled successfully and the optimal gap distance for diamond deposition can also be found. With applying a multi-torch setup in laser-assisted combustion flame CVD method, large-area diamond thin films were synthesized efficiently.
Adviser: Yongfeng Lu