Epitaxial variations of Ni films grown on MgO(0 0 1)

Epitaxial Ni films were deposited on (0 0 1)MgO by DC magnetron sputtering under ultra-high vacuum conditions for studies involving magnetic-multilayer applications. The deposition temperatures of the Ni films studied in this work were 100 and 400°C. Examination by transmission electron microscopy (TEM) and electron diffraction revealed that the film deposited at the lower temperature was predominately Ni[0 0 1]MgO[0 0 1] and Ni(0 1 0)MgO(0 1 0) oriented and smooth, as expected. However, the higher temperature films were predominately of the Ni MgO[0 0 1] and Ni MgO(1 0 0) orientation and facetted. The orientation has been confirmed by X-ray diffraction, where this orientation was observed to be four-fold degenerate. For each of these four orientations there also existed a twin orientation, reflected about the MgO(1 0 0) planes, giving eight possible orientations for the Ni crystallites on MgO. This epitaxial relationship was studied by dark-field TEM and electron diffraction. Because these films were polycrystalline and hence produced many diffraction spots from both the Ni and MgO with similar lattice spacings, electron diffraction patterns of the films were indexed using an electron diffraction image processing (EDIP) technique. In this technique, the polycrystalline electron diffraction pattern was converted into a graph, with the x-axis displaying lattice spacings and the y-axis, integrated intensity.     

Investigation of the competitive grain growth during solidification of single crystals of nickel-based superalloys

The competitive growth of columnar grains in a single-grain selector, which is used for directional solidification of single-crystal blades from nickel-based superalloys, has been investigated by electron back-scattered diffraction and local X-ray diffraction analysis. It has been found that the competitive grain growth in a starter block is determined by the crystallographic factor: rapidly growing grains with the axial orientation close to the [001] direction dominate in this part of the casting. For the competitive grain growth in a helicoidal separator, the geometric factor (the position of a grain at the input of the separator) is also important. The results obtained suggest that an appropriate geometry of the single-grain selector was chosen. In addition, the distribution of the orientations of columnar grains obtained by electron backscattered diffraction, can be used for approximate estimation of the yield of suitable (i.e., with the deviation of the axial orientation from the [001] direction within a specified tolerance) single-crystal blades.     

Liquid crystals: applications and industry

Liquid crystals (LCs) are mesogenic phases of matter which combine liquid fluidity with crystalline solid properties. Precise knowledge of the molecular orientations – close to the boundaries and within the material bulk – is necessary for understanding their flow behaviour, especially in microfluidic settings. While the boundary conditions are set, passively, by surface-induced molecular orientations, the bulk orientation in flow is determined, actively, by the anisotropic coupling between the flow and the molecular orientation. Together, the surface and the bulk orientations offer a range of topological constraints within microfluidic channels, which affect the evolution and sustenance of flow-induced phenomena in LC-based systems. The concept of topological microfluidics can be extended to different classes of anisotropic fluids, allowing us to explore and to employ such fluids as complex functional materials for microfluidics, thereby significantly broadening the reach of conventional microfluidics.     

Investigation of orientation relationships by EBSD and EDS on the example of the Watson iron meteorite

The suitability of the electron back‐scatter diffraction technique (supported by EDS) in order to study the complex microstructures of iron meteorites is demonstrated on the example of the Watson meteorite. The orientation relationships between the main phases kamacite, taenite and schreibersite/rhabdite as well as effects of the real structure have been investigated. In kamacite bands highly deformed blocks appear which show a contineous change of orientation. Plessitic regions are surrounded by deformed taenite lamellae. Also these lamellae show the typical M‐profile of the Ni concentration in cross section. In the center a martensitic microstructure has been proven. The white plessite is characterized by a high number of individual kamacite grains which however are separated mainly by low‐angle boundaries. So an orientation clustering occurs. The determination of orientation relationships was only possible for a single plessite region comparing the intensity distribution in pole figures with simulations. Schreibersite is brittle and shows a high number of microcracks. However, the strong deformation of kamacite does not allow us to decide whether an orientation relationship between the phosphides and the surrounding kamacite exists or not. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transmission electron microscopy study of defects in AlN crystals with rough and smooth surface grains

Defects present in (0 0 0 1) textured polycrystalline AlN grown by the sublimation–recombination method were analyzed using transmission electron microscopy (TEM) methods. Grains in the polycrystalline boule had either a smooth or a rough surface. The rough surface grains had mainly edge dislocations, whereas the smooth surface grains had some sub-grain boundaries and were mostly free of dislocations. Dislocations at the grain boundaries were pinned and could not be annihilated.     

