| Summary: | 碩士 === 國立成功大學 === 機械工程學系碩博士班 === 92 === The layer-by-layer carbon/silicon micro-nanocomposite films are deposited by ultra high vacuum ion beam sputtering system (UHV IBS) under different substrate temperature or at room temperature together with post vacuum annealing. The relations between deposition procedures, composition, micro-nano structure, temperature and mechanical properties are established after process and material analysis in this thesis. They are potentially used in the application of the surface modification of precision mechanics or micro electromechanical devices. The experiments are divided into two parts of single layer film and carbon/silicon multilayer film.
The results of deposition rate calibration show that the deposition rate of silicon film is higher than carbon film. The reason is the bonding strength of carbon higher than silicon. 40 nm carbon films deposited on silicon wafers at different temperatures are used to study the substrate’s temperature effect on the reaction of carbon to silicon. The results show the DLC begins to form nanocrystalline graphite (“glassy” carbon) when temperature increases. When substrate’s temperature is at 600 ℃, the carbon film begins to form silicon carbide. And when substrate’s temperature increases to 700℃, carbon and silicon react completely and the its topography is smooth. In addition, carbon/silicon micro-nanocomposite films were deposited at room temperature and then done by a series of post vacuum annealing to study the relation between films’ structure and mechanical properties at varied vacuum annealing temperature.
Two kinds of layer-by-layer films were prepared. First, single carbon film and two-layers carbon/silicon composite film were annealed at the same temperature and different time to study the relations of the structure and mechanical properties. The results show that the hardness of single carbon film is higher than two-layers carbon/silicon composite film due to the higher hardness of carbon film than silicon film. Both of the films decrease their hardness a little when annealing time increases. The reason is that carbon film is easy to graphitize at high temperature with increasing time. Second, three-layers carbon/silicon [a] composite films (Si/C/Si=50/200/50 nm), three-layers carbon/silicon [b] composite films (Si/C/Si=75/150/75 nm) and five-layers carbon/silicon composite films (Si/C/Si/C/Si=30/105/30/105/30 nm) were annealed at different temperature with the same time to study the relations of structure and mechanical properties. The results show the hardness is to increase when vacuum annealing temperature keeps at 700℃. The may be caused by the appearance of silicon carbide at 700℃. When vacuum annealing temperature increase to 900℃, the roughness of three-layers and five-layers carbon/silicon composite films increase obviously. It is caused by more crystallization of Si films in the multilayers at high temperature. The hardness of five-layer carbon/silicon composite films (Si/C/Si/C/Si=30/105/30/105/30 nm) and three-layers [a] carbon/silicon composite films (Si/C/Si=50/200/50 nm) are higher than three-layers [b] carbon/silicon composite films (Si/C/Si=75/150/75 nm). This is due to the total amount of carbon film and silicon film in the multilayer. In addition, the elastic modulus of five-layer carbon/silicon composite films is higher than three-layer carbon/silicon composite films to enhance the stiffness of materials. It is possible to promote the mechanical properties using multilayer composite structure by controlling the layer thickness and number.
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