An Incommensurate Superstructure of Hexagonal Tungsten Bronze

Incommensurate superstructures are interesting problems for high resolution electron microscopy. If modulations are formed within a plane of a host lattice parallel to the incident beam direction, their structures can be known directly from images (1,2,3). In this paper, an incommensurate superstructure of hexagonal potassium tungsten bronze, K0.3WO3, is observed by a 100B high-resolution electron microscope and its structure model is proposed. The hexagonal tungsten bronze was determined by Magneli (4) and its structure is shown in Fig. 1. The structure consists of WO6 octahedra and alkali metal ions. The alkali metal ions situated in hexagonal tunnels do not lie at the same level of the WO6 octahedra but at ¼ c above or below them. It was assumed that the alkali metal ions were distributed in a random fashion. Fig. 2 shows a structure image of K0.3WO3, taken along the [100] direction. The white spots correspond to hexagonal tunnels in Fig. 1. Fig. 3 shows an electron diffraction pattern taken along the [010] direction. Some additional weak superstructure spots are observed. The superstructure spot (indicated by A) is situated at a non-integral multiple position of the subcell spots along the c*-axis, indicating that the incommensurate superstructure has a multiplicity of 2.2 x c of the subcell. The non-integral periodicity can be seen in a high-resolution image taken along the [010] direction, as shown in Fig. 4. At the thick crystal regions, some weak dark bands running parallel to the c axis are observed, in which they have two different widths (2 x c or 2.5 x c) along the c axis. An average distance between the adjacent dark bands becomes about 2.2 x c, which is consistent with an optical diffraction pattern (inset in Fig. 4). One of the possible models for the incommensurate superstructure of the hexagonal tungsten bronze is proposed in Fig. 5. The superstructure arises from the local ordering of K ion vacancies located in the tunnels along the c axis. The vacancies are formed at every fourth or fifth site of K ions. We call them structures with n = 4 and n = 5. The incommensurate superstructure results from a mixture of the structure elements with n = 4 and n = 5, causing the formation of a non-integral periodicity observed presently. It should be noted in Fig. 4 that the image from a thin region does not show the superstructure but the image from a thick region does. It seems that this phenomenon arises from dynamical diffraction effects. This will be discussed in detail on the basis of the image calculation.

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Light Optical Diffraction Studies of Macromolecular Ultrastructure

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010006828x ◽

1970 ◽

Vol 28 ◽

pp. 258-259

Author(s):

Glen B. Haydon

Keyword(s):

High Resolution ◽

Diffraction Analysis ◽

Diffraction Pattern ◽

Electron Micrographs ◽

Optical Diffraction ◽

Electron Micrograph ◽

Its Analysis ◽

Resolution Electron ◽

Diffraction Patterns

Analysis of light optical diffraction patterns produced by electron micrographs can easily lead to much nonsense. Such diffraction patterns are referred to as optical transforms and are compared with transforms produced by a variety of mathematical manipulations. In the use of light optical diffraction patterns to study periodicities in macromolecular ultrastructures, a number of potential pitfalls have been rediscovered. The limitations apply to the formation of the electron micrograph as well as its analysis.(1) The high resolution electron micrograph is itself a complex diffraction pattern resulting from the specimen, its stain, and its supporting substrate. Cowley and Moodie (Proc. Phys. Soc. B, LXX 497, 1957) demonstrated changing image patterns with changes in focus. Similar defocus images have been subjected to further light optical diffraction analysis.

