优质金刚石合成的一般规律及分析

从晶体生长的一般规律出发,论述了碳原子的活化速度、堆积速度、熔蚀速度以及晶体生长速度与优质金刚石生长的关系,阐述了优质金刚石的合成方法,并提出了具体操作建议.     

用温度梯度法生长优质Ⅱa型金刚石大单晶

利用温度梯度法在国产六面顶压机上合成优质Ⅱa型宝石级金刚石。除氮剂Ti（Cu）的加入使合成金刚石的温度区间变窄且晶体生长更易俘获金属包裹体，通过采用稳定的组装、降低生长速度而获得了优质Ⅱa型金刚石大单晶。     

不同类型炭源材料与金刚石晶体的生长

研究炭源材料与金刚石晶体生长的关系问题,对炭源材料和金刚石合成技术的发展,有重要的实际价值.叙述了炭源材料的性能与金刚石晶体生长的关系.讨论了不同炭源材料转变金刚石的行径与影响转变效果的因素.在对炭源材料性能进行多种测试与分析的基础上,指出了合成金刚石炭源的优选原则及其重要性和必要性.     

石墨材料对人造金刚石晶体生长和质量的影响

石墨和金刚石是碳的同素异形体。石墨是金刚石晶体生长的主要原料。因此,开展对石墨材料与人造金刚石晶体生长关系的研究具有十分重要的意义。实践表明,在有或无熔媒参与下,都能由石墨获得金刚石,只是所使用的压力和温度不同而已。本文着重对一些具有代表性的石墨材料,例如,SM—1、SD—1、碳化硅分解石墨、天然石墨、上海光谱纯石墨和碳电极,定向石墨等进行了分析和研究。研究结果表明,石墨材料的纯度、石墨化程度、石墨的晶粒大小和择优取向等与金刚石晶体生长及其质量之间的关系是十分密切的,提出了有利于人造金刚石增大尺寸、提高强度的石墨材料的看法。此外本文就外界条件对石墨材料转变为金刚石的影响也做了必要的阐述。     

金刚石生长的驱动力

籽晶方法生长金刚石采用温度梯度技术,金刚石晶体生长驱动力来源于腔体内构造的温度梯度。工业上采用自发成核生长金刚石技术,金刚石生长的驱动力来源于金刚石晶体与石墨温度差。     

特殊类含硼金刚石合成的实验研究

介绍了特殊类型含硼金刚石的合成技术与特性.讨论了掺杂物含硼原料、合成工艺、实验条件对金刚石晶体生长的规律、性能和质量的影响,以及含硼金刚石合成机理和硼在合成中的作用.指出了进一步提高特殊类型含硼金刚石质量的方法与途径.     

Ⅱa型宝石级金刚石大单晶研究最新进展

用合金触媒利用温度梯度法合成优质Ⅱ a型宝石级金刚石.研究发现,在约5.4GPa和约1300℃的条件下,除氮剂的加入使合成金刚石的温度区间变窄及金刚石晶体生长过程中更易俘获包裹体而出现熔坑,从而影响晶体的生长速度.实验解决了组装的稳定性问题;并通过调整组装,在除氮剂合适的掺入量下,使合成优质金刚石的最大生长速度达到2.16mg/h.结果实验获得了4.3mm的优质Ⅱa型金刚石大单晶.红外测试分析表明该金刚石含氮量小于10-7.     

麝香体系结晶分离研究

研究了根据酮麝香、1,3-二甲基-2,4-二硝基-5-叔丁基苯晶体生长速度的不同,从对二者均达到饱和的溶液中分离得到1,3-二甲基-2,4-二硝基-5-叔丁基苯晶体的过程,计算了晶体生长速度并进行了实验验证。     

静压法合成人造金刚石晶体生长机理研究进展

文章综述了静压法合成人造金刚石晶体生长机理,但现有理论模型都存在不足,不能圆满解释合成中出现的各种现象.通过综述提出对金刚石晶体生长机理研究的必要性,并对其作出了展望.     

