40Ar+诱导无定形碳到金刚石纳米晶相变的研究

通过60 keV的⁴⁰Ar⁺辐照无定形碳靶合成了大量尺寸不同的金刚石纳米颗粒.高分辨透射电子显微镜配合能量色散X射线谱和电子衍射以及Raman谱分析的结果表明，这些嵌于具有扰动石墨结构薄膜中的纳米金刚石颗粒，其成核率很高(约为10¹³/cm²)，而且可以生长到较大的尺寸，有的甚至可以达到微米量级.对其相转变过程也进行了初步探讨. 关键词： 离子束 金刚石纳米晶 相变 透射电子显微镜     

一氧化碳合成金刚石薄膜的形貌和结构分析

利用微波等离子体化学气相沉积(MPCVD)技术，采用偏压增加成核(BEN)、两步生长的方法在一氧化碳(CO)和氢气(H₂)的环境下制备了金刚石薄膜. 利用扫描电子显微镜(SEM)、Raman光谱仪和透射电子显微镜(TEM)对金刚石薄膜的形貌和结构进行了分析. 研究发现金刚石晶粒在第一步成核及生长的过程中产生了层错和孪晶，而在第二步的生长过程中产生的层错和孪晶很少，最终形成的金刚石晶粒外表面比较光滑，包含有近五次对称或者平行的片状的孪晶，并可以观察到少量的位错. 而在样品的边缘由于等离子体的不均匀产生了比样品中心成核密度低的区域. 在这个区域中，发现了一个新的非金刚石的碳结构.     

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     

微波等离子体化学气相沉积合成掺氮金刚石薄膜的缺陷和结构特征及其生长行为

Diamond film was deposited in CH₄ and H₂ gas mixture with a small amount of N₂ by microwave plasma assisted chemical vapor deposition (MPCVD). Scanning electron microscopy, Raman spectroscopy and transmission electron microscopy were applied to characterize the film. The results showed that the growth of grains are different the central region and the edge. In the central region, diamond grains nucleated with a density as high as 4.8×10⁸ cm^-2 and were preferential in 〈001〉 orientation. The inner grains formed an area without stacking faults,which was surrounded by a rim with a high density of stacking faults. A growth model was suggested to interpret the morphological feature and the behavior of preferential growth. At the edge, the grains were identified to be 6H polytypes of diamond and a new twin relationship of grains was found. Besides, the effect of the N dopant on the growth behavior of the diamond film deposited by MPCVD was discussed in connection with the growth rate of the film. 关键词： 金刚石 结构表征 透射电子显微镜 多型金刚石     

Structure of crystalline and amorphous Ge probed by X-ray absorption and diffraction techniques

Results of experiments dedicated to the study of the structure under high pressure of amorphous Ge (a-Ge) and crystalline Ge (c-Ge) are reported. Energy-dispersive X-ray diffraction measurements of c-Ge have been collected at the DW11A beamline (DCI, LURE) using a heatable diamond anvil cell as pressure device up to 500?K. The a-Ge measurements have been performed at the ESRF, using the advanced set-up available at the BM29 beamline, which allows the simultaneous collection of X-ray absorption spectroscopy data and diffraction patterns used to monitor pressure and crystallization of a sample in a Paris–Edinburgh large-volume cell. The new structural data allowed us to obtain a reliable determination of the lattice parameters as a function of pressure and temperature in c-Ge and of the first-neighbor distance distribution in a-Ge.     

Evolution of amorphous carbon films into nano-crystalline graphite with increasing growth temperature in plasma-enhanced chemical vapor deposition

Amorphous carbon films (ACFs) have recently emerged as one of the best candidates for etching-resistant hardmask materials in advanced semiconductor manufacturing processes. Etching resistivity of ACFs is known to be improved by controlling the relative abundance between sp² and sp³ bonds. We have investigated the relative abundance between sp² and sp³ bonds in several ACFs, fabricated by plasma-enhanced chemical vapor deposition at different temperatures, which were analyzed by using X-ray photoemission spectroscopy, Raman spectroscopy, and transmission electron microscopy. We found that the relative abundance of sp² bond increased as the growth temperature was raised. Furthermore, the ACFs eventually evolved into nano-crystalline graphite with increasing growth temperature.     

Intergrowth microstructures of MnF2 subjected to shock compression

Intergrowth microstructures of MnF₂ subjected to shock compression at 4.4, 9.0 and 21.6 GPa were examined using transmission electron microscopy (TEM). Intergrowth microstructures consisting of rutile- and α-PbO₂-type phases were observed in samples shock-loaded to 4.4 and 9 GPa. The sample subjected to 21.6 GPa consisted of a twin structure with stacking faults, with a rutile-type but not the α-PbO₂-type phase. In the 9.0-GPa shocked sample, the phase ledge structure originating from a phase transition is directly captured by high-resolution transmission electron microscopy.     

