Formation and microstructural investigation of Ag-Cu alloy nanoclusters embedded in SiO2 formed by sequential ion implantation

We report on the formation of alloy nanoclusters in silica by Ag/Cu ion sequential implantation. The formation of alloy nanocluster has been evidenced by optical absorption spectra, selected area electron diffraction and energy dispersive X-ray spectra. The microstructure characters of nanoclusters have been studied by high resolution transmission electron microscopy. The lattice distortion of some nanoclusters has been observed. A model has been given to explain the distortion. Some defects (partial dislocation, stacking faults) have been found in nanoclusters.     

Formation of low-temperature deformation-induced segregations of nickel in Fe–Ni-based austenitic alloys

ABSTRACT

The authors present the results of an investigation in Fe–Ni-Cr austenitic alloys of the low-temperature deformation-induced segregations of nickel that form in the micro regions being (i) located close to grain- and subgrain boundaries and (ii) characteristic of the concentration and magnetic inhomogeneities indicated by the appearance of a dark diffraction contrast at the electron diffraction patterns taken from these regions typical (at the same time) of an enhanced value of Curie temperature. The observed effects were connected with the micro distortions caused by the local change of lattice parameter because of an increase in nickel concentration, as well as in the result of a magnetostriction dilatation. Using methods of the X-ray energy dispersive spectroscopy (XEDS) and atomic-probe body-section radiography (tomography – APT) has made it possible to determine the borders of those regions of austenite that were characteristic of an enhanced concentration of nickel in the fields of the localisation of a deformation-induced segregation of nickel in the vicinity of grain (subgrain) boundaries of austenitic alloys of the types Fe–13Cr–30Ni and Fe–37Ni–3Ti.     

Quantitative evaluation of nanotube content produced by arc discharge in a raw material

The amount of carbon nanotube in a raw material grown by electric arc discharge, ignited in different liquid environments, has been evaluated by combined use of X-ray diffraction, electron microscopy and differential thermal analysis (TG-DTA) in a reactive environment. X-ray diffraction was used to discriminate the various carbon microstructures utilizing the difference in lattice parameter between curved and planar graphite structures. The results are repeatable and in good agreement with TG-DTA measurements carried out in a reactive environment, where the relative amount of carbon nanostructures is evaluated on the basis of the difference in the reaction kinetics with atmospheric oxygen. In analyzed specimens, SEM and TEM show the presence of only two allotropic forms of carbon, namely nanotubes and globular particles, the relative amounts of which depend on the nature of the liquid surrounding the discharge and on the voltage applied to the electric arc.     

Phase transformations of carbon under extreme energy action

Experiments are performed on a high-current MIG generator (current amplitude 2.5 MA, current rise time 100 ns) to synthesize diamond-like carbon forms. Magnetohydrodynamic calculations carried out before the experiments show that the conditions required for synthesizing diamond-like structures appear during the compression of copper tubes 2–4 mm in diameter filled with graphite. The explosion products are analyzed on an EM-125 diffraction transmission electron microscope. During an explosion, the entire graphite is found to transform into cubic carbon: crystals with the simple cubic lattice and a lattice parameter a = 0.5545 nm and with the face-centered cubic lattice and a = 0.3694 nm are detected. The crystallite size is 5–25 nm.     

A detailed study of physical properties of ZnS quantum dots synthesized by reverse micelle method

In this article, zinc sulfide nanocrystal quantum dots were synthesized by reverse micelle method using polyvinyl pyrrolidone as surfactant. The various crystallite properties of these nanocrystals such as, size, d-spacing, lattice parameter, microstrain, intrinsic stress, X-ray density, specific surface area, dislocation density, porosity, and agglomeration number have been analyzed using X-ray diffraction spectrum. The transmission electron microscopy was used to calculate the size and monitoring morphology of the nanocrystals, while the scanning electron microscopy was utilized to investigate the surface morphology of nanoclusters. The various optical properties of zinc sulfide quantum dots such as absorption coefficient, extinction coefficient, optical band gap energy, Urbach energy, and threshold wavelength have been analyzed using UV-visible data. The photoluminescence was used to study the emission spectra of produced ZnS quantum dots. Moreover, Furrier Transform-Infrared studies revealed that ZnS quantum dots are pure.     

爆轰法合成碳包覆镍纳米颗粒的研究

 采用自制的负氧平衡复合炸药前驱体,在密闭容器中充氮气保护下爆轰合成了碳包覆镍纳米颗粒。利用X射线衍射、X射线荧光、透射电镜和拉曼光谱等技术,对爆炸产物的组成成分、结构形貌等进行了观测。结果表明,爆轰产物主要由具有面心立方结构的镍晶核和碳元素构成,此外还含有其它微量元素;合成的纳米颗粒呈球形或椭球形状,颗粒尺寸主要分布在10~25 nm范围,包覆的碳壳厚度约1~2 nm,核壳结构完备。结合观测结果,对爆轰法合成碳包覆纳米颗粒的形成机制进行了简单的讨论。     

Cu-Ni alloy nanocluster formation by ion implantation in silicate glasses: Structure and optical properties

