scholarly journals A STUDY OF MASS LOSS AND PRODUCT FORMATION AFTER IRRADIATION OF SOME DRY AMINO ACIDS, PEPTIDES, POLYPEPTIDES AND PROTEINS WITH AN ELECTRON BEAM OF LOW CURRENT DENSITY

1970 ◽  
Vol 18 (8) ◽  
pp. 574-580 ◽  
Author(s):  
K. S. STENN ◽  
G. F. BAHR
Keyword(s):  
Amino Acids ◽  
Electron Beam ◽  
Electron Microscope ◽  
Steady State ◽  
Mass Loss ◽  
Current Density ◽  
Product Formation ◽  
Electron Microscopic ◽  
Microscopic Specimen ◽  
Loss Of Mass

Amino acids, peptides, polypeptides and proteins were irradiated with electrons at 70-kv accelerating potential in an electron microscope mockup. Loss of mass and chemical changes occur almost instantaneously. For a given dose rate an organic object is converted to a steady state product. This is characterized by a poorly structured infrared pattern, unchanging elemental composition. The higher the polymerization of the target the smaller was the effect of the irradiation. Such studies conducted outside of the electron microscope reveal only qualitatively what might occur to the electron microscopic specimen during observation.

Electron-beam damage of oxides at high current densities

1989 ◽  
Vol 47 ◽  
pp. 634-635
Author(s):  
M. R. McCartney ◽  
J. K. Weiss ◽  
David J. Smith
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Current Density ◽  
Transition Metal Oxides ◽  
Time Resolved ◽  
Rapid Acquisition ◽  
Resolution Electron ◽  
Current Densities ◽  
Electron Stimulated Desorption ◽  
Channel Analyzer

It is well-known that electron-beam irradiation within the electron microscope can induce a variety of surface reactions. In the particular case of maximally-valent transition-metal oxides (TMO), which are susceptible to electron-stimulated desorption (ESD) of oxygen, it is apparent that the final reduced product depends, amongst other things, upon the ionicity of the original oxide, the energy and current density of the incident electrons, and the residual microscope vacuum. For example, when TMO are irradiated in a high-resolution electron microscope (HREM) at current densities of 5-50 A/cm2, epitaxial layers of the monoxide phase are found. In contrast, when these oxides are exposed to the extreme current density probe of an EM equipped with a field emission gun (FEG), the irradiated area has been reported to develop either holes or regions almost completely depleted of oxygen. ’ In this paper, we describe the responses of three TMO (WO3, V2O5 and TiO2) when irradiated by the focussed probe of a Philips 400ST FEG TEM, also equipped with a Gatan 666 Parallel Electron Energy Loss Spectrometer (P-EELS). The multi-channel analyzer of the spectrometer was modified to take advantage of the extremely rapid acquisition capabilities of the P-EELS to obtain time-resolved spectra of the oxides during the irradiation period. After irradiation, the specimens were immediately removed to a JEM-4000EX HREM for imaging of the damaged regions.

High-performance transmission electron microscopy of cryospecimens

1984 ◽  
Vol 42 ◽  
pp. 276-277
Author(s):  
U. B. Hezel ◽  
E. Zellmann ◽  
D. Hoffmeister
Keyword(s):  
Electron Microscope ◽  
High Performance ◽  
Chemical Fixation ◽  
Native State ◽  
Electron Microscopic ◽  
Transmission Electron ◽  
Microscopic Specimen ◽  
Electron Microscopes ◽  
The One ◽  
Subsequent Staining

Chemical fixation, resin embedding and subsequent staining with heavy metals can both produce artefacts and limit the resolution in the electron microscopic specimen /1-5/. The objective is thus to observe the specimens in the electron microscope in the frozen-hydrated state, the one most similar to the native state.All preparation steps such as cryofixation, cryosectioning and cryotransfer to the cryo-transmission electron microscope (CryoTEM) should be performed below 145K /5/ in order to observe the specimen in a matrix of vitrified ice avoiding any crystallization artefacts. In the CryoTEM itself the temperature of the frozen-hydrated specimen should be kept much lower to avoid devitrification caused by the electron beam /1/. - To meet all these requirements a special cryotransfer system and cryostage for the Zeiss transmission electron microscopes have been developed /7/.