High-pressure synthesis of a novel form of endohedral Li diamond from Li graphite intercalation compound

A novel form of hexagonal diamond containing Li atoms in the open rooms surrounded by sp³-bonded carbon atoms was successfully synthesized from a Li graphite intercalation compound under high pressure, as had been predicted by theoretical studies. High-pressure experiments with LiC₆ were performed in the pressure range from 0.1 MPa to 43 GPa using a diamond-anvil cell. In situ X-ray diffractometry and optical microscopy revealed that LiC₆ was transformed to a hexagonal-diamond form without losing Li atoms. The c-axis of the hexagonal-diamond form was considerably longer than that of the hexagonal diamond transformed from pure graphite, which was consistent with the predicted structure of the endohedral Li diamond. The observed high-pressure form exhibited a golden metallic gloss, which was also consistent with the calculated metallic band structure.     

Melting curve of silicon to 15 GPa determined by two-dimensional angle-dispersive diffraction using a Kawai-type apparatus with X-ray transparent sintered diamond anvils

The melting curve of silicon has been determined up to 15 GPa using a miniaturized Kawai-type apparatus with second-stage cubic anvils made of X-ray transparent sintered diamond. Our results are in good agreement with the melting curve determined by electrical resistivity measurements [V.V. Brazhkin, A.G. Lyapin, S.V. Popova, R.N. Voloshin, Nonequilibrium phase transitions and amorphization in Si, Si/GaAs, Ge, and Ge/GaSb at the decompression of high-pressure phases, Phys. Rev. B 51 (1995) 7549] up to the phase I (diamond structure)—phase II (β-tin structure)—liquid triple point. The triple point of phase XI (orthorhombic, Imma)—phase V (simple hexagonal)—liquid has been constrained to be at 14.4(4) GPa and 1010(5) K. These results demonstrate that the combination of X-ray transparent anvils and monochromatic diffraction with area detectors offers a reliable technique to detect melting at high pressures in the multianvil press.     

Transmission electron microscopy and X-ray diffraction study of microstructural evolution in magnetoresistive Cu–Fe–Ni ribbons

The evolution of the microstructure of a granular Cu₈₀Fe₁₀Ni₁₀ (at%) melt-spun ribbon is studied by transmission electron microscopy (TEM), energy-filtered transmission electron microscopy (EFTEM) and X-ray diffraction. This system is interesting as large giant magnetoresistance (GMR) values have been measured for this composition. We have shown the presence of two face-centred cubic phases, an (Fe,Ni)-rich phase and a Cu-rich phase. The lattice parameters of these two phases are close and no diffraction or elastic contrast is involved in displaying the two phases in TEM bright-field mode. With EFTEM imaging, we have shown the presence of a fine-scale (Fe,Ni)-rich precipitation inside the Cu-rich fcc matrix. The precipitates are 2–4 nm in the as-spun state and 4–6 nm after annealing for 2 h at 400°C. The lattice parameter of the Cu-rich phase in the as-spun sample is 0.3608 nm and 0.3610 nm for the (Fe,Ni)-rich phase. After a 24-h annealing treatment at 600°C, the mean diameter of the particle is 20 nm and the lattice parameter of the (Fe,Ni)-rich phase has decreased to 0.3600 nm, while that of the Cu-rich phase has increased to 0.3613 nm, which is consistent with a segregation of Fe and Ni in the precipitates. The composition and volume fraction of the two phases measured for this annealed sample are in good agreement with the Thermocalc® predictions.     

Diamond-like phase formation in an amorphous carbon films prepared by periodic pulsed laser deposition and laser irradiation method

Diamond-like carbon (DLC) films were fabricated by pulsed laser ablation of a liquid target. During deposition process the growing films were exited by a laser beam irradiation. The films were deposited onto the fused silica using 248 nm KrF eximer laser at room temperature and 10⁻³ mbar pressure. Film irradiation was carried out by the same KrF laser operating periodically between the deposition and excitation regimes. Deposited DLC films were characterized by Raman scattering spectroscopy. The results obtained suggested that laser irradiation intensity has noticeable influence on the structure and hybridization of carbon atoms deposited. For materials deposited at moderate irradiation intensities a very high and sharp peak appeared at 1332 cm⁻¹, characteristic of diamond crystals. At higher irradiation intensities the graphitization of the amorphous films was observed. Thus, at optimal energy density the individual sp³-hybridized carbon phase was deposited inside the amorphous carbon structure. Surface morphology for DLC has been analyzed using atomic force microscopy (AFM) indicating that more regular diamond cluster formation at optimal additional laser illumination conditions (∼20 mJ per impulse) is possible.     

