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A new structure model of Au4Mg is proposed for the long-period superstructure which exists in the Au–Mg alloys with 16–22 at.% Mg at 570–470 K and gives electron diffraction patterns of the two-dimensional antiphase structure of Cu3Pd-type (2d–Cu3Pd), with the aid of high-resolution structure images taken with the 1000 kV electron microscope. The superlattice has monoclinic symmetry with the space group P21/m (No. 11), and the lattice parameters are A = 5a, B = b, C = 4c and β = 90°, where a(= b) and c(≃a) are those of the fundamental face-centred cell. The structure can be described as the two-dimensional antiphase structure having the first- and second-kind boundaries parallel to (001) and (100), respectively, and the domain size of 2.5a × b × 2c. Nearest-neighbour Mg atom pairs are not formed across the second-kind boundaries in this structure, in contrast with the ideal 2d-Cu3Pd-type structure.

A superstructure of TiS1.62 is determined by 100 kV high-resolution electron microscopy, in which the arrangement of metal vacancies is obtained from structure images. The crystal has monoclinic symmetry (pseudo-hexagonal) with lattice parameters a = 11.9, b = 6.85, c = 11.5A, β = 90°. The space group is considered as F2m. Metal vacancies are confined to every second metal layer and ordered within the partly filled metal layer, resulting in formation of a (2H)22C type of superstructure. The ordered metal vacancy layers are arranged in 2C-type stacking sequence along the c axis, while sulfur atoms are arranged in 2H-type stacking sequence along the c axis.

The boundary structures of translation domains in the ordered β-Ni3Nb phase are studied by means of high resolution electron microscopy. Five structure models of translation domain boundaries in (100), (001), or (101) plane supported by superstructure images are proposed. Die Grenzstrukturen von Translationsdomanen in der geordneten β-Ni3Nb-Phase wird mittels hoch-auflosender Elektronenmikroskopie untersucht. Funf Strukturmodelle der Translationsdomanengrenzen in der (100)-, (001)- oder (101)-Flache, die durch Superstrukturdiagramm bestatigt werden, werden vorgeschlagen.

High-resolution front views of reconstructed (111) gold surfaces have been obtained by electron microscopy, using several layer-diffracted beams. From two different models for the reconstructed surface, we have computed images taking into account the interaction of the electrons with the reconstructed surface and with the bulk gold. Comparison between these computed images and the experimental ones allows us to choose which of the models corresponds best to the experimental evidence.

SUMMARY Easy preparation of thin crystalline specimen supports for high resolution electron microscopy has been achieved by thermic exfoliation of vermiculite. The thinnest layers obtained appear to be 1·8 nm thick and show the expected hexagonal array with a 0·46 nm lattice spacing. This periodic background could be suppressed either by optical filtering or by putting a zero crossing of the respective transfer function of the electron microscope objective over the diffraction spots of the crystal.

Determination rigoureuse de la position des rangees des atomes de vanadium paralleles au faisceau d'electrons incidents dans une feuille mince {100} et localisation precise de la maille sur l'image reticulaire

Hexagonal incommensurate long-period superstructures of the Cu-Sb alloys containing 18-20 at.% Sb have been investigated by means of superstructure imaging using a high-resolution electron microscope. Honeycomb-type distributions of hexagonal domains consisting of the commensurate superstructure of type 7ao-2H are observed. The incommensurabilities of superstructure can be interpreted well with a hexagonal model composed of the 7ao-2H domains surrounded by domain walls which contain higher Sb content than the domain interior. The observed image contrast is reproduced well with multislice computer simulations based on the structure models proposed for the 7ao-2H domain and the domain wall.

High-resolution electron microscopy (HREM) was performed on a modulated lattice structure (tweed structure) appearing prior to the FCC-FCT martensitic transformation of Fe-Pd alloys. The local lattice modulations of the cubic phase were quite irregularly distributed in the matrix, which supports the 'embryo model' of the tweed structure. Furthermore, the image simulation based on the model well reproduced the features observed in the high-resolution images.

Although facilities for high resolution electron microscopy (HREM) are available, interpretation of micrographs at high magnifications is far from unambiguous. The interpretation of the micrographs using a computed structure analysis program is therefore necessary. The paper presents the theory behind HREM, together with a computer method for image interpretation. Special reference is made to the JEOL JEM 200CX transmission electron microscope used in the study of sodium beta-alumina.

