Observations of Surface Diffusion at the Atomic Level by Means of Microcinematography in the Stem

1976 ◽  
Vol 34 ◽  
pp. 584-585
Author(s):  
M. S. Isaacson ◽  
D. Kopf ◽  
N. W. Parker ◽  
M. Utlaut
Keyword(s):  
Heavy Atom ◽  
Carbon Film ◽  
Uranium Atom ◽  
Dark Field ◽  
Atomic Scale ◽  
Carbon Substrate ◽  
Surface Phenomena ◽  
Direct Measurements ◽  
Thin Carbon ◽  
Dark Field Micrographs

We have previously indicated the potential application of the STEM for studying surface phenomena on an atomic scale and noted that direct measurements of atom motion in the STEM could be of use in obtaining an improved understanding of a variety of surface processes. In this paper we would like to present some further observations concerning the motion of heavy atom containing molecules on thin carbon substrates due to thermal diffusion.A typical example of heavy atom containing molecules migrating on a carbon substrate is shown in Fig. 1. The specimen is uranylchloride molecules on an ∼ 20 Å thick carbon film. The dark field micrographs have been taken with 17 second exposures. The beam is not irradiating the field of view between exposures. In this set of micrographs it appears that the uranium atom “spot” is migrating towards the large cluster in the lower portion of the field.

Contamination at Low Temperature

1977 ◽  
Vol 35 ◽  
pp. 558-559 ◽  
Author(s):  
J. Wall ◽  
J. Bittner ◽  
J. Hainfeld
Keyword(s):  
Low Temperature ◽  
Heavy Atom ◽  
Carbon Film ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Transmission Electron ◽  
Surface Migration ◽  
Thin Carbon ◽  
Scanning Transmission ◽  
Atom Migration

Contamination of biological specimens has been a practical limitation for many years. It is especially noticeable in the dark field STEM (Scanning Transmission Electron Microscope) since contamination only occurs near the area irradiated by the beam and since we are most often observing very thin specimens (20 - 40 Å). Contamination can be greatly reduced by baking the specimen to 100°C in vacuum prior to observation, (1), but such heating may alter biological structures and cause heavy atom migration away from heavy atom staining sites.Since contamination results from surface migration (2), it might be eliminated by cooling the specimen to a sufficiently low temperature. The Brookhaven STEM (3).is equipped with a cold stage capable of attaining -170°C with less than 5 Å vibration. Contamination was observed as a function of temperature for a clean carbon film and for two biological specimens. The specimens were prepared on slotted Titanium grids covered by a holey carbon film with thin carbon (˜ 20 A) stretched across the holes.

Processing of STEM Images of Unstained Tropomyosin Magnesium Paracrystals

1977 ◽  
Vol 35 ◽  
pp. 82-83
Author(s):  
S.D. Golladay
Keyword(s):  
Magnetic Tape ◽  
Sampling Rate ◽  
Carbon Film ◽  
Region Of Interest ◽  
Dark Field ◽  
Bright Field ◽  
Thin Carbon ◽  
Thin Carbon Film ◽  
Annular Detector ◽  
Scan Data

The banding patterns of unstained tropomyosin magnesium paracrystals have been observed in a STEM at 30 kV. The microscope is interfaced to a computer so that both bright field and dark field (annular detector) signals can be stored on magnetic tape. The data acquisition system imposes constraints on the image sampling rate and on the maximum number of picture elements per frame, but has the substantial advantage of eliminating the need for careful film processing and densitometry for quantitative microscopy. The system is extremely helpful when first scan images of relatively thick objects on a thin carbon film are desired. In this situation, the operator cannot adjust the gain and bias of the video signal properly until he has already scanned the specimen. However, first scan data stored on magnetic tape can be replayed with bias and gain adjusted digitally to provide the best display of any specified region of interest in the image. Figure 1 shows such a replay of the bright field (IB) and dark field (1A) images of the paracrystal which was analyzed. The specimen was fixed and air dried but unstained.

Mild detergent treatment of thin carbon substrate films

1994 ◽  
Vol 52 ◽  
pp. 326-327
Author(s):  
Martha N. Simon ◽  
Beth Y. Lin ◽  
Joseph S. Wall
Keyword(s):  
High Vacuum ◽  
Carbon Film ◽  
Ultra High Vacuum ◽  
Carbon Substrate ◽  
Mass Measurements ◽  
Thin Carbon ◽  
Freeze Dried ◽  
Biological Structures ◽  
Thin Carbon Film ◽  
Detergent Treatment

The preparation of biological specimens for the STEM by the wet film technique and subsequent freeze-drying, has been shown to preserve biological structures reasonably well and give good mass measurements on them. However, the thin (2-3 nm) carbon substrate film, prepared by ultra-high vacuum evaporation onto a freshly cleaved crystal of rock salt, is never perfect for the attachment of fragile biological structures. The film is floated on a dish of clean water and grids covered with holey film are placed face down on the floating thin carbon film. The grids are picked up from above one at a time such that the carbon film retains a droplet of water. This water is exchanged by washing and wicking and the specimen is injected into the drop followed by further washing and wicking. After the final wash, the grid is blotted between two pieces of filter paper (retaining solution less than 1 μm thick), plunged into liquid nitrogen slush, and freeze-dried under vacuum overnight.

