Simulations of Temperature Field in HFCVD Diamond Films over Large Area

A three-dimensional model was developed to investigate the influence of various hot filaments parameters on substrate temperature fields that significantly affect the nucleation and growth of diamond films over large area by hot-filament chemical vapordeposition (HFCVD). Numerical simulated results indicated that substrate temperature varies as a function of hot filamentsnumber, radius, temperature, emissivity, the distance between filaments, and the distance between substrate and filamentsarrangement plane. When these filaments parameters were maintained at the optimal values, the homogeneous substrate temperature region of 76 mm×76 mm with the temperature fluctuation no more than 5% could be obtained by a 80 mm×80 mmhot filaments arrangement plane. Furthermore, the homogeneous region could be enlarged to 100 mm×100 mm under thecondition of supplementary hot filaments with appropriate parameters. All of these calculations provided the basis for speciallyoptimizing the hot filaments parameters to dep     

Effect of Low Neutron Doses on the Properties of Synthetic Diamond Crystals

The effect of neutron irradiation on the properties of diamond crystals prepared in the Mn–Ni–C system (5.5 GPa, 1620–1670 K, 120–300 s) was studied. The results indicate that irradiation increases the strength of the crystals and reduces the concentration of paramagnetic centers. The observed changes are interpreted in terms of interaction between intrinsic defects and impurities.     

大尺寸6H-SiC半导体单晶材料的生长

报道了生长SiC单晶的PVT法生长工艺,研究了晶体生长温度、温度梯度、生长室压力、杂质等因素对晶体生长和晶体质量的影响,确定出合理的工艺条件,生长出φ45mmSiC单晶.X射线衍射表明,生长的单晶为6H多型结构,通过腐蚀法得到晶体中微管道密度约为10³cm^-2,位错密度约为10⁴～10⁵cm^-2.测试了SiC单晶的半导体特性,结果表明:晶体为n型,电阻率约300Ω·cm,迁移率90cm2V^-1S^-1,载流子浓度在10¹⁴cm^-3量级.     

SiC在异质衬底生长金刚石膜的作用分析

利用扫描电子显微镜 (SEM)、Raman光谱分析了Si衬底上金刚石膜核化和生长的过程 ,并着重分析了核化过程产生的SiC的性能。利用划痕法测量了在WC衬底上沉积SiC和未沉积SiC时生长金刚石膜的粘附力 ,同时还分析了WC衬底上有和没有SiC沉积层时表面附近金刚石膜的内应力。结果表明 ,SiC层大大地增强了含碳粒子的聚集和金刚石膜与衬底之间的粘附性 ,降低了金刚石膜与衬底之间的内应力     

Computational Modeling of Mineral Unmixing and Growth

A new finite element based simulation technique for mineral growth governed by the classical Cahn–Hilliard equation is presented. The particular format of the underlying Flory–Huggins free energy for non-ideal mixtures is characterized through a double-well potential. It allows for uphill diffusion driven by gradients in the chemical potential and thus provides the appropriate framework to simulate phase separation typically encountered in mineral unmixing and growth. For the finite element discretization, the governing fourth order diffusion equation is reformulated in terms of a system of two coupled second order equations. For the temporal discretization, a heuristic adaptive time stepping scheme is applied in order to simulate not only the early stages of phase separation but also the long term behavior of ageing and grain fusion. The basic features of the Cahn–Hilliard equation are elaborated by means of selected geologically relevant examples. In particular, isotropic and anisotropic mineral growth and symplectite formation are studied and the long term response in the sense of Ostwald ripening is illustrated.     

镍衬底上定向金刚石膜的成核与生长

提出了一种包括晶粒接种、高温退火、成核、生长四过程的薄膜沉积新方法 ,用射频等离子体增强热丝化学气相沉积系统 ,在Ni衬底上制备了定向金刚石膜。通过对成核和生长两过程工艺条件的研究 ,掌握了提高成核密度和金刚石定向生长规律。实验还表明 ,膜与Ni衬底之间未见Ni C H界面层的形成     

Numerical simulation of residual stresses in diamond coating on Ti-6Al-4V substrate

In this paper, we present numerical simulations of the residual stresses developed between diamond coatings and Ti-6Al-4V substrates when using chemical vapour deposition technique. The large difference in thermal expansion coefficients of diamond and titanium alloys results in high residual stresses in the diamond film. This could lead to interfacial cracking and material failure. The finite element method was used to simulate the cooling process of diamond films at various thicknesses and deposited at temperatures ranging from 600 °C to 900 °C. The influence of different parameters such as temperature, film thickness, material characteristics, geometry and edge effects are investigated for different case geometries. The film debonding and cracking is discussed and numerical results are compared with existing experimental and numerical results. Finally, some propositions are made to enhance the experimental process in order to reduce the residual stress intensities and the possible material degradation.     

