铁基触媒中碳化硼含量对含硼金刚石单晶表观活化能的影响

通过在铁基触媒中添加适量的碳化硼,制备出了具有不同硼含量的含硼金刚石单晶。利用差热分析仪,测量了含硼金刚石单晶的差热和热重。采用Kissinger方法,计算了含硼金刚石单晶在加热过程中发生氧化反应的表观活化能,对比分析掺硼量对含硼金刚石单晶热稳定性的影响。结果表明:差热和热重测量值与表观活化能计算值的变化规律基本一致;随着掺硼量的增加,含硼金刚石单晶的热稳定性先提高后降低,剧烈氧化时表观活化能随着掺硼量的增加而减小。     

透明硼皮金刚石的高压合成研究

 本文根据硼皮金刚石的理论模型，采用石墨中掺微量硼的方法，控制人造金刚石中的硼含量与分布，用高压合成出一种含微量硼元素的淡黄色透明的硼皮金刚石。这种新型金刚石具有强度高，耐热性好的特性，其抗氧化性能比一般黄金刚石约高200 ℃，其耐热性与强度也比一般含硼量高的黑金刚石高。     

高含硼金刚石的一阶Raman谱特性分析

对B4C为碳源、分别以FeNiCo与NiMnCo合金为触媒,高温高压下合成出的高含硼金刚石(B含量大于1wt%),进行了拉曼谱测试。实验表明:这类金刚石的室温一阶拉曼谱线位移分别为1324cm-1与1320cm-1,半峰宽(FWHM)分别为22cm-1及28cm-1。对比不同含硼量金刚石的拉曼谱发现,随着硼含量增加,拉曼位移的红移量增加,线宽加宽,峰值下降。这与硼杂质原子进入金刚石,造成晶格畸变与缺陷有关     

温度梯度法宝石级金刚石的合成及表征

利用温度梯度法,在5．0—5．7GPa,1250---1600℃条件下,研究了FeNiMnCo触媒合成宝石级金刚石的温度和压力区间,给出了P-T相图．基于有限元法的温度场模拟及碳素浓度梯度拟合结果表明,I型温度场只适合生长大尺寸优质板状及小尺寸塔状金刚石单晶;II型温度场可以合成出大尺寸优质板状或塔状金刚石单晶．该结论被Ib型及掺硼宝石级金刚石晶体生长实验所证实．提出碳素浓度梯度是决定晶体生长速度及合成晶体品质的关键因素．研究得到了只有触媒中温度场分布与晶体尺寸、形貌相匹配时,才能合成出优质宝石级金刚石单晶的晶体生长规律．揭示了{110},和{113}高指数晶面在Ib型金刚石“V”形区内的分布规律．通过傅里叶红外光谱检测发现,FeNiMnCo触媒合成金刚石的氮含量较低,较低的氮含量是由铁会降低金刚石氮含量所致．氮含量低有利于金刚石的光谱透过性．     

高温高压下掺硼宝石级金刚石单晶生长特性的研究

本文在5.1—5.6 GPa,1230—1600℃的压力、温度条件下,以FeNiMnCo作为触媒,进行单质硼添加宝石级金刚石单晶的生长研究.借助于有限元法,对触媒内的温度场进行模拟.研究得到了FeNiMnCo-C-B体系下,金刚石单晶生长的P-T相图.该体系下合成金刚石单晶的最低压力、温度条件分别为5.1 GPa,1230℃左右.研究发现,在单晶同一{111}扇区内部,硼元素呈内多外少的分布规律.有限元模拟结果给出,该分布规律是由在晶体生长过程中,{111}扇区的增长速度逐渐减小所致.{111}晶向的晶体生长实验结果表明,硼元素优先从{111}次扇区进入晶体.研究发现,这是该扇区增长速度相对较快,硼元素扩散逃离可用时间短导致的.另外,同磨料级掺硼金刚石单晶生长相比,对于温度梯度法生长掺硼宝石级金刚石单晶,由于晶体的增厚速度较慢,即使硼添加量相对较高,也可以实现表面无凹坑缺陷的优质金刚石单晶的生长.     

