Data-driven exploration for pressure-induced superconductors using diamond anvil cell with boron-doped diamond electrodes and undoped diamond insulating layer

ABSTRACT

Data-driven exploration for pressure-induced superconductors was performed based on the high-throughput first-principles screening of electronic band structures. In the screening conditions, we focused on the characteristics including a narrow band gap, flat band feature, and possibility of metallization under high pressure. The 27 promising compounds were screened out from the database of Atomwork for the candidates of new pressure-induced superconductors. Among the candidates, we actually synthesized three compounds in a single crystal, and all candidates exhibited the pressure-induced superconductivity. For the in-situ electrical transport measurements, we developed a novel configuration of diamond anvil cell with boron-doped diamond electrodes and an undoped diamond insulating layer. The discovered new pressure-induced superconductors via the data-driven approach and the developed diamond anvil cell were summarized in this paper.     

Thermodynamic and kinetic study on interfacial reaction and diamond graphitization of Cu Fe-based diamond composite

Cu-Fe based diamond composites used for saw-blade segments are directly fabricated by vacuum and pressure- assisted sintering. The carbide forming elements Cr and Ti are added to improve interfacial bonding between diamond and the Cu-Fe matrix. The interfacial reactions between diamond/graphite and Cr or Ti, and diamond graphitization are investigated by thermodynamics/kinetics analyses and experimental methods. The results show that interfacial reactions and graphitization of diamond can automatically proceed thermodynamically. The Cr3C2 , Cr7C3 , Cr23C6 , and TiC are formed at the interfaces of composites by reactions between diamond and Cr or Ti; diamond graphitization does not occur because of the kinetic difficulty at 1093 K under the pressure of 13 MPa.     

Mo离子注入对金刚石涂层附着性能的影响

采用Mo离子注入工艺对YG6硬质合金基体表面进行处理,用微波等离子体CVD(MPCVD)法沉积金刚石涂层,研究了Mo离子注入工艺对金刚石涂层附着性能的影响.结果表明,Mo离子注入后,硬质合金基体表面的化学成分发生了明显变化;采用适当剂量的Mo离子注入基体,可使CVD金刚石涂层的附着性能显著提高. 关键词： 金刚石涂层 Mo离子注入 硬质合金基体 附着性能     

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.     

Growth of diamond thin film on tool materials from a gas phase

Abstract

In the present paper, diamond films have been synthesized on tungsten carbide, sintered diamond and high pressure diamond by hot filament chemical vapour deposition method from the mixture gas of methane and hydrogen, and growth features of diamond were studied.     

电子助进化学气相沉积金刚石中发射光谱的蒙特卡罗模拟

采用蒙特卡罗方法，对源料气体为CH4/H2混合气的电子助进化学气相沉积（EACVD）中 的氢原子(H)、碳原子(C)以及CH基团的发射过程进行了模拟.研究了CH4浓度、反应室气压 和衬底偏压等工艺参数对发射光谱及成膜的影响.研究发现，CH基团可能是有利于金刚石薄 膜生长的活性基团，而碳原子不是；偏压的升高可提高电子平均温度及衬底表面附近氢原子 的相对浓度；通过氢原子谱线可测定电子平均温度并找到最佳成膜实验条件.该结果对EACVD 生长金刚石薄膜过程中实时监测电子平均温度，有效控制工艺条件，生长出高质量的金刚石 薄膜具有重要的意义. 关键词： 蒙特卡罗模拟 金刚石薄膜 发射光谱     

Co元素对硬质合金基底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平面波赝势方法, 研究了硬质合金刀具基底黏结相Co元素对金刚石涂层膜基界面结合强度的影响机理. 借助Materials Studio软件建立了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型, 采用CASTEP仿真软件计算了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型的最优稳定结构. 通过仿真计算, 获得了WC/Diamond膜基界面模型和WC-Co/Diamond膜基界面模型的界面结合能、电荷密度图及Mulliken重叠布居数. 经对比分析后发现, 硬质合金基底中磁性元素Co的存在能转移金刚石涂层膜基界面处W元素及C元素的电荷, 从而使膜基界面处的原子因失电荷而相斥, 这直接导致了金刚石涂层膜基界面间距变大, 使得金刚石涂层膜基界面结合能降低.     

Integrated microwave (centimeter-range) modulator on polycrystalline diamond layers

Measuring data for the parameters of a microstrip switching superhigh-frequency integrated circuit on a 100-μm-thick polycrystalline diamond film are reported. Measurements are taken in the frequency range 3–7 GHz. It is shown that the decay in developmental modulators is no greater than 1.5 dB in the on state and no less than 29 dB in the off state. Physicochemical analysis of the multilayer contact metallization technology as applied to synthetic diamond and a silicon p-i-n diode is carried out. The metallization is shown to be stable up to 400°C.     