Talc — a sheet silicate and tremolite — a chain silicate are found by electron microscopy and X-ray microanalysis to occur intergrown as bicrystals with sharp, fault-free boundaries in a talc-rich gemstone nephrite from Scortaseo, Puschlav Valley, Swiss Alps. The plane of intergrowth is the (010)-plane for both components. Curving, stepped interfaces are observed more rarely, and these suggest a reaction from tremolite to talc which stopped before completion. The Mg-ions necessary for this reaction may stem from the associated dolomite rock.

The fabric of high‐Tc Nb3Ge superconducting material synthesized by coevaporation in the vacuum has been investigated using 200‐kV high‐resolution electron microscopy. The grain texture deduced from the high‐resolution structure images, which consist of groups of small coaxial Nb3Ge grains (A15 structure) which have one cubic axis [001] in common, is observed and analyzed using the high‐resolution structure images. The coaxial grains are related by a rotation of approximately ±30° around the [001] axis. Crystallites of Nb5Ge3 composition having either a D88 structure or D8m structure are distributed at random in the fabric and are coherent with the adjacent Nb3Ge grains. The statistical distribution of grain sizes of each compound is reported. The average grain size of Nb5Ge3 compounds is smaller than half the average size of the Nb3Ge grains.

The oxidation of ZnTe surfaces, both in situ and ex situ, is studied by high-resolution electron microscopy. The in situ oxidation is induced by the incident electron beam inside the microscope column, and the process is followed in real time by atomic-resolution electron microscopy. The ex situ oxidation studies involve heating ZnTe crystals up to 260 °C in air for various periods, with subsequent observation by electron microscopy. In both cases, optical diffractograms are used to identify the phases present in the surface layers, using the lattice spacings of bulk ZnTe as an internal reference. For in situ oxidation, the oxidation sequence involved amorphization of the ZnTe crystal as Te is removed by a non-thermal electron stimulated process, with subsequent formation of hexagonal ZnO by oxygen diffusion into the sample. In ex situ oxidation, the main phases present are crystals of ZnO and Te metal, which usually give rise to layered surface regions, in the sequence ZnTe/Te/ZnO, with the large crystals (up to 100 nm) of Te in an epitaxial relationship with the bulk ZnTe and the small ZnO crystals (5 nm) in random orientations. This process involves the diffusion of Zn from the bulk ZnTe to the surface followed by reaction with oxygen in air to form ZnO. Mittels hochauflosender Elektronenmikroskopie wird die Oxydation von ZnTe-Oberflachen, sowohl in-situ als auch ex-situ, untersucht. Die in -situ-Oxydation wird durch den einfallenden Elektronenstrahl in der Mikroskopsaule induziert, und der Prozes wird in Realzeit durch atomar aufgeloste Elektronenmikroskopie verfolgt. Die ex-situ-Oxydationsuntersuchungen beinhalten die Aufheizung von ZnTe-Kristallen bis zu 260 °C in Luft mit verschiedenen Zeitdauern und nachfolgender Beobachtung durch Elektronenikroskopie. In beiden Fallen werden optische Beugungsdiagramme benutzt, um die in den Oberflachenschichten vorhandenen Phasen zu identifizieren, wobei die Gitterabstande von Volumen-ZnTe als inneres Bezugsmas benutzt werden. Bei der in-situ-Oxydation schliest die Oxydationsfolge die Amorphisierung des ZnTe-Kristalls ein, wobei Te durch einen nicht-thermischen elektronenstimulierten Prozes entfernt wird, mit nachfolgender Bildung von hexagonalem ZnO durch Sauerstoffdiffusion in die Probe. In der ex-situ-Oxydation sind die beteiligten Hauptphasen Kristalle von ZnO und Te-Metall, was gewohnlich Anlas zu geschichteten Oberflachenbereichen gibt mit der Folge ZnTe/Te/ZnO, mit grosen Te-Kristallen (bis zu 100 nm) in einer epitaktischen Beziehung mit Volumen-ZnTe und kleinen ZnO-Kristallen (5 nm) in statistischer Orientierung. Dieser Prozes schliest die Diffusion von Zn aus dem ZnTe-Volumen zur Oberflache gefolgt von einer Reaktion mit Sauerstoff der Luft zur Bildung von ZnO ein.

