Structural and magnetic properties of FePd and CoPd alloy epitaxial thin films grown on MgO single-crystal substrates with different orientations

FePd and CoPd alloy thin films were prepared on MgO single-crystal substrates of (001)_B1, (110)_B1, and (111)_B1 orientations at 600 °C by ultra high vacuum rf magnetron sputtering. L1₀-FePd(001) films with the c-axis perpendicular to the substrate surface are obtained on MgO(001)_B1 substrates. FePd epitaxial films consisting of L1₀(110) and L1₀(011) crystals are formed on MgO(110)_B1 substrates. The c-axis of L1₀(110) crystal is parallel to the substrate surface, whereas that of L1₀(011) crystal is 44° canted from perpendicular direction. L1₀-FePd(111) films with the c-axis 54° canted from the perpendicular direction are formed on MgO(111)_B1 substrates. L1₀ ordering degree of these FePd films varies depending on the substrate orientation. On the other hand, disordered CoPd thin films of (001)_A1, (110)_A1, and (111)_A1 orientations epitaxially grow on MgO substrates of (001)_B1, (110)_B1, and (111)_B1 orientations, respectively. The magnetization properties of L1₀ ordered FePd and A1 disordered CoPd thin films are influenced by the crystal structure, the ordering degree, and the film orientation.     

GaAs-AlGaAs外延结构中微区应力的电子背散射衍射分析

采用电子背散射衍射(EBSD)技术,以30～40nm的空间分辨率,显示GaAs-AlGaAs外延结构中的应力分布.将菊池花样质量IQ和Hough峰,以及晶格错配和局部转动等测量参数作为应力敏感参数,分析GaAs-AlGaAs周期外延层中的应变状态.通过对菊池花样进行快速傅立叶变换和强度计算识别微区应变区域.     

Atomistic simulation of epitaxial interfaces and polytypes

In this paper we discuss howab initio local density electronic structure calculations can be used to investigate extended defects such as interfaces and polytypes. LMTO-supercell calculations have been performed to understand the nature of bonding in epitaxial metal/ceramic interfaces such as Ag/MgO(001) and Ti/MgO(001). Cohesive and electronic properties of hexagonal polytypes of diamond, with different stacking sequences, have been predicted for the first time and compared with the available experimental data. The relative stabilities of 4H, 6H and 8H diamond polytypes have been calculated using a generalized version of force theorem.     

Electron structure of thin fullerene films deposited by various methods

The valence-band photoelectron spectra and the photoelectron energy loss spectra behind the C1s peak in the X-ray photoelectron spectra were studied in thin fullerene films deposited by various methods. The fine structure in the density of states near the valence band bottom observed for the fullerene films deposited by the method of pulsed supersonic molecular beam (SMB) with a helium carrier may be indicative of the presence of a long-range order. The spectra of π-plasmon losses in the films obtained by methods of thermal and SMB deposition exhibit a significant difference that can be related to a closer packing of C₆₀ molecules in the latter case.     

Electron microscope diffraction characterization of the fibrous structure of poly (sulphur nitride) crystals

The work reported here concerns the fibrous microstructure of macroscopic poly (sulphur nitride) crystals of current topicality in view of their metallic and superconducting properties. Following the outline of the synthesis by solid state polymerization, together with the achievement of the desired crystal habits appropriate for this study, methods for making the crystals accessible for transmission electron microscopy and diffraction are described. The principal features of the diffraction patterns were in accord with the crystal structure reported previously but additional ones were also observed which amongst others corresponded to a doubling of the unit cell and to twinnings, including a so far unreported twin mode on (¯1 0 1). The reflections were highly streaked along the layer lines and, significantly, the streaks were observed as a set of regularly spaced spots flanking the main reflections. This indicates the existence of a periodicity perpendicular to the chains beyond that of the atomic lattice. The spacing corresponds to 200 Å as obtained from the closest spot separation which, in turn, indicates a representative fibre diameter of this magnitude. The latter broadly corresponds to the 250 Å obtained as an upper limit of the wire diameter deduced from conductivity measurements by Civiak et al. The transmission image confirmed the existence of a longitudinal periodicity but this was of variable magnitude with a minimum of 25 Å. The latter is at least consistent with a fibre diameter of 30 Å previously observed on bromine-treated samples. Consistency with the diffraction pattern requires an integral relation between the range of periodicities seen, of which the 25 Å should be the basic and the 200 Å a representative maximum unit. The origin of the fibrous structure in terms of the solid state polymerization is discussed with two possible mechanisms in view: (1) phase separation during simultaneous polymerization and crystallization, and (2) twinning occurring during polymerization from solid solution. However, neither of these would account for the periodicities observed without invoking additional factors raised in the discussion.     

Direct synthesis of epitaxial zinc sulphide layers on zinc single-crystal substrates

Epitaxial thin zinc sulphide layers have been grown by direct synthesis on the basal face of zinc single crystals. Sulphur vapour reacted on the surface of the crystals, which were grown in sealed glass ampoules evacuated to 10^?6 torr. The thicknesses of the layers investigated varied from several hundred to 1000–1500 Å. The morphology, structure and epitaxy of the films were examined by electron microscope, electron and X-ray diffraction techniques. It was found that the film lattice had a sphalerite-type cubic structure, the perfection of the layer structure increasing with rise in both the substrate temperature and the sulphur vapour pressure. The layers were produced at substrate temperatures of 250°–400°C: polycrystalline ZnS films were obtained in the range 250°–300°C; at higher temperatures a definite texture gradually appeared and above 370°C, with a sulphur vapour pressure of 0.2–10 torr, the films became epitaxial. The following epitaxial relation was established:

$\text{{111} ZnS ∥ {0001} Zn}$

with

$\text{<110 > ZnS ∥ <11}\text{20}\text{> Zn}$

The zinc sulphide films reproduced the surface structure of the supporting zinc single crystals very well and could conveniently be used as electron microscope replicas.     

