A Study of Diamond Growth Instability at High Temperature-High Pressure

In this paper, crystal growth instability of diamond was studied in a Fe-Ni-C system at high temperature-high pressure (HPHT). As any other crystal grown from solution, the flat or smooth growth interface of the diamond crystal is highly sensitive to growth conditions. The growth front interface should be of great importance to understand the diamond growth process. The presence of cellular growth interface by transmission electron microscopy indicated that there existed a narrow constitutional supercooling zone in front of the growth interface. Several parallel layers with cellular interface by TEM directly suggested that the diamond grows from the solution of carbon in the molten catalyst layer by layer, which is in accordance with the result obtained by scanning electron microscopy in this paper. Impurities are trapped by rapidly advancing growth layers during the diamond growth and they impose a great effect on the growth front stability. As the growth front interface approaches the impurity particle to a distance of about 10-5~10-7 cm, appreciable molecular forces begin to operate between them, and the impurity particle is trapped as the growth rate reaches a critical value. As a result, the driving force for crystallization under the impurity particles becomes smaller, the front buckles under the particle. An impurity naturally reduces the growth rate to a different extent.

Relationship between the spatial position of the seed and growth mode for single-crystal diamond grown with an enclosed-type holder

The relationship between the spatial position of the diamond seed and growth mode is investigated with an enclosedtype holder for single-crystal diamond growth using the microwave plasma chemical vapor deposition epitaxial method.The results demonstrate that there are three main regions by varying the spatial position of the seed.Due to the plasma concentration occurring at the seed edge,a larger depth is beneficial to transfer the plasma to the holder surface and suppress the polycrystalline diamond rim around the seed edge.However,the plasma density at the edge decreases drastically when the depth is too large,resulting in the growth of a vicinal grain plane and the reduction of surface area.By adopting an appropriate spatial location,the size of single-crystal diamond can be increased from 7 mm×7 mm×0.35 mm to8.6 mm×8.6 mm×2.8 mm without the polycrystalline diamond rim.

Non-equilibrium phase diagram of stationary states for low-pressure diamond growth

Now, it is well known that stable diamond growth and etching of graphite can berealized simultaneously under low pressures, but it is difficult to explain by classicalthermodynamics.Based on the non-equilibrium thermodynamic coupling theorem. low-pressure diamondgrowth can be explained clearly as follows:The change of Gibbs free energy (G) is the criterion of reaction direction at constant tem-perature and pressure. Therefore,

A projective ternary phase diagram of stationary non-equilibrium states for low-pressure diamond growth

SINCE 1980,activated low-pressure diamond growth by chemical vapor deposition(CVD)pro-cess has been one of the worldwide interesting projects.However,in the last decades severalthermodynamic explanations were unsatisfactory.Bachmann et al.summarized a lot ofpublished experimental data into an empirical ternary carbon-hydrogen-oxygen(C-H-O)

FEM simulations and experimental studies of the temperature field in a large diamond crystal growth cell

We investigate the temperature field variation in the growth region of a diamond crystal in a sealed cell during the whole process of crystal growth by using the temperature gradient method （TGM） at high pressure and high temperature （HPHT）. We employ both the finite element method （FEM） and in situ experiments. Simulation results show that the temperature in the center area of the growth cell continues to decrease during the process of large diamond crystal growth. These results are in good agreement with our experimental data, which demonstrates that the finite element model can successfully predict the temperature field variations in the growth cell. The FEM simulation will be useful to grow larger high-quality diamond crystal by using the TGM. Furthermore, this method will be helpful in designing better cells and improving the growth process of gem-quality diamond crystal.

Synthesis of high grade octahedron diamond through epitaxial growth

The work was based on the relationship between the crystal structure and parameters of diamonds in the synthetic process, in which Ni Mn C powder catalyst was used. At first, the diamond crystals nucleated in a cubic octahedron morphology through controlling such synthetic parameters as temperature and pressure in a parameter region where cubic octahedron ctystals can be obtained. Then the diamond nuclei grew epitaxially into crystals with a perfect octahedron morphology through increasing the synthesis temperature and decreasing the synthesis pressure in a parameter region where octahedron crystals can be obtained.

