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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.
High to ultra-high vacuum removes the obstruction of air, allowing particle beams to deposit or remove materials without contamination. This is the principle behind chemical vapor deposition , physical vapor deposition , and dry etching which are essential to the fabrication of semiconductors and optical coatings , and to surface science .
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.
The langmuir (symbol: L) is a unit of exposure (or dosage) to a surface (e.g. of a crystal) and is used in ultra-high vacuum (UHV) surface physics to study the adsorption of gases. It is a practical unit, and is not dimensionally homogeneous, and so is used only in this field. It is named after American physicist Irving Langmuir.
The turbomolecular pump can be a very versatile pump. It can generate many degrees of vacuum from intermediate vacuum (≈10 −2 Pa) up to ultra-high vacuum levels (≈10 −8 Pa). Multiple turbomolecular pumps in a lab or manufacturing-plant can be connected by tubes to a small backing pump.
A roughing pump is any vacuum pump (typically mechanical) used to initially evacuate a vacuum system, as a first stage towards achieving high vacuum or ultra high vacuum.The term "roughing pump" derives from the vacuum range it works in, "rough vacuum", above 1x10 −3 torr (0.1 Pa).
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This is also called the regime of high vacuum, or even ultra-high vacuum. This is opposed to viscous flow encountered at higher pressures. [1] The presence of free molecular flow can be calculated, at least in estimation, with the Knudsen number (Kn). [2] If Kn > 10, the system is in free molecular flow, [3] also known as Knudsen flow. [4]
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