Re-examining mechanisms of radiation damage in organic specimens

1990 ◽  
Vol 48 (4) ◽  
pp. 812-813
Author(s):  
David A. Armstrong ◽  
Suichu Luo ◽  
David C. Joy
Keyword(s):  
Mass Loss ◽  
Radiation Damage ◽  
Low Dose ◽  
High Resolution Electron Microscopy ◽  
Limiting Factor ◽  
High Dose ◽  
X Ray ◽  
Resolution Electron ◽  
Significant Mass Loss ◽  
Significant Mass

Radiation damage to organic specimens is the major limiting factor in high resolution electron microscopy studies of biological systems. Electron beam irradiation compromises resolution by altering chemical microstructure, resulting in local mass loss and volume shrinkage in a specimen. All significant mass loss is thought to occur prior to a total incident dose of 50 electrons/ square angstrom If this is the case it is hard to reconcile the observation that images must be recorded at doses of less than 100 el/Å in order to avoid excessive mass loss and shrinkage while microanalytical (EDS and EELS) studies of the same tissue are routinely carried out at doses of 104 - 105el/Å2. Also, since most workers typically use either low dose (for imaging) or high dose (for microapalysis) there are apparently no studies in the literature which attempt to follow the process of radiation damage between these two extremes.We have chosen to investigate mass loss in polymer embedding resins such as are routinely used for TEM imaging as well as for X ray microanalytical applications.

High Resolution Electron Microscopy of a Novel Zeolite

1997 ◽  
Vol 3 (S2) ◽  
pp. 441-442
Author(s):  
P.A. Crozier ◽  
I.Y. Chan ◽  
C.Y. Chen ◽  
L.W. Finger ◽  
R.C. Medrud ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Low Dose ◽  
High Resolution Electron Microscopy ◽  
X Ray Diffraction ◽  
High Adsorption ◽  
Structural Units ◽  
X Ray ◽  
Resolution Electron ◽  
Crystal Structural

Low-dose high resolution electron microscopy (HREM) is a useful technique for elucidating the structure of zeolites. In recent years a number of zeolite structures have been solved using combinations of different characterization techniques including adsorption measurements, powder x-ray diffraction and low-dose high resolution electron microscopy (for example see ref. 2). We have used these techniques to study the structure of a novel zeolite material. However, great care must be exercised when interpreting data from these techniques in terms of crystal structural units. In this particular case, the structure was recently determined using single crystal x-ray diffraction and showed some surprises.Details of the synthesis of this zeolite are given elsewhere. The high adsorption capacity suggested that this zeolite possessed two interpenetrating channels (either a 10 and a 12 ring or two 12 ring channels). X-ray powder diffraction showed the material to be monoclinic with a= 18.5Å, b= 13.4 Å, c= 7.6 Å β = 101.5°).

Radiation Damage in Organic Molecules

1980 ◽  
Vol 38 ◽  
pp. 680-681
Author(s):  
Manoj Misra ◽  
R.F. Egerton
Keyword(s):  
Radiation Damage ◽  
Room Temperature ◽  
Organic Molecules ◽  
High Resolution Electron Microscopy ◽  
Limiting Factor ◽  
Biological Macromolecules ◽  
Nucleic Acid Bases ◽  
Slow Evaporation ◽  
Resolution Electron ◽  
Carbon Coated

Radiation damage is the main limiting factor in attempting high resolution electron microscopy of biological macromolecules1,2. To better understand the process of radiation damage, a systematic study of various amino acids, peptides and nucleic acid bases has been undertaken. We report here some preliminary results obtained with glycine, glycyl-glycine, cystine, cysteine and uracil at room temperature. Specimens of these compounds were prepared by slow evaporation of their aqueous solutions (except of glycylglycine which gave better crystals when the solvent used was N-propanol) on carbon coated grids.

High Resolution Study of the Metamict State in Zircon

1981 ◽  
Vol 39 ◽  
pp. 112-113 ◽  
Author(s):  
T. J. Headley ◽  
R. C. Ewing ◽  
R. F. Haaker
Keyword(s):  
High Resolution ◽  
Radiation Damage ◽  
High Resolution Electron Microscopy ◽  
Radioactive Waste Disposal ◽  
X Ray Diffraction ◽  
X Ray ◽  
Resolution Electron ◽  
Metamict Minerals ◽  
Resolution Study

Ceramic waste forms are being developed as solid hosts for radioactive waste disposal, Of concern is the effect of long-term radiation damage on crystalline integrity and subsequent leachability of the waste form. In preparation for understanding radiation damage effects, we have performed a high resolution study of the metamict state in natural zircons (ZrSiO4). Metamict minerals are a class of “amorphous” minerals, originally crystalline which have suffered extensive structural degradation over time from decay of internal radioactive impurities, principally U and Th. From x-ray diffraction evidence it is widely believed that the metamict state is amorphous in the sense of an isotropic glass. However, an electron microscope study performed some 15 years ago suggested that metamict zircons possess a structure composed of slightly misoriented crystallites about 100 Å in size, a structure indistinguishable from an isotropic glass by x-ray diffraction. We felt that high resolution electron microscopy could clearly delineate between the isotropic glass and misoriented microcrystalline concepts.