The Effect of Pressure on the Dissociation of H_2/CH_4Gas Mixture during Diamond Films Growth via Chemical Vapor Deposition

Monte Carlo simulations are adopted to study the electron motion in the mixture of H2 and CH4 during diamond synthesis via Glow Plasma-assisted Chemical Vapor Deposition (GPCVD). The non-uniform electric field is used and the avalanche of electrons is taken into account in this simulation. The average energy distribution of electrons and the space distribution of effective species such as CH3, CH+3, CH+ and H at various gas pressures are given in this paper, and optimum experimental conditions are inferred from these results.

Effects of submicron diamonds on the growth of copper in Cu-diamond co-deposition

Submicron diamonds were co-deposited on aluminum substrates with copper from the acid copper sulfate electrolyte by electro- lyte-suspension co-deposition. After submicron diamonds were added to the electrolyte, the shape of copper grains transformed from oval or round to polyhedron, the growth mode of copper grains transformed from columnar growth to gradual change in size, and the preferred ori- entation of copper grains transformed from （220） to （200）. Analyzing the variation of cathodic overpotential, it was found that the cathodic overpotential tended to remain tmchanged when copper plane （220） grew in the process of electrodepositing pure copper, while it tended to decrease with time when copper plane （200） grew in the process of co-deposition. It was inferred that copper plane （200） was propitious to the deposition of submicron diamonds.

Dislocation Mechanism of Diamond Crystal Growth from Fe-Ni-C System at High Temperature-High Pressure

Some dislocations, which are generated in the diamond single crystal during the diamond crystal growth from Fe-Ni-C system, may affect diamond crystal growth mode at high temperature-high pressure (HPHT). The concentric dislocation loops were successfully examined by Moire images. The surface morphologies of growing and as-grown diamond single crystals were observed by scanning electron microscopy (SEM). The concentric dislocation loops formation process and their effect on the diamond crystal growth mode were analyzed. It should be noted that whatever the nature of the dislocation is, should the Burgers vector of dislocation has a component at the direction normal to the growth interface, the dislocation will make the face parallel to the growth interface grow into spiral face. The presence of consecutive spiral steps on the diamond crystal surface also provides a direct evidence of the dislocation mechanism of diamond crystal growth.

Orientation variation along growth direction of millimeter free-standing CVD diamond thinned by mechanical grinding

A free-standing diamond film with millimeter thickness prepared by DC arc plasma jet was thinned successively by mechanical grinding. The orientation and quality of the diamond films with different thicknesses were characterized by X-ray diffraction and Raman spectroscopy, respectively. The results show a random grain-orientatinn distribution during the initial growth stage. As the film thickness increases, the preferred orientation of the diamond film changes from （111） to （220）, due to the competitive growth mechanism. Twinning generated during the nucleation stage appears to stabilize the preferential growth along the 〈110〉 direction. The interplanar spacing of the （220） plane is enlarged as the film thickness increases, which is caused by the increase of non-diamond-phase carbon and impurities under the cyclic gas. In addition, the quality of the diamond film is barely degraded during the growth process. Furthermore, the peak shift demonstrates a significant inhomogeneity of stress along the film growth direction, which results from competitive growth.

Multiple enlarged growth of single crystal diamond by MPCVD with PCD-rimless top surface

We report the simultaneous enlarged growth of seven single crystal diamond(SCD) plates free from polycrystalline diamond(PCD) rim by using a microwave plasma chemical vapor deposition(MPCVD) system. Optical microscope and atomic force microscope(AFM) show the typical step-bunching SCD morphology at the center, edge, and corner of the samples. The most aggressively expanding sample shows a top surface area three times of that of the substrate. The effective surface expanding is attributed to the utilization of the diamond substrates with(001) side surfaces, the spacial isolation of them to allow the sample surface expanding, and the adoption of the reported pocket holder. Nearly constant temperature of the diamond surfaces is maintained during growth by only decreasing the sample height, and thus all the other growth parameters can be kept unchanged to achieve high quality SCDs. The SCDs have little stress as shown by the Raman spectra. The full width at half maximum(FWHM) data of both the Raman characteristic peak and(004) x-ray rocking curve of the samples are at the same level as those of the standard CVD SCD from Element Six Ltd. The nonuniformity of the sample thickness or growth rate is observed, and photoluminescence spectra show that the nitrogen impurity increases with increasing growth rate. It is found that the reduction of the methane ratio in the sources gas flow from 5% to 3% leads to decrease of the vertical growth rate and increase of the lateral growth rate. This is beneficial to expand the top surface and improve the thickness uniformity of the samples. At last, the convenience of the growth method transferring to massive production has also been demonstrated by the successful simultaneous enlarged growth of 14 SCD samples.