空间低温氧化物熔体晶体生长的数字模拟研究

地面上 ,由于受浮力对流、分层和沉淀等因素的影响 ,难以阐明晶体生产和凝固现象的本质 ,从而无法获得组份均匀、结构完整和性能优良的材料 ,因此自七十年代以来 ,已进行了大量的空间晶体生长实验 ,但由于对空间环境在晶体生长过程中的流体效应参数缺乏了解 ,实验结果往往与设想的不一致。数字模拟方法可以模拟实际晶体生产过程 ,了解晶体生长参数的变化对晶体生长的影响 ,本文利用数字模拟的方法 ,对本实验室建立的空间三维实时观察装置中 ,低温生产NaNO3熔体晶体中的流体效应及温场进行了数字模拟研究 ,结果表明 ,在地面生长 ,熔体内部存在复杂的双涡流动模式 ,重力对熔体中的温场和速度场的分布产生强烈的作用 ,而在空间 ,当微重力水平达到一定程度时 ,可以使熔体中的流动模式简单化 ,从而降低流动效应对传热、传质造成的不稳定性和不均匀性 ,有利于提高晶体生长的质量。同时通过对流场中的温度分布分析表明 ,降低重力可以明显改变晶体生长固液界面附近的温度梯度 ,并使温场 ,速度场分布朝着稳态生长的方向发展     

Epitaxial growth on nickel-plated diamond seeds at high pressure and high temperature

Epitaxial growth on nickel-plated diamond seeds at high pressure and high temperature (HPHT) was observed with graphite as carbon source. The thickness of the electroplating nickel film which acts as a catalyst/solvent ranges from 54.6 μm to 255.6 μm. The relationship between the Ni film thickness and diamond growth rate is investigated. When the nickel film thickness is from 90 μm to 129 μm, diamond crystals can nearly grow up to three times as large as the original seeds at ∼ 5.8 GPa and ∼ 1460 °C within 14 min. The mechanism of the crystal growth with nickel-plated diamond seeds under HPHT is discussed. The results and techniques might be useful for high quality saw-grade diamonds production and large diamond single crystal growth.     

Synthesis of large single crystal diamond using combustion-flame method

A combustion flame method is used to synthesize large single crystal diamond in ambient atmosphere. The basic of this technique was originally described by Hirose and Kondo in 1988 [Hirose H, Komaki K. Eur Pat Appl 1988:EP324538]. The advantage of this method is the high growth rate of diamond films, which is about 60 μm/h [Alers P, Hanni W, Hintermann HE. A comparative study of laminar and turbulent oxygen-acetylene flames for diamond deposition. Diam Relat Mat 1992;2:393-6]. The diamond can grow on itself to achieve large single-crystal. Negative substrate-bias effects on diamond growth have been investigated. Diamonds films were characterized by scanning electron microscopy, Raman spectroscopy, and atomic force microscopy in tapping mode. For given conditions, diamond coatings with highly oriented {1 0 0} crystal facets were produced. Large singles crystals diamonds were obtained. The sizes of these crystals vary between 80 and 90 μm. These results are discussed with respect to the competing events occurring during the heteroepitaxial growth of diamond.     

High pressure–high temperature growth of diamond crystals using split sphere apparatus

An overview of the application of crystal growth fundamentals in the high pressure–high temperature production of diamond by solvent/catalyst technique is presented. The process, also called temperature gradient process, makes use of a molten catalyst to dissolve carbon from a source (graphite or diamond powder) and transport the dissolved carbon to a growth site where they precipitate on a diamond seed. The pressure and temperature requirements for the process are generally around 5.0–6.5 GPa and 1300–1700 °C, depending on the chemistry of the solvent used and the desired crystal geometry. In spite of major progress in the science and technology of diamond growth, large scale commercial production of diamonds single crystals for jewelry or electronic applications has not been feasible until recently. This has been mainly due to the substantial cost associated with the presses needed, and the difficulties in controlling the growth parameters and catalyst chemistry. The recent developments in the commercial production of diamond single crystals utilizing the Split Sphere pressurization apparatus are discussed.     

