239. High vacuum casting with electron bombardment heating

Vacuum ◽  
1967 ◽  
Vol 17 (1) ◽  
pp. 67
Keyword(s):  
High Vacuum ◽  
Electron Bombardment ◽  
Vacuum Casting

Effects of low-energy electron bombardment on the surface chemical structure and adhesive properties of polytetrafluoroethylene (PTFE)

1986 ◽  
Vol 1 (5) ◽  
pp. 717-723 ◽  
Author(s):  
J.A. Kelber ◽  
J.W. Rogers ◽  
S.J. Ward
Keyword(s):  
High Vacuum ◽  
Nitrogen Adsorption ◽  
Electron Bombardment ◽  
Polymer Chains ◽  
Ultra High Vacuum ◽  
Cross Linking ◽  
Cohesive Failure ◽  
Adhesive Properties ◽  
Rate Determining Step ◽  
Adsorption Of Nitrogen

The x-ray photoemission studies of polytetrafluoroethylene (PTFE) bombarded by lowenergy electrons in ultra-high vacuum conditions indicate that the major chemical changes induced by electron bombardment are defluorination of the surface and cross-linking of the polymer chains. The same electron bombardment process, when performed in the presence of 1×10−6 Torr ND3, also results in the adsorption of nitrogen-containing groups at the surface. The rate of nitrogen adsorption is linear for short electron bombardment times while the rates of defluorination and cross-linking are roughly exponential. However, at long bombardment times, the rates of nitrogen uptake, defluorination, and cross-linking become zero at the same time, indicating that defluorination of the surface is the rate-determining step in electron beam-induced adsorption of nitrogen-containing species. Regardless of whether the bombardment is carried out in ultra-high vacuum or in the presence of ND3, the maximum modification depth is less than 30 Å. Pull tests performed on PTFE samples bombarded by electrons in ultra-high vacuum, then removed into air and bonded to epoxy show epoxy-PTFE joint strengths of 280–360 1b/in.2 (psi), are compared to zero psi for untreated PTFE and ≃2000 psi for cohesive failure within the PTFE layer.

Ultra-high-vacuum, high-resolution Transmission Electron Microscopy at 400 kV

1986 ◽  
Vol 44 ◽  
pp. 606-609
Author(s):  
F. A. Ponce ◽  
S. Suzuki ◽  
H. Kobayashi ◽  
Y. Ishibashi ◽  
Y. Ishida ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Vacuum ◽  
Milling Process ◽  
Electron Bombardment ◽  
Ultra High Vacuum ◽  
Specimen Preparation ◽  
Ion Milling ◽  
Transmission Electron ◽  
Preparation Stage ◽  
Resolution Imaging

Electron microscopy in an ultra high vacuum (UHV) environment is a very desirable capability for the study of surfaces and for near-atomic-resolution imaging. The existence of amorphous layers on the surface of the sample generally prevents the direct observation of the free surface structure and limits the degree of resolution in the transmission electron microscope (TEM). In conventional TEM, these amorphous layers are often of organic nature originating from the electron bombardment of hydrocarbons in the vicinity of the sample. They can in part also be contaminants which develop during the specimen preparation and transport stages. In the specimen preparation stage, contamination can occur due to backsputtering during the ion milling process. In addition, oxide layers develop from contact to air during transport to the TEM. In order to avoid these amorphous overlayers it is necessary: i) to improve the vacuum of the instrument, thus the need for ultra high vacuum; and ii) to be able to clean the sample and transfer it to the column of the instrument without breaking the vacuum around the sample.

Development of High Temperature Electron Bombardment Evaporator for Ultra-High Vacuum

2012 ◽  
Vol 566 ◽  
pp. 608-611
Author(s):  
Sheng Fang Zhang ◽  
Jing Pei Liu ◽  
Guan Hua Zhang ◽  
Mei Hua Yang ◽  
Ai Ling Han ◽  
...  
Keyword(s):  
High Temperature ◽  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
High Vacuum ◽  
Electron Bombardment ◽  
Heating Power ◽  
Ultra High Vacuum ◽  
Molecular Beam Epitaxy Growth ◽  
Thermal Equilibrium State ◽  
Short Time

To improve the techniques of molecular beam epitaxy, the electron bombardment evaporator for high temperature evaporation in ultra-high vacuum is designed, and then its performances, such as power-temperature relationship, stability of beam flux as well as molecular beam distribution, are tested by using Ag source. Through adjusting the electric current of tungsten filament can achieve the remarkable heating power in high-voltage, and the crucible temperature rises with increasing heating power, and it exceeds 1600°C at around 60W. The evaporator can reach thermal equilibrium state in a quite short time and produce a highly stable beam flux of Ag at low deposition rate. A 9mm diameter homogeneous flux platform area is obtained at the position 60mm away from the nozzle, and this area can provide high quality beam flux for molecular beam epitaxy. These results show, the electron bombardment evaporator can meet the demands for ultra-high vacuum molecular beam epitaxy growth completely.

scholarly journals A HIGH-VACUUM CASTING FURNACE FOR PLUTONIUM

1953 ◽  
Author(s):  
J Anderson ◽  
R Thomas
Keyword(s):  
High Vacuum ◽  
Vacuum Casting

Space and Time Distribution of Hard X-Ray Emission in a Loop at the Beginning of a Flare

1994 ◽  
Vol 144 ◽  
pp. 275-277
Author(s):  
M. Karlický ◽  
J. C. Hénoux
Keyword(s):  
Time Distribution ◽  
Electron Bombardment ◽  
Spatial Evolution ◽  
Superthermal Electrons ◽  
Flare Loop ◽  
X Ray ◽  
Superthermal Electron ◽  
Flare Loops ◽  
Chromospheric Evaporation ◽  
Temporal And Spatial

AbstractUsing a new ID hybrid model of the electron bombardment in flare loops, we study not only the evolution of densities, plasma velocities and temperatures in the loop, but also the temporal and spatial evolution of hard X-ray emission. In the present paper a continuous bombardment by electrons isotropically accelerated at the top of flare loop with a power-law injection distribution function is considered. The computations include the effects of the return-current that reduces significantly the depth of the chromospheric layer which is evaporated. The present modelling is made with superthermal electron parameters corresponding to the classical resistivity regime for an input energy flux of superthermal electrons of 109erg cm−2s−1. It was found that due to the electron bombardment the two chromospheric evaporation waves are generated at both feet of the loop and they propagate up to the top, where they collide and cause temporary density and hard X-ray enhancements.

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