化学气相法合成高品级单晶金刚石微粉的应用基础研究

The high-grade diamonds synthesis is a key direction of man-made diamonds development. In this work, the hot filament chemical vapor deposition (HFCVD) is adopted to research a new technology of fabricating the high-quality single crystal diamond powders with micro size. To obtain the new technology for synthetizing free-standing single crystal diamonds, and improve the quality and homogeneity of crystals, the deposition parameters are optimized reasonably, and the proper substrate materials are chosen according to the difficulty of crystals fall off from the substrate, as well as the water cooled worktable are treated by the supersonic vibration to avoid the micro diamond crystals adhering strongly to the substrate and a high density crystals of diamond joining together to form a continuous films. In order to fabricating the high-grade single crystal diamond powders with ultra-fine grain size in quantity production, for one thing, the method of ultrasonicating diamond seeds in the photoresist solutions and spraying them onto the substrate using a spin coater machine, or without the seeds, controlling the nucleation density on the substrate is performed to disperse the isolated diamond crystals uniformly on the substrate; for another thing, the method of simulating the process of depositing diamond crystals in the HFCVD system and verifying them using the experimental method is performed to optimize the arrangement of the diamond seeds on the substrate relative to the grid arrangement of the hot filaments with the high-power. Additionally, the grain size distribution and the morphology of CVD synthesized diamond crystals are characterized, and meanwhile the abrasive-free polishing experiments are adopted for researching machining properties of CVD synthesized diamond powders. Therefore, this work lays foundations for industrial applications of CVD synthesized diamond powders, and meanwhile provides the new way for eliminating and repairing the defects of the HPHT diamond powders.

本项目以热丝化学气相沉积CVD法为基础，研发化学气相法合成高品级单晶金刚石微粉的新方法。通过合理优化热丝CVD工艺参数，采用适合晶粒脱附的衬底材料，施加基台超声振动避免晶粒附着或成膜，获得控制自支撑CVD单晶金刚石颗粒生长新工艺，提高CVD合成单晶金刚石颗粒生长质量和均匀性;采用光刻胶超声分离晶种和旋转甩胶或有效控制无籽晶成核密度等新措施，均匀分散衬底基盘金刚石晶种，通过对HFCVD系统合成颗粒金刚石的仿真模拟和实验验证，实现大功率热丝栅状排列结构和衬底模板金刚石晶种微粒合理排布的优化结合，获得适合于CVD高品级细晶粒单晶金刚石微粉批量合成的新技术.对CVD合成超细金刚石微粉的粒度分布及晶形质量等指标进行评价，结合游离磨料研磨抛光实验，研究CVD合成金刚石微粉的加工性能，为化学气相法合成高品级金刚石微粉的工业化应用打下基础，同时也为高温高压中、低级金刚石品级提高提供新途径。

金刚石单晶微粉通常指粒度在0.1 ~54 μm之间的超细磨料，主要用于工件表面的超精密光整加工。目前大部分人造单晶金刚石都是采用静态高压法合成，然而该方法设备复杂、工艺苛刻，难以合成细粒度的金刚石单晶颗粒，因此工业上所需的微粉级金刚石（38 μm以下）几乎都是采用机械破碎高温高压合成的中、细颗粒金刚石方法获得，但是这种方法工艺流程极其繁琐，使得生产效率受到严重制约，且经过破碎获取的金刚石微粒形状杂，品级低，即使经过适当的整形处理，仍不能获得批量化的较高品级微粒，严重限制了研磨抛光质量的进一步提高，因此迫切需要寻找新的方法来合成高品级金刚石微粉。.本项目以热丝化学气相沉积CVD法为基础，提出化学气相法合成高品级单晶金刚石微粉的新方法，通过研制新型超声振动基台的化学气相沉积装置，使置于工作台之上的金刚石微粒产生微小运动，有效减小晶体生长内应力以及金刚石颗粒与衬底的结合力，并结合化学腐蚀硅基衬底和高速离心沉降颗粒工艺，获得自支撑CVD单晶金刚石颗粒制备的新工艺，进一步提出了CVD合成有/无籽晶高品级金刚石单晶颗粒的新技术，揭示了该项技术多颗粒单晶金刚石同时生长及抑制成膜的新机制，并通过合理优化热丝CVD工艺参数及动态掺硼工艺，获得了单晶金刚石颗粒优质生长的新工艺。利用有限容积法仿真模拟及实测温度实验验证，实现了大功率热丝排列结构与进出气口合理排布的优化结合，有效保证了在衬底各处单晶颗粒金刚石生长粒度和质量均匀性，获得了适合于CVD高品级单晶金刚石微粉批量合成的新技术。在此基础上，对CVD单晶金刚石微粉的粒度分布及晶形质量进行测试研究，并与机械粉碎法金刚石微粉的行业标准相比较，结果显示该微粉中70~ 80 %的颗粒都具有高品级单晶晶体形态，与传统机械粉碎法金刚石微粉相比，在晶形及表面质量上占有绝对优势，将尤为适合高精密器件的抛光加工。本项目的研究内容不但为CVD合成高品级金刚石微粉的工业化应用打下基础，同时也为高温高压中、低级金刚石品级提高提供新途径。