Synthesis of micro- or nano-crystalline diamond films on WC-Co substrates with various pretreatments by hot filament chemical vapor deposition

Diamond films deposited on tungsten carbide can lead to major improvements in the life and performance of cutting tools. However, deposition of diamond onto cemented tungsten carbide (WC-Co) is problematic due to the cobalt binder in the WC. This binder provides additional toughness to the tool but results in poor adhesion and low nucleation density of any diamond film. A two-step chemical etching pretreatment (Murakami reagent and Caro acid, (MC)-pretreatment) and a boronization pretreatment have both been used extensively to improve adhesion of CVD diamond film on WC-Co substrates. Here we discuss the applicability of MC-pretreatment for a range of Co-containing WC-Co substrates, and demonstrate a controlled synthesis process based on liquid boronizing pretreatment for obtaining smooth and dense micro- or nano-crystalline diamond films on high Co-containing WC-Co substrates. Substrate treatments and deposition parameters were found to have major influences on the smoothness, structure and quality of the diamond films. The best quality diamond films were achieved under conditions of relatively high substrate temperature (T_s) and the best adhesion was achieved at T_s = 800 °C.     

高能电子照射对金刚石中缺陷电荷状态的影响

金刚石经电子辐照后会形成大量的点缺陷, 而这些缺陷很多都是带有电荷的. 提出一种用于研究缺陷电荷状态的新思路, 即利用扫描电子显微镜(SEM)的高能电子照射辐照区域, 通过比较SEM 照射前后的低温光致发光光谱, 为缺陷电荷状态的确定提供了一些依据. 关键词： 金刚石 点缺陷 电荷状态     

氮掺杂金刚石{100}晶面的缺陷发光特性

氮是金刚石中最常见的杂质之一, 其对金刚石的缺陷发光具有重要的影响. 氮可以与金刚石中的本征缺陷形成复合缺陷. 本文首先利用阴极射线发光照片(CL)对一个高温高压合成的氮掺杂金刚石进行表征, 发现{100}晶面为蓝色, 然后利用透射电子显微镜(TEM)对该晶面进行电子辐照及后续退火处理, 以引入本征点缺陷进而形成含氮的复合缺陷, 并利用低温光致发光光谱(PL光谱)表征其缺陷发光特性, 发现该晶面主要以氮-空位复合缺陷(NV中心)发光为主, 并伴随着较弱的503 nm发光. 关键词： 金刚石 缺陷 发光     

等离子体诱导碳纳米管到纳米金刚石的相变

采用氢等离子体，实现了碳纳米管向金刚石的结构相变，并实现了金刚石的高密度成核，有效成核密度可达10\+\{11\}／cm\+2以上，处于目前金刚石成核密度的最高行列，为制备优质的金刚石薄膜提供了保证.高分辨透射电镜、x射线衍射和拉曼光谱都证实了金刚石的形成.同时，对纳米金刚石晶粒的生成机理进行了初步探讨. 关键词： 等离子体 碳纳米管 纳米金刚石 结构相变     

The formation of a diamond layer on a carbide substrate during diamond interaction with Si,WC and Co

Abstract

A diamond layer was formed on a carbide substrate in an irregular temperature field at high pressures (HP). A gradient scheme of HP cell set-up has been developed, which provides for a simultaneous impregnation of opposite planes of a diamond layer by components that differ in melting temperature. The cell temperature field has been calculated and physico-mechanical properties of the obtained composite material have been studied.     

高长径比柱状金刚石的高温高压合成与机理研究

为了拓展金刚石的种类和解决金刚石工具使用过程中因把持力不足造成的使用寿命降低等, 在中国式六面顶压机上, 通过对FeNi触媒成分和工艺的优化, 成功合成出高质量长径比大于2.5, 平均粒度在0.8—1.0 mm的柱状金刚石晶体. 该晶体独特的形貌, 将极大改善金刚石工具的在使用过程中出现的"脱粒"现象. 另外, 实验中发现, 柱状金刚石晶体的生长速度也远大于传统晶体的生长速度. 采用扫描电镜(SEM)和能谱(EDS)等手段对柱状金刚石晶体及晶体周围触媒成分进行了表征; 结果表明, 柱状金刚石晶体在生长过程中存在{100}和{111}晶面拉长, 以及包覆在晶体周围的触媒成分偏析. 在此基础上, 阐明了柱状晶体生长机理.     

