Search

High-resolution electron microscopy is used to study interfaces between solids with varying degree of atomic ordering. Applying a recently developed technique the structure of amorphous germanium near (111) oriented crystalline silicon is described by its two-dimensional distribution function ρ(x,y) of atoms, and properties of ρ(x,y) are extracted from experimental images. Using extensive image simulations it is further shown that the technique is suitable to measure composition profiles at coherent heterointerfaces.

Growth of Ni on (001) Au has been widely studied. Furthermore it has been shown that a structural change occurs when an Au/Ni multilayer is heated up. This transformation can be described as an ordering which is unexpected from the equilibrium phase diagram. A high-resolution electron microscopy study of the transformation of a coherent Au/Ni multilayer is presented in this paper. The transformation has been characterized by in-situ HREM and by extensive image processings made on both simulated and experimental images.

The structure of grain boundaries in a granite-origin ultramylonite, composed mainly of fine-grained feldspar and quartz, was studied by high-resolution electron microscopy (HREM). At most of the boundaries, not only between the same minerals but also between different minerals, lattice fringes in adjacent grains meet at the interface with no other appreciable phases. In these boundaries, some of the straight segments correspond to a low-index plane of one of the connected grains. Boundaries containing voids, with a spheroidal shape elongated along the boundaries, were observed only between quartz grains. It is suggested that these boundaries were formed by healing of microcracks. The structural width of major boundaries, deduced from lattice-fringe imaging, is less than about 0.5 nm.

Environmental electron microscopy has become an important scientific method for fundamental studies of dynamic chemical reaction processes in heterogeneous catalysis and of catalytic growth of carbon nanotubes. Outstanding contributions are resulting from the ability to observe gas‐catalyst surface reactions in situ, on the atomic scale. A great deal of structural and chemical information including lattice modification of working catalysts is possible. This is key to understanding novel reaction processes, including release mechanism of structural oxygen in oxide catalysts in selective oxidation of hydrocarbons and to designing improved catalysts. This brief survey of the recent spectacular developments in environmental high resolution electron microscopy shows that new opportunities are being opened up in catalysis.

Glomerulocyte cellulosic bundles of Polyzoa vesiculiphora were investigated by microdiffraction and high-resolution electron microscopy. In each bundle, hundreds of cellulose microfibrils, having a rectangular cross-sectional shape, are packed regularly with their 0.6 nm lattice planes parallel to each other. Lattice images reveal that the 0.6 nm plane is parallel to the longer edge of the cross section which is similar to the lattice organization of cellulose with a squarish cross section in Valonia spp. More interestingly, all the microfibrils in a bundle have the same directionality of crystallographic c-axis, which suggests that the biosynthesis of the microfibrils within particular bundle occurs unidirectionally.

Submicrometer-grained (SMG) structures were produced in Cu and Ni using an intense plastic straining technique, and the grain boundaries and their vicinities were observed by high-resolution electron microscopy. The grain boundaries exhibited zigzag configurations with irregular arrangements of facets and steps, and thus they were found to be in a high-energy nonequilibrium state. A similar conclusion was reached earlier for SMG Al–Mg solid solution alloys which have much lower melting points than Cu and Ni, suggesting that nonequilibrium grain boundaries are a typical feature of metals processed by intense plastic straining.

The structures of martensites in a Cu–11.2 wt% Al–3 wt% Ni specimen, which was quenched from 1173 K, have been studied by high resolution electron microscopy (HREM) and diffraction techniques. Two kinds of martensites, i.e. β′1 and γ′1, coexisting adjacent to each other in the specimen were observed. The γ′1 matensite consists of microtwins with monoclinic structure. Three variants of the twin structure, i.e. {1 2 1}, {2 1 0} and {1 0 1} twins, are arranged within a single plate. The β′1 martensite possesses basically ordered N9R structure, but mixed with thin 2H domains. Some diffraction spots of this martensite shift along the [0 0 1] direction. In addition, extra weak reflections appear in the diffraction pattern due to heterogeneous atomic displacements. The microstructural features of the martensites are examined and discussed.

High-resolution electron microscopy was used to examine the structural features of grain boundaries in Al–1.5% Mg and Al–3% Mg solid solution alloys produced with submicrometer grain sizes using an intense plastic straining technique. The grain boundaries were mostly curved or wavy along their length, and some portions were corrugated with regular or irregular arrangements of facets and steps. During exposure to high-energy electrons, grain boundary migration occurred to reduce the number of facets and thus to reduce the total boundary energy. The observed features demonstrate conclusively that the grain boundaries in these submicrometer-grained materials are in a high-energy nonequilibrium configuration.