金刚石薄膜形核与长大动力学的研究

采用热丝ＣＶＤ法在半底上合成了金刚石薄膜，研究了工艺参数对金刚石形核与长大的影响规律。形核密度随甲烷深度的增加和抛光膏粒度的减小而增加，随衬底工上升而增加至极值后下降，衬底温度过低，形核密度增加但形核为球状。     

采用正交法研究金刚石偏压形核

在微波等离子体化学气相沉积装置中 ,采用正交试验法研究金刚石在镜面抛光的Si( 1 0 0 )面上的偏压形核过程中 ,形核时间、偏压电压、气压及甲烷浓度对形核密度的影响 ,研究结果表明 :形核密度随形核时间的增加而增加 ,适中的偏压电压和沉积气压有利于金刚石的形核 ,而甲烷浓度的影响很小。正交试验所得的最佳形核条件为偏压 -1 5 0V ;时间 1 2min ;气压 4kPa;CH4 比率 5 % ,在该条件下金刚石的形核密度达到 1 0 1 0 个 cm2 。     

脱钴对聚晶金刚石热稳定性能的影响

本文介绍了一种在碱性电解液中电解聚晶金刚石内金属钴的方法。通过BSE观察到聚晶金刚石内金属钴的堆积方式有两种:大部分钴沿着金刚石颗粒边界延伸并包围金刚石颗粒,少量的钴团聚在一起,呈岛状堆积。EDS确定脱钴区域残余的钴含量为2.75%,而未脱钴区域的钴含量为13.45%,即79.5%钴在电解过程中溶解,且深度为170μm。模拟聚晶金刚石复合片在钻头胎体合金上面的焊接温度,对脱钴及未脱钴聚晶金刚石复合片进行热处理,用光学体式显微镜观察其表面的裂纹,采用XRD固定ψ法检测脱钴聚晶金刚石的残余热应力仅为241.46kg·mm-2,而未脱钴试样残余热应力值为2094.79kg·mm-2,即脱钴处理能有效降低聚晶金刚石复合片在下井使用前的热应力,使其残余热应力降低至原来的1/10。     

温度梯度法合成金刚石大单晶的研究进展

介绍了金刚石大单晶的温度梯度法合成技术,详细综述了影响金刚石晶体形貌、晶体品质以及生长速度等相关因素的最新进展,简要叙述了掺杂对金刚石晶体晶形、性能的影响,最后指出了温度梯度法合成金刚石大单晶的发展方向。     

大面积场发射显示器支撑方案的计算机模拟

场发射显示器(FED)的支撑结构用来抵抗器件外部大气压对阴阳极板造成的形变影响.预先确定和优化支撑系统方案,对于降低大面积FED器件制造成本是十分重要的.本文通过有限元分析方法,对40英寸,长宽比43,采用墙式支撑条和2mm厚阴阳板的FED器件的支撑方案进行了模拟计算.通过给出170mm支撑墙在不同摆放位置情况下的极板应力以及形变分布,最后确定了二种可实际用于器件的支撑方案.     

基片位置对MWPCVD制备金刚石薄膜的影响

在石英钟罩式微波等离子体化学气相沉积实验装置中研究了基片位置对金刚石薄膜沉积质量的影响。扫描电子显微镜显微形貌观察和激光喇曼谱分析表明 ,对微波等离子体化学气相沉积制备金刚石薄膜而言 ,基片位置处于近等离子体球下游区域将有利于改善金刚石薄膜沉积质量。     

氧气对MWPCVD制备金刚石膜的影响

在水冷反应室式微波等离子体化学气相沉积装置中以混合的CH4/H2/O2为反应气体,研究了O2浓度对制备金刚石膜的影响.实验发现,很低浓度的O2会显著促进金刚石的沉积,并稍稍抑制非晶C的沉积,因而沉积膜中非晶C的含量急剧下降;较高浓度的O2会同时抑制金刚石和非晶C的沉积,但由于抑制金刚石的作用更强烈,沉积膜中非晶C的含量反而有所升高.另外,O2的存在,有利于沉积颗粒较小的金刚石膜.     

