Relaxed atomic structure of the interphase boundary in a “hemispherical nanoparticle-crystal” heterogeneous system

The structure of an fcc(001)/fcc(001) interphase boundary in a “nickel hemispherical crystal nanoparticle-palladium crystal substrate” system is investigated using molecular dynamics simulation with multiparticle potentials calculated in the framework of the embedded-atom method as a function of the angle of rotation of the nanoparticle. Relaxation transformations are found to occur in a component of the system under investigation with a larger lattice parameter. It is demonstrated that, under given annealing conditions, the system is characterized by a size dependence of the angle of rotation of a nanoparticle: the annealing leaves the location of large islands virtually unchanged but brings about a rotation of small nanoparticles into a parallel orientation or an orientation with a local energy minimum.     

冷轧铜板再结晶織构的形成

电解纯铜经88.7％冷轧后,所形成的轧制织构除稳定的(110)[112]舆(112)[111]外,还存在着一种(3,6,11)[533]织构。在较低温度下退火时,再结晶织构主要为(100)[001]、(358)[352]和舆(100)[001]成孪生取向的(122)[212]织构。随着退火温度的增加,(358)[352]织构逐渐减弱,立方织构(100)[001]则逐渐加强;当退火温度达到900℃时,开成了集中的(100)[001]织构。冷轧铜板在退火的过程中,具有(100)[001]再结晶晶粒首先形成,然后普遍地发生同位再结晶。其中具有(100)[001]取向的晶粒,继续发生选择性的生长,最后形成了集中的立方织构。本支中对轧制织构舆其再结晶织构取向间的关系也进行了分析,再结晶织构一般可认为是原有织构沿某一个[111]轴旋转45°,22°或38°的结果。同时,根据上述几何关系所绘出的理想极图舆实际测定的结果也是符合的。试验结果指出,不同加热速度和不同加热程序对形成最终的再结晶织构,不发生显著的影响,而退火温度对再结晶织构的形成起着主要的作用。     

Au@碳球复合结构中Au颗粒位置调控光吸收

采用时域有限差分（FDTD）法研究Au纳米颗粒@碳球（AuNPs@CS）复合结构的光吸收控制。发现Au纳米颗粒@碳球复合结构中Au颗粒的位置可以控制复合结构光吸收。模型计算中选取两粒Au纳米颗粒以最佳深度（0 nm）嵌入碳球表面。当两粒Au颗粒球心与碳球球心夹角为22.5°和45°时,复合结构光吸收较单一碳球光吸收明显增强;当夹角为315°、270°、180°、90°时,光吸收增量逐渐减小;当夹角为337.5°时,光吸收量低于单一碳球。这一结果主要归因于Au纳米颗粒位置变化可引起表面等离子体光强度和光散射方向的变化。改变碳球表面Au纳米颗粒的数量和位置,可以进一步调节AuNPs@CS复合结构的光吸收。     

Grain boundary wetting phase transition and analysis of the energy characteristics of grain boundaries in the Sns-(Zn/Sn)l system

Regularities of the interaction of tin grain boundaries (special Σ5 and general Σ17 〈001〉) and a Sn-Zn melt of equilibrium composition were studied. The grain boundary wetting phase transition temperature was determined; for Σ5 and Σ17, it is 216°C. More than 90% of the general grain boundaries were completely wetted by the melt over a range of temperatures, from the eutectic melting temperature to the tin melting temperature. It was shown that the anisotropy of interphase energy at the solid tin-Zn-Sn melt interface is 64 ± 10 mJ m^?2 at 216°C. The energies of the Σ5 and Σ17 grain boundaries in the range of 201–216°C were obtained on the basis of the experimental dependence of the dihedral angle on temperature.     

Solid-phase synthesis of L1<Subscript>0</Subscript>-FePd(001) epitaxial thin films: Structural transformations and magnetic anisotropy

The solid-phase synthesis of the L1₀-FePd magnetically hard phase in Fe(001)/Pd(001) epitaxial films has been experimentally investigated. The formation of three types of L1₀-FePd ordered crystallites whose c axes coincide with the 〈100〉 directions of the MgO(001) substrate begins at the Fe/Pd interface at a temperature of 450°C. After an increase in the annealing temperature to 500°C, structural rearrangement occurs and gives rise to the predominant growth of L1₀-FePd crystallites with the c axis perpendicular to the film plane. After 10-h annealing, the fraction of such crystallites becomes dominant, leading to large perpendicular anisotropy. The first magnetocrystalline-anisotropy constant of the L1₀-FePd phase has been determined and the second constant has been estimated. It has been shown that magnetic anisotropy in the L1₀-FePd(001) basal plane cannot be described by the biaxial anisotropy of the tetragonal crystal. The annealing above 500°C results in the evolution of L1₀-FePd to a disordered cubic phase.     