Conformational Study of trna, Using the High Resolution Scanning Electron Microscope

1970 ◽  
Vol 28 ◽  
pp. 254-255
Author(s):  
J. Langmore ◽  
J. Wall
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
Scanning Electron Microscope ◽  
Carbon Film ◽  
Dark Field ◽  
Specimen Preparation ◽  
Thin Carbon ◽  
Thin Carbon Film ◽  
The Moment ◽  
Scanning Electron

Individual molecules of yeast transfer RNA have been observed in the elastic dark field, inelastic dark field and “Z contrast” modes of the 5 Å high resolution scanning electron microscope. The operation, and contrast forming abilities of this instrument, are discussed elsewhere.Of particular interest here is the fact that the contrast in this microscope is very high, so that negative staining techniques are not required. This does, however, present a problem in specimen preparation. The single tRNA molecules are approximately 30 Å thick and 50 to 150 Å long and are supported only by a thin carbon film. Difficulties are being experienced at the moment in preserving the structure of the molecules during the specimen preparation stage.

Thin Carbon-Aluminum Films for Dark Field Electron Microscopy of DNA

1975 ◽  
Vol 33 ◽  
pp. 658-659
Author(s):  
George Ruben ◽  
Benjamin M. Siegel
Keyword(s):  
Low Frequency ◽  
Ultra Violet ◽  
Field Work ◽  
Dark Field ◽  
Carbon Films ◽  
Carbon Substrate ◽  
Aluminum Films ◽  
Naked Dna ◽  
Thin Carbon ◽  
Beam Currents

Carbon substrate films prepared by indirect evaporation have important features needed for the visualization of DNA in dark field work. These indirectly deposited carbon films can be made with minimum granularity and with a support thickness of about 10-20Å. They can mechanically withstand contact with aqueous solution and the high beam currents at condenser crossover in the microscope. The surface of freshly made carbon films used within a few hours wets and adsorbs DNA prepared by the Kleinschmidt method with its cytochrome c film. The low frequency binding on these carbon substrates even when fresh or after ultra-violet light activation makes them a marginal substrate film for DNA work (1,2). Unfortunately these films also lose their ability to wet and bind naked DNA or DNA spread with a basic protein within a period of a day.

Some Observations on the Adsorption of Heavy Atoms on Carbon Substrates

1976 ◽  
Vol 34 ◽  
pp. 498-499
Author(s):  
M. S. Isaacson ◽  
D. Kopf ◽  
N. W. Parker ◽  
M. Utlaut
Keyword(s):  
Surface Science ◽  
Heavy Atom ◽  
Carbon Film ◽  
Light Element ◽  
General Validity ◽  
Heavy Atoms ◽  
Potential Value ◽  
Thin Carbon ◽  
Carbon Substrates ◽  
Thin Carbon Film

In previous papers we have shown that the use of the atomic resolution STEM to study adsorption of heavy atoms on light element substrates could be of potential value in surface science. We indicated that we had undertaken a program to determine to what extent that was true and that one particular measurement we were attempting was to measure adatom-adatom spacing distributions. In this paper we would like to present some further results and also discuss the general validity of our approach.At present, our specimens are made by depositing 5 μl of a 10-4 - 10-5 M solution of a heavy-atom-containing molecule onto a thin carbon film. The drop is allowed to sit for about 20 seconds and then pipetted off the film. This results in the heavy atoms being deposited within a molecule and so if the molecule remains intact, the preferential spacings between heavy atoms which may be observed could be dependent upon the molecule.