金刚石膜上电子束蒸镀Ti/Ni/Au多层膜

经过相图分析提出了CVD金刚石膜上蒸镀Ti/Ni/Au的体系。采用该体系、富氧预处理工艺和电子束真空镀膜方法 ,金刚石膜和多层金属膜之间获得了良好结合强度。研究发现 :富氧预处理对多金属膜和金刚石膜之间的结合强度影响显著。进一步利用俄歇电子能谱 (AES)证实 :C向Ti中扩散层有 15 0nm之多 ,并出现了厚度约为 90nm稳定含量层 ,说明有确定化学比的反应产物生成 ;富氧处理在金刚石膜与Ti金属层之间增加了氧的含量 ,为形成TiO和TiC提供了合适的条件。     

Comparison of Cellular Automaton and Phase Field Models to Simulate Dendrite Growth in Hexagonal Crystals

A cellular automaton (CA)-finite element (FE) model and a phase field (PF)-FE model were used to simulate equiaxed dendritic growth during the solidification of hexagonal metals.In the CA-FE model,the conservation equations of mass and energy were solved in order to calculate the temperature field,solute concentration,and the dendritic growth morphology.CA-FE simulation results showed reasonable agreement with the previously reported experimental data on secondary dendrite arm spacing (SDAS) vs cooling rate.In the PF model,a PF variable was used to distinguish solid and liquid phases similar to the conventional PF models for solidification of pure materials.Another PF variable was considered to determine the evolution of solute concentration.Validation of both models was performed by comparing the simulation results with the analytical model developed by Lipton-Glicksman-Kurz (LGK),showing quantitatively good agreement in the tip growth velocity at a given melt undercooling.Application to magnesium alloy AZ91 (approximated with the binary Mg-8.9 wt% Al) illustrates the difficulty of modeling dendrite growth in hexagonal systems using CA-FE regarding mesh-induced anisotropy and a better performance of PF-FE in modeling multiple arbitrarily-oriented dendrites growth.     

Effect of Diamond Additions on Wettability and Distribution of SnAgCu Composite Solder

Diamond/SnAgCu composite solder bumps were prepared on Cu pad by mechanically incorporating diamond particles into Sn3.0Ag0.5Cu(SAC) solder powders,mixing with flux and reflowing at 260 ℃ for 60 s.The spreading areas of composite solder were calculated and the distributions of copper-coated diamonds were characterized.When diamond additions were below 3 wt%,the spreading area decreased with diamond additions,and the diamonds distributed mainly at the interface between solder and Cu pad;however,when additions were beyond 4 wt%,the discharge of diamond particle occurred,and the spreading area increased due to the reduction of surface energy.     

触媒合金渗硼对合成人造金刚石性能的影响

本文研究了触媒合金渗硼对合成人造金刚石性能的影响。结果表明，采用渗硼触媒合成金刚石，可提高金刚石的抗压强度、耐热性和优质粗晶粒百分比，但却使金刚石的单次合成产量降低。     

金属元素Co、Fe、Cu、Ti对孕镶金刚石基底CVD金刚石涂层膜基界面结合强度的影响

采用基于密度泛函理论的第一性原理理论法, 研究了金属元素Co、Fe、Cu、Ti对孕镶金刚石基底化学气相沉积金刚石涂层膜基界面结合强度的影响及其作用机理。界面结合能、电荷密度和化学键重叠布居数的计算结果表明:Co、Fe元素具有较强的电荷转移能力, Cu、Ti元素在沉积过程易生成金属碳化物过渡结构, 且Cu、Ti元素掺杂模型膜基界面间C原子成键较强, 成键也更接近理想金刚石C-C键, 这些原因导致Cu、Ti元素掺杂模型的膜基界面结合强度较强, Co、Fe元素掺杂模型的膜基界面结合强度较弱。据此, 可适当调整金属元素比例, 优化工艺参数, 从而改善孕镶金刚石钻头上沉积CVD金刚石涂层的性能。     

热丝CVD金刚石薄膜制备及碳纳米管形核作用的研究

利用热丝化学气相沉积法 (HF CVD)进行了金刚石薄膜制备和碳纳米管形核作用的研究。获得了制备金刚石薄膜的优化工艺参数。利用碳纳米管作为形核前驱获得了高质量的金刚石薄膜 ,其沉积速率可达 2 5 μm/h ,晶粒生长完美 ,而且没有出现聚晶现象。研究了碳纳米管涂料质量对薄膜沉积特性的影响 ,并对其机理进行了初步探讨