Study of the influence of the parameters of an experiment on the simulation of pole figures of polycrystalline materials using electron microscopy

A two-dimensional mathematical model of a polycrystalline sample and an experiment on electron backscattering diffraction (EBSD) is considered. The measurement parameters are taken to be the scanning step and threshold grain-boundary angle. Discrete pole figures for materials with hexagonal symmetry have been calculated based on the results of the model experiment. Discrete and smoothed (by the kernel method) pole figures of the model sample and the samples in the model experiment are compared using homogeneity criterion χ², an estimate of the pole figure maximum and its coordinate, a deviation of the pole figures of the model in the experiment from the sample in the space of L₁ measurable functions, and the RP-criterion for estimating the pole figure errors. Is is shown that the problem of calculating pole figures is ill-posed and their determination with respect to measurement parameters is not reliable.     

Oriented polycrystalline α-HgI2 thick films grown by physical vapor deposition

This work investigates the growth of polycrystalline α-HgI₂ thick films from physical vapor deposition. By varying the growth conditions, the as-deposited thick films are characterized by scanning electron microscopy, X-ray diffraction, current–voltage and photoconductivity measurements. The growth mechanism and its effects to the properties of these polycrystalline α-HgI₂ thick films are then discussed. Finally, the best deposition conditions for polycrystalline α-HgI₂ thick films compactly formed by separated columnar monocrystallines with uniform orientation along c-direction and with good crystallinity are reported.     

Structural Properties of CuGaxIn1-xSe2 Thin Films Deposited by Spray Pyrolysis

Thin films of CuGa_xIn_1-xSe₂ (x=0.0-1.0) have been prepared by spray pyrolysis onto soda-lime glass substrates heated to a temperature of 325° C. The structure, crystal orientations, lattice parameters and grain size of the experimental films have been studied using the X-ray diffraction and scanning electron microscopy. All the deposited films were polycrystalline and showed single phase with an intense (112) orientation. The lattice parameters, a and c of the films vary linearly with the change of gallium composition. The grain size of the films decrease with the increase of gallium content.     

Bildungsbedingungen und Struktur dünner Bi1−xSbx-Schichten

Thin polycrystalline Bi_1−xSb_x films in oriented state were deposited by flash evaporation techniques and by catode sputtering. In dependence on the conditions of formation the structure of these films was analysed by means of transmission electron microscopy, electron diffraction and electron beam microanalysis. Estimating the orientation, quality of surface and largeness of the average diameter of the crytallites the flash evaporation technique is superior to the catode sputtering under the experimental conditions chosen in this investigation. The Bi:Sb proportion does not change in comparison with the target, material of the source respectively, during the formation of the film.     

Effect of Thermal Annealing on Structural Properties,Morphologies and Electrical Properties of TiO2 Thin Films Grown by MOCVD

TiO₂ thin films, were deposited on Si(100) and Si(111) substrates by metalorganic chemical vapor deposition at 500 °C, and have been annealed for 2 min, 30 min and 10 hours at the temperature from 600 °C to 900 °C, in oxygen and air flow, respectively. XRD and atomic force microscopy characterized the structural properties and surface morphologies of the films. As‐deposited films show anatase polycrystalline structure with a surface morphology of regular rectangled grains with distinct boundaries. Rutile phase formed for films annealed above 600 °C, and pure rutile polycrystalline films with (110) orientation can be obtained after annealing under adequate conditions. Rutile annealed films exhibit a surface morphology of equiaxed grains without distinct boundaries. The effects of substrate orientation, annealing time and atmosphere on the structure and surface morphology of films have also been studied. Capacitance‐Voltage measurements have been performed for films deposited on Si(100) before and after annealing. The dielectric properties of TiO₂ films were greatly improved by thermal annealing above 600 °C in oxygen.     

Determination of orientation distribution function from pole figures with reflection coincidences

Three-dimensional texture analysis is now an efficient tool for examining polycrystalline materials. Owing to its widespread application, the possibilities and restrictions of determining the orientation distribution function on the basis of various kinds of experimental data should be recognized. With this in mind, the paper considers pole figures featuring reflection coincidence.     

F.C.C. Rolling Texture Transitions in Relation to Constraint Relaxation

A complete set of f.c.c. rolling texture predictions, obtained with the use of a relaxed constraint model, is presented in this paper. The whole spectrum of textures between the copper and brass types can be found if some components of reaction stresses (between grains and the matrix) are relaxed. The best prediction of the copper type texture is found if ϵ₁₃ is a free parameter and the other components of grain deformation tensor are controlled by reaction stresses. The best prediction of the brass type texture is obtained if ϵ₁₂, ϵ₁₃ and ϵ₂₃ are free parameters. However, a decisive factor for the texture transition from the copper to the brass type is the relaxation of the ϵ₁₂ component. We present for all the considered cases the orientation distribution functions (O.D.F.) and also the pole figures for some selected cases. Nous présentons pour tous les cas les fonctions de distribution d'orientations cristallines ainsi que dans certains cas — les figures de pǒles.     

