Showing papers on "Electron tomography published in 1983"

Direct surface imaging in small metal particles

Abstract: Atomic-level information about the surfaces of small metal particles has been recorded directly in recent observations with a 600-kV high-resolution electron microscope. Here, we have studied small polycrystalline particles of silver and gold tilted to bring their surfaces parallel to the electron beam. However, unlike previous workers using this normal reflection electron microscopy (REM) configuration, we have used conventional bright field axial imaging thereby considerably facilitating image interpretation. As well as clean, sharp surface images, morphological details of catalytic significance, such as the distribution of surface steps, particle facetting and the nature of surface reconstructions, have been obtained. Moreover, detailed computer simulations confirmed that the electron micrographs can be interpreted in terms of atomic columns and, in particular, established that some micrographs showed, for the first time in a transmission electron microscope (TEM), direct atomic-scale imaging of a reconstructed metal surface.

Electron Diffraction with the Transmission Electron Microscope as a Phase‐Determining Diffractometer—From Spatial Frequency Filtering to the Three‐Dimensional Structure Analysis of Ribosomes

Abstract: Chemists recognize X-ray crystal structure analysis and electron microscopy as powerful methods of analysis. In the last 20 years the basic ideas of X-ray diffraction analysis have been extended to the field of electron microscopy, whereby an image-forming apparatus is converted into an electron diffractometer, and through which an old dream of crystallographers can be realized—the measurement of the phase shift of scattered waves, a prerequisite for the direct calculation of structures. Its most important area of application, like that of the X-ray diffractometer, is in three-dimensional structure analysis—in all fields of science. However, beyond crystallography, aperiodic structures (comparable to crystals with a single unit cell) can also be analyzed three-dimensionally. In this progress report, the development of the first idea (spatial frequency filtering) to the analysis of ribosomal particles is outlined. Attention will be focused primarily on quantitative methods for the measurement of scattered rays, which are also usable beyond the conventional limit of resolution, down to atomic resolution. In the course of this work in 1968, the principle of the three-dimensional analysis of native biological crystal structures using the electron microscope, as worked with today in many laboratories, was developed. In Munich, however, further research focused on the three-dimensional analysis of aperiodic and individual (especially biological) objects. The analysis of 50S-subunits of the procaryotic ribosome of E. coli showed surprisingly good reproducibility of the results (although only within the same orientation), allowing the deduction of almost ideal average model structures from a limited number of particles.

The specimen thickness effect upon the electron microscope image contrast transfer of amorphous objects

Abstract: From experimental measurement the authors show that amorphous carbon specimens imaged by 100 keV conventional transmission electron microscopy (CTEM), with thicknesses as large as 100 nm behave like weak phase objects. The defocus of the phase transfer contrast function cannot be evaluated from the exit surface plane of the object but may be from its middle plane. A theoretical model explaining these results is propounded.

Electron microscopy study of zeolite ZK-14; a synthetic chabazite

Abstract: The defect structure of zeolite (K+, TMA+) — ZK-14, a synthetic chabazite, has been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM together with TEM bright field (BF) and dark field (DF) micrographs indicate that the hexagonal, platelet ZK-14 crystals are built up of crystalline blocks joined by twinning along (00.1). High resolution transmission electron microscopy (HRTEM) reveals faulting of the ideal AABBCC single 6-ring stacking sequence of ZK-14. This is consistent with an observed line broadening in its X-ray powder diffraction profile. Channel apertures are imaged, even for thick specimens.

Cryopump and sample holder for clean reconstructed surface observations in a transmission electron microscope

Abstract: The design and construction of a simple cryopump and sample holder which allow imaging of clean reconstructed surfaces prepared in situ in a transmission electron microscope are described. Applications to the Si(111)7×7 surface imaging are presented.

Electron Microscopy of Molecules

Abstract: Modern electron microscopes are capable of resolving individual molecules in organic crystals but the achievement of this resolution is determined by the contrast and radiation stability of the molecular crystal. This paper discusses the parameters of the molecule that affect the resolution and shows how the technique of high resolution electron microscopy has been applied to phthalocyanines and planar aromatic hydrocarbons.

R.B.S. Microscopic "Tomography"

Abstract: The resolving power of optical and electron microscopes is limited by diffraction, scattering being also a problem with electron microscopes, and ion source properties in the case of ion microprobes. Essentially, the resolution is determined by the hardware. We have developed a technique involving simple equipment but extensive computer analysis following the taking of data. The profile and internal constitution of periodic surfaces and micron sized objects is measured by irradiating them uniformly with a parallel beam of ions. The Rutherford backscattered spectra, observed at different angles using solid state detectors, are analyzed in a manner similar to that employed in tomography to yield the structure of the object irradiated. The ultimate resolution is determined by ion straggling, rather than diffraction.

Disappearance of topographical contrast in the backscattered electron image in scanning electron microscopy

Abstract: A computer analysis of the topographical contrast due to surface projection in the backscattered electron image in the scanning electron microscope is described. Present results show that disappearance of the topographical contrast may occur at a certain condition between the incident beam angle and the detector take‐off angle. This condition just corresponds to the experimental results previously reported.