高含硼金刚石合成的原子分子过程及其特点的初步探讨

在５．８ＧＰａ和１４８０℃条件下，首次用Ｂ４Ｃ作碳源，通过触媒合金（Ｎｉ７０Ｍｎ２５ＣＯ５及Ｆｅ５５Ｎｉ２９ＣＯ１６）的作用，合成出粒度为２０～２５μｍ，含硼量高于１ｗｔ％的黑色金刚石，晶体中存在大量针形体。最近艹勾清泉教授提出了这种金刚石形成的原子分子过程模型。用模型预言可能形成具有某些优异特性的针形硼皮及硼氮皮金刚石     

高氮含量宝石级金刚石单晶的高温高压合成

氮是金刚石（包括天然金刚石和人工合成金刚石）中最普遍的杂质,长期以来广受研究者的关注. 人工合成出类似天然金刚石的具有较高氮含量的金刚石晶体是极富挑战性的研究课题. 本工作通过在合金溶剂和石墨碳源中添加含氮物质,利用温度梯度法在国产六面顶高压设备上合成出了系列大尺寸、高氮含量的宝石级金刚石单晶. 借助显微红外光谱,对合成的金刚石晶体中的氮含量进行了测定. 研究发现随着含氮物质添加量的提高晶体中氮含量基本呈线性增加. 最终合成出了氮含量高达1707 ppm的毫米级高氮含量金刚石单晶,以及最大尺寸达3.5 mm,氮含量达1520 ppm的绿色高氮宝石级金刚石单晶.     

FeMn粉末触媒对合成金刚石的影响

 利用FeMn粉末触媒在国产六面顶压机上进行了合成金刚石单晶的实验,研究了高温高压条件下（5.7 GPa、1 550 ℃）,石墨-FeMn粉末触媒体系中金刚石单晶的生长特性。通过光学成像显微镜观测表明：合成出的金刚石单晶呈浅黄色,晶形完整,且都是八面体,晶体里含有白色物质,粒度集中在0.3~0.5 mm;通过扫描电镜观测了晶体的表面形貌,表面有熔坑;通过穆斯堡尔谱,发现粉末触媒里主要是FeMn合金和独立状态的Fe,金刚石内部主要是Fe和Fe₃C;利用X射线荧光光谱,检测出样品里有Fe和Mn元素。     

预处理石墨对合成金刚石性能的影响

 本文介绍了对合成金刚石用石墨片进行预处理的方法。研究表明，用已处理过的石墨片合成出粒度组、强度高、完整单晶多的金刚石，金刚石中Ni、Mn、Co、Si的含量明显减少，而氮的含量明显增加。并观察到触媒片两面都能均匀地生长理想的金刚石晶体。该预处理方法不仅提高金刚石的质量，而且有可能为认识石墨转化为金刚石的机理提供一些依据。     

Ni-Mn粉末触媒中固溶碳的作用效果和机理初探

 在国产DS6×800A型六面顶压机上，对比研究了含与不含固溶碳的Ni-Mn粉末触媒，采用直热式静压触媒法合成金刚石的差异。实验表明：Ni-Mn粉末触媒中固溶碳的存在，不仅可以提高金刚石的合成单产、细化金刚石晶粒，而且在同工艺条件下，能得到晶形完整度较高的金刚石单晶。     

退火温度对硼掺杂纳米金刚石薄膜微结构和p型导电性能的影响

采用热丝化学气相沉积法制备硼掺杂纳米金刚石 (BDND) 薄膜, 并对薄膜进行真空退火处理, 系统研究退火温度对BDND薄膜微结构和电学性能的影响. Hall效应测试结果表明掺B浓度为5000 ppm (NHB) 的样品的电阻率较掺B浓度为500 ppm (NLB) 的样品的低, 载流子浓度高, Hall迁移率下降. 1000 ℃退火后, NLB和NHB 样品的迁移率分别为53.3和39.3 cm²·V^-1·s^-1, 薄膜的迁移率较未退火样品提高, 电阻率降低. 高分辨透射电镜、紫外和可见光拉曼光谱测试结果表明, NLB样品的金刚石相含量较NHB样品高, 高的硼掺杂浓度使薄膜中的金刚石晶粒产生较大的晶格畸变. 经1000 ℃退火后, NLB和NHB薄膜中纳米金刚石相含量较未退火时增大, 说明薄膜中部分非晶碳转变为金刚石相, 为晶界上B扩散到纳米金刚石晶粒中提供了机会, 使得纳米金刚石晶粒中B浓度提高, 增强纳米金刚石晶粒的导电能力, 提高薄膜电学性能. 1000 ℃退火能够恢复纳米金刚石晶粒的晶格完整性, 减小由掺杂引起的内应力, 从而提高薄膜的电学性能. 可见光Raman光谱测试结果表明, 1000℃退火后, Raman谱图中反式聚乙炔 (TPA) 的1140 cm^-1峰消失, 此时薄膜电学性能较好, 说明TPA减少有利于提高薄膜的电学性能. 退火后金刚石相含量的增大、金刚石晶粒的完整性提高及TPA含量的大量减少有利于提高薄膜的电学性能. 关键词： 硼掺杂纳米金刚石薄膜 退火 微结构 电学性能     

Ground-state properties of boron-doped diamond

Boron-doped diamond undergoes an insulator-metal or even a superconducting transition at some critical value of the dopant concentration. We study the equilibrium lattice parameter and bulk modulus of boron-doped diamond experimentally and in the framework of the density functional method for different levels of boron doping. We theoretically consider the possibility for the boron atoms to occupy both substitutional and interstitial positions and investigate their influence on the electronic structure of the material. The data suggest that boron softens the lattice, but softening due to substitutions of carbon with boron is much weaker than due to incorporation of boron into interstitial positions. Theoretical results obtained for substitution of carbon are in very good agreement with our experiment. We present a concentration dependence of the lattice parameter in boron-doped diamond, which can be used for to identify the levels of boron doping in future experiments. The text was submitted by the authors in English.     

