Resolution Micrographs Research Articles

Electron Crystallographic Determination of the Structure of Bacteriorhodopsin

The light driven proton pump bacteriorhodopsin (bR) occurs naturally as two-dimensional crystals. A three-dimensional density map of the structure, at near atomic resolution, has been obtained by studying the crystals using electron cryo-microscopy to obtain diffraction patterns and high resolution micrographs (1).New methods have been developed for analysing micrographs from tilted specimens, incorporating the methods previously developed for untilted specimens that enable large areas to be analysed and corrected for distortions. Data from 72 images, from both tilted and untilted specimens, have been analysed to produce the phases of 2700 independent Fourier components of the structure. The amplitudes of these components have been accurately measured from 150 diffraction patterns. Together, these data represent about half of the full three-dimensional transform to 3.5 Å. The distribution of the data which is included in the map is shown in fig. 1. For specimen tilts up to around 20° the data is essentially complete. For higher tilts the data is more sparsely sampled, and is at present about half complete.

High Resolution Transmission Electron Microscopy of an automobile catalytic converter

Understanding of catalytic processes requires detailed knowledge of the catalyst. As heterogeneous catalysis is a surface phenomena the understanding of the atomic surface structure of both the active material and the support material is of utmost importance. This work is a high resolution electron microscopy (HREM) study of different phases found in a used automobile catalytic converter.The high resolution micrographs were obtained with a JEM-4000EX working with a structural resolution better than 0.17 nm and equipped with a Gatan 622 TV-camera with an image intensifier. Some work (e.g. EDS-analysis and diffraction) was done with a JEM-2000FX equipped with a Link AN10000 EDX spectrometer. The catalytic converter in this study has been used under normal driving conditions for several years and has also been poisoned by using leaded fuel. To prepare the sample, parts of the monolith were crushed, dispersed in methanol and a drop of the dispersion was placed on the holey carbon grid.

Monte Carlo simulation of oxygen ordering in YBa 2 Cu 3 O z .

Abstract Oxygen ordering in the basal plane of YBa2Cu3Oz has been studied by Monte Carlo simulations of a two-dimensional anisotropic Ising model. The orthorhombic to tetragonal transition is found to be second order at high temperature in agreement with previous CVM calculations. At low temperatures, a cell-doubled orthorhombic phase appears near stoichometry z=6.5, intermediate between the single cell orthorhombic and tetragonal phases. At very low temperatures, long-lived transient O Cu O chain ordering is observed to lead to triple and fivefold unit cells. Where not obscured by transient ordering, the transition lines bordering the orthorhombic cell-doubled phase are found to be second order. The observed equilibrium and non-equilibrium structures correlate well with atomic resolution micrographs and diffraction data from the YBa2Cu3Oz system.

Image processing enhancement of high-resolution TEM micrographs of nanometer-size metal particles

The high-resolution TEM detectability of lattice fringes from metal particles supported on substrates is impeded by the substrate itself. This effect appears in both amorphous and crystalline substrates. In the former case, it is due to substrate-generated phase contrast features; in the latter case it is due to the intermixing of fringes from particle and substrate. Single value decomposition (SVD) and Fourier filtering (FFT) methods were applied to standard high resolution micrographs to enhance lattice resolution from particles as well as from crystalline substrates. SVD produced good results for one direction of fringes, and it can be implemented as a real-time process. Fourier methods are independent of azimuthal directions and allow separation of particle lattice planes from those pertaining to the substrate, which makes it feasible to detect possible substrate distortions produced by the supported particle. This method, on the other hand, is more elaborate, requires more computer time than SVD and is, therefore, less likely to be used in real-time image processing applications.

Inversion boundaries in GaAs grown on Si

Inversion boundaries in GaAs grown on Si were investigated by high-resolution transmission electron microscopy. These boundaries were found microscopically to follow {110} planes, even when they appeared macroscopically along other planes, such as {111}. High resolution micrographs from edge-on {110} inversion boundaries were taken in [110] and [100] projection. In certain areas, shifts of the images of {111} and {200} planes across the boundaries were observed. Image simulations confirmed that the visibility of these shifts can only be observed for specific imaging conditions and within a limited range of sample thickness.