UHV microscopy of the reconstructed Au(001) surface

We investigate the microstructure of the reconstructed Au(001) surface using ultra-high vacuum transmission electron microscopy (UHV-TEM). Bulk single crystal Au(001) surfaces were prepared via standard metallographic techniques followed by repetitive cleaning of the surface with ion milling and annealing. After a clean surface was obtained, the (001) surface was found to reconstruct into two nearly orthogonal domains of dimensions (5 × n) where n ranges between 15 and 21. The unit cell vectors of the surface cell are parallel to the 110 directions of the unreconstructed fcc (001) surface. Analysis of the diffuse scattering and dark field micrographs indicates that the surface is sheared with a complicated domain and periodicity structure which depends upon the local geometry of the substrate.     

Growth and evolution of epitaxial erbium disilicide nanowires on Si (001)

Sub-monolayer amounts of Er deposited onto Si (001)react with the substrate to form epitaxial nanowires of crystalline ErSi₂. The growth of uniaxial structures occurs because the different crystal structures of ErSi₂ and Si have a good lattice match along one Si<110> crystallographic axis but a significant mismatch along the perpendicular Si<110> axis. The nucleation, growth, and subsequent evolution of ErSi₂ nanowires were investigated as functions of erbium coverage on the Si (001) surface, annealing time, and annealing temperature. Low annealing temperatures (620 °C) and times (5 min) produced ErSi₂ nanowires with widths of a few nanometers, heights less than one nanometer, and lengths of several hundred nanometers. For longer annealing times at low temperature, the surface roughened without significant ripening of the wires. Annealing at intermediate temperatures (∼700 °C) caused stacking faults to form along the long axis of the nanowires and their lengths to ripen. At high temperature (800 °C), the wires broke apart into short segments with stacking faults. Received: 30 January 2002 / Accepted: 31 January 2002 / Published online: 3 May 2002     

Dependence of plastic relaxation in GaAs films on nucleation of the first as monolayer on Si(001) substrates

The structure of GaAs films grown on Si(001) vicinal substrates (6° rotation about 〈011〉 axis) formed in two ways of nucleation, As deposition on Si and substitution of Si monolayer by As monolayer, is studied. X-ray diffractometry is used to find that the rotation direction of a crystal lattice depends on the manner of nucleation. An optional model of the formation of film dislocation structures is proposed.     

Broad-line NMR investigation of the amorphous component of poly(trans-1,4-butadiene) and poly(4-methyl pentene-1) crystals wetted by carbon disulfide

Broad-line (proton) NMR measurements were made at temperatures from -15 to -96°C on crystals of poly(4-methyl pentene-1) wetted with a nonprotonated solvent, CS₂. The mobile fraction, A_n, is found to depend on the crystal morphology and subsequent annealing treatments of dried crystals. A_n varies with temperature in the -30 to -70°C region; changes in the slope of the A_n vs temperature plot in this region with annealing treatment are interpreted in terms of changes in the amorphous portions of the lamellae. Previous NMR results for poly(trans-1, 4-butadiene) have been reanalyzed and the new A_n values obtained are given; annealing dry PTBD crystals at 80°C is shown to bring about a significant decrease in A_n.     

Extended planar boundary inclinations in fcc single crystals and polycrystals subjected to plane strain deformation

When fcc single crystals with high-symmetry crystal orientations are deformed to moderate strains by rolling, tension or channel die compression, long dislocation boundaries inclined to the extension axis form. Similarly, long dislocation boundaries are often found in grains embedded in polycrystals deformed in the same manner. These extended planar boundaries (EPBs) are characteristically -30-40° from the extension direction and contain the transverse specimen axis. The objective of the present article is to demonstrate that EPBs formed during plane strain deformation are parallel to equivalent slip planes, a pair of hypothetical slip systems used for analyses of the strain and crystal rotation components in place of the larger number of physical slip systems. The coincidence of EPBs and equivalent slip plane inclinations is shown to account for persistent observations of EPBs in the angle range -30-40° from the rolling direction, in rolled single crystals of various initial orientations. The tendency of EPBs towards tilt or twist boundary character can also be rationalized on the basis of the equivalent slip system concept and consideration of the dislocation types available to be incorporated into EPBs.     

