ISSN:0741-0581    

DOI:10.1002/jemt.1060120302

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractFour kinds of works on the detection of displacement of atoms in crystals are shown. The irregular small displacement of atoms has been detected, with an accuracy of about 0.1 Å around dislocations and stacking faults in Au crystals as shown by their electron microscope images. The displacement of the atomic images is recorded by aberration‐free focus (AFF). Even when the periodic displacement of atoms in SiC and TaS2crystals is around 0.1% of the lattice constant, this displacement has been revealed as the weak‐contrast anomaly in the images. Using in situ observations by a TV system attached to an electron microscope, the rapid movements of atoms that have taken place within 1/30 sec have been recorded. Using the technique of successive subtraction of the images by TV system and image sigma, only the images of moving atoms in Au crystal have been recorded each 1/10

ISSN:0741-0581    

DOI:10.1002/jemt.1060120303

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractHigh‐voltage electron microscopy has shown itself advantageous for the study of natural science, including biology, but especially for materials science. The most important advantage for materials science is for in situ experiments about the detailed processes of the phenomena that occur in bulk materials. The present paper is mainly concerned with several types of in situ experiments that have been carried out in the Research Center for Ultra‐High Voltage Electron Microscopy, Osaka University. The following subjects have been studied: (a) fundamental problems, such as the conditions necessary for in situ experiments, functional features of specimen treatment devices, and the effects of electron irradiation; (b) the dislocation behavior of crystals under various conditions; (c) high‐temperature behavior of refractory materials, mainly ceramic composites; (d) new applications of electron irradiation effects, such as amorphization of crystalline materials and electron‐irradiation‐induced foreign‐atom implantation; (e) environment‐matter interaction, mainly chemical amorphization of alloys; and (f) future trends of the in situ experiment, such as combinations with Auger valency electron spectroscopy and high‐resolution elec

ISSN:0741-0581    

DOI:10.1002/jemt.1060120304

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractA scanning electron microscope of ultra‐high‐vacuum (UHV‐SEM) with a field emission gun (FEG) is operated at the primary electron energies of from 100 eV to 3 keV. The instrument can form the images that contain information on surface chemical composition, chemical bonding state (electronic structure), and surface crystal structure in a microscopic resolution of several hundred angstroms (Å) using the techniques of scanning Auger electron microscope, scanning electron energy loss microscope, and scanning low‐energy electron diffraction (LEED) microscope. A scanning tunneling microscope (STM) also has been combined with the SEM in order to obtain the atomic resolution for the solid surface.The instrumentation and examples of their applications are presented both for scanning LEED microscopy

ISSN:0741-0581    

DOI:10.1002/jemt.1060120305

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractRecent studies of high‐resolution electron microscopy on the high‐Tcsuperconductors of Y‐Ba‐Cu‐O and Bi‐Ca‐Sr‐Cu‐O are presented. The observed images of crystals thinner than 3 nm, taken under conditions that approached the Scherzer defocus condition, directly show the arrangements of cations and oxygen‐vacant positions. The results reveal structural characteristics of the atomic scale; this offers important insights into the origin of the high‐Tcsuperconductivity. The usefulness of high‐resolution electron microscopy for studying complicated crystal structures is demonstrate

ISSN:0741-0581    

DOI:10.1002/jemt.1060120306

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThree observations described here were chosen not only to represent our recent interface studies in ceramics, but also to demonstrate how different the present status of interface research is with respect to the level of high‐resolution electron microscopy. Certain common features may be found among the problems of ceramic interface studies. Importance of basal plane grain boundary, for example, is one of the characteristics of this type of heterogeneous compound. The crystalline heterogeneity has been ignored largely in the grain boundary structure study since it has been developed primarily for cubic metals. The new area of basic grain boundary interface structure study is opened now that description of this type of interface has become engineeringly importan