Sequential ion implantation (copper and nickel) in silica and soda-lime glasses has been performed. The formation of copper-nickel alloy nanocluster in the glass host has been evidenced by synchrotron radiation-based techniques, namely X-ray diffraction and absorption spectroscopy. The nanocrystals' lattice parameter value was estimated, indicating the formation of Cu₅₅Ni₄₅ alloy particles. Optical absorption spectra are also discussed. Received 6 May 1999 and Received in final form 22 September 1999     

Ni nanoparticles fabricated by laser ablation in water

Nickel nanoparticles were fabricated by ablating a bulk Ni target with pulsed 337-nm laser radiation in distilled water. Transmission electron microscope images of the removed material show spherical particles with two size scales: tens of nm and hundreds of nm. Phase explosion and Rayleigh–Plateau hydrodynamic instability are suggested as being responsible for this distribution. An X-ray diffraction pattern of the ablated material demonstrates the presence of both nickel and nickel oxide.     

纳米镍粉体的晶格膨胀

采用阳极弧放电等离子体技术成功制备了各种不同晶粒尺寸的纳米镍粉体材料，并利用X射线衍射(XRD)、透射电子显微镜(TEM)和相应选区电子衍射(SAED)等测试手段对所制备的样品的晶体结构、晶格参数、形貌、粒度进行性能表征. 实验结果表明：阳极弧等离子体法制备的镍纳米粉的晶体结构与相应的块物质相同，为fcc结构的晶态. 不同晶粒尺寸的纳米镍粉体的晶格常数均大于完整单晶镍的晶格常数，晶格畸变表现为晶格膨胀. 晶格常数和晶胞体积随着晶粒尺寸的减小而增大，晶格畸变量与晶粒尺寸的倒数成正比. 镍纳米粉体的晶格膨胀主要是由于受到表面能和表面张力的作用而引起的，可以利用纳米晶体的热力学理论作定性解释. 关键词： 镍纳米粉体 晶格常数 晶格膨胀 晶胞体积     

Studies on optical,mechanical, dielectric properties of bisthiourea nickel bromide NLO single crystal

Bisthiourea nickel bromide (BTNB) single crystal has been grown by solution growth technique at room temperature. The crystal structure and lattice parameters were determined for the grown crystal by single crystal X-ray diffraction studies. Optical constants like band gap, refractive index, reflectance, extinction coefficient and electric susceptibility were determined from UV–vis-NIR spectrum. Nonlinear optical property was discussed to confirm the SHG efficiency of the grown crystal. The mechanical strength of the grown crystal was analyzed using Vickers microhardness tester. The dielectric constant and dielectric loss of bisthiourea nickel bromide are measured in the frequency range of 50 Hz to 5 MHz at different temperatures. The ac conductivity studies were carried out on bisthiourea nickel bromide crystals. In order to investigate the growth mechanism and surface features, etching studies are carried out for the crystal. Photoconductivity studies were carried out on bisthiourea nickel bromide crystals.     

FLAPW calculations of the EFG in semimetallic arsenic and antimony under varying pressure

The variation of the electric field gradient (EFG) at nuclear sites with pressure in semimetallic arsenic and antimony has been calculated using the full-potential linearized augmented plane wave (FLAPW) method. The results are compared with NQR data, which are available up to a pressure of 2 GPa. The calculated EFG depends sensitively on the values of the lattice parameters used. A theoretical investigation of the relationship between c/a and the internal parameter z, using FLAPW methods, has been carried out and compared with available X-ray diffraction data for arsenic and antimony. For antimony, the FLAPW calculations give results which are consistent with the experimental pressure variation of both the lattice parameters and the EFG. In the As case, the use of theoretical values of z leads to good agreement with the measured pressure variation of the EFG. This revised version was published online in August 2006 with corrections to the Cover Date.     

Structure and magnetic state of the films deposited by laser ablation of composite nickel and palladium targets

Transmission electron microscopy, electron diffraction, and vibrating-sample magnetometry are used to show that a metastable hcp structure can form in both nickel and Ni-Pd alloy films during alternating sputtering of the Ni and Pd components of composite targets. The hcp lattice parameters increase monotonically when the palladium content in a sputtered target increases in the range 0–75%. The ratio of the hcp lattice parameters c/a is close to the ideal ratio for the hcp lattice (1.63) within the limits of experimental error. In the as-deposited state, nickel and Ni-Pd alloy films with an hcp structure have no magnetic moment. Upon annealing, the films transform into a ferromagnetic state with an fcc structure. The concentration dependence of the lattice parameter of the fcc solid solution a ₀ is found to exhibit a positive deviation from Vegard’s law, which is characteristic of alloys with a concave liquidus line.     

Three-dimensional periodic lattice of ZrO<Subscript>2</Subscript> nanocrystals in transparent silica matrix

The conditions for synthesizing an opal-zirconia-carbon nanocomposite in the form of monolithic (without pores) transparent silica with an ordered distribution of nanocrystals throughout the sample have been determined. Zirconia nanocrystals form a three-dimensional periodic lattice of nanoclusters with sizes ranging from several nanometers to several tens of nanometers. This nanocomposite exhibits properties typical of photonic crystals. The samples have been studied using electron microscopy, X-ray diffraction, photoluminescence, and Raman scattering. The structural state and spatial arrangement of zirconia nanocrystals and carbon clusters in the nanocomposite have been elucidated. Optical transmission and optical reflection photoluminescence spectra of the nanocomposites have been measured.     

