在自支撑金刚石膜体中发现网状、河流状和环状三种裂纹形式,这几种裂纹形式依沉积温度不同而不同.首次采用了原子力显微镜分析了金刚石自支撑膜体裂纹断裂机制,发现了穿晶断裂和沿晶断裂两种机制,其中,在网状裂纹中,穿晶断裂机制占主要地位;环状裂纹中,沿晶断裂机制占主要地位,而河流状裂纹是两种机制的混合.对应X射线衍射结果,(111)晶面占优的膜体易于开启穿晶断裂机制,(220)晶面占优的膜体易于开启沿晶断裂机制.使用Raman 谱测试的膜体中的本征应力在几十到几百MPa之间,且在膜体中存在应力剖面分布.Raman谱的结果还显示低缺陷的膜体组织有利于阻挡裂纹扩展.通过建立简单力学分析模型,推测了膜体组织对断裂强度的作用.根据实验结果和力学模型,制备了最厚2mm、最大直径120mm的无裂纹自支撑金刚石膜.
Crack patterns in self-standing diamond film were observed as network-shape pattern, river-shape and circle-shape pattern, depending on growth temperature. Fracture mechanism was firstly studied by atomic force microscope (AFM) on the fractured section. Both intergranular fracture and transgranular fracture were found by this technique. Transgranular fracture was easy to observe in network-shape pattern, and intergranular fracture was found in circle-shape pattern. The river-shape pattern seemed to result from the combination of inter- and trans-granular fracture. X-ray diffraction (XRD) test was done on all of growth side, nucleation side and fractured section of the film body. Corresponding to XRD results, transgranular fracture took place in the film with (111)-crystalline surface being dominant in all of the three detected surfaces. Intergranular fracture occurred in the film with (220)-crystalline surface being dominant in all of the three detected surfaces. Raman test showed that the intrinsic stress was in the range of several tens MPa to several hundreds MPa. Micro-Raman test on fractured section indicated that there was the distribution of stress in the film body. Also by micro-Raman, testing along the crack path indicated that crystalline structure with few defects was benefit for blocking the propagation of crack. A mechanical model was set up to analyze the effect of dominant surface on fracture strength. Based on the experimental results and mechanical analysis, crack-free self-standing diamond films with 2mm in thickness and 120mm in diameter were successfully grown by controlling the crystalline structure of the films.
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