【作者】 李多生；

【导师】 左敦稳；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 化学气相沉积金刚石膜具有优异的热学、电学、声学、光学、力学等综合性能,在机械、电子、光学及生物工程等领域具有广阔的应用前景。近年来,曲面金刚石膜在国防领域受到极大的重视,但是大尺寸金刚石厚膜球冠的制备研究还处于起步阶段,对其制备机理及生长过程中工艺参数的影响规律还不清楚,因此开展大尺寸金刚石厚膜球冠制备机理及工艺研究具有重要的理论意义和工业应用价值。本文主要开展的研究工作如下:1.对直流等离子体CVD大尺寸金刚石厚膜生长进行了有限元仿真研究,采用流体动力学FLUENT有限元仿真软件对厚膜球冠生长的空间温度场、压力场、速度场进行仿真数值研究;分析了不同表面形状基体对模拟结果的影响。仿真结果表明:反应室的速度场、压力场分布是不均匀的,无论是凸球面还是凹球面,在基体的中心区速度都较小,随着半径的增加而增大,但在其它相同的工艺条件下,凸面的基体能使等离子体流具有更好的流动特性,因而能较好的进行大尺寸金刚石厚膜球冠的生长。无论是凹面或凸面,基体表面的温度场分布都较均匀,沿着基体表面到等离子体发射区呈均匀的梯度分布,这是保证金刚石膜生长的重要条件。同时发现凹面基体的侧面和基体的生长面的温差比凸面大,在膜的边缘膜内有较大的应力。2.对直流等离子体喷射CVD法制备大尺寸金刚石厚膜球冠制备机理开展了深入研究,详细分析了金刚石厚膜球冠生长过程。对金刚石膜的生长动力学,成核机理和生长机理等进行了研究;超原子H及活性基团如CH3、C2H2等是非平衡态下CVD制备金刚石膜的必要条件;基体曲率半径、金刚石膜生长附着行为对金刚石膜生长有重要影响;保持稳定均匀的等离子体弧,是制备高质量的金刚石膜的关键。3.对直流等离子体喷射CVD法制备大尺寸金刚石厚膜球冠工艺开展了研究,发现生长工艺对金刚石膜的质量产生重要影响。基体温度、碳源浓度、沉积室压强、基体曲率半径及基体与等离子体的间距等生长工艺参数对制备的大尺寸金刚石厚膜球冠质量密切相关,并研究了其影响规律。通过对这些参数的合理选择及优化,是能够制备出高质量大尺寸金刚石厚膜球冠的。4.对制备的大尺寸金刚石厚膜球冠进行了微观结构特征的研究,运用扫描电镜(SEM)、原子力显微镜(AFM)、拉曼光谱(Raman)、X射线衍射(XRD)、X射线光电子能谱(XPS)等现代先进测试技术对大尺寸金刚石厚膜球冠成核密度、表面形貌、表面粗糙度、成分、结构等进行了深入研究,从微观结构上表征了金刚石膜的本质特征。5.对大尺寸金刚石厚膜球冠的应力形成机理、应力大小、类型、分布及其对大尺寸金刚石厚膜球冠性能产生的影响进行了系统的分析,发现膜的制备工艺如基体温度,甲烷浓度等是金刚石膜应力的主要影响因素。同时也对膜的断裂机理、显微硬度等力学性能进行了研究,探讨了大尺寸金刚石厚膜球冠制备工艺参数对其性能的影响,寻求制备低应力金刚石膜,提高膜的力学性能的有效途径。更多还原

【Abstract】 Diamond films synthesized by chemical vapor deposition (CVD) have some outstanding properties such as high thermal conductivity, high band gap, low electrical conductivity, high IR transparency, high hardness, and high chemical inertness, etc. It has been considered as a promising material for many applications in mechanics, electron, optics and biology engineering. In recent years, convex diamond film has been widely more regarded in national defence field. But study on large size spherical diamond thick film just now begins, and preparation mechanism and process of diamond film are rarely reported.Thus it is important to develop experiment and theory investigation on large size spherical diamond thick film. The main work and the results obtained in this dissertation are as follows:1. FEM simulation study was carried out on the growth of diamond film by FLUENT. The results showed that the velocity field of spherical molybdenum substrate was not uniform, and it was much lower in center spherical substrate than that of the edge of spherical substrate. Fluctuation of plasma velocity field is harmful to growth of spherical diamond film. The pressure is the biggest in center of spherical substrate and tends to decrease at the ambient. In center small area of spherical substrate, plasma velocity was so low, which results in very high pressure field in center area of spherical substrate. Fluctuant velocity and pressure distribution have negatively influenced on the growth of spherical diamond film. Plasma better flows in convex substrate than the concave substrate, which is help to prepare high quality diamond film. The temperature field of the substrate is uniform, which is one of the major facts to successfully synthesize large size spherical diamond thick film. The results also shows that, although velocity and pressure field simulated are non-uniform, high quality spherical diamond film can be prepared. Meantime, it was found that diamond film has more stress by concave spherical substrate.2. Preparation mechanism and the growth course of large size spherical diamond thick film by DC plasma jet CVD were widely studied, meantime, growth dynamics, nucleation and growth mechanism of diamond film were also investigated. It was found that, in non-equilibrium state, the existence of super atom H, activated radical as CH3, C2H2 was necessary factors for preparing large size spherical diamond thick film. It was also showed that substrate curvatures, adhesion power of between diamond film and substrate, and plasma arc behavior have important influences on diamond film quality.3. Preparation process of large size spherical diamond thick film was widely investigated and the results showed that it has an important influence on the quality of diamond film. Substrate temperature, CH4 concentration, chamber pressure, substrate curvature and distance between substrate and plasma are closely related with diamond film quality. To optimize these processes parameters, and high quality large size spherical diamond thick film can be prepared.4. The techniques based on X ray diffraction (XRD), scanning electron microscopy (SEM), atom force microscopy (AFM), X ray photoelectron spectroscopy (XPS), Raman spectroscopy etc. were used to investigate microstructure, nucleation density, surface roughness, orientation evolution and impurities of spherical diamond film respectively.5. Study on the mechanism and distribution of the stress of diamond film was carried out by XRD, and the stress has an important influence on performance of the diamond film. At the same time, the fracture mechanism and microhardness were also analyzed in detail. It is advantaged to synthesize high quality diamond in a low methane concentration and suitable substrate temperature.更多还原