Observation des images en champ clair dans les directions [001] et [012). Analyse de la structure locale en liaison avec la diffusion en diffraction de l'odre a courte distance. Modele structurale dans la projection [001] qui permet d'expliquer la distribution de la diffusion en diffraction de l'ordre a courte distance

The contrast of electron microscope lattice images of a vanadium monosulphide with superstructures was dynamically calculated on the basis of the multislice method. Interactions of 80 waves were analysed. It was shown that the vacancy-rich vanadium sites were imaged as white spots not only at the very thin part but also at the thicker part inside the first equal-thickness contour, which appeared at the thickness of 60 A. A non-stoichiometric vanadium monosulphide, VS1.155, quenched imperfectly from the preparation temperature at 1217 °C, was examined on the basis of the lattice image observation by a 100 kV high-resolution electron microscope. Orderings in the inter- as well as intralayers could be recognized directly from the arrangement of the white spots. Interpretable lattice images appeared exclusively inside the first equal-thickness contour. A mixture of some different types of images was observed in a crystal fragment; in some band-like regions the 4C-type superstructure was found with almost the same structure as Fe7S8. Each band extended parallel to the (001) plane with thickness of at most 50 A and the orientation was in a twin relation to that of the adjoining one. The other regions showed less well-defined lattice images, although they gave the broad diffraction peaks ranging from the 4C- to 3C-type reflexions. In order to determine the phase relations at high temperatures the specimen was heated by focusing an electron beam on the portion slightly apart from the area under examination. The technique enabled us to observe only the heating effect. Upon heating, the 4C type first increased in volume, seen by the thickening of some bands. On further heating the 3C type increased in intensity on the diffraction pattern. The structure of the 3C type was estimated to be almost the same as Fe7Se8 except that the vacancy concentration fuctuated among the partially occupied vanadium layers.

High-resolution electron microscopy has revealed a difference in morphology of the crystallites of samples of LaPO 4 which are good and poor catalysts for the hydrolysis of aromatic chlorides. In the good catalysts an acicular habit is such as to expose chains of La and PO 4 ions which run parallel to the c axis of the crystal. Observations of lattice fringes include those of forbidden reflections, suggesting some modification of the structure, as well as revealing structural imperfections.

Single crystal pointed filaments produce a beam with high brightness and coherency — characteristics of great value in high resolution electron microscopy. However, they frequently have very short useful lifetimes due to their destruction by arcing within the gun. By improving the vacuum, reducing oil vapors and adopting a new cleaning process for gun components, these pointed filaments used with a conical Wehnelt cylinder can have a useful lifetime of 15–20 h.

The crystal structure of Au–Cd (30–32%) alloys has been studied at atomic level with a 1 MV electron microscope. The experimental images can be fitted well with many-beam dynamical calculations for the long-period superstructure (LPS) designated as 7a0−2H type. The structures with incommensurate periods consist of a number of domains of the 7a0−2H structure separated by antiphase boundaries which are composed of orthorhombic cells. The result demonstrates the potentiality of high-voltage, high-resolution electron microscopy for direct determination of the atomic arrangements in modulated structures of alloys.

Electron microscopists are on the threshold of achieving their ultimate goal: atomic resolution and identification. Success depends on a little more technology and a lot more dollars.

The microstructures of silicide Ni 5 Si 2 , which formed in self-supporting Ni-Si lateral-diffusion couples, have been studied using high-resolution electron microscopy. Two polytypes for Ni 5 Si 2 have been observed and the actual composition of one polytype is confirmed to be Ni 31 Si 12 . Local variations of the crystal structure of Ni 5 Si 2 are also observed and the results are compared to computer-simulated images.

High-resolution observations of Au–20.2 at.% Mg alloy have been carried out by using a 1 MV electron microscope. The many-beam images with the [001] axial illumination are interpreted in terms of the double hexagonal superstructure of 9a 0−4H type. With the aid of computer simulations by the multislice method, it is revealed that two kinds of interpretable image are obtained for different specimen thicknesses at the optimum defocus. The imaging conditions are discussed in comparison with the orthorhombic structure of the D023 type.

