Cryogenic Gloves

Ultra high vacuum
Concepts involved
Advanced Definition
the kinetic theory of gases
gas transport and pumping
Vacuum Pumps and Systems
Typical uses for UHV
UHV is required for the surface of many analytical techniques such as:
X-ray photoelectron spectroscopy (XPS)
Auger electron spectroscopy (AES)
Ion mass spectrometry (SIMS)
Thermal desorption spectroscopy (TPD)
growth of thin films and preparation techniques to stringent purity requirements, such as molecular beam epitaxy (SEM) and chemical vapor deposition in UHV (CVD)
angle resolved photoemission spectroscopy (ARPES)
UHV is required for these applications to reduce contamination of surface, reducing the number of molecules reaching the sample over a given period. At 0.1 MPa (106 Torr), it only takes one second to cover a surface with a contaminant, the pressures are much lower than necessary to experience long.
UHS is also needed for:
Particle accelerators
Atomic physics experiments using cold atoms, ions such as trapping or making Bose-Einstein
Achieving ultra high vacuum
extraordinary measures are necessary to achieve UHV, including the following:
High pumping speed possibly several vacuum pumps in series and / or parallel
Minimize the surface in the room
conductance high quality tubing for the pumps short and fat, without obstruction
Use materials with low outgassing as some stainless steels
Avoid creating gas wells trapped behind bolts, empty, welding etc.
Electropolish all metal parts after machining or welding
Using materials of low vapor pressure (ceramic, glass, metal, Teflon if raw)
Cook the system (250 C and 400 C) to remove water or hydrocarbons adsorbed on the walls
chamber walls Chill at cryogenic temperatures in use
Avoid all traces of hydrocarbons, including oils for skin in a fingerprint always use gloves
Degassing is an important issue for UHV systems. Venting can occur from two sources: surface and bulk materials. Outgassing from materials in bulk is minimized by careful selection of materials with low vapor pressure (such as glass, stainless steel, and ceramics) for the whole interior of the system. Even materials that are not generally regarded as absorbent degassing can, including most plastics and metals. For example, ships filled with a highly gas-permeable materials such as palladium (which is a sponge for hydrogen capacity) to create particular problems of degassing.
Degassing of surfaces is a more subtle problem. At very low pressures, the gas molecules are adsorbed more on the walls that float in the room, so that the total area within a room is more important than its volume to reach UHV. Water is a major source of outgassing due to a thin layer of water vapor readily absorbs everything that every time the room is open to the air. The water evaporates from the surface too slowly to be completely removed at room temperature, but fast enough to provide a continuous level of background contamination. Removal of water and gas cooking generally requires similar system to UHV 200-400 C, while the pumps are running. When using the chamber, the walls of the chamber can be cooled with liquid nitrogen to further reduce outgassing.
Hydrogen and helium gases are the most common background in a well-designed UHV system cooked. The hydrogen is diffused from the grain boundaries in stainless steel. Helium can diffuse through the steel and glass of the outside air.
In general, there is no vacuum pump that can run all the way from atmospheric pressure to ultra-high vacuum. Instead, a series of pumps is used, as the appropriate level of pressure for each pump. Pumps commonly used to achieve UHV include:
Turbomolecular pumps (especially compounds and / or magnetic B.