Electron microscopy: probing the atomic structure and chemistry of grain boundaries, interfaces and defects

At the heart of ‘ dynamic embrittlement’ phenomena is the stress-induced segregation of microscopic quantities of embrittling impurities to fracture surfaces. Grain boundaries and interfaces are often the natural weak links in a material. The structural and chemical information of such internal interfaces can be probed on an atomic scale using transmission electron microscopy. High-resolution electron microscopy can be used to determine the atomic coordinates of crystalline interfaces. Electron-energy-loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy can be performed on any boundary or defect and can provide chemical information such as composition and bonding. The spatial resolution of EDS is limited by low collection efficiency to around 10 Å. The more efficient signal collection for EELS allows almost atomic resolution for light elements. EELS fine structure offers a fingerprint of the local boundary arrangements, and also insight into the bonding (and possible reactivity) of boundaries and other defects. Overall, electron microscopy can be used to identify the atomistic characteristics of those interfaces susceptible to dynamic embrittlement. The structural and electronic information obtained can be used as a starting point for semi-empirical and ab initio simulations.     

Electron microscope study of non-stoichiometric titania

The distribution and coexistence of Magnéli phases (Ti_nO_2n−1) withn=4, 5 and 6 in hydrogen-reduced TiO₂ has been investigated using transmission electron microscopy. The major phase was Ti₅O₉. Ti₆O₁₁ was found in Ti₅O₉ grains in the form of narrow lamellae (<10 nm wide) epitaxially intergrown on (001) planes. The Ti₄O₇ phase, however, was never observed as a second phase in Ti₅O₉ grains but formed single-phase grains. The Ti₅O₉ phase was twinned on the (011)_r planes of the rutile subcell structure and the Ti₆O₁₁ lamellae were pinned to these twins. This pinning may be responsible for the hysteresis that occurs during the oxidation-reduction of non-stoichiometric TiO₂. We also report observations onin situ oxidation of the line phases.     

Electron diffraction of precipitates at copper-cordierite interfaces

The precipitation of copper particles at the interface between a copper rod and a MgO-Al₂O₃-SiO₂ ceramic was investigated by Robinson back-scattered SEM and convergent beam micro-diffraction TEM. A 20 μm wide zone depleted of copper separated the copper rod from a 70 μ m region of copper-containing particles dispersed in the ceramic matrix. The precipitates were crystallographically identified as elemental copper by matching of convergent beam, inelastically-scattered, Kikuchi patterns.     

Electron microscope investigation of defect structures in V6O13

The crystallinity of a sample of V₆O₁₃ has been investigated by high resolution electron microscopy. Specimen crystals show a high degree of perfection in the (001) layers of octahedra, with only occasional defects, but the layers are not stacked in a regular fashion. Preliminary analysis of the spacings has shown that defects occur when additional CS planes are inserted into the V₆O₁₃ structure.     

Microstructural investigation of interfaces in CMCs

This paper is focused on the importance of pyrocarbon interfaces in two types of ceramic matrix composites (C_f–SiC and SiC_f–SiBC), during creep tests under argon. The development of micromechanisms which consume energy and then allow a damage tolerance, depends on the morphology of the fiber/matrix interphase, which has been investigated by TEM and HRTEM.     

Electron heat conductivity of epitaxial graphene on silicon carbide

The diagonal component of the electron heat conductivity tensor of epitaxial graphene formed in a semiconductor has been investigated within a simple analytical model. It is shown that the heat conductivity sharply changes at a chemical potential close to the substrate band gap edge. Low-temperature expressions for the heat conductivity are derived.     

Experimental investigation on the piezo-composite actuator with piezoelectric single-crystal layer

Studies on muscle mimicking actuators have increased in the last two decades due to the possibility of various applications for compact lightweight actuators including small unmanned aircrafts, missile, and biomimetic robots. Piezoelectric materials have been used in a variety of applications ranging from shape control of structure and active vibration control of structure to noise suppression due to compact size and good frequency response. Conventional polycrystal piezoelectric ceramic materials, however, have limited actuating strains and displacement, hindering their use in actuators for small aerospace vehicles. In this study, the design and fabrication method of an actuator with a piezoelectric single-crystal layer were investigated to increase the actuation strain and displacement. From a comparison of the performance of the LIPCA-C2 and LIPCA-S prototypes, it was found that the new LIPCA-S2, which has much higher coefficient of the unimorph actuator, can generate an actuating displacement more than twice that of LIPCA-C2.     

Electron microscope examination of the surface topography of ion-bombarded copper

Transmission electron microscopy of thin, polycrystalline copper foils has revealed the formation of a sputtering structure after bombardment at normal incidence with Xe⁺, Cu⁺, or Pb⁺ ions of 50 to 80 keV energy. In general, the surface of each individual grain degenerates into a hill and valley structure, so as to develop those {100} faces lying nearest to the plane of the surface. The sputtering structure has been found to be independent of any prior electropolishing surface structure. Similarity between the spacing and crystallographic direction of the sputtering structure, and the general appearance of the dislocation arrays produced by ion bombardment, suggests that these dislocations could influence the initiation of the structure. A tentative model based on this hypothesis is proposed to account for the periodicity of the observed sputtering effect.