La microscopie electronique a haute resolution couplee avec la diffraction electronique fournit une excellente methode de caracterisation des polytypes. Illustration des differentes etapes de cette analyse. Presentation de quelques aspects theoriques de l'interpretation des images a haute resolution et de plusieurs cas illustrant le type d'informations pouvant etre obtenu

The incommensurate structure of strontium diniobate, Sr2Nb2O7, is formed below 488 K with a one-dimensional lattice modulation along the [100] direction. A model of the atom displacements due to this lattice modulation has been proposed from an analysis of the systematic extinction of the extra reflections due to the incommensurate structure. High-resolution electron microscopy clearly reveals the lattice modulation in the incommensurate phase. The observed images are well interpreted by image simulation of the proposed model.

The ordering mechanism in Ni3Mo is re-examined by means of high resolution electron microscopy. A more precise ordering sequence than was previously established is proposed and an unambiguous model for the metastable long period antiphase boundary structure Ni3.4Mo is found. Computer simulations on the stable Ni3Mo phase, exhibiting a stacking fault perpendicular to the electron beam, are performed to explain the non-expected high resolution images. Der Ordnungsmechanismus in Ni3Mo wird erneut mittels hochauflosender Elektronenmikroskopie untersucht. Es wird eine genauere als die fruher festgestellte Ordnungsfolge vorgeschlagen und ein eindeutiges Modell fur die metastabile langperiodische Antiphasengrenzstauktur N3,4Mo gefunden. Computersimulationen an der stabilen Ni3Mo-Phase, die einen Stapelfehler senkrecht zum Elektronenstrahl ergeben, werden durchgefuhrt, um die nicht erwarteten hochaufgelosten Bilder zu erklaren.

SUMMARY Nb3Ge-films synthesized on Mo-substrates by the co-evaporation method show a characteristic fabric with a quasi-twelvefold symmetry around the [001]-axis of the A15-type cubic structure. Among approximate +30°- and ±60°-rotation boundaries, grain boundaries having rotation angles between 28° and 29° are observed most frequently in the Nb3Ge-films. Using the high resolution electron micrographs, a Σ17-boundary having an ideal rotation angle of 28.07° is analysed and plausible boundary models on the atomic level are proposed.

The mechanism of coloration in CdSe-glass was investigated by HREM (high resolution electron microscopy) and microanalysis of X-ray dispersive spectroscopy. The results indicate that the colorations of CdSe-glass arise from both non-crystalline and crystalline forms of the CdSe particles.

The incommensuration of two high Tc Bi-Sr-Ca-Cu-O compounds has been investigated by electron diffraction and high resolution electron microscopy. The results suggest discommensuration rather than sinusoidal modulation of the atomic positions.

Thirteen anthracites of various origin were studied by modern electron microscopy techniques, microdiffraction, bright field, dark field and lattice imaging in the raw and progressively heat-treated state. The anthracites are known to behave like hard carbons below HTT 2000°C and like soft carbons above 2500°C. We have found that flattening of the pores, which is not present in hard carbons, occurs in anthracites and that this flattening induces a preferred orientation of the carbon planes above 1700°C, which in turn allows graphitization. This evolution of the carbon structure, demonstrated for the first time, is the essential phenomenon for anthracites. It becomes hidden by the promoting effect of impurities included in anthracites, if their concentration is too high.

Five different malignant tumors and two nasal polyps were examined by electron microscopy for diagnosis purposes. In all cases occasional large cells containing lysosomes interconnected by characteristic junctions were observed. The interlysosomal junctions appeared organized in zig-zag and ladder like configurations. The ultrastructural and morphometric analyses of these junctions postulated that the two configurations represented the same structure viewed in two different sectioning planes. High-resolution electron microscopic evidence suggests that the interlysosomal junction is organized as a 35-40 A thick pleated ribbon extending between a 200-A wide interlysosomal space, in close contact with the adjoining lysosomal membranes, without apparent integration into the membrane.

The structure of silica glass was investigated by high-resolution electron microscopy. Observed dark field images were compared with those calculated by a kinematical electron diffraction theory on the basis of random and crystallite models. Bright small spots with sharp contrast were observed in the dark field image, which were found to originate from crystallites. It was indicated that small crystallites of about 17 A in size were present in silica glass.

High resolution electron microscopy of ultrathin sections confirms the presence of a membrane surrounding the tapetal rods in the cat. Cats depleted of taurine exhibit disruption and disorganization of this membrane, probably the first stage of more severe tapetal degeneration. Histochemical localization of zinc shows it to be present on the periphery of the tapetal rods. The amount of zinc present on the periphery of the tapetal rods of taurine depleted cats was greatly reduced. Taurine in feline tapetum, confirmed by autoradiography and direct measurement, was also greatly reduced in taurine-depleted cats. We conclude that both taurine and zinc are localized on the periphery of the tapetal rods and that they contribute to the stability of the membrane. We have also confirmed earlier reports that the cat tapetal rods contain riboflavin and no detectable cysteine.

