金刚石单晶生长的声发射实时检测初探

采用声发射检测技术,对高温高压下人造金刚石单晶的生长过程进行了检测和分析。利用由PCI-8型声发射仪和LMD-800型铰链式六面顶压机组成的声发射检测系统,检测了金刚石单晶的生长过程。将金刚石单晶生长和不生长过程中检测到的声发射信号进行对比和频谱分析,结果表明:声发射信号与金刚石单晶生长过程存在对应关系;金刚石单晶生长对应的声发射信号是一种低频信号,可以利用声发射信号的变化规律研究金刚石单晶在高温高压条件下的原位反应机理。     

Ib型金刚石大单晶的限形生长

金刚石的限形生长有利于其后续加工.对于磨料级金刚石限形生长的研究已经比较透彻,但金刚石大单晶的限形生长尚缺乏全面系统的研究.本文以Fe Ni(64wt%:36wt%)合金为触媒,利用高温高压下的温度梯度法在5.6 GPa时对不同温度下分别沿(100)面和(111)面生长的Ib型金刚石大单晶的晶形进行了研究.研究表明:随着温度的升高,沿(100)晶面生长的金刚石大单晶的晶形分别为板状、塔状直至尖塔状,而沿(111)面生长的金刚石大单晶的晶形则分别为塔状和板状;分析了不同温度下分别沿(100)面和(111)面生长金刚石大单晶不同晶形高径比的变化情况.利用不同压力和温度下的金刚石大单晶合成实验绘制了沿(100)和(111)面生长金刚石大单晶的晶形在V形生长区域内的分布示意图,表明沿(111)面生长的金刚石大单晶V形区温度下限明显比以(100)面生长的高,而沿这两面生长金刚石大单晶的V形区温度上限差别并不明显.对不同生长面V形区温度上下限的差别进行了解释,据此实现了Ib型金刚石大单晶的限形生长.     

高温高压金刚石单晶生长界面的研究

 利用扫描电镜及Auger电子谱技术研究了高温高压下金刚石单晶生长界面的特性，观察到了金刚石单晶表面及金属膜表面的沟槽结构及金刚石-金属、金属-石墨两个主界面间的过渡层结构及界面间C原子电子组态的变化。     

高温高压条件下石墨的再结晶与金刚石单晶的生长

 用电子显微镜观察到了在高温高压条件下再结晶石墨的形状随温度变化而改变的规律。实验表明：从石墨向金刚石的转变，与石墨在催化剂——溶剂合金中的再结晶状态有关，类球形再结晶石墨是转变成金刚石小单元的基础。金刚石晶体的不同形态及其多样化的表面结构表明金刚石单晶的生长具有比较复杂的过程。研究了具有一定规则形状由类球形再结晶石墨晶粒组成的聚合体，这种聚合体将在适当温度压力下转变成金刚石颗粒。本研究给出了生长粗颗粒、晶形完整的金刚石单晶的原则办法。     

合成人造金刚石的高压腔内电阻率变化研究

 通过时人造金刚石合成腔内材料电阻率变化的某些宏观规律研究，分析了在不同高温高压条件下，合成腔内所发生的相变过程。本文采用的研究方法，表明了对封闭的高温高压腔内所发生的反应从外部进行动态连续观测的可能性与价值，为研究人造金刚石成核、生长的规律提供了较好的手段。     

钢筋混凝土动态粘结滑移声发射特性试验

为研究不同加载速率下钢筋混凝土粘结-滑移损伤破坏过程中的损伤特征,对钢筋混凝土粘结试件进行了0.01 mm/s～10 mm/s四种不同速度的拔出试验。采用实时动态的声发射监测技术对整个试验过程进行监测,对试验过程中的声发射信号进行声发射振幅-振铃计数特性及功率谱峰值频率特性分析。结果表明,随着滑移速率的增加,声发射振幅-振铃计数拟合曲线变缓,在0～50 k Hz和100～150 k Hz频率范围内的声发射事件比重分别减小和增加。损伤过程的声发射特性对钢筋混凝土粘结滑移损伤演化规律的研究具有重要的价值。     