室外换热器迎面风速对空气源热泵结霜特性的影响

对不同迎面风速条件下空气源热泵系统室外换热器表面霜层生长特性进行了实验研究,测量了翅片表面动态霜层厚度、换热器结霜量,显微观察了霜晶生长过程。实验结果表明,迎面风速的降低使得空气源热泵机组室外换热器表面霜层厚度加速增长,结霜周期随迎面风速的下降呈近乎线性地减小,而且相对湿度越低,结霜周期下降的速度越快;因此,减小室外换热器迎面风速将恶化空气源热泵机组结霜/除霜周期中的平均性能。对霜晶形态的显微观察发现,低迎面风速工况下霜层厚度增长速度加快的原因是由于空气源热泵蒸发器壁面温度降低造成的霜晶形态的改变,翅片表面柱状冰晶始终在高度方向快速生长,这种现象与低环境温度工况下翅片表面霜晶生长形态类似。换热器总结霜量随迎面风速的减小而下降,造成霜层平均密度降低。     

The displacement disorder of atoms in diamond crystals revealed by X-ray imaging plate detector

Cylindrical Imaging Plate Area Detector of Rigaku (IPD) was used to register the X-ray diffraction patterns from diamond crystals grown by Chemical Vapor Deposition (CVD) process. The analysis revealed a deviation from cubic diamond lattice symmetry. X-ray diffraction patterns have been taken by oscillation and stationary crystal methods. Due to high resolution, sensitivity and speed, the IPD detector, allows registration of scattering in the vicinity of Bragg reflections such as broadening, splitting, and satellite reflections. These details were recognized via comparison with the diffraction pattern from a nearly perfect natural diamond crystal and a single crystal of silicon, which were used as diffraction standards. We report data on highly oriented diamond film (HOD) on (001) Si. Powder diffraction patterns show a split of the 111 diffraction line. The line at 2.056 Å corresponds to cubic diamond, and the other line at 2.036 Å is assigned to a disordered polytype. Two superstructure spots were located at 4.076 Å and 4.092 Å. Creation of this polytype during growth annihilates desired heteroepitaxy. The issues of lattice disorder, specifically for diamond crystals, are discussed in the framework of kinematical theory of X-ray diffraction.     

水溶液中硫酸钾晶体生长动力学

The single crystal growth rates of potassium sulfate in pure aqueous solution under different conditions were determined by photomicrography in a flow system for crystal growth. The effects of themain controlling factors, such as supersaturation, crystal size, solution velocity and crystal growth temperature, on crystal growth rates of potassium sulfate were discussed in detail by using non-linear regression from the experimental data, and several empirical relationships were given. The results showed that the growth rates of crystals increased with supersaturation, crystal size, solution velocity and temperature. Moreover supersaturation was the most important controlling factor influencing growth rates of crystals, crystal size and solution velocity were the secondary and temperature was the least.Furthermore, It was found that the growth rate of crystals along the [100] crystallographic axis was higher than that along the [001] in the same condition. The effect of every factor on crystal growth rates along the [100] crystallographic axis was stronger than that along the [001].     

