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     

Characterization of a growth-front interface in a HPHT-grown diamond crystal by transmission electron microscopy

The growth-front interface of a diamond single crystal, which was grown from the Fe-Ni-C system under high pressure and high temperature (HPHT), has been directly observed by transmission electron microscopy (TEM) for the first time. The presence of a cellular interface suggests that the diamond is grown from solution and there exists a narrow supercooling zone in front of the solid–liquid interface. Diamond-growth parallel layers were also found, which indicates that the diamond grows from solution layer by layer. It provides direct evidence that the diamond is synthesized through graphite dissolution and transformation to subcritical diamond particles in a molten catalyst, diamond subcritical particle connection to form diamond clusters, diffusion of the diamond clusters to the growing diamond, and unification of the diamond clusters on the growing diamond crystal. Received: 17 July 2000 / Accepted: 27 October 2000 / Published online: 10 January 2001     

氦、氘对纯铁辐照缺陷的影响

在核聚变堆的辐照环境中, 核嬗变产物氢、氦对结构材料的抗辐照性能将产生很大的影响. 本实验采用离子注入和电子辐照模拟研究了氦和氘对具有体心立方结构的纯铁的影响. 采用离子加速器在室温分别对纯铁注入氦离子和氘离子, 经500℃时效1 h后在高压电镜下进行电子辐照.结果表明: 室温注氦和室温注氘的纯铁在500℃时效后分别形成间隙型位错环和空位型位错环. 在电子辐照下, 间隙型位错环吸收间隙原子而不断长大, 而空位型位错环吸收间隙原子不断缩小. 通过计算位错环的变化速率发现, 空位型位错环比间隙型位错环吸收了更多的间隙原子, 即室温注氘纯铁的位错偏压比室温注氦纯铁的偏压参量大, 这意味着相同实验条件下空位型位错环对辐照肿胀的贡献大于间隙型位错环对辐照肿胀的贡献. 利用氦-空位复合体和氘-空位复合体的结构, 分析了注氦和注氘后在纯铁中形成不同类型位错环的原因. 关键词： 氦 氘 辐照损伤 位错环     

Microstructural analysis of neutron irradiated titanium and rhenium

The defect structure in α-titanium and rhenium irradiated with neutrons at 0.4T _m (T _m = absolute melting temperature) has been analyzed using transmission electron microscopy. In rhenium, the vacancies agglomerate into voids whereas in titanium, vacancy dislocation loops lying on the prism planes are the only vacancy type defects observed. In both metals, dislocation segments and network fragments are the main evidence of interstitial type defects. The presence of dislocation loops rather than voids in titanium irradiated at this temperature is an anamalous result when compared to results on other similarly irradiated pure metals. Possible explanations for the preferential formation of loops rather than voids in the titanium are discussed.     

Positron annihilation in the quenched and electron-irradiated NiSb intermetallic compound

Samples of the near equiatomic NiSb compound were irradiated by 3 MeV electrons at 20 K or quenched from 1103 K and 1333 K and subsequently annealed isochronally. The behaviour of defects created by quench or irradiation were studied by the positron annihilation technique. Only one recovery stage was found around 425 K for quenched specimens, but two distinct stages (100 K and 425 K) were observed after irradiation. The 425 K stage is ascribed to the migration of Ni vacancies giving dislocation loops. The recombination of mobile interstitials with vacancies after irradiation is assumed to occur between 100 K and 250 K. Doppler broadening and lifetime variations of positrons as a function of the measuring temperature in these irradiation samples are discussed.     

On the interaction between a vacancy and self-interstitial atom clusters in metals

Atomic-scale computer simulation is used to study the interaction between a vacancy and a cluster of self-interstitial atoms in metals with hcp, fcc and bcc crystal structure: α-zirconium, copper and α-iron. Effects of cluster size, atomic structure, dislocation nature of the cluster side and temperature are investigated. A vacancy can recombine with any interstitial in small clusters and this does not affect cluster mobility. With increasing sizes clusters develop dislocation character and their interaction with vacancies depends on whether the cluster sides dissociate into partial dislocations. A vacancy recombines only on undissociated sides and corners created with undissociated segments. Vacancies inside the cluster perimeter do not recombine but restrict cluster mobility. Temperature enhances recombination by either increasing the number of recombination sites or assisting vacancy diffusion towards such sites. The results are discussed with relevance to differences in irradiation microstructure evolution of bcc, fcc and hcp metals and higher level theoretical modelling techniques.     