中国3个商业性钻石产地天然钻石的DiamondView^(TM)图像及其意义

对采自我国3个商业性产地山东蒙阴、辽宁瓦房店、湖南常德地区的236片/颗天然钻石样品进行了系统的DiamondViewTM(DV)荧光图像分析,结合CL照相和FTIR的定量计算,探讨了钻石样品DV图像发光结构模式和荧光颜色方面的差异性及其原因。结果表明,3个产地钻石的DV图像和CL图像显示的钻石生长结构基本一致;钻石的发光结构模式与钻石内部氮、氢元素的种类和浓度分布趋势没有明显的一致性,DV图像模式并不完全受钻石类型控制,但DV图像的色调与钻石存在的杂质元素及晶体缺陷有关。钻石的DV图像特征受钻石的生长环境、结晶条件、后期熔蚀、辐照损伤等因素综合制约。从统计学的角度看,3个产地钻石的DV发光模式和荧光颜色有一定的差异,这种差异可以作为区分不同产地来源的钻石的宏观的统计学特征。DiamondViewTM技术在揭示天然钻石生长结构方面和CL发光照相技术效果近似,但更加便利。

REACTION PROBABILITIES OF ENERGETIC SPECIES AT GROWING DIAMOND FILM SURFACES BY MOLECULAR DYNAMICS SIMULATION

A Molecular Dynamics (MD) simulation with Tersoff empirical many-bodypotential has been employed to investigate the growth processes of diamond film with energeticspecies deposition. In the present study, we have studied the reaction probabilities of energeticspecies with energies of 0.1 e V to 10eV at the substrate temperature of 1100K. In the cases of thediamond growth on the surface with H passivation, the reaction probability of hydrocarbon speciesconsiderably increases when the species energy is higher than 2eV. This means that the diamond filmcan grow in the case of high incident species energy without the process of hydrogen abstraction,which is needed in the case of incident species with low energy. The reaction mechanism of energeticspecies on hydrogen passivated diamond surface is also discussed.

Diamond Particles Deposited among Nickel/Copper Particles in Energy Controlled CH₄/H₂RF Discharge Plasmas

Formation of diamond particles was investigated in an energy-controlled CH4/H2 radio-frequency (RF) discharge plasma. Here, in particular, it was examined how diamond particles grew on a nickel substrate under an influence of Cu vapor that was supplied from a heated Cu wire. Here, the plasma was generated by a hollow-magnetron-type (HMT) RF plasma source at the frequency of 13.56 MHz. Total pressure was kept at 100 mTorr. Diamond particles grew besides Ni and Cu particles. From Raman spectrum the substrate surface was covered with thin graphite film deposited as a background layer. It was shown that diamond could grow in a self-organized manner even when the other atomic gas species such as Ni and Cu were contained in the gas at the same time during the growth process.

以体重增长缓慢为主要临床表现的Shwachman-Diamond综合征2例临床诊治分析

目的探讨Shwachman-Diamond综合征(SDS)的临床特征及其早期诊治。方法总结2例SDS患儿的诊治经过;复习国内外对该病的最新研究进展,总结其主要临床表现及治疗。结果SDS初期临床表现不典型,生长障碍和脂肪泻是部分SDS患儿的首发表现,血清淀粉酶/脂肪酶下降提示胰腺功能不全,临床医生应对这类患儿尽早进行基因学检查明确诊断;伴髓系恶性转化的SDS患者预后较差。结论SDS病变可累及多系统,主要临床表现为生长障碍、骨髓衰竭和胰腺外分泌功能障碍。对于症状不典型者要尽早行基因学检查明确诊断。SDS有向骨髓增生异常综合征/急性髓系白血病转化的风险,需要定期监测骨髓,以提高患者的长期生存。