Probing structural integrity of single walled carbon nanotubes by dynamic and static compression

We report on a first study of single walled carbon nanotubes (SWCNTs) after application of dynamic (shock) compression. The experiments were conducted at 19 GPa and 36 GPa in a recovery assembly. For comparison, an experiment at a static pressure of 36 GPa was performed on the material from the same batch in a diamond anvil cell (DAC). After the high pressure treatment the samples were characterized by Raman spectroscopy and transmission electron microscopy (TEM). After exposure to 19 GPa of shock compression the CNT material exhibited substantial structural damage such as CNT wall disruption, opening of the tube along its axis (“unzipping”) and tube shortening (“cutting”). Dynamic compression to 36 GPa resulted in essentially complete CNT destruction whereas at least a fraction of the nanotubes was recovered after 36 GPa of static compression though severely damaged. The results of these shock wave experiments underline the prospect of using SWCNTs as reinforcing units in material WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Nano-polycrystalline diamond synthesized through the decomposition of stearic acid

ABSTRACT

Here we report a novel route for synthesizing nano-polycrystalline diamond (NPD) using stearic acid (C₁₈H₃₆O₂) as a starting material under high pressure and high temperature. The obtained NPD shows a transparent dark-yellowish color similar to the standard NPD synthesized from graphite and consists of extremely fine diamond grains (～10?nm). The temperature required for the present synthesis of pure transparent NPD is as low as 1000°C at 13 and 17?GPa, which is surprisingly lower than that for conventional NPD synthesis (1800–2000°C). The amorphous-like, extremely poorly crystalline graphite produced by the thermal decomposition of stearic acid likely provides preferential nucleation sites for diamond and significantly lower the activation energy. The removal of volatile components such as H₂O generated through the decomposition from the system is a key to obtain pore-free transparent NPD. Magnesite, MgCO₃ and periclase, MgO can be used as an efficient H₂O remover through the hydration reaction.     

石墨烯的透射电子显微学研究

石墨烯（Graphene）是近几年迅速发展起来的研究热点材料之一.利用透射电子显微镜（TEM）研究Graphene的结构特征和原子动态过程,是 Graphene研究的重要进展.文章评述了利用透射电子衍射方法对Graphene的层数、堆垛方式、取向和表面形貌等结构特征进行的研究工作,介绍了利用高分辨透射电子显微术在Graphene的表面缺陷、边缘结构及吸附原子等研究领域取得的最新结果.     

High pressure studies using two-stage diamond micro-anvils grown by chemical vapor deposition

Ultra-high static pressures have been achieved in the laboratory using a two-stage micro-ball nanodiamond anvils as well as a two-stage micro-paired diamond anvils machined using a focused ion-beam system. The two-stage diamond anvils’ designs implemented thus far suffer from a limitation of one diamond anvil sliding past another anvil at extreme conditions. We describe a new method of fabricating two-stage diamond micro-anvils using a tungsten mask on a standard diamond anvil followed by microwave plasma chemical vapor deposition (CVD) homoepitaxial diamond growth. A prototype two-stage diamond anvil with 300?µm culet and with a CVD diamond second stage of 50?µm in diameter was fabricated. We have carried out preliminary high pressure X-ray diffraction studies on a sample of rare-earth metal lutetium sample with a copper pressure standard to 86?GPa. The micro-anvil grown by CVD remained intact during indentation of gasket as well as on decompression from the highest pressure of 86?GPa.     

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。     

Synthesis and characterization of nano-sepiolite by solvothermal method

Nano-sepiolite with novel morphology has been fabricated by solvothermal method in different conditions. The nano-sepiolite was characterized by X-ray fluorescence analysis, X-ray powder diffraction, thermal gravimetry analysis, differential thermal analysis and infrared spectroscopy. Scanning electron microscopy observations revealed that using of solvothermal route led to nano-wires of sepiolite. The reactions have been performed in several conditions to find out the role of different factors such as the aging time and temperature of the reaction in the solvothermal on the size and morphology of the nano-structures.     

Multiwalled carbon nanotubes mass-produced by dc arc discharge in He–H2 gas mixture

Uniform cathode deposits (longer than 15 mm), containing multiwalled carbon nanotubes (MWNTs) inside, were produced by dc arc discharge evaporation with a computer-controlled feeder of a pure-carbon electrode without a metal catalyst in a He–H₂ gas mixture. The purification of MWNTs was carried out to remove amorphous carbon and carbon nanoparticles. High-resolution transmission electron microscopy observations and Raman scattering studies show that the MWNTs possess a high crystallinity and a mean outermost diameter of ∼ ∼10 nm. It has been confirmed that the current density in the electron field emission from a purified MWNT mat can reach 77.92 mA/cm², indicating that the purified MWNTs are a promising candidate electron source in a super high-luminance light-source tube or a miniature X-ray source.     

Investigation of nanocrystalline CoFe 2 O 4 by positron annihilation lifetime spectroscopy

Nanoparticles of cobalt ferrite prepared by the co-precipitation method with crystallite size varying from 4.7 to 41 nm have been characterized by positron annihilation lifetime spectroscopy. Three lifetime components are fitted to the lifetime data. The shortest lifetime component is attributed to the delocalized positron lifetime shortened by defect trapping. The intermediate lifetime is assigned to the positron annihilation in diffuse vacancy clusters or microvoids at the grain boundaries and at the grain-boundary triple points. The longest component corresponds to the pick-off annihilation of ortho-positronium formed at the larger voids. The variations in these lifetimes and their relative intensities with annealing temperature and crystallite size have been studied in detail.