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.     

W过渡层结合界面对金刚石薄膜在WC-6%Co上的附着力的影响

 在微波等离子体化学气相沉积装置中,采用负偏压形核等方法,研究两种不同的W过渡层/基体结合界面对金刚石薄膜与WC-6%Co附着力的影响。采用氢等离子体脱碳、磁控溅射镀W、高偏压碳化等方法,在YG6衬底表面形成化学反应型界面,W膜在碳化时和基体WC连为一体,极大地增加了W膜与基体的附着力,明显优于直接镀钨、碳化形成的物理吸附界面。在高负偏压下碳化,能提高表面粗糙度,增加膜与基体机械钳合,而负偏压形核增加核密度,从而增加膜与基体的接触面积,结果极大地提高了金刚石薄膜的附着力。     

MPCVD方法制备军用光学元件纳米金刚石膜

介绍了用MPCVD方法制备纳米金刚石膜的工艺。用MPCVD方法实验研究了在光学玻璃上镀纳米金刚石膜:膜层厚度为0 4551μm,粒度小于200nm,表面粗糙度小于29 5nm,最大透过率为80%;平均显微硬度为34 9GPa,平均体弹性模量为238 9GPa,均接近天然金刚石的力学性能。与衬底材料表面应力-2 78GPa相比,具有较好的抗压和耐磨效果。     

Spin filter,spin amplifier and spin diode in graphene nanodisk

Graphene nanodisk is a graphene derivative with a closed edge. The trigonal zigzag nanodisk with size N has N-fold degenerated zero-energy states. It can be interpreted as a quantum dot with an internal degree of freedom. The ground state of nanodisk is a quasi-ferromagnet, which is a ferromagnetic-like state with a finite but very long life time. We investigate spin-filter effects in the system made of nanodisks and leads. A novel feature of the nanodisk spin filter is that its spin can be controlled by the spin current. We propose some applications for spintronics, such as spin memory, spin amplifier and spin diode. It is argued that a spin current is reinforced (rectified) by feeding it into a nanodisk spin amplifier (diode). Graphene nanodisk would be a promising candidate of future electronic and spintronic nanodevices.     

Solution of N-S equations based on the quadtree cut cell method

With the characteristic of the quadtree data structure, a new mesh generation method, which adopts square meshes to decompose a background domain and a cut cell approach to express arbitrary boundaries, is proposed to keep the grids generated with a good orthogonality easily. The solution of N-S equations via finite volume method for this kind of unstructured meshes is derived. The mesh generator and N-S solver are implemented to study two benchmark cases, i.e. a lid driven flow within an inclined square and a natural convection heat transfer flow in a square duct with an inner hot circular face. The simulation results are in agreement with the benchmark values, verifying that the present methodology is valid and will be a strong tool for two-dimensional flow and heat transfer simulations, especially in the case of complex boundaries. Supported by Japan Society for the Promotion of Science (Grant No. C20560175) and the National Natural Science Foundation of China (Grant Nos. 10872159 and 40675011)     

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.     

C18, C8, and perfluoro reversed phases on diamond for solid-phase extraction

In spite of advances in solid-phase extraction (SPE) technology there are certain disadvantages to current SPE silica-based, column packings. The pH range over which extraction can occur is limited and each column is generally only used once. New diamond-based reversed SPE phases (C₁₈, C₈, and perfluorinated) were developed in our laboratories. Studies were done which show that these phases do not have the same limitations as traditional silica-based stationary phases. The synthesis and properties of these diamond-based phases are presented, and the stability, percent recovery, and column capacity are given for the C₁₈ phase.     

Optimal matrix-segmentation by rectangles

We study the problem of decomposing a nonnegative matrix into a nonnegative combination of 0-1-matrices whose ones form a rectangle such that the sum of the coefficients is minimal. We present for the case of two rows an easy algorithm that provides an optimal solution which is integral if the given matrix is integral. An additional integrality constraint makes the problem more difficult if the matrix has more than two rows. An algorithm that is based on the revised simplex method and uses only very few Gomory cuts yields exact integral solutions for integral matrices of reasonable size in a short time. For matrices of large dimension we propose a special greedy algorithm that provides sufficiently good results in numerical experiments.     

钻石颜色分级体系的探讨

按照国家标准的要求,研制了一种更好的用于钻石颜色分级的仪器和方法,其检测结果受检测环境条件、人员、样品大小的影响很小。采用该方法对不同标准比色石进行测试,结果表明这些比色石的颜色均匀性并不理想。因此提出了钻石量化渐变色级体系的构想,使钻石分级定量化,使钻石分级真正统一到一个标准。该构想可以统一全球的钻石分级标准,使钻石分级技术更加科学、公正、合理。     

河南某地粘土矿物新型传压介质研制及金刚石合成工业试验

河南某地粘土矿物具有优异的传压和密封性能,是传统金刚石合成用传压介质辅料叶蜡石的替代品.将该粘土矿物按照粗(-1.4 mm+0.5 mm)、中(-0.5 mm+0.25 mm)、细(-0.25 mm)三个粒级进行配比,重量比为4∶4∶2,并添加5;水玻璃作为粘结剂,混合均匀,作为密封材料.白云石按照粗(-0.18 mm+0.15 mm)、细(-0.15 mm)两个粒级进行配比,重量比为8∶2,添加8;水玻璃,混合均匀,作为传压材料.经粉压成型和焙烧热处理,制成传压层在内部,密封层在外部,外形尺寸为65 mm×65 mm×32.5 mm,内径为38.5 mm的分体型复合传压介质.经金刚石合成工业试验得出,金刚石产品单产量为116.0 ct,≥130 N颗粒含量为28.0;,≥40/60目颗粒含量为77.5;,单位锤耗为0.28 g.该新型传压介质的使用性能跟常规叶蜡石传压介质相当,合成出的金刚石产品两者之间没有明显差异.