Positron annihilation studies on the migration of deformation induced vacancies in stainless steel AISI 316 L

Positron lifetime measurements were carried out at room temperature before and after isochronous annealing of cylindrical, machined fatigue specimens and of round slabs of austenitic stainless steel AISI 316 L deformed in compression. Annealing experiments are evaluated in terms of vacancy migration and sinking to grain boundaries and dislocations. The model assumes spherical grains with a homogeneous initial distribution of vacancies. A vacancy migration enthalpy of H^M _V=(0.9±0.15) eV was found. It is concluded that positron trapping at dislocation lines does not significantly contribute to positron lifetime measurements at room temperature and that single vacancies are the dominating positron traps. Positron annihilation depth profiling on cross-sectional areas prepared from machined specimens using a positron microprobe with 10 μm spatial resolution shows that machining of cylindrical specimens creates vacancies up to 5 mm below the surface. Received: 11 August 2000 / Accepted: 13 November 2000 / Published online: 28 February 2001     

高温氧气热处理对TiO_2晶体结构和铁磁性的影响

金红石TiO_2晶体先在真空中进行退火处理,随后在1173 K的氧气中进行不同时间(2 h、5 h、8 h)的热处理.理论上,通过Doppler程序计算了晶体中存在单空位、双空位和间隙O原子时的正电子湮没寿命.实验上,利用正电子湮没寿命谱仪、符合多普勒能谱仪和超导量子干涉仪分别表征了氧气退火后晶体内部的缺陷结构和常温铁磁性.分析结果得出:真空退火晶体的常温铁磁性主要与O空位的存在相关联;而经过氧气退火后,虽然极大地减少了氧空位,但晶体中却产生了大量的Ti双空位,这使得晶体的常温铁磁性有所增加.     

强流脉冲电子束作用下金属纯Cu的微观结构状态——空位簇缺陷及表面微孔结构

利用强流脉冲(HCPEB)电子束技术对多晶纯Cu进行了辐照处理,并利用透射电镜对HCPEB诱发的空位簇缺陷进行了表征.实验结果表明,HCPEP辐照金属可在纯Cu表层诱发大量的过饱和空位,并形成四方形空位胞及空位型位错圈和堆垛层错四面体(SFT),HCPEB瞬间的加热和冷却诱发的幅值极大的应力和极高的应变导致的整个原子平面的位移是空位簇缺陷形成的主要原因.此外,扫描电镜分析表明HCPEB辐照可以在纯Cu表面形成高密度、弥散分布和尺寸细小的微孔.过饱和空位或空位团簇沿晶体缺陷向表面扩散、凝聚是表面微孔形成的根     

Fe-Cr合金辐照空洞微结构演化的相场法模拟

Fe-Cr合金作为包壳材料在高温高辐照强度等极端环境下服役,产生空位和间隙原子等辐照缺陷,辐照缺陷簇聚诱发空洞、位错环等缺陷团簇,引起辐照肿胀、晶格畸变,导致辐照硬化或软化致使材料失效.理解辐照缺陷簇聚和长大过程的组织演化,能更有效调控组织获得稳定服役性能.本文采用相场法研究Fe-Cr合金中空洞的演化,模型考虑了温度效应对点缺陷的影响以及空位和间隙的产生和复合.选择400—800 K温度区间、0—16 dpa辐照剂量范围的Fe-Cr体系为对象,研究在不同服役温度和辐照剂量下的空位扩散、复合和簇聚形成空洞的过程.在400—800 K温度区间,随着温度的升高,Fe-Cr合金空洞团簇形核率呈现出先升高后下降的趋势.考虑空位与间隙的重新组合受温度的影响可以很好地解释空洞率随温度变化时出现先升高后降低的现象.由于温度的变化将影响Fe-Cr合金中原子离位阀能,从而影响产生空位和间隙原子.同一温度下,空洞半径和空洞的体积分数随辐照剂量的增大而增大.辐照剂量的增大,级联碰撞反应加强,空位与间隙原子大量产生,高温下空位迅速的扩散聚集在Fe-Cr合金中将形成更多数量以及更大尺寸的空洞.     