X-Ray Optical Properties of C/C-Multilayers Prepared by Pulsed Laser Deposition (PLD)

1995 ◽  
Vol 382 ◽  
Author(s):  
R. Dietsch ◽  
T. Holz ◽  
H. Mai ◽  
S. Hopfe ◽  
R. Scholz ◽  
...  
Keyword(s):  
Thermal Stability ◽  
Driving Forces ◽  
Mass Density ◽  
Grazing Incidence ◽  
High Resolution Electron Microscopy ◽  
Limiting Factor ◽  
Silicon Substrates ◽  
X Ray ◽  
Atomic Transport ◽  
Resolution Electron

ABSTRACTThe mass density of thin a-C films prepared by PLD is determined by the parameters of the ablation process. This fact results from various concentrations of sp3 and sp2 bounded atoms in the films, that are created for different laser power densities. Thus more diamondlike or more graphite-like layers are obtained. The alternate deposition of layers with different mass densities enables the preparation of C/C- multilayers that show X-ray optical activity. In the present investigations C/C-multilayers were deposited on silicon substrates at room temperature under UHV-conditions.The double layer thickness d was changed in the range from 74Å through 18Å. High quality interfaces and very reproducible average d-spacing resulted in an energy resolution of 0.7% for 120 period stacks. Due to chemically almost equivalent layers the chemical driving forces of atomic transport in these multilayers vanish. Thus e.g. thermal stability is observed up to 700°C for an appropriate heat treatment. The limiting factor of thermal stability is caused by SiC-formation from reactions between layer stack and silicon substrate.In-situ ellipsometry, grazing incidence x-ray diffraction, high resolution electron microscopy (HREM) and image processing were applied for specimen characterization.

Tem and Hrem Study Of mGH-Temperature Aluminum Ion Implantation to 6H-SiC

1998 ◽  
Vol 512 ◽  
Author(s):  
A. A. Suvorova ◽  
I. O. Usov ◽  
O. I. Lebedev ◽  
G. Van Tendeloo ◽  
A. V. Suvorov
Keyword(s):  
Electron Microscopy ◽  
Low Dose ◽  
High Resolution Electron Microscopy ◽  
Implantation Dose ◽  
Structural Defects ◽  
High Dose ◽  
Dislocation Loops ◽  
Aluminum Ions ◽  
Transmission Electron ◽  
Resolution Electron

ABSTRACT6H silicon carbide wafers were implanted with 40–50 keV aluminum ions to a dose of 1.5 × 1014 – 1.5 × 1016 cm−2 at high temperatures (1100°C–1700°C). The substrate temperature and the implantation dose were varied to investigate the influence of the implantation parameters on the formation of structural defects. Conventional transmission electron microscopy (TEM) and high resolution electron microscopy (HREM) techniques were applied to study the defects. We found that for low dose implants {0001} interstitial dislocation loops are formed but for high dose implants aluminum precipitates associated with {0001} half-loops are formed.

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

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.

Electron microscopy of rabbit FC crystals

1983 ◽  
Vol 41 ◽  
pp. 730-731
Author(s):  
Robert A. Grant ◽  
Laura L. Degn ◽  
Wah Chiu ◽  
John Robinson
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Molecular Replacement ◽  
X Ray ◽  
X Ray Crystallography ◽  
Resolution Electron ◽  
Replacement Technique ◽  
Hydrated Crystal ◽  
Molecular Structure Analysis

Proteolytic digestion of the immunoglobulin IgG with papain cleaves the molecule into an antigen binding fragment, Fab, and a compliment binding fragment, Fc. Structures of intact immunoglobulin, Fab and Fc from various sources have been solved by X-ray crystallography. Rabbit Fc can be crystallized as thin platelets suitable for high resolution electron microscopy. The structure of rabbit Fc can be expected to be similar to the known structure of human Fc, making it an ideal specimen for comparing the X-ray and electron crystallographic techniques and for the application of the molecular replacement technique to electron crystallography. Thin protein crystals embedded in ice diffract to high resolution. A low resolution image of a frozen, hydrated crystal can be expected to have a better contrast than a glucose embedded crystal due to the larger density difference between protein and ice compared to protein and glucose. For these reasons we are using an ice embedding technique to prepare the rabbit Fc crystals for molecular structure analysis by electron microscopy.