Electron microscopy with atomic sensitivity enables us to obtain a direct image of the intra-molecular structure of metallofullerenes encapsulated inside single-walled carbon nanotubes. By a comparison of high-resolution images with a simulation to extract the relative atom positions for encaged metal atoms in each molecule, the distribution of the molecular orientations and interactions between adjacent molecules in metallofullerene peapods have been statistically analyzed. The results are suggestive of strong interactions between fullerene–fullerene and fullerene–tube in peapods at room temperature.

Studies of high-pressure synthesized Hg-Ba-Ca-Cu-O superconductor by electron diffraction and high-resolution electron microscopy are reported. The results of electron diffraction indicate that two superconducting phases 1212 and 1223 exist in the sample and their cell parameters are a=b=3.8 Angstrom, c=12.7 Angstrom and a=b=3.8 Angstrom, c=15.8 Angstrom, respectively. High-resolution electron micrographs were taken from the two phases Hg-1212 and Hg-1223 and from the region of the intergrowth of the two phases. The relation between the structure and superconducting transitional temperature T-c is discussed.

We investigated defects in CdZnTe crystals produced from various conditions and their impact on fabricated devices. In this study, we employed transmission and scanning transmission electron microscope (TEM and STEM), because defects at the nano-scale are not observed readily under an optical or infrared microscope, or by most other techniques. Our approach revealed several types of defects in the crystals, such as low-angle boundaries, dislocations and precipitates, which likely are major causes in degrading the electrical properties of CdZnTe devices, and eventually limiting their performance.

The technique of high-resolution electron microscopy represents a powerful method for characterizing the microstructure of thin films and surfaces. We demonstrate its usefulness by reference to some recent studies of metals, semiconductors, and oxides, in particular, showing that it can be used to follow physical and chemical changes inducedin situ by the electron beam orex situ as a result of annealing or chemical treatment.

The fine structure of unhydrated cement clinker Ca4Al6SO16 (C4A3S) and its four superstructures have been studied by means of electron diffraction and high resolution electron microscopy (HREM). The match between experimental images and simulated ones verifies the result of X-ray structural analysis: C4A3S having a cubic lattice with space group l43m,Z = 2. The frequent apperance of forbidden reflections such as 1/2, −1/2, 0 along the 〈110〉* directions of C4A3S imply the presence of superstructures which may be due to an orderly inverse occupation of Ca2+ ions. Various structure models based upon the observed structural images have been proposed for these four superstructures. A new cubic phase witha′ = 1.5 nm is also found by selected area electron diffraction (SAED).

The atomic structures of heterophase interfaces with large misfits (>14% in Ag/Ni and Au/Ni) and with small misfits (∼2% in Ag/NiO and Au/NiO) have been studied by high-resolution electron microscopy (HREM). It is found that all interfaces are strongly faceted on (111) planes. This indicates that (111) interfaces have the lowest interfacial energy in both metal/metal and metal/metal-oxide systems. For the metal interfaces, this also agrees with determinations of interfacial energies by lattice statics calculations. The large misfit of Ag/Ni and Au/Ni interfaces is accommodated by misfit dislocations. Observations of misfit localization by HREM are in good agreement with images derived from computer simulation, based on relaxed structures, obtained in embedded atom calculations. All misfit dislocations at the Ag/Ni and Au/Ni interfaces lie exactly in the plane of the interfaces, while the dislocations at Ag/NiO and Au/NiO interfaces reside at a stand-off distance, 3 to 4 (111)Ag or (111)Au interplanar spacings from the interfaces.

Atomic-scale grain boundary (GB) migration has been directly observed by high-resolution transmission electron microscopy (HREM). Atomic-scale motion of high-angle tilt GBs as well as twist and general GBs at gold island grains with a number of planar facets has been studied at ambient and elevated temperatures. GB migration mechanisms depend on GB structure and geometry. Strong indications for cooperative effects has been found. In this case, as has been proposed before, atoms may undergo small shifts in their lattice positions to be incorporated into the growing grain in a collective mode. At high temperature and in the absence of a strong driving force such small lattice regions are observed to fluctuate back and forth between the two grains. Faceted GBs typically move in spurts. This appears to be inherent to GB migration, whenever the motion is controlled by different structural entities. For some GB geometries the motion was found to proceed by the lateral propagation of atomic-scale steps.

In a recent work on phase equilibria relations in the BaO:Fe2O3:TiO2 system the existence of sixteen ternary compounds was confirmed. Most of the new found compounds apparently have a new structural type. In this work we employed electron diffraction and high-resolution microscopy in attempt to understand the structures of the new compounds. Since the present work was done on the compounds prepared by solid-state reaction, it also provides a correlation with a single-crystal x-ray work on some of the similar compounds prepared by crystallization from a melt.

TiB2 nano-lamellae, grown in-situ within a TiAl intermetallic melt, have been examined by high resolution electron microscopy. The use of the Stuttgart ARM enables Ti and B columns to be distinguished in the HREM images. Examination of the internal structure of the T1B2 platelets reveals extensive prismatic faulting on {1010}TiB2, {0110}TiB2 and {1100}TiB2 planes. Externally, the TiB2 platelets exhibit an orientational relationship {1010}TiB2 // {001}B2 and [0001]TiB2 // B2 with interleaving platelets of B2-phase, with the predominating interface planes being {1010}TiB2 // {001}B2. The minor facets of the TiB2 platelets are [0001]TiB2 // B2. {0110}TiB2 and {1100}TiB2, with the latter two facets showing no relationship with the interleaving B2-phase. No preferred orientation relationship of the TiB2 with the surrounding γ-TiAl and α2-Ti3Al phases is observed.

Periodic antiphase boundaries in the intermetallic compound Cu3Pd have been studied by high resolution electron microscopy and image simulation. The intensity profiles across the boundary were recorded and the thickness of the boundary compared to the values deduced from X-ray and neutron diffraction data. It is shown that electron microscopy always minimizes the thickness of the boundary. The possible factors for this discrepancy are analysed and discussed.

The characterisation of line defects in interfaces, observed using high-resolution electron microscopy, is discussed. Characterisation is carried out by mapping a closed circuit initially constructed around a defect into a reference space. This process has been generalised to incorporate operations other than translations, and has also been expressed mathematically, and thereby related to recent developments based on symmetry theory. Examples of the characterisation of dislocations in twin interfaces in hexagonal-close-packed crystals and an interfacial dispiration are presented as illustrations.

In the present work we report the systematic studies of Maya blue paint using High Resolution Electron Microscopy, Electron Energy Loss, Scanning Electron Microscopy and Related Techniques. A model to explain the well known properties of the paint such as: acid resistance is piesented

Surface diffusion process of tungsten(W)-atoms on MgO (001) surfaces was studied by high-resolution electron microscopy (HREM) in the time resolution of 1/60 s. The W-atoms were prepared on single crystalline MgO (001) films at 300°C by vacuumdeposition of WO3 or W-metal. Analysis of the recorded images revealed individual jump-process of the W-atoms in the substrate temperature from R.T. to 400°C, and gave the barrier potential (Ed) and the pre-exponential factor (D0). The diffusion processes on terraces and along steps were also compared in viewpoint of the jump length.

Combined high-resolution electron microscopy, computer modeling, and image simulations are used to study the structure of the Σ=5 (210) [001] tilt boundary in the ordered compound AuCu3. On the experimental side, we have prepared thin samples cut in a bulk bicrystal containing an interface close to the above (θtilt ≈ 37°). The high-resolution images obtained at 400 kV along the [001] tilt axis show that among possible configurations, the boundary adopted predominantly a symmetrical one. Theoretically, using the standard geometrical approach, we derived possible atomic configurations of the boundary and we identified some of the defects allowing for the coexistence between these variants. Finally, we performed energy minimizations using these geometrical models and an n-body potential adapted to this compound. In agreement with the experiment, one of the two possible symmetrical variants is associated to the lowest excess energy. Moreover, the computations show that large variations affect the spacing of (210) atomic planes near the boundary.

We report the results of a crystallographic analysis of antiphase boundaries (APB) in Cu3Au obtained by using high-resolution electron microscopy. Our observations corroborate the conclusions of previous work, based on conventional electron microscopy, which indicate that antiphase boundaries are mainly located in the cube planes. We found that the deviation of the average APB orientation from the cube planes is related to the formation of kinks on an atomic scale. Moreover, the identification of the boundary plane shows that the APBs are mostly conservative. These results are discussed and interpreted in the framework of a pairwise potential approach with predominant nearest neighbor interactions.

The direct measurement of the composition variations in transition metal multilayers has been carried out using the atom-probe and the position sensitive atom-probe (POSAP). The atom-probe and POSAP do not have sufficient resolution to determine the crystal structure and this complementary information has been obtained using high resolution electron microscopy.

The defects which occur in polycrystalline aluminum nitride are very detrimental to the beneficial physical and electrical properties. 'Dome-like' or 'D' defects, consisting of a flat basal fault joined to a curved planar fault, are examined by high-resolution electron microscopy. The basal segments are shown to contain a thin ∼5Å layer of a second phase and are associated with a stacking-fault and an antiphase boundary. A structural model is proposed for the defect which incorporates a layer of alumina at the basal segment of the 'D' defect. The formation of thisdefect is discussed.

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

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.

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.

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 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.

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.

Layered bismuth oxides of the general formula $(Bi_2O_2)^{2+}$ $(A_{n-1}B_nO_{3n+1})^{2-}$ where A = Bi or Ba, B = Ti, Fe, W and n = number of perovskite layers have been investigated by high resolution electron microscopy. Lattice images obtained for n = 1 to 6 members show stacking of (n-1) perovskite layers sandwiched between dark bands due to the $(Bi_2O_2)^{2+}$ layers. It was possible to resolve the perovskite layer structures in some of the oxides. A highly ordered structure was observed upto the n = 3 member, whereas higher members show superstructures, dislocations and stacking faults arising from the side-stepping of $(Bi_2O_2)^{2+}$ layers as well as ferroelectric domain walls.

The nucleation and glide of misfit dislocations in GaAs/Si system is investigated using transmission electron microscopy. GaAs epilayers of different thicknesses were examined by electron microscopy (plan and cross-section) and the elastic strain remaining in the film has been related to the average spacing of the misfit dislocations at the interface. A model is developed based on minimum energy considerations to determine the strain-thickness relationship. The theoretical predictions of strain relaxation are compared with experimental observations using high resolution electron microscopy.

High resolution microscopy of ceramics has its specific problems due to the difficulties in preparing thin foils. Most of these Problems however can be overcome and recent years a lot of effort has been concentrated on electron microscopy of ceramics because of their high technological importance. Some results on important ceramics such as SiC, Mg-Si-O, ZrO2 -ZrN and Si-Al-O-N obtained by high resolution microscopy will be briefly discussed here.

High resolution electron microscopy has proven to be a powerful technique to determine structural characteristics of zeolites (l–2),symmetry variations and identification of several kind of defects.Together with ideal projected potential images, the microscopist usually finds in electron micrographs the influence of electro-optical parameters and alterations of the crystallinity of the material under electron irradiation. One of the purposes of this workis to contributetothe understanding of the degradation process of zeolites under electron irradiation in the electron microscope and in this way, discriminate when it is possible, what is reliable information recorded in the images obtained in high resolution conditions.

Publisher Summary This chapter reviews the current results about high-resolution electron microscopy studies on quasicrystals. From the results it can be concluded that structures of icosahedral and decagonal quasicrystals can be described as aperiodic arrangements of some atom clusters, which have the same symmetry as those of the quasicrystals, with definite linkages. There is variety in aperiodic arrangement of the atom clusters and atomic arrangements in the atom clusters, depending on quasicrystalline alloys. High-resolution electron microscopy is the most powerful tool for studying the varied structures. However, it has many limitations for carrying out precise structure analysis about atomic arrangements, because of its limited resolution compared with diffraction and the use of images projected along the incident beam. To proceed to the more precise structure analysis of the quasicrystals, combining high-resolution electron microscopy with the diffraction method becomes more important. The atomic arrangements of Al–Ni–Co, Al–Pd–Mn, and Al–Pd decagonal quasicrystals, were proposed using the results of x-ray diffraction.

Recently, significant advances have been made in establishing a theoretical basis for explaining the many structural-sensitive physical properties of amorphous materials. Viewed from both the theoretical and experimental realms, reversible annealing dependency and the structural relaxation mechanism of the amorphous solids are conceptually deducible from the concept of localized structural fluctuations. In the case of annealing, however, the limiting temperature below which no permanent atomiclevel rearrangements occur is not known and may well be dependent on several intrinsic properties of the amorphous state. In an effort to establish this limiting temperature, amorphous Cu60-Zr 40 samples have been annealed using a 1kv pulsed laser. Samples annealed during 1200, 800, 600 400, and 200 μ sec. have been analyzed by using Differential Scanning Calorimetry (DSC), High Resolution Electron Microscopy (HREM), and microanalysis. Analysis of the DSC indicates variations in both height and the shape of the exotherms from the samples annealed above 600 μ sec. duration. The results from HREM of these samples indicate the onset of amorphous-crystalline transition evidenced during 200 μ sec. annealing.

The growth characteristics of Co/Cr multilayers have been studied in cross-section with a 400kV high-resolution electron microscope. The growth directions for bcc Cr were predominantly while the axes of the observed crystallite fringes were mainly and . The hcp Co crystallites grew predominantly in the direction while the areas with strong fringes were along a projection. This observed structure was in agreement with that obtained from analysis of large angle X-ray scattering spectra. The columnar structure was found to be present with the layers growing right through the columns.

Recently a lot of work has attempted to correlate the activity of Co and Mo sulfide catalysts with observations of high resolution electron microscopy. Hydrodesulfuration (HDS) bulk sulfide catalysts are specially suited for this type of study. We prepared unsupported molybdenum sulfide by three methods: the homogeneous sulfide precipitation (HSP) (1), co-maceration (CM) (2), and impregnated thiosalt decomposition (ITD) (3). Pure cobalt sulfide was prepared only by HSP, and two Co-Mo sulfides in the ratios of 0.3 and 0.5 at. % were prepared by HSP and ITD. The samples were treated with a mixture of 20% H2S/H2 for 4 hrs. at 400 C. In all Co/Co+Mo mixtures the presence of Co9S8 and MoS2 was identified in both, ESP and ITD treatments. Characterization was done by high resolutibn electron microscopy. The ITD method can be considered a better method, as opposed to ESP for the preparation of mixed catalysts. This method produces poorly crystalline specimens that are usually associated to higher chemical activity.

A series of Mo/Si multilayer films (MLF) has been fabricated by e-beam evaporation onto (100) silicon substrates at substrate temperatures (Ts) in the range of 300 to 600K, with deposition rates varying from 0.5 to 3A/s. The quality of the samples fabricated at 525K≤Ts≤575K with a deposition rate of 1A/s was found by high-resolutlon electron microscopy to be comparable to that of sputtered films. The major differences between the structures of the e-beam evaporated samples and the sputtered ones were that the thicknesses of the Mo on Si interfaces were larger, and the Si on Mo interfaces were smaller, for the e-beam MLF.

A new high resolution electron microscopy investigation of indentationinduced hexagonal silicon has been carried out using the JEOL 4000EX electron microscope. The better resolution of the microscope enables one to extract more structural information about this intriguing phase and its interface with the cubic phase. A new structural model for the cubic/- hexagonal interface is presented. Image simlations are carried out over a wide range of thickness and defocus for the new model and also a previous model due to Tan et al.

Structures of CdTe-Cd0.6Mn0.4Te superlattices which are caused by the lattice mismatch between suterlattice layers have been studied by high resolution electron microscopy (HREM). In thin-layer superlattices, the crystal lattice in each layeris elastically distorted, resulting in the change of the crystal symmetry from cubic to rhombohedral. The presence of the small rhombohedral distrotion has been confirmed through a phase contrast effect in HREM images. In a thick-layer superlattice, the lattice mismatch is accommodated by dissociated misfit dislocations. Burgers vectors of partial misfit dislocations have been identified from the shift of lattice fringes in HREM images.

The preparation of interfaces for TEM investigation is inherently prone to the production of artifacts. In some cases it is possible to avoid potential hazards in the interpretation of high-resolution images by creating the interfaces in pre-existing, thin, TEM specimens so that no further preparation is required. As an example of this approach, results from a study of interfaces produced by the heat-treatment of iron-bearing olivine TEM samples are presented. Image simulations are presented which show that even in these favorable situations, the greatest care must be taken in interpreting image contrast at interfaces in high-resolution electron micrographs.

Recent molecular beam epitaxy (MBE) studies have shown that depending on surface conditions of GaAs two different growth modes, layer-by-layer or island, occur at the initial stage of the growth of ZnSe on (100) GaAs. In this study, we have observed various types of GaAs surfaces used for the MBE growth of ZnSe by reflection electron microscopy and ZnSe islands on a GaAs substrate by cross-sectional high resolution electron microscopy. Results of these observations suggest that the occurrence of two growth modes is determined by atomistic structures of GaAs surfaces such as the surface stoichiometry or the density of atomic steps.

ALTHOUGH electron microscope contrast may be increased by the use of objective apertures, accurate focusing in thin-section work is still difficult and, in order to obtain an in-focus picture of a particular field, it is very helpful to find a small dense particle, or a hole in the membrane, on which to focus. An obvious solution to this problem is to distribute small dense particles on the specimen.