A stochastic theory for clustering of quenched-in vacancies-V. Temperature dependence of cluster density

It is known that the density of vacancy loops in quenched aluminium and stacking fault tetrahedra in quenched gold show a saturation for low ageing temperatures. The physical mechanism leading to this effect is not well understood. In this paper we consider a simple model which allows us to obtain the temperature dependence of total density. The analysis shows that the plateau region arises due to the fact that the number of absorption sites of a cluster is larger than the number of emission sites. The temperature dependence of the average number of vacancies in a cluster and the single vacancy concentration in equilibrium with the clusters are discussed.     

质子辐照对纯铝薄膜微观结构的影响

利用透射电子显微镜(TEM)详细分析了不同剂量的质子辐照纯铝薄膜样品的微观结构, 质子的能量E=160 keV.实验表明,质子辐照能够在Al薄膜中诱发空位位错圈,在实验范围内,位错密度随辐照剂量的增加而增加;质子辐照在1×10¹¹—4×10¹¹/mm²范围内随辐照剂量的增加,位错圈数量密度以及位错圈尺寸都随之增加.在较高剂量6×10¹¹/mm²辐照下,位错圈数量密度减小,但其尺寸显著 关键词： 质子辐照 空位簇缺陷 位错圈 微观结构     

AISI 304L奥氏体不锈钢表面微孔结构的强流脉冲电子束快速制备与表征

 利用强流脉冲（HCPEB）电子束技术,对AISI 304L奥氏体不锈钢进行了辐照处理,并利用透射电子显微镜对HCPEB诱发的空位簇缺陷进行了表征。实验结果表明,HCPEB辐照金属可在辐照表层诱发大量的过饱和空位,并形成空位型位错圈和堆垛层错四面体（SFT）。利用金相显微镜、扫描电子显微镜和非接触式光学轮廓仪,对其表面形貌进行了详细的表征,发现电子束处理后的样品表面形成了高密度、弥散分布和尺寸细小的微孔,表面微孔是由于HCPEB轰击诱发的大量空位(簇)缺陷,以线或面等结构缺陷为路径,向表层迁移导致空位的累积而形成的。采用HCPEB技术,选择合适的材料和辐照工艺参数,可以成功地制备出表面多孔金属材料。     

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.     

氢离子辐照纯钒中形成的位错环

钒合金作为聚变堆候选材料, 其辐照损伤行为一直是关注的重点. 研究辐照时形成的位错环的性质, 其意义在于揭示纯钒中辐照空洞的长大机理. 这种机理表现为不同类型位错环对点缺陷吸收的偏压不同, 从而影响金属的辐照肿胀. 本文利用加速器对纯钒薄膜样品进行氢离子辐照, 然后, 利用透射电镜的inside-outside方法分析氢离子辐照所形成的位错环的类型. 结果表明, 在氢离子辐照纯钒中没有发现柏氏矢量b=<110>的位错环, 只有柏氏矢量b=1/2<111>和b=<110>的位错环, 这两种位错环的惯性面处于{110}-{112}之间. 能确定性质的位错环全部为间隙型位错环, 未发现空位型位错环.     

金刚石集群NV色心的光谱特征及浓度定量分析

金刚石NV-色心具有优越的光致发光特性,可实现高灵敏度物理量探测。其中,NV-色心的浓度是影响其宏观领域物理量探测灵敏度的重要因素之一。分析了金刚石在NV-色心制备过程中产生的发光缺陷,研究了不同的电子注入剂量与NV-色心浓度的关系。首先,对金刚石进行电子辐照并高温真空退火,制备了NV-色心;然后,利用拉曼光谱仪测试了金刚石在电子辐照前、电子辐照后及退火后三个阶段中的荧光光谱,分析了金刚石在NV-色心制备过程中的光谱特性;最后,对生成的NV-色心的浓度进行了估算,并探究了不同电子注入剂量对NV-色心浓度的影响规律。结果表明,金刚石经电子注入后生成了524.7,541.1,578和648.1 nm发光中心。其中,HPHT合成金刚石经电子注入后普遍存在524.7 nm中心。电子注入后的金刚石经高温(≥800 ℃)真空(≥10-7 Pa)退火后,空位自由移动,不稳定的缺陷消失,当空位靠近氮原子时被束缚而形成氮空位色心。对于氮含量100 ppm的金刚石,当电子注入产生的空位含量小于120 ppm(2.1×1019 cm-3)时,NV-色心浓度与电子注入生成空位的含量的关系符合Boltzmann分布。该研究为利用氮含量100 ppm的金刚石实现定量NV-色心浓度的制备提供了参考依据,为NV-色心在宏观物理量精密测量的应用奠定了基础。     