Solid-state synthesis in Ni/Fe/MgO(001) epitaxial thin films

Solid-state synthesis in Ni/Fe/MgO(001) bilayer epitaxial thin films has been studied experimentally. The phase sequence Fe/Ni→(～350°C)Ni₃Fe→(～400°C)NiFe→(～ 550°C)γ_par is formed as the annealing temperature increases. The crystal structure in the invar region consists of epitaxially intergrown single-crystal blocks consisting of the paramagnetic γ_par and ferromagnetic NiFe phases, which satisfy the orientation relationship [100](001)NiFe ∥ [100](001) γ_par. It has been shown that the nucleation temperatures of the Ni₃Fe, NiFe, and γ_par phases coincide with the temperatures of solid-state transformations in the Ni-Fe system.     

Phase transformations in Mn/Fe(001) films: Structural and magnetic investigations

The solid-phase synthesis in epitaxial Mn/Fe(001) bilayer film systems with 24 at % of Mn has been shown to start at a temperature of 220°C with the formation of a γ-austenite lattice and the Mn and Fe films react completely under annealing to 600°C. In the sample cooling process after annealing below 220°C, the γ austenite undergoes a martensitic transformation to an oriented ∈(100) martensite. When the annealing temperature is increased above 600°C, Mn atoms migrate from the γ-lattice, which becomes unstable, and the film is partially again transformed to the epitaxial Fe(001) layer. The solid-phase synthesis in Mn/Fe(001) bilayer nanofilms and multilayers is assumingly determined by the inverse ε → γ martensitic transformation in the Mn-Fe system. The existence of a new low-temperature (～220°C) structure transition in the Mn-Fe system with a high iron content is assumed.     

Structure and magnetic properties of CoPtCu:Ag nanocomposite films with (001) texture

Nanocomposite (001) textured CoPtCu:Ag films consisting of well separated L1₀ structure CoPtCu nanoparticles have been prepared using a CoPt/Cu/Ag multilayer precursor on SiO₂/Si(100) substrate by magnetron sputtering and subsequent vacuum thermal annealing. With a Cu concentration of 6–10% and Ag of 10–20% in atomic ratio, the films start ordering at an annealing temperature of 450 °C, which is roughly lower by 150 °C than that needed for most CoPt-based films especially with (001) texture. The perpendicular coercivities for the film are in the range from 5 kOe to 7 kOe after annealing at 500 °C in vacuum. The (001) texture for the film is partially due to the formation of an Ag underlayer after annealing, the decreasing of the ordering temperature is most-likely related to the formation of CoPtCu alloy nanoparticles in the film. PACS 75.30.Gw; 75.50.Kj; 75.70.Ak     

Effects of draw-down ratio and annealing treatment on structure formation in extruded strands of a thermotropic liquid crystalline copolyester

The molecular orientation, thermal behavior, and crystal lattice structure in extruded strands of a thermotropic liquid crystalline polymer (LCP) were studied with wide-angle x-ray diffraction (WAXD) and differential scanning calorimetry (DSC). The purpose of this work is to elucidate the effects of draw-down ratio and annealing treatment on the structure development in the LCP strands. The crystal orientation function markedly increased with increasing draw-down ratio, but the increase of orientation function saturated at higher draw-down ratio. Annealing treatment below 250°C slightly increased the degree of orientation, whereas the molecular orientation was relaxed by annealing at 270°C. In addition, the thermal properties and crystal lattice structure were sensitive to the annealing treatment. The change of DSC curves with annealing temperature suggested that the initial crystalline texture of as-extruded samples was reorganized into a more ordered structure by the annealing treatment. Draw-down ratio had some effects on the thermal properties. The molecular orientation facilitated the crystallization during annealing.     

Determination of migration of ion-implanted Ar and Zn in silica by backscattering spectrometry

It is well known that the refractive indices of lots of materials can be modified by ion implantation, which is important for waveguide fabrication. In this work the effect of Ar and Zn ion implantation on silica layers was investigated by Rutherford Backscattering Spectrometry (RBS) and Spectroscopic Ellipsometry (SE). Silica layers produced by chemical vapour deposition technique on single crystal silicon wafers were implanted by Ar and Zn ions with a fluence of 1–2?×10¹⁶ Ar/cm² and 2.5?×10¹⁶ Zn/cm², respectively. The refractive indices of the implanted silica layers before and after annealing at 300°C and 600°C were determined by SE. The migration of the implanted element was studied by real-time RBS up to 500°C. It was found that the implanted Ar escapes from the sample at 300°C. Although the refractive indices of the Ar-implanted silica layers were increased compared to the as-grown samples, after the annealing this increase in the refractive indices vanished. In case of the Zn-implanted silica layer both the distribution of the Zn and the change in the refractive indices were found to be stable. Zn implantation seems to be an ideal choice for producing waveguides.     