Substrate crystal recovery for homoepitaxial diamond synthesis

Homoepitaxial chemical vapor deposition (CVD) of diamond requires high quality substrate crystals. This paper describes the process of diamond substrate crystal recovery so that the original substrate can be reused for multiple synthesis processes. A three-stage treatment is applied after homoepitaxial CVD growth. First the original substrate is separated by laser cutting, then the cut surface is mechanically polished, and finally polycrystalline material at the edges of the recovered seed plate is laser trimmed. This recovery process yields reusable diamond substrates that do not differ appreciably from their original state in terms of stresses and impurity concentrations. While the recovery process was demonstrated using HPHT seed substrates the process can also be applied to the as-grown CVD diamond plates. Infrared absorption spectral analysis, surface profilometry, birefringence imaging and Raman spectroscopy are performed after each processing step to monitor crystal quality. The nitrogen concentration in the substrate crystal remains constant throughout CVD and recovery processes. When using HPHT type Ib substrates the detected nitrogen concentration is 110–180 ppm. The nitrogen is mainly incorporated in form of C center defects and no transformation to other forms of defect centers occurs during the CVD process. Birefringence imaging showed a low level of internal stress within the HPHT crystals. No change is observed during CVD growth and recovery processes. It is shown that the polycrystalline rim removal is essential for repeatable CVD deposition on the same seed substrate. Substrate crystal recovery allows growth of up to 20 crystals from one original seed.     

Growth strategy for controlling dislocation densities and crystal morphologies of single crystal diamond by using pyramidal-shape substrates

The growth of millimetre-thick diamond single crystals by plasma assisted CVD is complicated by the formation of unepitaxial defects, particularly at the edges of the crystal. These defects tend to encroach on the top surface hence limiting the maximum thickness to typically a few hundreds of micrometres. Dislocations are another type of defects that are also particularly formed at the edges of the crystal. They thread through the diamond film, strongly affecting its characteristics. The growth on pyramidal-shape substrates having different angles and orientations was carried out in an attempt to solve those issues. It was found that the pyramidal-shape tends to disappear after a certain thickness is grown. The inclined faces of the pyramid not only helped in preserving the crystal morphology over a large thickness but also deviated dislocations towards the edges of the crystal, hence limiting their occurrence at the surface. Using this strategy, millimetre-thick diamond single crystals presenting a reduced dislocation density were successfully grown.     

Diamond deposition on Ni3Ge single- and polycrystalline substrates

In order to find new materials for heteroepitaxial diamond growth Ni₃Ge single- and polycrystalline wafers were produced and used as substrates for diamond deposition in a microwave plasma system.The cubic phase Ni₃Ge substrate revealed to be an interesting and potential material for heteroepitaxial diamond chemical vapour deposition due to its: (1) lattice parameter matching within <1% the lattice parameter of diamond; and (2) coexistence with carbon up to its (congruent) melting point. Thus centimetre-size crystal boules were pulled from the melt using the Czochralski crystal growth method. These boules were sectioned into wafers and polished.Low-pressure diamond was grown on the Ni₃Ge wafers under various deposition conditions. The orientation of isolated diamond single crystals grown on the Ni₃Ge substrate surface show that heteroepitaxial nucleation occurred. Diamond nucleation was low, as seeding methods to enhance nucleation were not used.     

Crystal forms of natural microdiamonds

Geometrical crystallographic features of rare diamond micro-crystals (0.3–0.5 mm in diameter) from kimberlites having different complex flat and smooth faces are described. Such polyhedrons of microdiamonds are typically composed of two or more combinations of seven different crystal forms belonging to hexoctahedral symmetry class: octahedron, cube, rhombic dodecahedron, trisoctahedron, trapezohedron, tetrahexahedron and hexoctahedron. Many of them are not yet known for macro-crystals of this mineral. All these forms are found as small faces on the octahedral crystals. Both flat and smooth faces of octahedron and cube on such crystals have their own growth sectors. Flat faces of rhombic dodecahedron, different trisoctahedrons, trapezohedrons and hexoctahedrons occur as so-called faces of degeneration of octahedral growth planes. Nature of tetrahexahedron flat faces is not clear. An investigation of the complex diamond polyhedrons should give a new idea on crystal morphology of diamond, make more precise its symmetry and be important for the explanation of the nature of diamond on the whole.