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Structural analysis of the surface-layer protein of spirillum serpens by high-resolution electron microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100077268 ◽

1983 ◽

Vol 41 ◽

pp. 738-739

Author(s):

W. H. Wu ◽

R. M. Glaeser

Keyword(s):

Electron Microscopy ◽

Surface Layer ◽

Structural Analysis ◽

High Resolution ◽

Low Dose ◽

High Resolution Electron Microscopy ◽

Optical Diffraction ◽

Surface Layer Protein ◽

Morphological Unit ◽

Resolution Electron

Spirillum serpens possesses a surface layer protein which exhibits a regular hexagonal packing of the morphological subunits. A morphological model of the structure of the protein has been proposed at a resolution of about 25 Å, in which the morphological unit might be described as having the appearance of a flared-out, hollow cylinder with six ÅspokesÅ at the flared end. In order to understand the detailed association of the macromolecules, it is necessary to do a high resolution structural analysis. Large, single layered arrays of the surface layer protein have been obtained for this purpose by means of extensive heating in high CaCl2, a procedure derived from that of Buckmire and Murray. Low dose, low temperature electron microscopy has been applied to the large arrays.As a first step, the samples were negatively stained with neutralized phosphotungstic acid, and the specimens were imaged at 40,000 magnification by use of a high resolution cold stage on a JE0L 100B. Low dose images were recorded with exposures of 7-9 electrons/Å2. The micrographs obtained (Fig. 1) were examined by use of optical diffraction (Fig. 2) to tell what areas were especially well ordered.

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Voltage-center COMA-free alignment for high-resolution Electron Microscopy

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010016978x ◽

1994 ◽

Vol 52 ◽

pp. 410-411

Author(s):

K. Ishizuka ◽

K. Shirota

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Incident Beam ◽

Chromatic Aberration ◽

High Resolution Electron Microscopy ◽

Beam Deflection ◽

Objective Lens ◽

Main Magnetic Field ◽

Beam Direction ◽

Resolution Electron

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.

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The Contribution of Intermediate-Voltage, High-Resolution Electron Microscopy In Materials Science: An Appraisal

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100181142 ◽

1990 ◽

Vol 48 (1) ◽

pp. 478-479

Author(s):

John L. Hutchison

Keyword(s):

High Resolution ◽

Materials Science ◽

High Resolution Electron Microscopy ◽

Optical Diffraction ◽

The Past ◽

Resolution Electron ◽

Extreme Sensitivity ◽

Electron Microscopes ◽

New Generation ◽

Small Metal Particles

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.

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High-Resolution Cryo-Electron Microscopy of Biological Macromolecules

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100179385 ◽

1990 ◽

Vol 48 (1) ◽

pp. 126-127

Author(s):

Yoshinori Fujiyoshi

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Diffraction Pattern ◽

Superfluid Helium ◽

Copper Phthalocyanine ◽

Optical Diffraction ◽

Irradiation Damage ◽

Biological Macromolecules ◽

Cross Sectional ◽

Instrumental Resolution

The resolution of direct images of biological macromolecules is normally restricted to far less than 0.3 nm. This is not due instrumental resolution, but irradiation damage. The damage to biological macromolecules may expect to be reduced when they are cooled to a very low temperature. We started to develop a new cryo-stage for a high resolution electron microscopy in 1983, and successfully constructed a superfluid helium stage for a 400 kV microscope by 1986, whereby chlorinated copper-phthalocyanine could be photographed to a resolution of 0.26 nm at a stage temperature of 1.5 K. We are continuing to develop the cryo-microscope and have developed a cryo-microscope equipped with a superfluid helium stage and new cryo-transfer device.The New cryo-microscope achieves not only improved resolution but also increased operational ease. The construction of the new super-fluid helium stage is shown in Fig. 1, where the cross sectional structure is shown parallel to an electron beam path. The capacities of LN2 tank, LHe tank and the pot are 1400 ml, 1200 ml and 3 ml, respectively. Their surfaces are placed with gold to minimize thermal radiation. Consumption rates of liquid nitrogen and liquid helium are 170 ml/hour and 140 ml/hour, respectively. The working time of this stage is more than 7 hours starting from full LN2 and LHe tanks. Instrumental resolution of our cryo-stage cooled to 4.2 K was confirmed to be 0.20 nm by an optical diffraction pattern from the image of a chlorinated copper-phthalocyanine crystal. The image and the optical diffraction pattern are shown in Fig. 2 a, b, respectively.

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