Formation and crystal structure of metallic inclusions in a HPHT as-grown diamond single crystal

One of the most important characteristics associated with crystal growth technology is the entrapment of inclusions by the growing crystal. Diamond single crystals prepared under high temperature-high pressure (HPHT) usually contain metallic inclusions. In the present paper, metallic inclusions in a diamond grown from a Fe-Ni-C system using the HPHT method have been, for the first time, systematically examined by transmission electron microscopy (TEM). Energy dispersive X-ray spectrometry (EDS) , combined with selected area electron diffraction (SAD) patterns, has been used to identify the chemical composition and crystal structure of the metallic inclusions. The metallic inclusions were found to be composed mainly of cubic γ-(FeNi), face-centered cubic (FeNi)₂₃C₆, ortho-rhombic Fe₃C and hexagonal Ni₃C, which may have been formed through the entrapment of molten catalyst by the growth front or through reaction of the trapped melt with contaminants in the diamond. Received: 19 June 2000 / Accepted: 21 June 2000 / Published online: 16 August 2000     

Temperature dependence of conductance character in nanotube peapods

Recent electrical transport measurements on metallofullerene-doped nanotube peapods are reviewed. In temperature-dependent conductance measurements, it was found that the temperature plays a crucial role in charge transfer between the nanotube and entrapped metallofullerenes and it is shown that the metallofullerenes can function as electron donors and transfer charge to the carbon nanotube host. The amount of charge transferred varies with temperature. At room temperature, the doped nanotube shows p-type conduction. As the temperature decreases, the conductance becomes n-type and even metallic behavior is observed at still lower temperatures, indicating the degenerate state caused by doping. Received: 4 November 2002 / Accepted: 7 November 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. E-mail: chiu@fkf.mpg.de     

The effect of phason defects on the radiation-induced swelling of quasicrystalline materials

The radiation-induced vacancy swelling of quasicrystals is considered. In quasicrystals, the dislocation kinetics involves the formation of phasons: vacancy- and interstitial-like localized topological defects. Phasons interact with radiation-induced point defects (PD; vacancies and interstitials) and influence the swelling behavior of quasicrystals. After absorption of vacancies, phasons of the interstitial type transform into phasons of the vacancy type and vice versa. In other words, phasons are the recombination centers of alternating polarity for PD. Assuming that (i) the production rate of phasons is proportional to the dislocation climbing rate and (ii) voids are the sinks for mobile phasons, the set of rate equations for PD and phasons is formulated and analyzed both analytically and numerically. It is shown that the swelling rate is lower in quasicrystals compared with crystals. Growth rates of loops and voids, as well as the swelling rate, strongly depend on the phason concentration which is controlled by phason diffusion to sinks.     

Structural and optical properties of nanophase zinc oxide

Nanophase zinc oxide samples were synthesized by a two-step solid-state reaction method. The phase structure and microstructure were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The vibrational Raman spectra were compared with those from the bulk and their grain size dependence was also examined. Their photoelectric behavior was studied by X-ray photoelectron spectroscopy (XPS). The peaks at 1044.5 and 1021.4 eV were recorded as corresponding to the respective binding energies of Zn 2p_1/2 and Zn 2p_3/2, and the photoelectron spectrum of O 1s in the as-prepared powder was located at 531.2 eV. A strong visible emission centered at 580 nm was clearly observed in the nanosized zinc oxide at room temperature. Photoluminescence (PL) spectra were investigated as a function of grain size after different heat treatments. The origin of the luminescence is attributed to the recombination of electrons in singly occupied oxygen vacancies with photoexcited holes in the valence band. Received: 30 June 2001 / Accepted: 20 February 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: mszhang@nju.edu.cn