Incrystal growth, aKnudsen cell is aneffusionevaporator source for relatively low partial pressure elementary sources (e.g. Ga, Al, Hg, As). Because it is easy to control the temperature of the evaporating material in Knudsen cells, they are commonly used inmolecular-beam epitaxy.
The Knudsen effusion cell was developed byMartin Knudsen (1871–1949). A typical Knudsen cell contains acrucible (made ofpyrolyticboron nitride,quartz,tungsten orgraphite), heating filaments (often made of metaltantalum),water cooling system,heat shields, and anorifice shutter.
The Knudsen cell is used to measure thevapor pressures of a solid with very low vapor pressure. Such a solid forms a vapor at low pressure bysublimation. The vapor slowly effuses through the pinhole, and the loss of mass is proportional to the vapor pressure and can be used to determine this pressure.[1] Theheat of sublimation can also be determined by measuring the vapor pressure as a function of temperature, using theClausius–Clapeyron relation.[2]
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