High Resolution Electron Microscopy of Twist Grain Boundaries

Preliminary experimental high resolution micrographs have been obtained for a Au thin film containing a [001], Σ=5 (θ=36.5 °) twist boundary. Other twist boundary cases such as the [001], Σ=13 (θ= 22.6°) and [111] low angle (˜3°) have also been fabricated. In order to assess whether the atomistic boundary structure is being imaged, extensive computer simulations of the Σ=5 bicrystal images have also been undertaken. Structurally, several contributions to the scattering must be considered which include: both upper and lower surface layers, bulk contributions above and below the interface and the relaxed interfacial structure at the composite film midplane. The effect of specimen orientation on image features is also evaluated for dynamical diffraction conditions. Likewise, the types of image features which arise by including bulk lattice reflections or alternately including only the reflections arising from the interface and surfaces will be discussed. Several schemes for analyzing twist boundary structures flat-on or near flat-on will be presented for a wide range of microscope conditions for a 400 kV microscope.

High Resolution Micrograph of a Column

High Resolution Micrograph of a Column

In-Situ Transmission Electron Microscopy and Computer Simulation Study of the Kinetics of Oxygen Loss in Yba2Cu3OZ

AbstractHigh resolution transmission electron microscopy during in‐situ quenching of YBa2Cu3Oz is used to study the kinetics of microdomain formation during oxygen loss in this system. Image simulations based on atomic models of oxygen‐vacancy order in the basal plane of this material generated by Monte Carlo calculations are used to interpret high resolution micrographs of the structures obtained by quenching. The observed domain structures agree well with those obtained from the simualtions.

Capacitance and conduction properties of semi-insulating polycrystalline silicon films

Semi-insulating polycrystalline silicon (SIPOS) is a nonlinear, resistive film which is widely used as a passivant in high-voltage planar electronic devices. We present current-voltage and capacitance-voltage data, taken from SIPOS capacitor structures, which are quite different from similar results in the literature. We propose that our data may be explained by the existence of a change in the current transport mechanism in the film at an anomalously low electric field value. We present an atomic resolution micrograph of the SIPOS/silicon interface which points to a possible morphological reason for the uniqueness of the current transport properties.

Electron microscopy of cardiac myosin: its shape and properties as determined by the regulatory light chain.

Structural properties of dog cardiac myosin and the influence of the regulatory light chain (LC2) on the shape of myosin heads were investigated by electron microscopy. LC2 was reversibly removed using a neutral protease from myopathic hamsters (Margossian, J. Biol. Chem. 260 (1985) 13747-54). The distribution of myosin head length centred around 17 nm with the mean length being 18.9 nm. Statistical analysis suggested that myosin heads became more globular upon removal of LC2. No extensive aggregation of myosin could be detected after LC2 was dissociated, either by sedimentation velocity or by gels run under non-denaturing conditions. The centre-to-centre distance between heads remained constant at about 21 nm, regardless of the presence or absence of LC2. The distribution of length of the globular region reveals two peaks at 7.5 and 9.5 nm, suggesting an extended and a shorter configuration of this region. The decrease in mass at the head/tail junction upon LC2 removal suggests that it is the binding site for the regulatory light chains. A bend at 57 nm from the head/tail joint was sometimes noticed, corresponding to the myosin hinge region. In high resolution micrographs individual particles revealed invaginations along the contours of the head, possibly delineating the boundaries of structural domains within the head. The conformation of arrowheads in actin decorated with either subfragment 1 (S1) or heavy meromyosin (HMM) was investigated in the presence and absence of LC2.

Enhanced oxygen diffusion and precipitation in silicon

SUMMARYProlonged annealing of Cz‐silicon at 758 K results in the formation of ribbon‐like oxygen precipitates on {311} planes interpreted as the coesite phase. From this an enhancement of the oxygen diffusion coefficient by more than three orders of magnitude is inferred. Excess selfinterstitials are accommodated in extrinsic dislocation loops on {111} planes (‘loopites’) and probably also in ‘blob’‐like defects visible in high resolution micrographs with little detectable lattice strain. Evidence is presented that coesite ribbons can nucleate on {311} steps on loopites and vice versa.

Scanning optical microscopy by objective lens scanning

The authors present high resolution micrographs obtained with a scanning optical microscope where the scanning is achieved by mechanically scanning the objective. This approach is very important in the microscopy of heavy or awkwardly shaped objects.

Application of Hrem in Studying Amorphisation of Intermetallic Compounds

ABSTRACTElectron irradiation induces many intermetallic compounds to become amorphous. As this irradiation is capable of producing only isolatedpoint defects for each collision event, an understanding of this amorphisation proqess has a special significance with respect to the understanding of amorphous materials. This paper will report the results of HREM observations of an intermetallic compound in the Cu-Ti alloy system. High resolution micrographs will be presented to demonstrate that the energy associated with the irradiation induced chemical disordering is the major driving force in the amorphisation process. Also, the utility of the HREM in the study of amorphisation and the amorphous structure will be discussed.