Mixed-phase solidification of thin Si films on SiO2

Mixed-phase solidification (MPS) is a new beam-induced solidification method that can produce large-grained and highly (1 0 0)-surface textured polycrystalline Si films on SiO₂. The grains resulting from this mixed-phase solidification (MPS) method, which was conceived based on a well-known phenomenon of coexisting solid–liquid regions in radiatively melted Si films, are found to be essentially devoid of various intragrain defects that always plague, and subsequently degrade the utility of large-grained Si films previously obtained using other crystallization techniques. It is experimentally shown that multiple exposures are required in order to generate such a polycrystalline microstructure from an initial amorphous precursor. The observed trends are conceptually explained in terms of the melt being initiated primarily at grain boundaries in polycrystalline films, and melting and solidification subsequently proceeding laterally at interface-location specific rates as determined by the local thermodynamic factors, which include the anisotropic surface and interfacial energies of the grains, and the unusual local thermal profile—all transpiring within a near-equilibrium but nonisothermal and dynamic environment that needs to address the thermal and stability requirements associated with the coexisting solid–liquid regions.     

Crystal structure refinement from electron diffraction data

A procedure of crystal structure refinement from electron diffraction data is described. The electron diffraction data on polycrystalline films are processed taking into account possible overlap of reflections and two-beam interaction. The diffraction from individual single crystals in an electron microscope equipped with a precession attachment is described using the Bloch-wave method, which takes into account multibeam scattering, and a special approach taking into consideration the specific features of the diffraction geometry in the precession technique. Investigations were performed on LiF, NaF, CaF₂, and Si crystals. A method for reducing experimental data, which allows joint electron and X-ray diffraction study, is proposed.     

Fast synthesis of Cu‐doped ZnO nanosheets at ambient condition

A new, fast and low cost method to produce Cu‐doped ZnO nanosheets is reported for the first time in this paper. Zinc foil specimens were immersed into CuSO₄ aqueous solutions with various concentrations for 3 seconds and then dried at ambient condition. The immersed specimens were characterized with a scanning electron microscope, an X‐ray diffractometer and a transmission electron microscope. The results show that Cu‐doped ZnO nanosheets with a multilayer structure on a cupper layer are formed. Cu‐doped ZnO nanosheets show hexagonal crystalline structure and comprises polycrystalline grains with diameters of 5∼10 nm. A physical modal is suggested to explain the prepared Cu‐doped ZnO nanosheet structure, based on the chemical reactions and a metallurgical cell.     

断续磨削加工聚晶金刚石的机理研究

分别采用超声振动冲击和脉冲激光加热技术对开槽金刚石砂轮断续磨削加工聚晶金刚石过程中的机械冲击和热冲击进行了模拟实验研究.研究结果表明,在断续磨削加工过程中,由于开槽砂轮和工件之间接触面积变化引起的磨削力周期性变化,有利于聚晶金刚石材料加工表面上的晶粒产生脆性微细破碎去除;由于开槽砂轮和工件之间接触面积变化引起的热冲击,有利于聚晶金刚石材料加工表面上的晶粒产生微细裂纹和疲劳破碎.实验结果表明,开槽金刚石砂轮磨块切入部分的磨粒以破碎损耗为主,磨块切出部分的磨粒以机械磨耗、氧化、石墨化损耗为主.     

Oriented Thin Films of the Low-Band-Gap Polymer PTB7 by Friction Transfer Method

Low-band-gap polymers are promising materials for organic photovoltaic application. We prepared an oriented thin film of a low-band-gap polymer, PTB7, by friction transfer method. The oriented film showed a strong dichroic absorption in the whole visible range. The orientation of molecular chain was characterized by two-dimensional grazing incident X-ray diffraction (2D-GIXD) with synchrotron radiation. 2D-GIXD results showed PTB7 molecular plane parallel to the substrate plane, i.e., “face on orientation.”     

Ihnomogeneous Distribution of Doping Elements in Polycrystalline GaP

The distribution of Te and Zn in polycrystalline GaP ingots grown by SSD method was studied by means of the contact resistance measurements between a tungsten carbide probe and a lapped sample surface. The differencies in carrier concentrations measured in differently oriented GaP :Te crystal grains were found as high as one order of magnitude. In GaP: Zn crystals the constant Zn concentration throughout the sample was observed.     

Low-temperature Si epitaxy on large-grained polycrystalline seed layers by electron–cyclotron resonance chemical vapor deposition

The epitaxial thickening of polycrystalline Si films on glass substrates is of great interest for the realization of crystalline Si thin film solar cells and other large-area thin film devices. In this paper we report on the epitaxial growth of Si at temperatures below on polycrystalline seed layers using electron–cyclotron resonance chemical vapor deposition. The Si seed layers were prepared by aluminum-induced crystallization. The quality of the ECRCVD-grown films strongly depends on the orientation of the underlying seed layer grains. Due to a mainly favorable orientation of the seed layers more than 73% of the substrate area were epitaxially thickened. It turned out that a (1 0 0) preferential orientation is favorable for epitaxial thickening. This, however, is not the only requirement for successful low-temperature epitaxial growth of Si.