Electron-beam damage and analysis at low temperature

1990 ◽  
Vol 48 (4) ◽  
pp. 806-807
Author(s):  
Yoshio Bando ◽  
Yoshizo Kitami ◽  
Masato Yokoyama
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Low Temperature ◽  
Mass Loss ◽  
Radiation Damage ◽  
Liquid Helium ◽  
Inorganic Materials ◽  
Specimen Holder ◽  
Analytical System ◽  
Beam Damage

Elemental analysis for beam-sensitive materials is limited by radiation damage due to inelastic scattering of electrons. The amorphization and the mass loss often occure during the observation under a focused electron beam. It has been so far understood that the electron beam damage is effectively reduced by decreasing the specimen temperature. The cryo-electron microscope using liquid helium colled specimen holder is useful to minimize the radiation damage of the beam-sentitive materials. In the present paper, we have studied the radiation damage of various insulating inorganic materials in terms of the rate of the amorphization and the selective mass loss, which are observed at a room temperature (300K) and a low temperature (20K). All measurements are performed on a JEM-4000FX high-resolution analytical electron microscope with full analytical system. The specimen fragments placed on a holey carbon supporting grid are cooled down to about 20K. using a liquid helium specimen holder attached with a Be retainer.

Electron microscopic observations of toxoplasma ‘Nicolle et Manceaux’ grown in tissue cultures (first note)

Parasitology ◽  
1955 ◽  
Vol 45 (3-4) ◽  
pp. 449-451 ◽  
Author(s):  
H. Meyer ◽  
I. de Andrade Mendonça
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Irregular Surface ◽  
Tissue Cultures ◽  
Electron Microscopic ◽  
Tissue Cells ◽  
In The Beginning ◽  
The Way

Toxoplasma ‘Nicolle et Manceaux’ has been examined in the electron microscope in in toto preparations from tissue cultures.The extracellular as well as the intracellular forms of the parasite are too thick for an adequate penetration of the electron beam, and the inner structure of Toxoplasma is not revealed in these preparations.The whole parasite is covered by a very delicate, transparent mantle which may extend to form large membranes. They show no structure in the electron microscope. No sheath has been observed which protects the shape of the parasite. Most of the free forms have an irregular surface and tend to become flat and large.Several pictures illustrate the way in which Toxoplasma penetrates the tissue cells. In the beginning of parasitism the limits between cytoplasm and parasite are difficult to recognize. The region of the cytoplasm around the parasite is gradually dissolved and a vacuole is formed.

Characterization of a Fixed Beam Electron Microscope with a Field Emission Gun

1976 ◽  
Vol 34 ◽  
pp. 526-527
Author(s):  
Wah Chiu ◽  
Robert M. Glaeser
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Field Emission ◽  
Current Density ◽  
Beam Current ◽  
Beam Current Density ◽  
Objective Lens ◽  
Electron Beam Current ◽  
Beam Electron ◽  
Fixed Beam

One of the objectives of our research program is to obtain a 2.0 Å point to point resolution in a fixed beam bright field electron microscope. The resolution in the fixed beam electron microscope is limited by a number of factors: electron beam coherence, energy spread, objective lens stability, mechanical stability, and specimen stability. This paper presents systematic studies of the mentioned factors in our JEM 100B fixed beam electron microscope equipped with a field emission gun operating at ∼ 1800°K.The most important characteristic of a field emission gun is its high brightness in the emitter source. In order to estimate the brightness at the specimen plane, one needs to measure the electron beam current density and the angle of illumination. The electron beam current density has been measured by means of a lithium-drifted silicon detector located below the normal position of the photographic plates. The angle of illumination can be estimated from the size of the condenser aperture and its distance from the specimen plane.

Electromigration in Al/W and Al(Cu)/W Interconnect Structures

1991 ◽  
Vol 225 ◽  
Author(s):  
C-K. Hu ◽  
P. S. Ho ◽  
M. B. Small ◽  
K. Kelleher
Keyword(s):  
Electron Microscope ◽  
Steady State ◽  
Scanning Electron Microscope ◽  
Drift Velocity ◽  
Current Density ◽  
Electron Microprobe ◽  
Temperature Range ◽  
Final Steady State ◽  
Current Densities ◽  
Scanning Electron

ABSTRACTThe electromigration drift velocity of Al in Al(3wt.% Si), Al(2wt.%Cu), and Al(2wt.%Cu,3wt.%Si) was measured in a temperature range 133 to 220 °C with current densities of 1.0 to 1.5×106A/cm2. In Al(3wt.% Si), a significant Al depletion at the cathode end and accumulation at the anode end of stripe were observed within a few hours at 1.5×106A/cm2 and 200°C. In addition, local hillocks and voids along the metal lines were observed. For Al(Cu,Si), the Al drift velocity was slowed down by Cu addition. The majority of hillocks started to grow at a distance about 6 μm away from the cathode end with current density of 1.5×106 A/cm2. The drift velocity of Al in Al(Cu,Si) was found to be a function of time starting with an initial low value and increasing to a an final steady-state value. The behavior was attributed to the migration of Cu and dissolution of Al2Cu precipitates. The activation energies of the depletion 3 Aμm of Al(2%,Cu, 3%Si) was determined to be 0.90±02 eV. The dissolution and growth of A12Cu in the tested samples of Ti/Al(2%Cu)/Ti/TiN were observed using the scanning electron microscope and an electron microprobe.