国产六面顶压机多晶种法合成宝石级金刚石单晶

对国产六面顶压机平台下使用多晶种法合成宝石级金刚石单晶进行了系统的研究. 通过合理调整温度梯度法的合成腔体组装, 采用多晶种法, 探索多晶种法金刚石合成的压力和温度区间, 在单个合成腔体内放置3–5颗金刚石晶种, 成功合成出多颗(3–5)优质Ib型宝石级金刚石单晶. 多颗晶种的引入, 单次实验合成的多个金刚石晶体晶形及品质一致; 同时, 晶体的整体生长速度也有明显的增大. 多晶种法金刚石单晶合成的研究, 可以有效地利用腔体空间、提高单次金刚石单晶合成的效率, 解决压机大型化下高温高压资源利用率低的问题; 同时, 为宝石级金刚石单晶商业化生产提供重要的依据. 关键词： 金刚石 国产六面顶 多晶种 温度梯度法     

硒化锌单晶薄膜近带边发射的荧光寿命

在2K下,对常压MOCVD方法生长的ZnSe单晶薄膜进行了光致荧光近带边发射谱的测量和辨认.并采用激光超短脉冲技术和时间相关单光子计数技术相结合的方法,对其在2K下近带边发射的荧光寿命进行了测量和分析,并讨论了自由激子弛豫过程.     

高温高压法人造金刚石合成中工艺曲线的确定

以SPD6×2000型六面顶压机为合成设备,在高温高压条件下确定了合成金刚石的最低成核压力.采用合理的二次升压工艺方法,在暂停油压86MPa,生长油压94MPa,合成功率3500W的条件下成功地减少了劣晶的生成,合成出了晶型完整、表面平整的优质金刚石单晶.结果表明在最低成核压力点下对石墨进行再结晶的处理对合成高品级金刚石是完全必要的.     

非恒功率加热技术的研究

 讨论了高温高压生长金刚石单晶的非恒功率加热技术的理论和实验依据，并用配有计算机的装置在国产六面顶高压设备上实现了工业化生产规模的非恒功率加热技术，同时生长出了优质粗颗粒单晶。     

A relation between a metallic film covering on diamond formed during growth and nanosized inclusions in HPHT as-grown diamond single crystals

One of the most important characteristics and basic phenomena during diamond growth from liquid metal catalyst solutions saturated with carbon at high temperature–high pressure (HPHT) is that there exists a thin metallic film covering on the growing diamond, through which carbon-atom clusters are delivered to the surface of the growing diamond by diffusion. A study of microstructures of such a metallic film and a relation between the thin metallic film and the inclusions trapped in HPHT as-grown diamond single crystals may be helpful to obtain high-purity diamond single crystals. It was found that both the metallic film and the HPHT as-grown diamond single crystals contain some nanostructured regions. Examination by transmission electron microscopy suggests that the microstructure of the thin metallic film is in accordance with nanosized particles contained in HPHT as-grown diamond single crystals. The nanosized particles with several to several tens of nanometers in dimension distribute homogeneously in the metallic film and in the diamond matrix. Generally, the size of the particles in the thin metallic film is relatively larger than that within the diamond matrix. Selected area electron diffraction patterns suggest that the nanosized particles in the metallic film and nanometer inclusions within the diamond are mainly composed of f.c.c. (FeNi)₂₃C₆, hexagonal graphite and cubic γ-(FeNi). The formation of the nanosized inclusions within the diamond single crystals is thought not only to relate to the growth process and rapid quenching from high temperature after diamond synthesis, but also to be associated with large amounts of defects in the diamond, because the free energy in these defect areas is very high. The critical size of carbide, γ-(FeNi)and graphite particles within the diamond matrix should decrease and not increase according to thermodynamic theory during quenching from HPHT to room temperature and ambient pressure. Received: 13 September 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-0531/295-5081; E-mail: yinlw@sdu.edu.cn     

HPHT Synthesis of Different Shape Coarse-Grain Diamond Single Crystals

Synthesis of coarse-grain diamond crystals is studied in a China-type SPD6× 1670T cubic high-pressure apparatus with high exact control system. To synthesize high quality coarse-grain diamond crystals, advanced indirect heat assembly, powder catalyst technology and optimized synthesis craft are used. At last, three kinds of coarse- grain diamond （about 0.85 mm） single crystals with hexahedron, hex-octahedron and octahedron are synthesized successfully under HPHT （about 5.4 GPa, 1300-1450℃）. The growth characters of different shape crystals are discussed. The results and techniques might be useful for the production of coarse-grain diamonds.     

Microstructure of high-pressure-synthesized diamonds under rapid quenching and electron irradiation

A type of synthetic diamond single crystal about 0.4–0.5 mm in dimension prepared under high pressure–high temperature (HPHT) in the presence of a FeNi molten catalyst was quenched from HPHT and irradiated with 300 keV electrons at room temperature. Transmission electron microscopy was employed to examine the microstructure of the diamond single crystal before and after electron irradiation. It was found that there exists a large amount of cellular interfaces in the quenched diamond sample, which indicates the growth condition of the diamond under HPHT. Hexagonal dislocation loops about several tens of nanometers in dimension were observed in the high-pressure-synthesized diamond single crystal before electron irradiation, which strongly suggests that a number of vacancies were quenched-in due to rapid quenching from high temperature at the end of diamond synthesis, and were aggregated in the synthetic diamond to form vacancy disks on the (111) plane, the collapse of such vacancy disks forming vacancy-type dislocation loops. After electron irradiation, it was found that defect clusters present as interstitial-character dislocation loops were formed in the electron-irradiated region of the diamond. The interstitial dislocation loops grow with increase of the irradiation time. The present study, in comparison to previous work on ion implantation on diamond, indicates that electron irradiation does not induce a phase transformation but produces interstitial dislocation loops due to the migration of interstitial atoms and vacancies. The result of the study directly indicates that interstitials and vacancies in diamond are mobile at room temperature under electron irradiation. Nitrogen, as the most important kind of impurity contained in the HPHT as-grown diamond, probably acts as nucleation of the interstitial loops. Received: 16 November 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. E-mail: yinlw@sdu.edu.cn     

山东产大颗粒高温高压合成钻石的多种谱学方法研究

山东济南中乌新材料有限公司利用六面顶油压机生产出大颗粒钻石,为了掌握这些合成钻石的品质及与天然钻石的区分方法,采用宽频诱导发光光谱仪（GV5000）、红外光谱仪、钻石特征光谱检测仪（PL5000）、激光诱导击穿光谱仪和X射线能谱仪,对该公司生产的225粒无色、蓝色和黄色高温高压（HPHT）合成钻石进行检测,并与天然钻石对比。HPHT合成钻石样品的晶形以（111）晶面和（100）晶面共存的聚形为主导。原石切磨成圆钻形成品的出成率在20%~67%之间,净度级别为VVS-P,颜色级别为D-H。通过GV5000分析,三种颜色样品均可观察到立方八面体生长结构发光图案,无色HPHT合成钻石为强蓝色荧光和磷光,发光峰位于495 nm,与晶格中的顺磁氮有关;蓝色HPHT合成钻石为蓝-绿蓝色荧光和蓝色磷光,发光峰位于501 nm,与晶格中的顺磁氮、硼有关;黄色HPHT合成钻石为弱绿色荧光和磷光,显示556和883 nm Ni+相关发光峰,这些特征可与天然钻石相区分。红外光谱分析表明,无色HPHT合成钻石在1 332~1 100 cm-1无明显氮相关吸收,在2 802 cm-1有B0相关吸收,为含有少量硼的Ⅱa型;蓝色HPHT合成钻石位于1 294 cm-1有与B-相关的强吸收,归属为Ⅱb型;黄色HPHT合成钻石位于1 130和1 344 cm-1有与孤氮相关的明显吸收,归属为Ⅰb型。PL5000光致发光光谱显示,三种颜色HPHT合成钻石可检测到659,694,707,714和883 nm等镍相关缺陷发光峰。相比之下,无色和黄色天然钻石通常为Ⅰa型,具有1 282和1 175 cm-1等聚合氮的红外光谱吸收,光致发光光谱通常可检测到415 nm（N₃）零声子线,由孤氮、硼和镍等缺陷导致的光谱特征极为罕见。因此,红外光谱和光致发光光谱特征可作为重要的鉴别依据。激光诱导击穿光谱仪检测到无色HPHT合成钻石的出露包裹体主要成分为Fe。X射线能谱分析显示,对于含包裹体较多的样品,无色和蓝色HPHT合成钻石可检测到Fe,黄色HPHT合成钻石可检测到Fe和Ni,为其中包裹体的成分,这可作为HPHT合成钻石鉴定性特征。综上所述,通过GV5000超短波紫外荧光和磷光测试,配合红外光谱和光致发光光谱特征,结合包裹体成分特征,可以有效区分该研究的合成钻石和天然钻石。     

Effects of additive NaN_3 on the HPHT synthesis of large single crystal diamond grown by TGM

In this paper,large single crystal diamond with perfect shape and high nitrogen concentration approximately 1671-1742 ppm was successfully synthesized by temperature gradient method (TGM) under high pressure and high temperature (HPHT).The HPHT synthesis conditions were about 5.5 GPa and 1500-1550 K.Sodium azide (NaN3) with different amount was added as the source of nitrogen into the synthesis system of high pure graphite and kovar alloy.The effects of additive NaN3 on crystal growth habit were investigated in detail.The crystal morphology,nitrogen concentration and existing form in synthetic diamond were characterized by means of scanning electron microscope (SEM) and infrared (IR) absorption spectra,respectively.The results show that with an increase of the content of NaN3 added in the synthesis system,the region of synthesis temperature for high-quality diamond becomes narrow,and crystal growth rate is restricted,whereas the nitrogen concentration in synthetic diamond increases.Nitrogen exists in diamond mainly in dispersed form (C-centers) and partially aggregated form (A-centers).The defects occur more frequently on crystal surface when excessive NaN3 is added in the synthesis system.     

Dependence of Limited Growth Rate of High-Quality Gem Diamond on Growth Conditions

The growth rate of diamond has been investigated for a long time and researchers have been attempting to enhance the growth rate of high-quality gem diamond infinitely. However, it has been found according to previous research results that the quality of diamond is debased with the increase of growth rate. Thus, under specific conditions, the growth rate of high-quality diamond cannot exceed a limited value that is called the limited growth rate of diamond. We synthesize a series of type Ib gem diamonds by temperature gradient method under high pressure and high temperature （HPHT） using the as-grown {100} face. The dependence of limited growth rate on growth conditions is studied. The results show that the limited growth rate increases when synthetic temperature decreases, also when growth time is prolonged.     

Industrial diamonds grown in Ni70Mn25Co5--graphite--sulfur system under HPHT

This paper reports that diamond single crystals were synthesized from sulfur-added Ni70Mn25Co5+C system under high pressure and high temperature(HPHT).It was found that additive sulfur had inhibited the nucleation and growth of diamond to some extent.X-ray diffraction of the collected sample indicated that under the synthesis conditions,a new compound MnS had been formed through the reaction of additive sulfur with manganese in the catalyst.The MnS has a fcc structure,and its average crystal size was about 30 nm.By scanning electron microscope,the {111} surface of diamond was found to be flat,while there was usually a large depression on the central region of {100}.Further observation showed that there were many small upside-down pyramidal pits in the expression.The results of x-ray photoelectron spectroscopy shows that MnS can only be detected in the depression in the range of detection precision.It was inferred that MnS had been dissolved in the melted alloy during the growth experiment,and precipitated in the sequent quenching process.     

Shape-controlled synthesis of diamond crystal by epitaxial growth under high pressure and high temperature conditions

In this paper, the diamond epitaxial growth mechanism has been studied in detail by employing several types of diamond as a seed in a catalyst-graphite system under high pressure and high temperature (HPHT) conditions. We find that the diamond nucleation, growth rate, crystal orientation, and morphology are significantly influenced by the original seeds. The smooth surfaces of seeds are beneficial for the fabrication of high-quality diamond. Our results reveal that the diamond morphology is mainly determined by the original shape of seeds in the early growth stage, but it has an adjustment process during the growth and leads to well symmetry. Additionally, we have also established the growth model for the twinned diamond grown on several seeds, and proposed the possible growth processes by tracking the particular shapes of seeds before and after treatment under HPHT conditions. These results suggest that the shape-controlled synthesis of diamond with well morphology can be realized by employing certain suitable diamond seeds. This work is expected to play an important role in the preparation of trustworthy diamond-based electronic and photonic devices.     

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.