XRD study on the effect of the deposition condition on pulsed laser deposition of ZnO films

Using a pulsed laser deposition (PLD) process on a ZnO target in an oxygen atmosphere, thin films of this material have been deposited on Si(111) substrates. An Nd: YAG pulsed laser with a wavelength of 1064 nm was used as the laser source. The influences of the deposition temperature, laser energy, annealing temperature and focus lens position on the crystallinity of ZnO films were analyzed by X-ray diffraction. The results show that the ZnO thin films obtained at the deposition temperature of 400°C and the laser energy of 250 mJ have the best crystalline quality in our experimental conditions. The ZnO thin films fabricated at substrate temperature 400°C were annealed at the temperatures from 400°C to 800°C in an atmosphere of N₂. The results show that crystalline quality has been improved by annealing, the optimum temperature being 600°C. The position of the focusing lens has a strong influence on pulsed laser deposition of the ZnO thin films and the optimum position is 59.5 cm from the target surface for optics with a focal length of 70 cm.      

Interphase sizing temperature effect of LaRC PETI-5 on the dynamic mechanical thermal properties of carbon fiber/BMI composites

The dynamic mechanical thermal properties of carbon fiber-reinforced bismaleimide (BMI) composites processed using polyacrylonitrile(PAN)-based carbon fibers unsized and sized with LaRC PETI-5 amic acid oligomer as interphase material at 150°C, 250°C, and 350°C were investigated by means of dynamic mechanical thermal analysis. It was found that the storage modulus, loss modulus, tan δ and the peak temperature significantly depend on the sizing temperature as well as on the presence and absence of LaRC PETI-5 sizing interphase. The result showed that the carbon fiber/BMI composite sized at 150°C had the highest storage modulus at a measuring temperature of 250°C. The storage modulus decreased with increasing sizing temperature from 150°C to 350°C, being influenced by interdiffusion and co-reaction between the LaRC PETI-5 interphase and the BMI matrix resin. The present result is quite consistent with the interfacial result reported earlier in term of interfacial shear strength and interlaminar shear strength of carbon fiber/BMI composites. It is addressed that in the present composite system the sizing temperature of LaRC PETI-5 interphase critically influences not only the interfacial properties but also the dynamic mechanical thermal properties and its control is also important.     

Die Verfestigungserholung von plastisch verformten Steinsalzeinkristallen

Cylindrical rock salt single crystals have been plastically deformed by compression in the [001]-direction at room temperature to shear stresser τ _E of 200 N/cm² and 350 N/cm², respectively. Isochronal annealing experiments reveal, that workhardening recovers at >300° C. The characteristic annealing temperature was found between 400° C and 450° C. At 600° C the residual workhardening still amounts to 15–20%. The isochronal reduction of screw dislocation density between 400 and 600° C shows qualitatively the same behaviour as recovery of workhardening. From the isothermal annealing curves of the samples deformed to 200 N/cm² the activation energy for recovery of workhardening was found to be about 1 eV. Assuming that the kinetics of recovery can be explained by processes distributed in activation energy, an approximate spectrum of activation energies (with a maximum arising at ～1 eV) has been evaluated. The results show that recovery of workhardening after low deformation (stage I of the stress strain curve) is mainly due to the dislocations.     

Preferred orientation of ZnO nanoparticles formed by post-thermal annealing zinc implanted silica

High quality zinc oxide nanoparticles with (002) preferred orientation were prepared by post-thermal annealing zinc implanted silica at 700 °C using two methods. One method was annealing zinc implanted silica at 700 °C for 2 h in oxygen ambient; the other method was sequentially annealing zinc implanted silica at 700 °C in nitrogen and oxygen ambient for 1 h, respectively. X-ray diffraction (XRD), absorption and microphotoluminescence (micro-PL) results indicated that the latter method could create high quality ZnO nanoparticles with (002) preferred orientation and narrow size-distribution. X-ray photoelectron spectra (XPS) showed the formation of ZnO nanoparticles on a silica surface, where the ZnO nanoparticle content increased with increasing oxidation time in an oxygen environment. The processes of the transformation from Zn to ZnO are discussed.