Low Temperature Beam Damage to Biological Specimens in the Electron Microscope

1975 ◽  
Vol 33 ◽  
pp. 608-609
Author(s):  
K. Ramamurti ◽  
A. V. Crewe ◽  
M. S. Isaacson
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Low Temperature ◽  
Mass Loss ◽  
Cryogenic Temperatures ◽  
Signal Averaging ◽  
Damage Rate ◽  
Primary Damage ◽  
Significant Change ◽  
Beam Damage

It is now well recognized that serious limitations to resolution of details obtainable in biological specimens are imposed by the damage inflicted on the specimen by the electron beam. Several techniques, such as minimal exposure and signal averaging, have been proposed to overcome these limitations (see Ref. 1 for brief discussions and further references to literature). However, it would be clearly desirable to minimize the damage itself. A promising approach appears to be to cool the specimen to cryogenic temperatures.It should be emphasized that we do not expect any significant change in the primary damage rate of individual molecules, but we may hope that fragmentation would be reduced which would in turn, reduce the rate of mass loss, and secondary damages.Several studies with cooled specimens have been reported, but most of the results seem to be incluclusive and some of them even mutually contradictory.

scholarly journals Deathzones and exponents: A different approach to incorporating mass loss in stellar evolution calculations

2008 ◽  
Vol 4 (S252) ◽  
pp. 189-195 ◽  
Author(s):  
Lee Anne Willson
Keyword(s):  
Steady State ◽  
Mass Loss ◽  
Stellar Evolution ◽  
Loss Rate ◽  
Mass Loss Rate ◽  
Sample Selection ◽  
Evolutionary Changes ◽  
Loss Of Mass ◽  
New Generation ◽  
Loss Rates

AbstractObservations tend to select mass loss rates near the critical rate, Ṁcrit = M/L. There are two reasons for this. In some situations, such as near the tip of the AGB, the mass loss rate is very sensitive to stellar parameters. In this case, stars with Ṁ ≪ Ṁcrit have dust-free, hard-to-measure mass loss rates while stars with Ṁ ≫ Ṁcrit do not survive very long and thus make up a small fraction of any sample. Selection effects dominate the fitting of empirical formulae; observations of mass loss rates tell us more about which stars are losing mass than about how a star loses mass. In other situations, such as for some of the stars along the RGB, a steady state situation occurs where the loss of mass leads to a decrease in mass loss rate while the evolutionary changes lead to an increase; the result is a steady state with Ṁ = Ṁcrit. To determine the envelope mass and composition at the end of a phase of intensive mass loss requires stellar evolution models capable of responding on a time scale ~ tKH and thus, a new generation of stellar modeling codes.

Reversible bending of Si3N4 nanowire

2000 ◽  
Vol 15 (5) ◽  
pp. 1048-1051 ◽  
Author(s):  
Yingjiu Zhang ◽  
Nanlin Wang ◽  
Rongrui He ◽  
Qi Zhang ◽  
Jing Zhu ◽  
...  
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Current Density ◽  
Bending Strength ◽  
Electrostatic Force ◽  
Transmission Electron ◽  
High Flexibility

A reversible bending phenomenon of Si3N4 nanowires on the conductive carbon–formalin microgrid under an illumination of electron beam was observed using a transmission electron microscope. The nanowires exhibit high flexibility. The bending deflection is approximately proportional to the square of the current density (J) of the electron beam. The bending strength of Si3N4 nanowire is much higher than that of bulk Si3N4 materials. The force that bent the nanowires may be an electrostatic force.

A Reproducible Selective Stain for Cardiac Sarcoplasmic Reticulum

1974 ◽  
Vol 32 ◽  
pp. 214-215
Author(s):  
R. A. Waugh ◽  
J. R. Sommer
Keyword(s):  
Complex System ◽  
Electron Microscope ◽  
Sarcoplasmic Reticulum ◽  
Transmission Electron Microscope ◽  
Electron Microscopic ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Transmission Electron

Cardiac sarcoplasmic reticulum (SR) is a complex system of intracellular tubules that, due to their small size and juxtaposition to such electron-dense structures as mitochondria and myofibrils, are often inconspicuous in conventionally prepared electron microscopic material. This study reports a method with which the SR is selectively “stained” which facilitates visualizationwith the transmission electron microscope.

Sign in / Sign up

Export Citation Format

Share Document