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Ultra-high vacuum (often spelled ultrahigh in American English, UHV) is the vacuum regime characterised by pressures lower than about 1 × 10 −6 pascals (1.0 × 10 −8 mbar; 7.5 × 10 −9 Torr). UHV conditions are created by pumping the gas out of a UHV chamber.
Austenitic stainless steels are the most common choice for high vacuum and ultra-high vacuum systems. Not all alloys are suitable; e.g. the free-machining 303 steel contains sulfur, which tends to outgas. Alloys with good weldability under argon arc welding are usually chosen. 304 stainless steel is a common choice of a stainless steel.
On the VUV ring, the endstations were usually UHV (ultra-high vacuum) chambers that were used to conduct experiments using methods such as XPS, UPS, LEEM, and NEXAFS. In some beamlines , there were other analytical tools used in conjunction with synchrotron radiation, such as a mass spectrometer , a high-power laser , or a gas chromatography ...
In systems where the substrate needs to be cooled, the ultra-high vacuum environment within the growth chamber is maintained by a system of cryopumps and cryopanels, chilled using liquid nitrogen or cold nitrogen gas to a temperature close to 77 kelvins (−196 degree Celsius). Cold surfaces act as a sink for impurities in the vacuum, so vacuum ...
Its construction and principle of operation is simple. It consists of a titanium filament through which a high current (typically around 40 A) is passed periodically. This current causes the filament to reach the sublimation temperature of titanium, and hence the surrounding chamber walls become coated with a thin film of clean titanium.
Bell jars are generally used for classroom demonstrations or by hobbyists, when only a relatively low-quality vacuum is required. Cutting-edge research done at ultra-high vacuum requires a more sophisticated vacuum chamber. However, several tests may be completed in a bell jar chamber having an effective pump and low leak rate.
Ultra-high vacuum chambers, common in chemistry, physics, and engineering, operate below one trillionth (10 −12) of atmospheric pressure (100 nPa), and can reach around 100 particles/cm 3. [4] Outer space is an even higher-quality vacuum, with the equivalent of just a few hydrogen atoms per cubic meter on average in intergalactic space. [5]
Free molecular flow describes the fluid dynamics of gas where the mean free path of the molecules is larger than the size of the chamber or of the object under test. For tubes/objects of the size of several cm, this means pressures well below 10 −3 mbar. This is also called the regime of high vacuum, or even ultra-high vacuum.
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