Films That Wet Without Glow Discharge

1985 ◽  
Vol 43 ◽  
pp. 716-717
Author(s):  
J.S. Wall ◽  
J.F. Hainfeld ◽  
K.D. Chung
Keyword(s):  
Glow Discharge ◽  
Rock Salt ◽  
Unit Length ◽  
Carbon Film ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Specimen Preparation ◽  
Thin Carbon ◽  
Scanning Transmission ◽  
Thin Carbon Film

Mass measurements with the Scanning Transmission Electron Microscope (STEM) provide a direct link between biochemistry and the information in the dark field STEM image of an unstained biological specimen. Total mass of a complex mass of individual components, mass per unit length, mass per unit area, or change in mass distribution following biochemical treatment, are easily determined.Accuracy and preparation requirements have been described elsewhere. In the past year, we have made significant progress in specimen preparation, developing a “wet film” technique which eliminates the need for glow discharge treatment of grids. The method is similar to the Valentine technique but uses minute quantities of specimen. A thin carbon film is evaporated under UHV conditions onto freshly cleaved rock salt. The thin carbon is floated off the rock salt onto distilled water and a titanium grid with a thick, holey carbon film laid on top of it. After a few minutes, the grid is picked up from above by grasping its edge with a tweezer and turned over so that the adhering drop of water is facing upward.

Improved preservation of freeze-dried biological specimens

1992 ◽  
Vol 50 (1) ◽  
pp. 736-737
Author(s):  
Martha N. Simon ◽  
Beth Y. Lin ◽  
Joseph S. Wall
Keyword(s):  
Freeze Drying ◽  
Carbon Film ◽  
Scanning Transmission Electron Microscope ◽  
Carbon Substrate ◽  
Final Thickness ◽  
Thin Carbon ◽  
Freeze Dried ◽  
Scanning Transmission ◽  
Thin Carbon Film ◽  
Strong Attachment

Specimens prepared by the wet-film technique (injecting unstained biological specimens into a drop of buffer on a thin carbon substrate which has never seen air, washing extensively, blotting to a thin layer of liquid, plunging the grid into nitrogen slush, and freeze-drying overnight) then visualized in the scanning transmission electron microscope (STEM) usually have reasonably wel1-preserved structures. However, there is a certain variability from day to day and sometimes even from one area to another on a given grid. This can occur for different reasons which may be inextricably related. The thin carbon film can be non-uniform at the molecular level with hot spots for strong attachment of some specimens, a part of a biological specimen may attach strongly while the rest of it thrashes about in Brownian motion ruining any perceivable structure, and the final thickness of liquid before freeze-drying may vary slightly which may affect the preservation of the structure.

Utilizing Dark Field Electron Microscopy to Produce Lantern Slides

1974 ◽  
Vol 32 ◽  
pp. 116-117
Author(s):  
J. N. Meador ◽  
C. N. Sun ◽  
H. J. White
Keyword(s):  
Electron Microscope ◽  
Electron Micrographs ◽  
Dark Field ◽  
Limiting Factor ◽  
Clinical Laboratories ◽  
Field Electron ◽  
Time Element ◽  
Field Electron Microscopy ◽  
Dark Field Electron ◽  
Dark Field Micrographs

The electron microscope is being utilized more and more in clinical laboratories for pathologic diagnosis. One of the major problems in the utilization of the electron microscope for diagnostic purposes is the time element involved. Recent experimentation with rapid embedding has shown that this long phase of the process can be greatly shortened. In rush cases the making of projection slides can be eliminated by taking dark field electron micrographs which show up as a positive ready for use. The major limiting factor for use of dark field micrographs is resolution. However, for conference purposes electron micrographs are usually taken at 2.500X to 8.000X. At these low magnifications the resolution obtained is quite acceptable.

Observation of Atom Rows in Thorium Pyromellitate Using a Field Emission STEM

1977 ◽  
Vol 35 ◽  
pp. 80-81
Author(s):  
H. Todokoro ◽  
S. Nomura ◽  
T. Komoda
Keyword(s):  
Field Emission ◽  
Amorphous Carbon ◽  
Carbon Film ◽  
Dark Field Image ◽  
Dark Field ◽  
Amorphous Carbon Film ◽  
Atomic Size ◽  
Wide Range ◽  
A Chain

It is interesting to observe polymers at atomic size resolution. Some works have been reported for thorium pyromellitate by using a STEM (1), or a CTEM (2,3). The results showed that this polymer forms a chain in which thorium atoms are arranged. However, the distance between adjacent thorium atoms varies over a wide range (0.4-1.3nm) according to the different authors.The present authors have also observed thorium pyromellitate specimens by means of a field emission STEM, described in reference 4. The specimen was prepared by placing a drop of thorium pyromellitate in 10-3 CH3OH solution onto an amorphous carbon film about 2nm thick. The dark field image is shown in Fig. 1A. Thorium atoms are clearly observed as regular atom rows having a spacing of 0.85nm. This lattice gradually deteriorated by successive observations. The image changed to granular structures, as shown in Fig. 1B, which was taken after four scanning frames.

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