A novel method was developed to deposit a large crystal diamond with good facets up to 1000 μm on a tungsten substrate using a microwave plasma enhanced chemical vapor deposition （MPCVD）. This method consists of tw...A novel method was developed to deposit a large crystal diamond with good facets up to 1000 μm on a tungsten substrate using a microwave plasma enhanced chemical vapor deposition （MPCVD）. This method consists of two steps, namely single-crystal nucleation and growth. Prior to the fabrication of the well-faceted, large crystal diamond, an investigation was made into the nucleation and growth of the diamond which were affected by the O2 concentration and substrate temperature. Deposited diamond crystals were characterized by scanning electron microscopy and micro-Raman spectroscopy. The results showed that the conditions of single-crystal nucleation were appropriate when the ratio of H2/CH4/O2 was about 200/7.0/2.0, while the sub- strate temperature Ts of 1000℃ to 1050℃ was the appropriate range for single-crystal diamond growth. Under the optimum parameters, a well-faeeted large crystal diamond was obtained.展开更多
Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is ...Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is indicated that the entire facet dendrite shapes are obtained by using regularized phase field model. Steady state tip velocity of dendrite drives to a fixed value when γ≤0.13. With further increasing the anisotropy value, steady state tip velocity decreases and the size is smaller. With the increase in the undercooling and coupling parameter, crystal grows from facet to facet dendrite. In addition, with increasing coupling parameter, the facet part of facet dendrite decreases gradually, which is in good agreement with Wulff theory.展开更多
目的利用三维有限元法评估腰椎经皮内镜下不同的关节突成形部位对椎体活动度(range of motion, ROM)的影响。方法建立正常L3～5三维有限元模型,模拟腰椎经皮内镜技术分别在L5上关节突"尖部"或"基底部"做直径0.75 c...目的利用三维有限元法评估腰椎经皮内镜下不同的关节突成形部位对椎体活动度(range of motion, ROM)的影响。方法建立正常L3～5三维有限元模型,模拟腰椎经皮内镜技术分别在L5上关节突"尖部"或"基底部"做直径0.75 cm圆柱状骨切除以模拟椎间孔成形,从而获得正常L3～5模型、关节突尖部成形模型和关节突基底部成形模型。给予特定加载条件,比较3种模型在前屈、后伸、左右侧曲、左右旋转工况下L3～4、L4～5节段ROM变化情况。结果 L5上关节突尖部成形后,在后伸、左右侧屈、左右旋转状态下L4～5节段ROM均较正常明显增大,以左旋最为明显;L5上关节突基底部成形后,在左右旋转状态下L4～5节段ROM较正常稍微增大。L5上关节突尖部、基底部成形后在6种不同运动状态下临近节段L3/4的ROM均无明显变化。结论腰椎经皮内镜技术下,L5上关节突尖部成形较关节突基底部成形对L4～5节段ROM影响较大。L5上关节突成型对临近节段L3～4的ROM无明显影响。展开更多
基金supported by the Natural Science Foundation of Hubei Province of China(2008CDB255)the Educational Commission of Hubei Province of China(No.Q20081505)the Key Laboratory for Green Chemical Process of the Ministry of Education of China (No.RGCT200801)
文摘A novel method was developed to deposit a large crystal diamond with good facets up to 1000 μm on a tungsten substrate using a microwave plasma enhanced chemical vapor deposition （MPCVD）. This method consists of two steps, namely single-crystal nucleation and growth. Prior to the fabrication of the well-faceted, large crystal diamond, an investigation was made into the nucleation and growth of the diamond which were affected by the O2 concentration and substrate temperature. Deposited diamond crystals were characterized by scanning electron microscopy and micro-Raman spectroscopy. The results showed that the conditions of single-crystal nucleation were appropriate when the ratio of H2/CH4/O2 was about 200/7.0/2.0, while the sub- strate temperature Ts of 1000℃ to 1050℃ was the appropriate range for single-crystal diamond growth. Under the optimum parameters, a well-faeeted large crystal diamond was obtained.
基金Projects(50331040 60171034) supported by the National Natural Science Foundation of China
文摘Numerical simulation based on phase field method was performed to describe the solidification of silicon. The effect of anisotropy, undercooling and coupling parameter on dendrite growth shape was investigated. It is indicated that the entire facet dendrite shapes are obtained by using regularized phase field model. Steady state tip velocity of dendrite drives to a fixed value when γ≤0.13. With further increasing the anisotropy value, steady state tip velocity decreases and the size is smaller. With the increase in the undercooling and coupling parameter, crystal grows from facet to facet dendrite. In addition, with increasing coupling parameter, the facet part of facet dendrite decreases gradually, which is in good agreement with Wulff theory.