ISSN:0741-0581    

DOI:10.1002/jemt.1060120307

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThermionic emission properties of several kinds of refractory carbides, nitrides, and borides of the transition metals in the form of powder were investigated with a newly developed measuring device and evaluated by the figure of merit defined as the ratio of the effective work function to the working temperature at which the vapor pressure becomes 1 × 10−5Torr. There are several materials whose thermionic emission properties are better than those of tungsten or compatible to those of tungsten among the carbides and borides, such as TaC, HfC, ZrC, LaB6, and CeB6, as judged by the figure of merit. New preparation methods for carburization, nitriding, and boriding of the wires of matrix metals and alloys were successfully developed for using these materials as the cathode of the electron microscope. Other necessary techniques such as spot welding and electrolytic etching were also developed. From the brightness characteristics, it was found that some of carbides, carbide solid solutions, and borides such as HfC, ZrC (Ta0.8–0.7Hf0.2–0.3)C, TaB2, and HfB2are very good emitters comparable to LaB6. It is emphasized that the work functions of the carbide‐solid solutions (Ta0.8Hf0.2)C and (Ta0.7Hf0.3)C, which have low rates of evaporation at high temperature, show no remarkable rise as compared with that of HfC, so that their figures of merit are better than that of HfC. Feasibility of providing good cathodes with HfC and (Ta0.8Hf0.2)C tips was demonstrated by taking high‐resolution electron m

ISSN:0741-0581    

DOI:10.1002/jemt.1060120308

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe critical voltages for systematic reflections and splits of Kikuchi lines were measured using a high‐voltage electron microscope to investigate the atomic temperature factors in cubic crystals. The split of the Kikuchi line at the intersection with the forbidden 222 Kikuchi line as well as the critical voltage of the 333 reflection for Si and Ge decreased steeply with temperature. The temperature dependence showed that the anharmonic contribution to the atomic‐temperature factor for Si and Ge is extremely weak in the temperature range 300 ∼ 1078 K. On the contrary, theBfactors obtained from the measured critical voltages for Al, Cu, and Fe varied nonlinearly with temperature, suggesting the importance of the anharmonic effect in the vibration of atoms. The observed temperature dependence of the critical voltages for the metals were compared with calculations based on harmonic, quasi‐harmonic, and anharmonic approximations. The quasi‐harmonic approximation that takes into account the thermal expansion modification reproduces well the observed values for Fe but not those for Al and Cu. The effect of intrinsic anharmonic vibration should be considered for reproducing the results for Al and Cu. Fitting the measured critical voltages with the calculated ones, we estimated the values for coefficients of the isolated atom potentials. The results are in good agreement with those obtained by neutron and X‐ray

ISSN:0741-0581    

DOI:10.1002/jemt.1060120309

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractSingle crystalline composite films of iron and MgO are prepared by a simultaneous vacuum deposition technique. The structures of the composite films, especially of the iron crystallites embedded, are studied by high‐resolution electron microscopy and nanometer‐area electron diffraction. The α‐iron (b.c.c.) crystallites of 1 nm in size are epitaxially embedded in single crystalline MgO films, the orientation being (011)[100]Fe/(001)[100]Mgoand (001)[110]Fe//(001)[100]Mgo. A heat treatment of the as‐grown films at 500–1,000°C brings about a phase transformation of the crystallites from α‐iron to γ‐iron (f.c.c.), followed by a grain growth of α‐iron and finally the growth of the spinel, MgFe2O4. The γ‐iron crystallites transformed are circular plates and have strains at the periphery to accommodate the surrounding MgO‐matrix. The magnetic property of the composi

ISSN:0741-0581    

DOI:10.1002/jemt.1060120310

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe structure of amorphous Se films, in the topological random system, has been studied by the computer‐simulation, electron diffraction (ED), and high‐resolution transmission electron microscopy (HRTEM). As an example of HRTEM of the cellular random system, our recent investigation on Ba‐ferrites is reviewed beforehand. In HRTEM images of spin‐glass BaTi2–xSnxFe4O11(x<0.6), magnetic clusters or clusters of FeO6‐octahedra surrounded by TiO6‐octahedra have been found. The structure of BaSn2Fe4O11(x = 2) has been determined. The ordering of Sn (Ti) and Fe ions increases with increasing x, which interprets the change from the spin‐glass state to nonspin‐glass state at x = 0.6. It is shown that a cluster of polarized lattice ions is detectable in images of polar‐glass BaxK2–xFexTi6–xO13(x ≥ 1.2). The structure models of amorphous Se films forming on a substrate have been constructed on a computer, and their radial distribution function (RDF) and HRTEM images have been calculated. Experimental RDF and HRTEM images have been obtained from vacuum‐deposited amorphous Se films and are compared with the calculated ones. It is concluded that in the as‐deposited films most of Se molecules may be composed of Se atoms as small as three and that by the electron‐beam irradiation the molecules link to form spiral chains in amorphous state and then arrange to have

ISSN:0741-0581    

DOI:10.1002/jemt.1060120311

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY