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Recently, quantum wells (QW) have been constructed using the (In0.532Ga0.468)As/ (In0.522Al0.478)As system (hereafter InGaAs/In Al As), which is lattice matched to InP (lattice constant of 5.869Å). In order to understand the properties of such QWs, it is important to have knowledge of the structure and composition of interfaces. For III-V materials, compositional changes affect the frequency component of the high resolution electron microscopy (HREM) image intensity (I200). This underlies the “chemical imaging” approach. Simulations for InGaAs/InAlAs interfaces suggest optimum conditions of microscope defocus df=-50nm and sample thickness t=14nm in the orientation. A double-QW structure, consisting of InGaAs/ InAlAs/ InGaAs layers with nominal thicknesses of 4nm/ 2nm/ 4nm (respectively), and embedded in InAlAs layers, has been studied. All the layers were grown by molecular beam epitaxy at 500°C on a InP substrate, with 60s growth interrupts between layers in the QW region.

Multiple sclerosis (MS) is characterised by the active degradation of the myelin sheath, and is thought to be precipitated by an autoimmune response to one or more of the sheath’s protein components. Myelin basic protein (MBP) is generally considered to be the antigen responsible for autoimmunity and is one of the most abundant proteins of the sheath. Knowledge of the tertiary structure of MBP, and its organisation on lipid layers and within the compacted myelin multilayers, is essential to understanding the organisation of the myelin membrane and the mechanisms of development of autoimmunity in MS. MBP has hitherto not proved crystallisable for structural studies by X-ray diffractometry despite much effort in this area. We have initiated high-resolution electron microscopical analyses of MBP. When imaged as individual particles, a recurring motif is that of a “C” shape in projection, of approximately 2 nm in thickness and 8 nm in length (Figure a – field of view; Figure b – class averages after single particle analysis; Figure c – 3D reconstruction). The total length of this particle is less than would be expected if the polypeptide chain were fully extended. Crystallisation experiments on MBP using monolayers of lipid mixtures (phosphatidylcholine, phosphatidylserine, dioleoyl phosphatidylethanolamine, galactocerebroside) yielded microcrystalline structures with a repeating pattern of packed protein molecules of size 5 nm, with an arm width of 2 nm and total length of 10-11 nm (Figure d). Molecular modelling of MBP based on the schemes proposed by Stoner and Martenson, and using coordinates of the β sheet backbone of bacteriochlorophyll A protein and energy minimisation of intervening segments, yielded a compact structure of size and appearance consistent with the electron microscopical data (Figure e). The bend of the C shape appears due to a natural curvature in the β sheet. These results are fully congruous with MBP having a regular secondary structure and domains that are potentially flexible with respect to one another. Energy minimisation experiments were performed on this model structure after specific post-translational modifications such as phosphorylation of specific sites (e.g., Ser7, Thr98) and conversion of arginine residues to citrullines. These results are consistent with biochemical data on accessibility of these sites to modification, and provide a framework for hypothesising scenarios of myelin sheath degradation in MS.

Venom from the rattlesnakeCrotalus atroxcontains a mixture of enzymes that induce a localized effect leading to hemorrhaging, necrosis and edema. As a member of the crotalid family of snake venoms,Crotalus atroxvenom contains a C-type lectin that will agglutinate blood cells in a Ca2+-dependent fashion. The lectin is a hydrophilic protein, consisting of two covalently linked, 135 amino acid residues, identical subunits that are rich in aspartic acid, glutamic acid and lysine. Sequence homology with known carbohydrate recognition domains (CRDs) indicates that rattlesnake venom lectin (RSLV) contains a CRD motif that is not linked to accessory domains. Preliminary X-ray diffraction and sedimentation analysis has indicated that lectin fromCrotalus atroxforms decamers composed of two five-fold symmetric pentamers. Single particles of RSVL imaged at – 171°C displayed two distinct orientations on the specimen support (Figure a) following incubation in a crystallization Teflon well, coated with a lipid monolayer consisting of phosphatidylcholine and monosialoganglioside. When lying in an end-on orientation, the lectin exhibited a “pentagonal ring” with an outer diameter of 6.7 nm and an inner hollow core of 1.7 nm. A side orientation was also seen, whereby a thickness of 5.8 nm was measured for the lectin. Image processing of 2280 single particles placed in 100 classes (Figure b) led to 3D reconstructions of RSVL (Figure c). Density limited 3D reconstructions showed the lectin to be made of two five-fold symmetrical rings covalently linked between the five subunits that constitute each ring of this homodimer. These results are consistent with sedimentation and preliminary X-ray diffraction analysis on the shape of RSVL and provide the framework for structural verification by 2D electron crystallography.

Surface-diffusion process of atoms is one of the important factors for understanding various types of surface-related phenomena such as thin-film growth and catalysis reaction[l]. Development of field ion microscope (FIM) was a great breakthrough for the study of the process in atomic level. The diffusion process of Rh and Re atoms on tungsten surfaces was quantitatively studied, and the barrier potential (Ed) and the pre-exponential factor (D0) were successfully determined[2]. Recent development of scanning tunneling microscope (STM) has also enabled us to measure directly the moving of Pb and Sb-atoms on Ge and Si (111) surfaces[3, 4]. The time-resolution of these methods is, however, not sufficient to trace the diffusion process in detail.In previous papers, we reported the first experiment of tracing the diffusion process of tungsten(W)-atoms on terrace-regions of MgO (001) surfaces in the time-resolution of 1/60 s.using dynamic high resolution electron microscopy[5,6]. The values Ed=0.18 eV and Do=1.5x10−14 cm2/s were successfully determined from the video-tape images. In the present study, we have observed diffusing atoms along the surface-steps and studied the phenomena quantitatively.

The interaction between an incident electron and the atoms in condensed matter results in various inelastic scattering processes. Thermal diffuse scattering or phonon scattering is the result of atomic vibrations in crystals. This process does not introduce any significant energy-loss (< 0.1 eV) but produces large momentum transfer. Valence-loss (or plasmon for metals and semiconductors) excitation, which characterizes the transitions of electrons from the valence band to the conduction band, involves an energyloss in the range of 1 -50 e V. Atomic inner-shell ionization is excited by the energy transfer of the incident electron, resulting in an ejected electron from the deep-core states. Continuous energy-loss spectra can also be generated by an electron which penetrates into the specimen and undergoes collisions with the atoms in it, resulting in Bremsstrahlung and leading to emission of x-rays with continuous energy. The electron Compton scattering refers to the collision of the incident electron with an electron belonging to the specimen. In an electron energy-loss spectrum (EELS), the zero-loss peak is composed of elastically and thermal diffusely scattered electrons. The low-loss region is dominated by valence-excitations.

Electron microscopy is a fundamental tool in materials characterization. In the case of nanostructured materials we are looking for features with a size in the nanometer range. Therefore often the conventional TEM techniques are not enough for characterization of nanophases. High Resolution Electron Microscopy (HREM), is a key technique in order to characterize those materials with a resolution of ~ 1.7A. High resolution studies of metallic nanostructured materials has been also reported in the literature. It is concluded that boundaries in nanophase materials are similar in structure to the regular grain boundaries. That work therefore did not confirm the early hipothesis on the field that grain boundaries in nanostructured materials have a special behavior. We will show in this paper that by a combination of HREM image processing, and image calculations, it is possible to prove that small particles and coalesced grains have a significant surface roughness, as well as large internal strain.

Accurate alignment of an electron microscope is important when the highest achievable resolution is demanded. In a conventional alignment for high-resolution electron microscopy, the incident beam direction is aligned for the object point imaged at a viewing-screen center. It should be noted however that the object point corresponding to the viewing-screen center does not usually located on the magnetic-field axis of an objective lens due to lens misorientation and/or beam deflection caused by a leakage field around the objective lens. Then, the voltage-center and coma-free conditions cannot be satisfied simultaneously, even if a magnetic-field is rotationally symmetric. We implemented last year a proposed scheme to satisfy both coma-free and voltage-center conditions. This alignment scheme however requires a suitable deflector at the objective image plane.In this report, we summarize ordinary alignment procedures for high resolution electron microscopy and propose a new alignment procedure, which we call a lens-field axis alignment. Using this alignment we can satisfy the coma-free and voltage-center conditions simultaneously.

It has been known for many years that materials such as zeolites, polymers, and biological specimens have crystalline structures that are vulnerable to electron beam irradiation. This radiation damage severely restrains the use of high resolution electron microscopy (HREM). As a result, structural characterization of these materials using HREM techniques becomes difficult and challenging. The emergence of slow-scan CCD cameras in recent years has made it possible to record high resolution (∽2Å) structural images with low beam intensity before any apparent structural damage occurs. Among the many ideal properties of slow-scan CCD cameras, the low readout noise and digital recording allow for low-dose HREM to be carried out in an efficient and quantitative way. For example, the image quality (or resolution) can be readily evaluated on-line at the microscope and this information can then be used to optimize the operating conditions, thus ensuring that high quality images are recorded. Since slow-scan CCD cameras output (undistorted) digital data within the large dynamic range (103-104), they are ideal for quantitative electron diffraction and microscopy.

In a conventional alignment for high-resolution electron microscopy, the specimen point imaged at the viewing-screen center is made dispersion-free against a voltage fluctuation by adjusting the incident beam direction using the beam deflector. For high-resolution works the voltage-center alignment is important, since this alignment reduces the chromatic aberration. On the other hand, the coma-free alignment is also indispensable for high-resolution electron microscopy. This is because even a small misalignment of the incident beam direction induces wave aberrations and affects the appearance of high resolution electron micrographs. Some alignment procedures which cancel out the coma by changing the incident beam direction have been proposed. Most recently, the effect of a three-fold astigmatism on the coma-free alignment has been revealed, and new algorithms of coma-free alignment have been proposed.However, the voltage-center and the coma-free alignments as well as the current-center alignment in general do not coincide to each other because of beam deflection due to a leakage field within the objective lens, even if the main magnetic-field of the objective lens is rotationally symmetric. Since all the proposed procedures for the coma-free alignment also use the same beam deflector above the objective lens that is used for the voltage-center alignment, the coma-free alignment is only attained at the sacrifice of the voltage-center alignment.

Titanium aluminides are a class of intermetallics whose application to a variety of advanced structures may yield substantial improvements in system performance. Before titanium aluminides can realize their full potential, a number of deficiencies such as lack of ductility must be overcome through improved processing. Difficulties inherent in traditional methods have prompted the development of the ultrastructure approach to materials processing. Chemical processing has best potential for ultrastructure control because articles are constructed from atomic level up. The availability of nanostructured materials may be essential to the development of intermetallics with acceptable levels of ductility. The focus of this work is to use high resolution electron microscopy (HREM) techniques to characterize the structure and chemistry of the chemically-derived, nanocrystalline intermetallic powders that have potential to enable ultrastructure processing of advanced intermetallics and alloys.In an attempt to produce salt-free TiAl3, a dilute hexane solution of Ti[N(SiMe3)2]3 was combined with an excess of (AIH3) at room temperature to yield a very fine, steel-gray powder.

The recently synthesized compound K0.19Ba3.81Mo22O34 is a representative of the ternary and quaternary reduced molybdenum oxides in which clusters built from molybdenum octahedra are arranged in layers of composition AxByMo4n+2O6n+4. The number of trans-edgesharing molybdenum octahedra in the cluster is represented by n. The general concept of cluster condensation is formulated and discussed elsewhere. For K0.19Ba3.81Mo22O34, n is equal to 5. A ternary representative, likewise with n = 5, is In6Mo22O34.By x-ray structure analysis, K0.19Ba3.81Mo22O34 proved to crystallize in space group P21/a with parameters a = 0.9908(2) nm, b = 0.9353(2) nm, c = 1.5951(3) nm, and β = 98.78(2)°. The potassium atoms were found to reside on the same sites as the barium atoms with an almost statistical distribution.We studied K0.19Ba3.81Mo22O34 by high-resolution electron microscopy (HREM). Small fragments of a crystal were investigated using a Philips CM30/ST microscope operating at 300 kV (point resolution 0.19 nm). At appropriate orientations of the crystal fragments, HREM images reveal domains of two ordered polytypes: a monoclinic and an orthorhombic one (Figs. 1 and 2).

With the advances in instrumentation and the capability of point-to-point resolution better than 0.2 nm, high resolution electron microscopy (HREM) is becoming more widely used for the quantitative study of both surfaces and internal interfaces. The elegance of the technique lies in its ability to deduce atomic-scale information on a localized scale. Without the proper analysis, however, HREM images can easily be misinterpreted. We investigate the considerations necessary for quantification of HREM images, using the measurement of the grain boundary volume expansion via the lattice fringe displacement technique as an example. The volume expansion, a parameter directly related to the grain boundary energy, is measured (in length units on the order of tenths of Å) as a rigid body translation normal to the boundary. It can be determined experimentally using statistical techniques which locate and fit the peak and valley positions in an experimental HREM image such that a direct measurement of the lattice fringe displacements is made.

The Group III-nitride semiconductors A1N, GaN, and InN are of interest for their potential applications in short wavelength optoelectronic devices. This interest stems from their direct wideband gapswhich range from 1.9 eV (InN), to 3.4 eV (GaN), to 6.2 eV (A1N). If high quality nitride films can besuccessfully grown, then optoelectronic devices with wavelengths ranging from the visible to the deepultraviolet region of the electromagnetic spectrum are theoretically possible. Recently, LED's basedon GaN and InGaN QW's were demonstrated. Also, their excellent thermal properties make them ideal candidates for high-temperature and high-power devices. Many problems plague nitride research, especiallythe lack of suitable substrate materials that are both lattice- and thermal-matched to the nitrides. The crystal structure of these materials is strongly influenced by the substrate and its orientation.For example, although the equilibrium crystal structure of these nitrides is wurtzite, zincblende phase can be nucleated under nonequilibrium growth conditions but only on cubic substrates. These zincblende nitrides represent new material systems with properties that differ from their wurtzite counterparts. Recently, good quality material has been produced employing metalorganic vapor phase epitaxy (MOVPE) and reactive molecular beam epitaxy (RMBE) techniques with incorporation of buffer layers.

Following the discovery of a large scale synthesis of fullerenes, the existence of the related carbon nanotubes was suggested by high resolution electron microscopy (HREM). Larger scale syntheses of these nanotube-rich materials has now been reported and has sparked interest worldwide. Because the HREM technique essentially observes the projection of a three dimensional object onto a two-dimensional plane, the three dimensional shape of the object is usually not apparent in typical HREM images. However, as we report here, by rotating along the axis of single carbon nanotube, and recording the images in succession by HREM, the non-cylindrical nature of these tubes is revealed, especially near the sealed ends of the nanotubes. In addition, from electon diffraction and X-ray diffraction, we find the spacing between the planes to be 3.398(8) Å on average. This is in contrast to earlier reports which suggested an interlayer distance of 3.35 Å, similar to the graphite interplanar spacing.

Zeolites constitute an important class of catalyst materials in the petrochemical industry. Zeolites are aluminosilicates with their framework structures made up of SiO4 (or AlO4) tetrahedra. The catalytic properties such as selectivity and activity are closely related to the structure sensitive properties of zeolites, e.g. shape selectivity, diffusivity, etc. Understanding these properties requires detailed structure characterization of the zeolites. High resolution electron microscopy (HREM) has been successfully applied to solve some zeolite structures when combined with experimental data from other techniques, e.g. absorption experiment. The connectivities of n-member rings in the zeolite frameworks can be directly deduced from the corresponding HREM images. However, radiation damage to the zeolite framework structures by the electron beam necessitates the use of low dose imaging techniques.

Fe-Zn alloy coatings on sheet steel have been widely used by automobile industry due to their superior corrosion resistance and manufacturability. In order to investigate the interface structure between various phases in the Fe-Zn system and their crystallographic relations, steel sheets coated with electrogalvanized pure zinc were heat-treated at various temperatures and the resulting structures were examined in HREM with special attention to the formation of brittle Fe-Zn intermetallic phases.Due to extreme difficulties in preparing cross-sectional TEM specimens from a thin Zn-based coating, little microstructural information is currently available for the interfacial region. A special technique was developed to overcome these difficulties in the present investigation. Instead of using the epoxy on the sandwiched specimens, as commonly adopted to prepare cross-sectional TEM specimens in electronic and photonic devices, 3mm of pure zinc was electrodeposited on top of the coating (15 μm) to be examined.

The molecular organization of polymer solids near surfaces is important for understanding properties such as adhesion, friction, mass transport, and fracture initiation. Materials comprised of small molar mass atoms or molecules can exhibit detailed reorganization near free surfaces. It might be expected that the perturbing influence of a free surface on structure would be even more pronounced for materials comprised of large macromolecules. Local information about structure near surfaces of inorganic materials is often obtained by High Resolution Electron Microscopy (HREM). Unfortunately, direct imaging of local structure in solid polymers by HREM is problematic because of the extreme sensitivity of organic molecules to electron beam irradiation. However, the systematic application of low dose techniques and the development of stable high voltage instrumentation has made it possible to apply HREM techniques to certain polymer systems. Here, we describe our recent studies which have concerned the microstructure of polymer solids near surfaces. In these experiments we used a JEOL 2000 EX TEM operating at 200 kV and a JEOL 4000 EX TEM operating at 400 kV.

The examination of surfaces requires not only that they be free of adsorbed layers but the environment of the sample must also be maintained at high vacuum so that the surfaces remain clean. The possibility of resolving surface structures with atomic resolution has provided the motivation for optimizing intermediate and high voltage electron microscopes for this particular application. Electron microscopy offers a variety of techniques which have the capability of achieving atomic level detail of surfaces including plan-view imaging, REM and profile imaging. Operation at higher voltages permits reasonable pole piece dimensions thereby providing space for in situ studies yet still compatible with high resolution. Moreover, video systems can be attached which permit observation and recording of dynamic phenomena without compromising microscope performance.

TEM hollow cone illumination can produce high resolution images having atomic number (Z) contrast within a lattice image. Inorder to produce these images, the contribution of four sources of electrons should be considered. These are the main, inelastically scattered, elastically scattered, and diffracted beams. This abstract discusses these sources of electrons to the hollow cone (HC) image, and then goes further to propose a possible method of extending the resolution of the electron microscope by using diffracted HC beams to form holograms which should remove the limitation on resolution imposed by the objective lens and inelastically scattered electrons. A Philips EM 430T was used to take the electron micrographs.

Methods for the preparation of significant quantities of C60 clusters separated from carbon soot were recently reported by Krätschmer and co-workers. Evidence that these clusters have the “Buckminsterfullerene” structure with five-fold and six-fold carbon rings on the surface of a sphere (soccer-ball structure) has been provided by several techniques. NMR shows a single type of carbon bonding, and IR peaks consistent with modes characteristic of this system have been identified. Since C60 can be isolated and has stable “graphitic” bonding, it represents a unique opportunity to observe individual stable carbon molecules with transmission electron microscopy in order to test the morphology deduced from other techniques. Also, the study of packing sequences and defect structures in C60 crystals found by x-ray diffraction to have an FCC lattice constant of 1.41 nm provides important new information on variations of crystallization with conditions such as solvent type and crystallization rate.

The mineral component of human dental enamel is formed by nonstoichiometric carbonated hydroxyapatite crystals. The presence of relatively large amounts of impurities in mature enamel crystals as well as their external shape are related to their growing mechanism. Enamel crystal growth was investigated previously directly with low resolution electron microscopy or by comparison with synthetic apatite crystal growth. The growing process of enamel crystals is still unknown and the aim of this study was to investigate foetal enamel growth during secretory stage by high resolution transmission electron microscopy.Developing enamel from 5 month-old human foetuses was fixed for 3 hours in a 2% glutaraldehyde and 2% paraformaldehyde solution in 0.1 M sodium cacodylate buffer. After 2 hour postfixation in 1% OsO4in the same buffer and embedding in Epon, non decalcified ultrathin sections were obtained with a Sorvall-Porter MT-2C microtome equipped with a diamond knife and floated on demineralized water saturated against hydroxyapatite (200mg/l). The sections were observed in a Philips EM 430 transmission electron microscope operating at 300 kV equipped with a double tilt specimen holder. This microscope possessed a Sherzer resolution of 0.19 nm and the absence of drift and astigmatism was checked for each micrograph by an optical diffraction.

Taking advantages of “Imaging Plate” (IP), i.e., a wide dynamic range and good linearity for electron intensity, high resolution electron microscope (HREM) images and electron diffraction (ED) patterns were quantitatively investigated. Observations of HREM images and ED patterns were made by the TEM-IP System (PIXsys TEM) using electron microscopes JEM-4000EX and JEM-2000FX, respectively. The data on the IP with an effective size of 102×77 mm2 was converted into digital data of 2048 × 1536 pixels with 4096 gray levels and analyzed with the IP-processor of the PIXsys TEM and a large-computer ACOS-2020.Since the IP is highly sensitive to incident electrons, the beam convergence can be lowered for HREM observations, and so the effect of the dumping envelope due to the beam divergence can be reduced. In Fig. 1, an HREM image of an oxide W-Ta-O, taken at a direct magnification of 1,500,000x and an exposure time of 2 s, shows fine contrast of partially ordered cation distributions. Although the phase contrast of the HREM image is rather weak, the image was recorded with about 1100 effective gray levels which are much larger than the 256 gray levels normally used in a conventional image processing system. Intensity distributions in two parts of the image near the crystal edge (A) and at a relatively thicker region (B) are visualized with perspective drawings in Figs. 2(a) and 2(b), and compared quantitatively with contour maps in Figs. 3(a) and 3(b), respectively. It was noticed that projected atomic potentials of the block structure unit (see the inset of Fig. 1) were revealed faithfully in A, having intensity minima at heavy atomic columns (H), whereas the low potential regions (L) have sharp intensity maxima at the thicker region B. These observed images will be compared quantitatively with calculated ones, taking into account the dynamical diffraction effect.

Over the past five years or so the development of a new generation of high resolution electron microscopes operating routinely in the 300-400 kilovolt range has produced a dramatic increase in resolution, to around 1.6 Å for “structure resolution” and approaching 1.2 Å for information limits. With a large number of such instruments now in operation it is timely to assess their impact in the various areas of materials science where they are now being used. Are they falling short of the early expectations? Generally, the manufacturers’ claims regarding resolution are being met, but one unexpected factor which has emerged is the extreme sensitivity of these instruments to both floor-borne and acoustic vibrations. Successful measures to counteract these disturbances may require the use of special anti-vibration blocks, or even simple oil-filled dampers together with springs, with heavy curtaining around the microscope room to reduce noise levels. In assessing performance levels, optical diffraction analysis is becoming the accepted method, with rotational averaging useful for obtaining a good measure of information limits. It is worth noting here that microscope alignment becomes very critical for the highest resolution.In attempting an appraisal of the contributions of intermediate voltage HREMs to materials science we will outline a few of the areas where they are most widely used. These include semiconductors, oxides, and small metal particles, in addition to metals and minerals.

Surface profile imaging at resolutions of better than 2Å is highly suitable for studies of surface structures and reactions. In the case of semiconductor materials, the main challenge is to prepare surfaces free of any contamination. The technique has previously been used to study surface reconstructions of Si and CdTe. In our previous observations, clean surfaces of CdTe were obtained by careful control of the incident electron beam within a JEM-4000EX high resolution electron microscope with a pressure of 10-7 torr. In the present study, observations of reconstructions and dynamic phenomena on CdTe surfaces were carried out with a Phillips-430ST, modified for Ultra-High Vacuum in the vicinity of the specimen and equipped with an in situ heating facility. The base vacuum in the region of the sample could usually reach ∼3×l0-9 torr after baking the microscope column at ∼120°C for 36 hours. The CdTe specimen was prepared by cutting a large single crystal into 3mm discs in a [110] direction, then mechanically polishing to a thickness of ∼20 microns, and finally ion milling to perforation.When viewed along a [110] projection, the CdTe sample was found to be dominated by clean or nearly clean (111) and (110) surfaces(with amorphous materials less than 5Å) whilst the (001) surface was usually very short and rough. A completely clean surface was obtained by in situ annealing of the crystal to about 200°. The (110) surface was then found to be reconstructed with a very characteristic chevron appearance in the manner described previously. Long and flat CdTe(OOl) surfaces were obtained by insitu annealing of the crystal at ∼510°C at which temperature edges of the crystal started to gradually sublime. Characterization of the surface structure was then possible when the crystal was cooled back down to temperatures below about 300°C. It was found that the (001) surface had a (2×1) reconstruction at temperatures below about 200°C which transformed reversibly into a (3×1) reconstruction over the approximate temperature range of 200°C

Considerable interest has been generated in metallic superlattice structures by the discovery of anomalous variations in their physical properties as a function of layer thickness. We have prepared Cu-Pd superlattice samples consisting of 400 alternating layers of Cu and Pd, and with modulation wavelengths in the range 1.4-4.0 nm by dual electron beam evaporation. in a UHV system. Prior to depositing a superlattice film, a Cu buffer layer with a thickness of 130 nm was deposited onto a cleaved mica substrate. In order to study the growth morphology, crystal structure and atomic ordering near the interface, both plan-view and cross-sectional specimens of a Cu-Pd superlattice film have been studied using an Hitachi H-9000 high resolution electron microscope.Fig. 1 is a typical cross-sectional TEM image of the as deposited Cu-Pd superlattice film, showing the morphology of the growth of the crystallites and the crystal structures of the mica substrate, Cu buffer layer and Cu-Pd superlattice. The TEM image clearly shows a structure consisting of alternating layers of Cu and Pd with the expected thicknesses of approximately 1.15 nm. In this image the light and dark contrast regions are associated with the Cu and Pd layers, respectively. Fig. 2 shows a cross-sectional HREM image of the interface between the mica substrate and the Cu buffer layer. The interface, indicated by arrows, is uneven and the Cu buffer layer contains some textured polycrystalline grains, with a mean diameter of 10 nm. Many defects are observed in the Cu buffer layer. Fig. 3 is a cross-sectional HREM image of the Cu-Pd superlattice, along the [110] orientation, showing clear evidence of epitaxial stacking. The interface between the Cu and Pd layers is not atomically sharp, and the degree of abruptness of the interface between the Cu and Pd layers was within two to three monolayers. The structural coherence of the crystal planes was found to extend over several composition modulation periods, and was limited by the presence of structural defects. Many misfit dislocations were observed at the Cu-Pd interface, as indicated by arrows in Fig. 3, and the mean spacing between misfit dislocation is about 10 nm. Since the mismatch between the lattice constants of Cu and Pd is 7.5%, the multilayer structure must be considerably strained in order to accommodate this mismatch; however a significant dislocation density is also observed. As shown in Fig 4, some highly faulted regions were found within the multilayer structure and contained dislocations, stacking faults, microtwins and four differently oriented domain structures. Both the plan-view and cross-sectional HREM observations of the Cu-Pd superlattice have revealed a columnar mode of growth with a mean crystallite diameter of 100 nm, as shown in Figs. 1, 5 and 6. The crystal structure of the boundary region is quite imperfect and the modulation-layer sequence is vague, which might be caused by interdifusion between the Cu and Pd layers. It is obvious that such a growth morphology results in a structure with planar anisotropy.

Unfortunatly Wolfgang Kunath died January 1990High resolution electron microscopy and image processing are being used to determine the molecular packing within the crystal unit cell of the, organic-azo calcium salt. Due to the beam sensitive nature of the organic moiety which contains both aromatic and and aliphatic components, low dose techniques were used. This concisted of, searching the sample in the diffraction mode to find single crystals exibiting point like reflection to at least .2nm resolution, (fig. 1). Focusing and astigmatism correction was performed by moving the beam of the crystal (off axis). The beam was then moved on axis and a series of four, 10 e/A images taken, (fig. 2). Images were primarily recorded using an on line T.V. recording device. These images were then available for processing using the Semper image processing system. Two crystal orientations were found. Type 1 consisted of thin plate like crystals up to 5um diameter and generally 10nm to 20nm thick. Type 2 were thicker crystals with a 3.2nm lattice spacing. The power specrta of the first low dose images were calculated to asses the quality of the of the structural information present. For the type 1 crystal the power spectrum had to show at least second order reflections in two directions ( fig. 3 ). Type 2 crystals showed the 3.2nm reflection often down to the fith order. These crystals also showed parallel side bands corresponding to a d-spacing of about .8nm. With these results the unit cell was found to be tetragonal with a= .78nm b= 3.2nm c= .78nm. In accordance with the diffraction patterns exibited.

Digital computers are becoming widely recognized as standard accessories for electron microscopy. Due to instrumental innovations the emphasis in digital processing is shifting from off-line manipulation of electron micrographs to on-line image acquisition, analysis and microscope control. An on-line computer leads to better utilization of the instrument and, moreover, the flexibility of software control creates the possibility of a wide range of novel experiments, for example, based on temporal and spatially resolved acquisition of images or microdiffraction patterns. The instrumental resolution in electron microscopy is often restricted by a combination of specimen movement, radiation damage and improper microscope adjustment (where the settings of focus, objective lens stigmatism and especially beam alignment are most critical). We are investigating the possibility of proper microscope alignment based on computer induced tilt of the electron beam. Image details corresponding to specimen spacings larger than ∼20Å are produced mainly through amplitude contrast; an analysis based on geometric optics indicates that beam tilt causes a simple image displacement. Higher resolution detail is characterized by wave propagation through the optical system of the microscope and we find that beam tilt results in a dispersive image displacement, i.e. the displacement varies with spacing. This approach is valid for weak phase objects (such as amorphous thin films), where transfer is simply described by a linear filter (phase contrast transfer function) and for crystalline materials, where imaging is described in terms of dynamical scattering and non-linear imaging theory. In both cases beam tilt introduces image artefacts.

Epitaxical growth of GaAs on (001)Si substrates can result in formation of inversion boundaries resulting from the presence of monatomic height (a/4[001]Si) steps on the Si substrate surface or nucleation of GaAs initiated with As or Ga in two areas in the same plane. The lack of TEM evidence for the presence of the inversion boundaries in the GaAs film which characterized earlier research in this area has been a source of speculation about the mechanism of inversion boundary elimination. Recently Liliental-Weber et al. have shown, both experimentally and by computer simulation, that the energetically most favorable (110) inversion boundaries could be imaged edge-on in an atomic resolution microscope for thicknesses in the narrow range of 21-26 nm. Earlier multislice calculations indicated no contrast changes across the boundary for imaging at 200 kV for samples thinner than 18 nm.In the present work image simulations were performed for the (110) inversion boundary in GaAs. The aim was to interpret the high resolution image contrast observed in the GaAs thin film grown on Si on JEOL 200CX microscope operating at 200 kV. Other microscope parameters used for computation were: Cs=1.2 mm, DEL=8 nm (half width of a Gaussian spread of focus due to chromatic aberration), ALPHA=0.9 mrd (semi-angle of beam convergence), R=7 nm-1 (objective aperture radius). Simulation were performed for a wide range of thicknesses (up to 31 nm) and focus (-17 to -127 nm) and the results are shown on the simulated image map in Fig. 1. The simulated image map demonstrates that the contrast change ({111} fringe shift) indicating the (110) inversion boundary in the GaAs thin film imaged along direction can be observed for specimens 11 nm thick for focus -127 nm, for 15 nm and above 23 nm thick specimens for a wide range of calculated focus values.

The alloy of composition Ni4Mo develops, at temperatures below 860 °C, an ordered Dla-structure which is based on the fcc-lattice. This alloy has been widely investigated with respect to its physical properties and its ordering behaviour. High resolution studies are rare and concentrated mainly on its short-range order structure. The aim of the present work was to develop a detailed understanding of image contrast and to apply the results to antiphase-boundary studies in ordered Ni4Mo by means of a JEOL 4000 EX electron microscope.In high-resolution electron microscopy, depending on defocus and foil thickness, a large variety of different images is obtained. Only a few of these allow a direct interpretation concerning the location and the type of the atoms. By computing a through-focus/through-thickness map (TFTT map) before starting experimental work it is possible to determine the proper conditions at which images can be obtained which are closely related to the projected potential.

Since the epock-making results of 1.5 Å point-to-point resolution obtained with the 500 kV HREM in Kyoto in 1978, we are convinced of the validty of the high voltage electron microscope for the high resolution. However, in order to attain the higher resolution of about 1.3 Å, which is required to resolve a carbon-carbon distance in an aromatic hydrocarbon, there remain so many problems to be solved. In 1990 a new 1 MeV microscope with twin-tank (JE0L-ARM1000) in top-entry type has been installed in Kyoto university aiming to achieve such high resolution.The stability of high voltage is especially important for high resolution because the energy spread of the incident electron beam attenuates the phase transfer function and reduces the image contrast in higher spatial frequencies region. In order to suppress the high voltage fluctuation lower than 1 p. p. m. at 1 MeV and to monitor it, the twin-tank system is adopted, which has produced also satisfactory results in the previous high voltage electron microscopes in Kyoto. Fig. 1 shows the stability of the high tension measured at the top of the accerelating column of the new 1 MeV microscope. The fluctuation is evidently suppressed to less than 1 × 10-6 for five minutes long. The ripple monitored on a sincroscope is also less than 1 p.p.m. The chromatic abberation constant Cc is 3.6mm.

Alloys based on TiAl are being considered as potential candidate materials for advanced aerospace applications. The interphase interfaces and twin interfaces in these alloys play important roles during deformation and can vary with ternary additions. Various HREM studies of interphase interfaces have been made in metallic systems during the last few years. When combined with image simulations, HREM has the capability of revealing local structural and compositional information. This investigation discusses HREM analyses of the crystallography of γ/α2 interfaces, twin interfaces and stacking faults in γ-TiAl with ternary additions of Mn and Ta.The γ-TiAl alloys were solutionized at 1200°C for 2 hrs, isothermally aged for 24 hrs at 900°C in the α2+γ phase field and quenched. Thin foil specimens were polished in a 5% sulphuric acid/methanol electrolyte at -40°C and 20V. The samples were examined in Philips EM420T and JEOL 4000EX microscopes at 120 and 400 kV, respectively. Image simulations were perfomed with the TEMPAS multislice programs, using typical operating conditions for a JEOL 4000EX.

Intermetallic compounds of the type RE2Fe17Cx (RE= rare earth element) are promising candidates for permanent magnets. In case of Y2Fe17Cx, the Curie temperature increases from 325 K for x =0 to 550 K for x = 1.6 . X ray and electron diffraction reveal a carbon - induced structural transformation in Y2Fe17Cx from the hexagonal Th2Ni17 - type (x < 0.6 ) to the rhombohedral Th2Zn17 - type ( x ≥ 0.6). Planar crystal defects introduce local sheets of different magnetic anisotropy as compared with the ordered structure, and therefore may have an important impact on the coercivivity mechanism .High resolution electron microscopy ( HREM ) on a Philips CM30 / Super Twin has been used to characterize planar crystal defects in rhombohedral Y2Fe17Cx ( x ≥ 0.6 ). The basal plane stacking sequences are imaged in the [100] - orientation, showing an ABC or ACB sequence of Y - atoms and Fe2 - dumbbells, for both coaxial twin variants, respectively . Compounds resulting from a 3 - week annealing treatment at high temperature ( Ta = 1000 - 1100°C ) contain a high density of planar defects.

Layered materials draw attention in recent years in response to the world-wide drive to discover new functional materials. High-Tc superconducting oxide is one example. Internal interfaces in such layered materials differ significantly from those of cubic metals. They are often parallel to the layer of the neighboring crystals in sintered samples(layer plane boundary), while periodically ordered interfaces with the two neighboring crystals in mirror symmetry to each other are relatively rare. Consequently, the atomistic features of the interface differ significantly from those of cubic metals. In this paper grain boundaries in sintered high-Tc superconducting oxides, joined interfaces between engineering ceramics with metals, and polytype interfaces in vapor-deposited bicrystal are examined to collect atomic information of the interfaces in layered materials. The analysis proved that they are not neccessarily more complicated than that of simple grain boundaries in cubic metals. The interfaces are majorly layer plane type which is parallel to the compound layer. Secondly, chemical information is often available, which helps the interpretation of the interface atomic structure.

Co-Cr thin films have been studied extensively as leading candidates for perpendicular recording media. The development of microstructure in this system has been reported by a number of investigators. These studies have revealed a general growth scenario in which a fine grained, randomly oriented "transition layer" forms first, followed by the development of columnar grains having their hcp c axes textured normal to the film plane. However, it has been found that such columns are not present in very thin (∽10 nm) layers. Also, it has been inferred from electron microdiffraction studies that both c and a axis texturing occurs in these same films. However, direct evidence for this texturing is still needed. In this work, high resolution electron microscopy (HREM) has been employed to examine very thin (5-10 nm) Co-Cr layers.

The fabrication of multilayer films (MLF) with layer thicknesses down to one monolayer has led to the development of materials with unique properties not found in bulk materials. The properties of interest depend critically on the structure and composition of the films, with the interfacial regions between the layers being of particular importance. There are a number of magnetic MLF systems based on Co, several of which have potential applications as perpendicular magnetic (e.g Co/Cr) or magneto-optic (e.g. Co/Pt) recording media. Of particular concern are the effects of parameters such as crystallographic texture and interface roughness, which are determined by the fabrication conditions, on magnetic properties and structure.In this study we have fabricated Co-based MLF by UHV thermal evaporation in the prechamber of an atom probe field-ion microscope (AP). The multilayers were deposited simultaneously onto cobalt field-ion specimens (for AP and position-sensitive atom probe (POSAP) microanalysis without exposure to atmosphere) and onto the flat (001) surface of oxidised silicon wafers (for subsequent study in cross-section using high-resolution electron microscopy (HREM) in a JEOL 4000EX. Deposi-tion was from W filaments loaded with material in the form of wire (Co, Fe, Ni, Pt and Au) or flakes (Cr). The base pressure in the chamber was around 8×10−8 torr during deposition with a typical deposition rate of 0.05 - 0.2nm/s.

The quaternary semiconducting compound GaxIn1-xAsyP1-y has important applications in optoelectronic devices, in the form of heterostructures and quantum wells. Lattice matching between two materials with a composition difference (Δx,Δy) is achieved if Δy≈2.2Δx. Furthermore, decomposition structures have been described in these compounds; the decomposition is expected to follow Δy≈=Δx (Fig. 1). In the present study the sensitivity of high-resolution electron microscope (HREM) images for these composition variations is investigated.GaxIn1-xAsyP1-y layers lattice-matched to InP (x=0, y=0) have been studied with HREM in [001] plan view specimens, and in and cross-sections. The experimental images were interpreted using image simulations. The observations can be summarized as follows: (1) Even small differences in composition between lattice-matched layers (Δx≈0.17, Δy≈0.37) lead to appreciable HREM-image contrast in cross-section specimens (Fig. 2). -orientations are less sensitive, but interfaces associated with Δx≈0.26, Δy≈0.56 still show good composition contrast (Fig. 3).

Recent structural studies of amorphous alloys by precise X-ray and neutron diffraction, Mossbauer spectroscopy and NMR have shown an atomic ordering developing beyond the first neighbor atomic distance, which is called a medium range ordering (MRO) of atoms in amorphous alloys. Lattice fringe images extending in a range of 1 to 2 nm have been observed in amorphous alloys by high resolution electron microscopy(HREM), indicating a possible formation of the MRO structures. In our HREM study of amorphous Pd77.5Cu6Si16.5 alloy ribbons, MRO domains with α-Pd-like structure were observed under the most appropriate underfocus condition. For more detailed understanding of MRO structure, it is necessary to calculate HREM images for possible MRO models and compare them with observed ones. In this study, we calculated HREM images for an amorphous Pd80Si20 with (1) a dense random packing(DRP) structure, (2) a FCC MRO structure( a FCC cluster embedded in the DRP structure) and (3) an icosahedral MRO structure( an icosahedral cluster embedded in the DRP structure).

In the superconducting Bi-Sr-Ca-Cu-O system, ideal compositions of the low Tc(Tc∼90 K) and the high Tc(Tc∼110K) phases are Bi2Sr2CaCu2Oy(y∼8:2212 phase) and Bi2Sr2Ca2 Cu3Oy (y∼10:2223 phase), respectively. The fundamental structures of these phases are tetragonal with parameters: at=bt=0.54 and ct=3.08 nm for the 2212 phase, and at=bt=0.54 and ct=3.71 nm for the 2223 phase. These phases have incommensurate structures with modulation along their b-axes. In this study, the modulated structures of Pb-doped 2212 and 2223 phases have been investigated by means of high resolution electron microscopy and electron diffraction. Samples Bi2-xPbxSr2CaCu2Oy(x=0-0.4, melt-quenched and annealed) and Bi2−xPbxSr2Ca2Cu3Oy(x=0-0.6, sintered) were observed in high resolution electron microscopes operating at 200 kV and 1 MV.Analysis of the incommensurate modulated structures of the 2212 and 2223 phases was made by using samples Bi2Sr2CaCu2Oy and Bi1.6Pb0.4Sr2Ca2Cu3Oy. The lattice parameters of the incommensurate superstructures are a=at and c=ct for both of these phases, but b∼5bt and b∼bt for the 2212 and 2223 phases, respectively.

Zeolites are very suitable for high-resolution electron microscopical investigation since their pore structure often allows an unambiguous interpretation of the images, especially when taken with the electron beam parallel to one of the pore channel direction. HREM can give very useful information on a number of subjects of major importance in zeolite synthesis a.Nucleation;b.Defect characterization;c.Characterization of growth mechanisms of denser phases;d.Structure determination;e.Identification of small metal particles inside the zeolite matrix.f.Structural changes due to (catalytic) reactions.

Many of the most interesting specimens are so severely damaged during the electron microscopical imaging that no useful image emerges from the electron noise. One method of reducing this radiation damage is to cool the specimen, and if this helps it seems reasonable to cool it down as far as possible. This goal is reached most straightforwardly by using the Siemens helium-cooled superconducting objective lens designed by I. Dietrich and co-workers.

Structural study using electron microscopy is indispensable in the fields of physics, chemistry and biology because electron microscopy provides structural images from only small regions of a specimen. The high sensitivity of structure analysis in electron microscopy, however, results in the inevitable problem of irradiation damage in biological and organic materials. Many methods have been tried to reduce the irradiation damage, for example, by raising accelerating voltage, developing high sensitivity recording systems, cooling specimen temperature, etc. Cryoprotection may be the most promising method available for reducing damage at present. The cryoprotection effect from room temperature to liquid helium temperature has interested many researchers for about 15 years, although it is still open to controversy. Recently, the International Experimental Study Group made an interesting attempt to resolve the problem of the cryoprotection factor by cooling specimens in electron microscopes in independent experiments, as closely coordinated as possible with one another. In that paper, although the critical doses measured in each laboratory agree satisfactorily at room temperature, no agreement among the values was observed at very low temperatures.

Any attempt to study the relationship between the electronic and atomic struc ture of isolated defects in semiconductors by high resolution electron microscopy must deal with the following difficulties: (i) The limited point reso lution of modern TEM instruments, which has fallen by about 1Å from 3.8Å to 2.8Å (with tilt) over the last decade. This is still not sufficient to resolve the individual atomic columns in any semiconductor. (ii) The fundamental difficulties in obtaining both high spatial resolution structural information and high energy resolution spectroscopic data from the same, isolated, defect. (iii) The considerable difficulties in extracting chemical, or atomic number information from electron scattering and imaging experiments with high spatial resolution. Among other problems, the separation of composition variation effects from those of thickness is an important problem. Some of our recent approaches to these problems are outlined below.

The technique of surrounding virus particles with a neutralised electron dense stain was described at the Fourth International Congress on Electron Microscopy, Berlin 1958 (see Home & Brenner, 1960, p. 625). For many years the negative staining technique in one form or another, has been applied to a wide range of biological materials. However, the full potential of the method has only recently been explored following the development and applications of optical diffraction and computer image analytical techniques to electron micrographs (cf. De Hosier & Klug, 1968; Markham 1968; Crowther et al., 1970; Home & Markham, 1973; Klug & Berger, 1974; Crowther & Klug, 1975). These image processing procedures have allowed a more precise and quantitative approach to be made concerning the interpretation, measurement and reconstruction of repeating features in certain biological systems.

Elucidation of the 3-D molecular structure of actin has been a challenge to protein crystallo-graphers and electron microscopists ever since the pivotal role of this 43-kDa protein in muscle contraction - and later in cellular motility and cytoskeletal architecture - has been recognized. In its functional form actin is polymerized into filaments (F-actin) which are made of two linear strands of actin subunits helically twisted around each other with a pitch of about 72 nm and an axial stagger of 2.75 nm. In most in vivo situations F-actin is complexed with stoichiometric amounts of accessory proteins - e.g. tropomyosin, troponin, crosslinking or capping proteins - via specific binding sites the actin molecule has for these proteins. While ultimately one would like to reveal a near-atomic resolution model of the actin filament, as a first step towards this goal one would be quite happy to obtain a high resolution electron density map of the actin molecule which, in turn, requires the availability of large and well ordered 3-D crystals.

Diffraction patterns of crystals having long period superlattices are described by their matrix lattice reflections, M = ha* + kb* + lc*, and a set of satellite reflections S appearing around each matrix reflection, which are characterized by S = m1a* + m2b* + m3c*. For usual superstructures the m's become rational numbers but for certain superstructures they are irrational. The latter are called the incommensurate superstructures. Crystal structure analysis by the conventional diffraction methods is based on perfectly periodic structures and generally cannot be applied to the crystals having the irrational superstructure periodicities. This paper deals with the study of such crystals using the high resolution lattice imaging method and the types of information obtained are discussed. It was intended that the study not only supplement the information on statistically averaged structures obtained from diffraction data but also provide further understanding of the incommensurate structures.

High resolution electron microscopy images of crystals are obtained by making some beams, diffracted by the crystal, interfere with the transmitted beam. For some experimental conditions, to be carefully defined for each specimen, the image can be shown to represent atomic columns; thus information in the atomic range is obtained, though it must be stressed that interpretation of these structure images must be done carefully as artefacts can give effects not linked with the crystal structure. In the last 3 years, this technique has been applied to the study of surfaces where it has given some striking results.

The recent advent of high-resolution electron microscopes (HREMs) capable of resolving sub-2-Ångstrom detail on a routine basis has led to an enormous increase in the range of materials which can be usefully studied. Not only is it possible to resolve individual atomic columns in low index zones of most common metals but observations of semiconductors, for example, are no longer restricted to the traditional [110] zone, thereby making it feasible at last to obtain two-dimensional information about surfaces, interfaces and other planar defects. There is a worldwide upsurge of interest in the capabilities of these machines and the so-called medium-voltage (300-400kV) HREMs are selling rapidly despite their considerable expense. Our objective here is to provide a brief and selective overview of the latest applications and likely trends in HREM studies of materials - further details can be found elsewhere in these proceedings. No attempt is made to review instrumentation developments since they are being considered separately.

The recent proliferation of the so-called intermediate-voltage HREMs has led to a vast expansion in the ranges of materials which are nowadays being examined on the atomic scale. Impressive-looking micrographs containing detail as fine as 1A are comparatively easy to obtain. However, relating this image information in a quantitative manner to particular features of the object can be tedious and time-consuming even when the imaging conditions (eg. objective lens focus, illumination angle, focal spread) and the specimen parameters (eg. thickness, orientation, composition) are well-known. The presence of residual astigmatism and/or incident beam misalignment leads to spurious image features which can seriously compromise this process of interpretation, but it is difficult, even for skilled operators, to adjust these variables with sufficient precision that their effects are negligible.

The study of ordered alloys by means of conventional X-ray diffraction methods is hampered by the fact that even single crystals of such alloys are invariably fragmented in symmetry related domains; unscrambling of such combined patterns into mono domain patterns is usually not straightforward. In electron diffraction it is on the other hand often possible to select a single domain on the image and obtain a mono-domain diffraction pattern.The use of suitable high resolution imaging techniques allows often to derive a trial structure, for which the image and the diffraction pattern can be calculated and compared with the observations. It is our intention to demonstrate how the combined use of both techniques allows the determination of crystal structures of rather complicated alloys in the gold-manganese and gold-magnesium systems.

For thin crystals and weak-phase objects, the phase grating approximation indicates that intensities are directly proportional to the projected lattice potencial VZ (x, y). Additionnally at the optimum focus condition, i. e. γ = π/2 (see ref. (2) for details) both electron diffraction and optical transform patterns are identical. Therefore, for very thin crystals, i.e. t < 102A, and several types of zeolites, including ZSM-5, Faujasites X, Y, erionites and A-type zeolites, the main assumptions of the phase grating approximation hold, making possible a complete study of structural features taking place at a nearly atomic scale. The method used to characterize the ultraestrncture of those zeolites are high resolution electron microscopy, Fourier analysis in the computer of the digitized micrographs and Laser optical diffractometry.