Ferromagnetic resonance of cobalt nanoparticles used as a catalyst for the carbon nanotubes synthesis

Catalyst is considered to be the most crucial parameter for the growth of carbon nanotubes. In this work we study the ferromagnetic resonance (FMR) spectra of the catalyst nanoclusters. Moreover we report for the first time the angle FMR studies of catalyst particles with and without CNT layer. The dependencies of the FMR spectra, X-ray diffraction (XRD) patterns, Raman spectra and morphology of the CNT layers on the growth conditions are discussed.     

Rearrangement of the Structure of Paratellurite Crystals in a Near-Surface Layer Caused by the Migration of Charge Carriers in an External Electric Field

The process of formation of surface structures in a paratellurite crystal (α-TeO₂) in an external electric field has been studied by in situ X-ray diffraction (XRD) measurements. This process is reversible and its dynamics (duration of tens of minutes) corresponds to the formation of a screening layer near the insulator–metal interface owing to the counter migration of oxygen ions and vacancies in the external electric field. The formation of domains has been observed in the experiment as the broadening and splitting of the XRD curve and is explained by mechanical stresses that appear in the high electric field near the surface in view of the piezoelectric effect and are responsible for a ferroelectric α–β phase transition. A change in the lattice parameter near the anode (surface of the crystal with a positive external charge) has been detected simultaneously. This change is due to the local rearrangement of the crystal structure because of the inflow of oxygen ions in this region and outflow of oxygen vacancies.     

Noble-gas nanoclusters with fivefold symmetry stabilized in superfluid helium

Macroscopic samples (volume approximately cm(3), atomic density approximately 10(19) -10(20) cm(-3)) of noble-gas nanoclusters (size approximately 5-6 nm) were produced in superfluid helium by an impurity-helium gas injection technique. X-ray diffraction measurements show that the samples consist of weakly interacting nanoclusters with fivefold symmetry, such as icosahedra and decahedra. These results open new opportunities for fundamental research of nanoclusters of noble gases and other materials in well-controlled environments using experimental techniques requiring bulk samples.     

30CrMnSiNi2A晶格参量的测量及回复规律研究

针对X射线衍射领域中晶面衍射峰重叠问题,提出一种新的重叠峰分离方法.采用RU-200V转靶衍射仪对30CrMnSiNi2A晶格参量及其回复规律进行研究,得出不同回火温度下晶格参量与碳含量的变化关系.研究结果发现:由于碳的过饱和度不同以及合金元素的影响,30CrMnSiNi2A与高碳马氏体晶格参量的变化规律虽基本符合,但其变化速率存在差异.在不同回火温度下晶格参量a基本与碳含量无关,随着回火温度升高,a值略有下降.晶格参量c则随碳含量的变化幅度较大,从淬火态到180℃回火态出现一个陡降过程,随着回火温度升高,其变化幅度又趋于平缓.     

强流脉冲电子束作用下纯镍表面的应力特征

 利用强流脉冲电子束（HCPEB）装置对多晶纯镍进行轰击,采用X射线衍射及扫描电子显微镜等技术,详细分析了受轰击样品的变形组织与结构。通过分析建立了强流脉冲电子束诱发的应力特征与变形结构之间的关系,并对目前现有的几种应力波数值模拟结果进行了讨论。实验结果表明：强流脉冲电子束能够在材料表层诱发约5GPa的应力,造成纯镍表面发生孪生塑性变形。除了热膨胀引起的表层横向准静态热应力外,强流脉冲电子束产生的等离子体脉冲爆炸可以直接诱发幅值很高的冲击应力波,二者的共同作用是引起表层微观结构变化的直接原因。     

In situ X-ray diffraction investigation of porous silicon strains induced by the freezing of a confined organic fluid

High resolution X-ray diffraction is used to perform an in situ measurement of the variations of the lattice parameter of the nanometer size crystallites of porous silicon, induced by the freezing of a confined organic fluid, dodecane. Two p⁺ type PS layers of 60 and 70% porosity are investigated, and the variations of their lattice parameter with the temperature (in the range 150–300 K) are measured. The experimental curves are discussed in relation with the results of a previous calorimetric study of the freezing of confined dodecane. We explain the observed strains by the presence of capillary stresses, that appear in the layer due to the formation of internal liquid-vapour meniscus during the freezing process of the confined fluid. Received 22 October 1999 and Received in final form 25 March 2000     

Electron diffraction investigation of catalytic particles at the tips of carbon nanotubes

Catalytic nickel particles at the tips of carbon nanotubes grown under different physicochemical conditions are experimentally studied by high-energy electron diffraction. The spacings of the crystal lattice are determined. It is demonstrated that the nanoparticles consist of a supersaturated solid solution of carbon in nickel with an abnormally high carbon content.