氢终端金刚石薄膜生长及其表面结构

氢终端金刚石的导电性问题是目前限制其在器件领域应用的关键因素.传统的氢终端金刚石制备工艺由于金刚石中含有杂质元素以及表面的加工损伤的存在,限制了氢终端金刚石的电特性.在金刚石衬底上直接外延一层高纯、表面平整的氢终端金刚石薄膜成为一种可行方案,但该方案仍存在薄膜质量表征困难,表面粗糙度较大等问题.本文采用微波等离子体化学气相沉积(CVD)技术,在含氮CVD金刚石衬底上外延一层亚微米级厚度金刚石薄膜,并研究分析了不同甲烷浓度对金刚石薄膜生长以及导电性能的影响.测试结果显示:金刚石薄膜生长厚度为230—810 nm,且外延层氮浓度含量低于1×10^(16) atom/cm^(3),不同的甲烷浓度生长时,金刚石外延层表面出现了三种生长模式,这主要与金刚石的生长和刻蚀作用相关.经过短时间生长后的金刚石薄膜表面为氢终端(2×1:H)结构,而氧、氮元素在其中的占比极低,这使得生长后的金刚石薄膜具有P型导电特性.霍尔测试结果显示,甲烷浓度为4%条件下生长的氢终端金刚石薄膜导电性最好,其方块电阻为4981Ω/square,空穴迁移率为207 cm^(2)/(V·s),有效地提升了氢终端金刚石电特性,为推进大功率金刚石器件发展应用起到支撑作用.

铱衬底上金刚石外延形核与生长:第一性原理计算

异质外延为金刚石晶圆合成提供了一个有效的实现路径,而Ir衬底上金刚石形核生长技术经过20多年的发展已经有能力制备最大直径为3.5英寸的晶体,开启了金刚石作为终极半导体在电子信息产业应用的大门。然而,表面形核、偏压技术窗口、金刚石外延生长等一系列发生在异质衬底上的问题都需要从生长热力学的角度给予解释。本研究针对化学气相沉积气氛中金刚石如何实现外延形核与生长这一关键问题,利用第一性原理计算从原子尺度对金刚石形核生长过程展开了系列探究。研究结果如下:C原子在Ir衬底表面位点吸附比在体相位点吸附更稳定,表明无偏压条件下金刚石形核只能在衬底表面发生;离子轰击作用下非晶氢化碳层中sp3杂化C原子个数随着离子动能的增加呈现先增大后减小的变化规律,证实了金刚石高密度形核存在一定的离子动能与偏压大小窗口;金刚石沿着Ir衬底外延生长时界面结合能最低(约为–0.58 eV/C),意味着界面结合能是决定外延形核生长的主要热力学因素。本研究阐明了偏压辅助离子轰击促进金刚石单晶外延生长的热力学机制,对于指导金刚石及其他碳基半导体生长具有重要意义。

金刚石半导体及功率肖特基二极管研究进展和挑战

金刚石作为一种超宽禁带半导体,是下一代功率电子器件和光电子器件最有潜力的材料之一。其产业化仍需解决几个关键技术问题:大尺寸单晶外延生长、高质量晶圆制备技术、高效可控的掺杂技术及先进终端结构。首先,介绍了拼接生长以及异质外延获得大尺寸单晶衬底的研究进展。进而,综述了大尺寸单晶金刚石位错、缺陷调控技术及其加工技术的研究进展。最后,从功率器件设计及制备角度总结了金刚石掺杂及终端结构设计面临的挑战并提出了潜在的解决方案。