Hopping conductivity in polycrystalline diamond films

The results of the experimental study of the conductivity of a polycrystalline diamond film by dielectric spectroscopy are presented. A diamond film about 200 μm thick was grown by microwave plasma-assisted chemical vapor deposition for 180 h. Two pronounced local peaks in the frequency dependence of the conductivity were observed. The relevant frequencies were temperature-dependent. These data permit us to hypothesize that the hopping mechanism of conductivity occurs in the polycrystalline diamond film. Two types of electrically active centers with different activation energies and relaxation times are involved in the conductivity.     

金刚石中GR1中心的光致发光特性研究

金刚石中空位存在中性、负电及正电三种状态, 且空位-空位、空位-杂质之间可以形成更多复合缺陷. 利用低温光致发光光谱研究了金刚石经辐照产生的中性空位的发光特性, 对进一步研究其他复合缺陷的发光性能提供了重要的指导意义. 关键词： 金刚石 中性空位 GR1中心     

Demonstration of diamond field effect transistors by AlN/diamond heterostructure

This is the first report on an AlN/diamond heterojunction field effect transistor (HFET). The AlN epilayer is grown on oxygen‐terminated (111) diamond substrates using metalorganic vapor phase epitaxy at a temperature as high as 1240 °C. The transistor and gate capacitance–voltage characteristics indicate that the HFET behaves as a p‐channel FET with a normally‐on depletion mode. The HFET channel is located at the AlN/diamond interface, and holes are accumulated in diamond close to the interface. The development of the AlN/diamond HFET creates a new possibility for diamond‐based power electronics. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

在强碳化物形成元素衬底上生长金刚石薄膜的物理机制探索

作者在研究金刚石表面金属化机理中发现,该物理过程是用化学气相沉积(CVD)方法在强碳化物形成元素上生长金刚石薄膜的逆物理过程。推断在强碳化物形成元素上,诸如WSi,Ta等,生长金刚石薄膜,其界面有相应的碳化物,诸如WC,SiC,TaC等出现,继而生长的金刚石薄膜实质是在相应的碳化物背底上择优取向成核生长的。从而揭示在强碳化物形成元素上生长金刚石薄膜的物理机制是:W(Si,Ta)等→WC(SiC,TaC)等→金刚石薄膜。 关键词：     

Strength and plastic deformation of polycrystalline diamond composites

ABSTRACT

The use of nanopolycrystalline diamond has allowed a systematic study on deformation of polycrystalline diamond composites (PCDCs). Bulk PCDCs samples containing either Co or SiC as a binding agent were deformed under high pressure and temperature to strains up to 18% at strain rates ～10^?5?s^?1. All samples exhibit strong work hardening. The strength of PCDCs depends on the amount and type of binding agents and is consistently weaker than that of diamond single crystals. The weakening may be due to the binder materials, which play an important role in affecting grain boundary structures. In SiC-based PCDC, significant grain fragmentation occurs. Nearly all grain boundaries are wetted by SiC after large deformation, resulting in lower strength. In Co-based PCDC, the microstructure is dominated by dislocations, deformation twins, and separated grain boundaries. The density of deformation twins increases significantly with strain, with the twin domain width reaching as low as 10–20?nm at 14% strain.     

Dependence of nitrogen vacancy color centers on nitrogen concentration in synthetic diamond

Crystallization of diamond with different nitrogen concentrations was carried out with a FeNiCo-C system at pressure of 6.5 GPa. As the nitrogen concentration in diamond increased, the color of the synthesized diamond crystals changed from colorless to yellow and finally to atrovirens (a dark green). All the Raman peaks for the obtained crystals were located at about 1330 cm^-1 and contained only the sp³ hybrid diamond phase. Based on Fourier transform infrared results, the nitrogen concentration of the colorless diamond was < 1 ppm and absorption peaks corresponding to nitrogen impurities were not detected. However, the C-center nitrogen concentration of the atrovirens diamond reached 1030 ppm and the value of A-center nitrogen was approximately 180 ppm with a characteristic absorption peak at 1282 cm^-1. Furthermore, neither the NV⁰ nor the NV^- optical color center existed in diamond crystal with nitrogen impurities of less than 1 ppm by photoluminescence measurement. However, Ni-related centers located at 695 nm and 793.6 nm were observed in colorless diamond. The NE8 color center at 793.6 nm has more potential for application than the common NV centers. NV⁰ and NV^- optical color centers coexist in diamond without any additives in the synthesis system. Importantly, only the NV^- color center was noticed in diamond with a higher nitrogen concentration, which maximized optimization of the NV^-/NV⁰ ratio in the diamond structure. This study has provided a new way to prepare diamond containing only NV^- optical color centers.