The structure of a complex two-dimensional supercell observed by high-resolution electron microscopy in a layered bismuthate has been deduced from structural chemistry principles. It is proposed that this superstructure should form the basis for a new type of homologous series of related structures. An n = 5 member of the series, with composition Bi18Ti9Fe14O66, has been synthesized and shown to have regions with the same two-dimensional superstructure.

The lattice imaging technique of high resolution electron microscopy has emerged to be a powerful method for investigating ultramicrostructures of crystals at the unit cell level. This technique can indeed be considered to be crystallography in real space. In this article, the principles and applicability of lattice imaging have been discussed along with a variety of applications. The applications discussed include the study of structures of solids, defects and dislocations, topochemistry of solid state reactions and silicate minerals.

High-resolution electron microscopy was performed on a new manganese dioxide (Rb0.27MnO2) with a giant tunnel to clarify the problem whether the 2x5 tunnel exists as a uniform structure unit, or some lattice defects or intergrowths must be present to stabilize such a giant tunnel. Neither defects nor intergrowths were observed in the crystal, and all the lattice images showed uniform fringes, indicating that the compound exists as a homogeneous crystal.

The enhanced resolution available in the latest generation of medium-voltage high-resolution electron microscopes can be utilized to study semiconductor interfaces in zone axes such as 〈100〉, 〈111〉 and 〈112〉, as well as the more familiar 〈100〉. This permits both “structural imaging” and three-dimensional reconstruction from two different projections. Preliminary results on semiconductor interfaces obtained with the JEOL 4000EX 400 kV instrument with point resolution better than 1.7 A are presented. In the discussion of interpretation of interface images the serious limitation of signal-to-noise ratio is raised. This is particularly poor in the case of ion-thinned samples. If signal-to-noise ratio could be improved to the theoretical shot-noise limit, it would permit much more extensive image interpretation and perhaps new classes of experiment such as point-defect imaging. We show that the high signal-to-noise ratio is attainable with in-situ specimen cleaning in a UHV electron microscope and report some results on Si surface science performed with our home-modified UHV high-resolution instrument.

Specimens were prepared from autopsied and biopsied human liver and lymph nodes and from Thorotrast granulomas surgically removed from patients who had been injected with this colloidal thorium dioxide. The lattice images of Thorotrast particles in the liver, lymph nodes, and Thorotrast granuloma, and in the Thorotrast solution, were observed by high-resolution electron microscopy. The fringe spacing of 0.32nm corresponding to the (111) atomic plane of ThO2 was determined. The mean particle sizes in the tissues and solution were estimated to be 10.8 and 8.1nm, respectively. Two kinds of recrystallization pattern were observed at the boundaries of particles in granular aggregates. Calcium needles coexisted with Thorotrast particles only in Thorotrast granulomas. The atomic rearrangement was more remarkable in the tissues than in the Thorotrast solution. Based on these experimental data, a model is proposed to explain the mechanism for the growth of granular aggregates of Thorotrast in human tissues; macrophages may take up Thorotrast particles and those particles may then unite tightly through atomic rearrangement.

Pristine and iodinated (SN)x were studied by high resolution electron microscopy. High resolution electron micrographs showing lattice fringes up to 0.22 nm were obtained. In these electron micrographs, the texture of (SN)x crystals was elucidated to be fibrillar or mosaic; the lattice fringes were observed in domains extended along the molecular axis (b-axis) and very narrow in the perpendicular direction. Each crystallite varied from place to place in size but maintained the b-axis orientation. The high resolution image of iodinated (SN)x did not show directly the location of iodine atoms and their presence was deduced only from the optical transform of the image. The optical transform showed that iodine atoms were not intercalated uniformly, but localized at the skin region on (SN)x fibers, where the crystal lattice was highly distorted. Then the iodination of (SN)x is supposed to result in the destruction of the crystal lattice by invasion of iodine atoms or to take place preferentially at a distorted crystal region.

Thin oriented films of some organic compounds can be prepared by either the vacuum-deposition method or the Langmuir-Blodgett method. The characterization of the structure of thin films is carried out by electron microscopy. The orientation of thin films is determined by several experimental methods : electron diffraction, decoration and high resolution electron microscopy for the vacuum-deposited films, and shadowing and replica methods for L-B films.