高精度红外光谱面扫揭示蒙阴多期生长金刚石的氮杂质特征

赋存在古老克拉通岩石圈地幔约150~200 km^([1-2])深处的金刚石被称为“岩石圈型金刚石”。岩石圈型金刚石记录了侵入岩石圈地幔的含碳熔流体活动^([3]),对研究克拉通岩石圈地幔的形成与演化具有重要意义。一些早期成核生长的金刚石在漫长的地幔留存期间往往会受到多期增生事件的影响,从而形成复杂的金刚石生长结构。这些多期生长金刚石的结构特征直接反映了不同期次含碳熔流体的性质,为限制岩石圈地幔交代过程、俯冲物质的输入以及地质时期内地幔条件的变化起到了重要作用^([4]),是我们追溯金刚石生长历史和探究相关重大地质构造事件的基础。在我国,前人对华北克拉通多期生长金刚石的结构特征研究工作大致分为三个发展阶段:一是早期通过阴极发光(CL)/荧光图像(DV)定性分析^([5]);二是CL生长结构分析结合红外光谱点测/线扫定量分析^([6-8]);三是红外光谱面扫分析^([9-10]),从定性到定量,从点到线到面,逐渐建立了对华北克拉通多期生长金刚石结构特征的认识。其中,点测方法在分析金刚石氮杂质相关信息(含量、缺陷类型)时产生的误判极为严重(尤其对于原石)。而线扫方法虽然比点测方法严谨,但受限于测试点的取向和密度,有时也会造成空间信息的丢失。尤其对于本文所研究的多期生长金刚石样品,该方法会导致其氮杂质分布特征分析不准确。随着技术的发展^([11-12]),高精度红外光谱面扫方法已逐渐成为研究金刚石中氮杂质分布特征最可靠的空间分析方法,为金刚石生长结构特征的研究提供了更深入的视角。本研究选取了24颗来自华北克拉通鲁西地区蒙阴金伯利岩胜利I号岩管产出的含包裹体原生金刚石样品,对其进行了切片处理。通过DV-CL的图像分析发现,24个薄片近半数(10/24)为“具有晶核的复杂多期环带生长结构(三/四期)。随后,我们从这些蒙阴多期生长金刚石中挑选了4个具有特征生长结构的薄片样品(SD-297、SD-346、SD-372、SD-398)进行了高精度FTIR Mapping测试,分析了薄片样品的A、B中心氮含量(N_(A)、N_(B))、总氮含量(N_(T))、B中心转化率(ⅠaB%),并进行了详细的填图和分析工作,得到的如下主要认识。(1)4个薄片均为特殊的“混合型金刚石”,其中样品SD-297、SD-372、SD-398为“ⅠaAB+Ⅱa+ⅠaA”类型,样品SD-346则缺少第三期,为“ⅠaAB+Ⅱa”类型。这4个薄片样品的第一、二期特征基本保持一致,第一期为高N_(T)、ⅠaB%的“ⅠaAB”核心,第二期为金刚石中少见的几乎不含氮的Ⅱa生长区。除样品SD-346外,其余三个薄片第三期为低N_(T)、ⅠaB%的ⅠaA生长区。本研究样品给出了有别于前人研究中华北克拉通金刚石的全新混合生长类型,并以夹在高ⅠaB%晶核和低ⅠaB%外层生长期次间的Ⅱa生长区为特征。(2)对于具有第三期生长的3个薄片样品的氮杂质特征比较一致,首先是高度熔蚀的晶核具有较高的N_(T),大多在200~300μg/g,且B中心氮的比例很高,大于70%,指示了更古老的生长年龄;其次是与晶核相接的生长期次为特殊的Ⅱa生长区,几乎不含氮,最外层生长期次则具有远低于晶核的较低的N_(T)(20~40μg/g)和ⅠaB%(2%~4%),指示了较短的地幔留存时间。以Ⅱa生长区为间隔,不同期次间的氮含量和B中心转化率呈现一种“陡变”差异,几乎不存在过渡,指示了三期不同性质的熔流体来源。通过DV-CL结合高精度FTIR Mapping的研究工作,我们认为蒙阴多期生长金刚石的内部结构和氮杂质相关特征指示了鲁西地区古老岩石圈地幔至少经历了三期及以上的含碳熔流体活动。(3)样品SD-346晶形为浑圆状十二面体的溶蚀形态,其第一、二期生长结构和氮缺陷分布特征与其他3颗金刚石保持一致。同时,从FTIR Mapping中还观察到样品SD-297、SD-372和SD-398的第三期生长结构遭受了不同程度的破坏。据此推断样品SD-346并非为两期生长,而是第三期生长结构被流体溶蚀的“假两期”生长。这进一步说明了在进行FTIR Mapping工作时要注意原石的形态及形貌学特征,两者结合的分析能避免金刚石生长分期的误判,并为金刚石的生长结构提供细致的参考,以还原更真实的金刚石生长历史。

激光法制备超细纳米金刚石的相变机理

为了研究激光法制备纳米金刚石的相变机理,采用纳秒脉冲激光冲击微米级石墨悬浮液,并做强酸高温氧化提纯处理,结合X射线衍射、喇曼光谱、高分辨率透射电镜等表征手段以及热力学和动力学分析方法,对实验结果进行了理论分析和实验验证。合成得到分散均匀、尺寸在4nm^12nm的超细纳米金刚石。结果表明,纳秒激光辐照下,石墨是通过固态-气态-液态-固态的形式转变为金刚石结构的;与毫秒脉冲激光相比,高功率密度、短脉宽的纳秒激光为金刚石核的生长提供了大的过冷度,提高了金刚石的形核率和生长速率;但是纳米金刚石的生长温度范围极小,冷却过程中石墨结构与金刚石结构同时形核、长大,引起金刚石颗粒表面的石墨化,限制了纳米金刚石的生长。