The Use of Symmetry in the TEM Analysts of Precipitate Morphologies

ABSTRACTThis study points out how symmetry properties inherent in precipitation reactions can be exploitet to facilitate and improve the accuracy of a morphological analysis by TEM. A method is given for the simple determination of the direction and distribution of needle precipitates and the habit plane of plate precipitates based on the use of symmetry properties of the matrix crystal. The bicrystal symmetry of different orientation relationships between cubic crystals and its connection with observed and equilibrium shapes is illustrated with examples of high resolution micrographs of Ge precipitates in an Al matrix.

High resolution electron microscopy of long range ordered alloys

In this paper a survey is given of the application of high resolution electron microscopy and selected area electron diffraction to the study of long range ordered alloys. The characteristic features of the diffraction effects and of the imaging of ordered alloys are discussed. Group theoretical considerations allow prediction of microtexture of such alloys.A number of simple alloy structures are imaged and it is shown, by means of simulated images, that under suitable diffraction conditions the columns of minority atoms are represented as bright dots. The columns of majority atoms are only visible at very small thicknesses. Subsequently a number of one- and two-dimensional long period superstructures derived from these simple structures are analysed, using high resolution micrographs. Finally the observed microtexture of the same alloy superstructures is compared with the predictions of group theory. Strongly non-conservative antiphase boundaries are found to dissociate inapb’s which are as close to conservative as is compatible with thefcc lattice.

Ultrahigh resolution electron microscopy of the surface structure of (110) Ag 2O

An ultrahigh resolution transmission electron microscope and diffraction investigation of the residual oxidized silver on the surface of (111) Au films has shown that it is possible to resolve a monolayer coverage of silver atoms and the atomic structure of crystalline Ag 2O surfaces. Localized patches often under 100 Å in lateral extent show a reoriented (110) oxide which often exhibits a (2 × 1) surface superstructure. The structure of various different layer coverages has been analyzed from the high resolution micrographs via digital image processing and model building to interpret surface morphology.

Ultraligh resolution electron microscopy of the surface structure of (110) Ag 2O

Abstract An ultrahigh resolution transmission electron microscope and diffraction investigation of the residual oxidized silver on the surface of (111) Au films has shown that it is possible to resolve a monolayer coverage of silver atoms and the atomic structure of crystalline Ag 2 O surfaces. Localized patches often under 100 A in lateral extent show a reoriented (110) oxide which often exhibits a (2 × 1) surface superstructure. The structure of various different layer coverages has been analyzed from the high resolution micrographs via digital image processing and model building to interpret surface morphology.

Experimental high resolution electron microscopy evidence of a surface compound on bismuth (00.1) plane

We have observed thin films of bismuth (00.1) by high resolution electron microscopy. Micrographs show that, superimposed on the normal hexagonal structure, of lattice spacing 2.27 Å, there exist, locally, two fringes systems with spacings 13.6 and 7.8 Å, under an angle of 100°. These two phenomena, structure image and additional fringes, interact weakly. Electronic diffraction patterns show corresponding extra spots. These correspond to a new phase on the surface, different from the bismuth. Furthermore, we have made optical diffraction patterns from such high resolution micrographs, which give information on very small regions of the crystal ( ∼ 150 Å). This allows us to reconstruct the coïncidence cell between bismuth and the surface phase: this cell is an elongated parallelogram.

Preparation of metal specimens for HREM by ultramicrotomy

The preparation of aluminum specimens by ultramicrotomy for high resolution electron microscopy is reported. Illustrative examples of high resolution micrographs from aluminium and an aluminium/aluminium oxide interface obtained with the specimens are presented.

Visualization of protein subunits of equine ferritin

The first electron microscope study was carried out by Farrant in 1954. He established the characteristic appearance of the ferritin molecule, that of an iron micelle surrounded by a protein shell. The microcrystallinity of the iron core was demonstrated by Massover and Cowley in 1972 utilizing darkfield illumination to show lattice spacing of between 2.2 Å and 9.5 Å. The protein shell can be shown by negative staining techniques but because of the granularity of the stain details of the protein substructure remained unresolved. Massover was able to demonstrate the subunits by rotary shadowing with uranium oxide, but again the profile of the subunits was not resolved. An electron density map study of apoferritin indicated the subunits were cylindrical in shape with the approximate dimensions of length 55 Å and diameter 27 Å. A bismuth stain developed by Ainsworth and Karnovsky to enhance the electron opacity of ferritin in ultrathin sections has been used to produce the high resolution micrographs of the ferritin protein subunits shown in figures 1-4. The cores of the molecules show lattice spacings in both bright-and dark-field between 2.2 Å and 9.5 Å.