Recent advances in electron microscopy have opened up exciting new possibilities for examination of the fine structure of matter. Whereas X-ray or neutron-based methods give structures averaged out over about 1018 unit cells, high resolution electron microscopy can reduce this to some 104 unit cells. It is, as it were, now possible to study local variations in the terrain instead of the landscape as a whole. These local variations may represent regions of chemical constitution and activity different from those of the main structure.

After reviewing some of the structural problems that high-resolution electron microscopy (HREM), either alone or in concert with allied, electron-based techniques, is unlikely to be able to clarify, a summary of problems for which the technique is of unique value is presented with the aid of illustrative examples. These are drawn from the study of zeolites and other aluminosilicates, Fisher-Tropsch and other catalysts, carbon and graphite including various intercalates of the latter, defective diamonds, shape-selective sorbents and quasi-crystalline solids. Additional techniques with which HREM may be readily combined (electron-energy-loss and X-ray emission spectroscopy as well as Compton scattering of electrons) are also briefly discussed.

In the quaternary system H–Nb2O5–WO3–NbO2F the phase WNb15O40F was prepared in form of light-yellow needles. The compound crystallizes in the monoclinic system with the unit cell dimensions a = 22.254 A, b = 3.829 A, c = 20.298 A and β = 114.29°, space group C 2. Electron optical investigations showed the crystal structure containing 5 x 3 x co-blocks of Nb—(O, F)-octahedra, with metal atoms in tetrahedral positions located at the junctions of every four blocks. X-ray investigations showed a range of homogeneity between (O, F)/ (W, Nb) = 2.556 < 2.563 (WNb15O40F) < 2.571. The hypothetical phase WNb18O47F2 with 6 x 3-blocks was found as a microdomain by electron microscopy.

A technique is presented for enhancing and combining electron microscope images of small clystalline areas. Phases obtained by Fourier transforming electron micrographs are merged with available more precise amplitudes, in a Fourier synthesis, to obtain a final estimated image. The procedure is illustrated with 42 individual images of the purple membrane from Halobacterium halobium. To show the power of combination, results based on 1, 2, 4, 8, 16, 32 and 42 images are presented. An estimate based solely on the micrograph data, i.e. ignoring the precise amplitudes, is also presented and is seen to be notably poorer. The level of uncertainty of the final image is assessed by stimulating 10 final images and superposing the results.

SUMMARY A comparative survey of computer simulated and experimentally obtained images shows that it is feasible to observe, end-on, isolated single sheets of trigonally bonded carbon atoms in graphitic substances directly by electron microscopy, provided that certain imaging conditions are employed. For a typical commercial instrument (Philips EM300 with a spherical aberration coefficient of 1.6 mm) authentic images are found whenever the objective lens is set at underfocus positions between 65 and 110 nm, with optimum contrast occurring near the ‘Scherzer’ imaging condition of 95 nm underfocus. At this latter focus position the fringe contrast is maximal when the sheet extends in the direction of the electron beam for a distance of about 5.5 nm; but sheets as narrow as 1.0 nm (i.e. containing some four widths of benzene rings in the direction of the electron beam) should be detectable.

The electron microscope surpassed the optical microscope in resolving power 50 years ago, though at the time it did not receive an enthusiastic reception from scientists, technologists or members of the medical profession. Today atomic resolution has been achieved and high resolution electron microscopes are making an impact in materials science, in materials technology and in diagnostic medicine in the same way that optical microscopes did in the 19th century.

In summary of the final discussion session of the conference on high-resolution electron microscopy, the prospects for the use of high-resolution imaging and related techniques are reported to be exciting for the analysis of crystal structures, crystal defects and crystal surfaces, but considerable difficulties in instrumentation may prevent rapid progress in some directions. In other directions the limitations imposed by the nature of the interactions of electrons with matter have already been approached.

La microscopie electronique a haute resolution permet d'etudier des phases nouvelles trop petites pour les etudes aux rayons X, comme les phases apparentees a σ; elle permet d'etudier plus facilement les structures locales et fortement desordonnees comme les parois de domaines et des domaines de quelques mailles unitaires; elle permet d'ordonner plus facilement les atomes de solute comme les colonnes d'atomes Ti dans Cu 4 Ti