Synthesis and characterization of p-type boron-doped IIb diamond large single crystals

High-quality p-type boron-doped IIb diamond large single crystals are successfully synthesized by the temperature gradient method in a china-type cubic anvil high-pressure apparatus at about 5.5 GPa and 1600 K.The morphologies and surface textures of the synthetic diamond crystals with different boron additive quantities are characterized by using an optical microscope and a scanning electron microscope respectively.The impurities of nitrogen and boron in diamonds are detected by micro Fourier transform infrared technique.The electrical properties including resistivities,Hall coefficients,Hall mobilities and carrier densities of the synthesized samples are measured by a four-point probe and the Hall effect method.The results show that large p-type boron-doped diamond single crystals with few nitrogen impurities have been synthesized.With the increase of quantity of additive boron,some high-index crystal faces such as {113} gradually disappear,and some stripes and triangle pits occur on the crystal surface.This work is helpful for the further research and application of boron-doped semiconductor diamond.     

Boron distribution in the subsurface region of heavily doped IIb type diamond

For the first time investigations of the boron distribution in the subsurface region of HPHT boron-doped diamond that is promising for applications in electronics were carried out by X-ray photoelectron (XPS) and Raman spectroscopy. It was found from XPS data that the boron content decreased gradually more than one order of magnitude in depth of surface. The first-principle calculations have shown that the Raman polarizability in the crossed polarization configuration should increase considerably with boron doping. The Raman spectra from as-grown and polished surfaces of heavily boron-doped diamond are discussed in the context of theoretical results.     

热灯丝CVD金刚石膜硼掺杂效应研究

利用Ｒａｍａｎ谱和Ｘ射线衍射微分析研究了金刚石膜硼掺杂效应．研究发现，在硼浓度较低时，金刚石膜中非晶碳（Ｓｐ²键合）含量减少，而随着硼浓度增加，金刚石膜的Ｒａｍａｎ特征峰（Ｓｐ^３）向低频方向漂移，并且展宽和出现不对称．这是由于硼掺杂引起晶格变化及Ｆａｎｏ互作用所致 关键词：     

Semiconductor diamond heater in the Kawai multianvil apparatus: an innovation to generate the lower mantle geotherm

Semiconductor diamond is considered the best heater material to generate ultra-high temperatures in a Kawai cell. In two pioneering studies, a mixture of graphite and amorphous boron (or boron carbide, B₄C) was converted to semiconductor diamond in the diamond stability field and was confirmed to generate 2000°C and 3500°C, respectively. Following these works, we synthesized a homemade boron-doped graphite block with fine machinability. With this technical breakthrough, we developed a semiconductor diamond heater in a smaller Kawai-type cell assembly. Here, we report the procedure for making machinable boron-doped graphite, and the performance of the material as a heater in a Kawai cell at 15?GPa using tungsten carbide anvils and at ～50?GPa using sintered diamond anvils. Furthermore, we present a finite element simulation of the temperature distribution generated by a semiconductor diamond heater, which is much more homogeneous than that generated by a metal heater.     

Effect of oxygen on regulation of properties of moderately boron-doped diamond films

Regulation of oxygen on properties of moderately boron-doped diamond films is fully investigated. Results show that, with adding a small amount of oxygen (oxygen-to-carbon ratio < 5.0%), the crystal quality of diamond is improved, and a suppression effect of residual nitrogen is observed. With increasing ratio of O/C from 2.5% to 20.0%, the hole concentration is firstly increased then reduced. This change of hole concentration is also explained. Moreover, the results of Hall effect measurement with temperatures from 300 K to 825 K show that, with adding a small amount of oxygen, boron and oxygen complex structures (especially B₃O and B₄O) are formed and exhibit as shallow donor in diamond, which results in increase of donor concentration. With further increase of ratio of O/C, the inhibitory behaviors of oxygen on boron leads to decrease of acceptor concentration (the optical emission spectroscopy has shown that it is decreased with ratio of O/C more than 10.0%). This work demonstrates that oxygen-doping induced increasement of the crystalline and surface quality could be restored by the co-doping with oxygen. The technique could achieve boron-doped diamond films with both high quality and acceptable hole concentration, which is applicable to electronic level of usage.