Possible applications of fraunhofer holography in high resolution electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 222-223 ◽  
Author(s):  
N. Bonnet ◽  
M. Troyon ◽  
P. Gallion
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Transfer Function ◽  
Radiation Damage ◽  
High Resolution Electron Microscopy ◽  
Far Field ◽  
Field Region ◽  
Crystalline Materials ◽  
Resolution Electron ◽  
The Ideal

Two main problems in high resolution electron microscopy are first, the existence of gaps in the transfer function, and then the difficulty to find complex amplitude of the diffracted wawe from registered intensity. The solution of this second problem is in most cases only intended by the realization of several micrographs in different conditions (defocusing distance, illuminating angle, complementary objective apertures…) which can lead to severe problems of contamination or radiation damage for certain specimens.Fraunhofer holography can in principle solve both problems stated above (1,2). The microscope objective is strongly defocused (far-field region) so that the two diffracted beams do not interfere. The ideal transfer function after reconstruction is then unity and the twin image do not overlap on the reconstructed one.We show some applications of the method and results of preliminary tests.Possible application to the study of cavitiesSmall voids (or gas-filled bubbles) created by irradiation in crystalline materials can be observed near the Scherzer focus, but it is then difficult to extract other informations than the approximated size.

Anisotropic radiation damage of potassium tetracyano platinate (KCP)

1978 ◽  
Vol 36 (1) ◽  
pp. 392-393
Author(s):  
N. Uyeda ◽  
E. J. Kirkland ◽  
B. M. Siegel
Keyword(s):  
Electron Diffraction ◽  
Radiation Damage ◽  
Structural Changes ◽  
High Resolution Electron Microscopy ◽  
Radiation Sensitivity ◽  
Resolution Electron ◽  
Damage Process ◽  
Diffraction Patterns ◽  
Fading Rate

The direct observation of structural change by high resolution electron microscopy will be essential for the better understanding of the damage process and its mechanism. However, this approach still involves some difficulty in quantitative interpretation mostly being due to the quality of obtained images. Electron diffraction, using crystalline specimens, has been the method most frequently applied to obtain a comparison of radiation sensitivity of various materials on the quantitative base. If a series of single crystal patterns are obtained the fading rate of reflections during the damage process give good comparative measures. The electron diffraction patterns also render useful information concerning the structural changes in the crystal. In the present work, the radiation damage of potassium tetracyano-platinate was dealt with on the basis two dimensional observation of fading rates of diffraction spots. KCP is known as an ionic crystal which possesses “one dimensional” electronic properties and it would be of great interest to know if radiation damage proceeds in a strongly asymmetric manner.

Nano-probe x-ray analysis and high-resolution imaging on planar defects in high-pressure synthesized infinite-layer superconductor

1994 ◽  
Vol 52 ◽  
pp. 728-729
Author(s):  
Y. Y. Wang ◽  
H. Zhang ◽  
V. P. Dravid ◽  
H. Zhang ◽  
L. D. Marks ◽  
...  
Keyword(s):  
High Pressure ◽  
High Resolution ◽  
Atomic Structure ◽  
Emission Spectra ◽  
High Resolution Electron Microscopy ◽  
Planar Defects ◽  
X Ray ◽  
Infinite Layer ◽  
Resolution Electron ◽  
Resolution Imaging

Azuma et al. observed planar defects in a high pressure synthesized infinitelayer compound (i.e. ACuO2 (A=cation)), which exhibits superconductivity at ~110 K. It was proposed that the defects are cation deficient and that the superconductivity in this material is related to the planar defects. In this report, we present quantitative analysis of the planar defects utilizing nanometer probe xray microanalysis, high resolution electron microscopy, and image simulation to determine the chemical composition and atomic structure of the planar defects. We propose an atomic structure model for the planar defects.Infinite-layer samples with the nominal chemical formula, (Sr1-xCax)yCuO2 (x=0.3; y=0.9,1.0,1.1), were prepared using solid state synthesized low pressure forms of (Sr1-xCax)CuO2 with additions of CuO or (Sr1-xCax)2CuO3, followed by a high pressure treatment.Quantitative x-ray microanalysis, with a 1 nm probe, was performed using a cold field emission gun TEM (Hitachi HF-2000) equipped with an Oxford Pentafet thin-window x-ray detector. The probe was positioned on the planar defects, which has a 0.74 nm width, and x-ray emission spectra from the defects were compared with those obtained from vicinity regions.

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