Measurement of Partial Pressure at Vacuum Conditions

Authored by: Igor Bello

Vacuum and Ultravacuum

Print publication date:  November  2017
Online publication date:  November  2017

Print ISBN: 9781498782043
eBook ISBN: 9781315155364
Adobe ISBN:

10.1201/9781315155364-26

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Abstract

Vacuum environment contains reactive gases whose composition changes with decreasing pressure. Accordingly, precise determination of pressure with gauges that measure pressure indirectly may not provide meaningful information. In high vacuum, the major component of residual gases is water vapor, which is reactive with many materials that are prepared under vacuum conditions. The reactive gases of vacuum background may incorporate into the growing structures in amounts proportional to their partial pressures. Particularly, electronic properties of semiconductors can change dramatically with impurities introduced into their microstructures. Very low densities of dopants or traces of chemical elements can be detected by chemical analyses using mass spectrometers. Mass spectrometers are also used in partial pressure measurement of gases in vacuum. These devices analyzing gases in vacuum are called residual gas analyzers (RGAs). RGAs are simple and portable devices, but indispensable at different material analyses, material syntheses, studying sorption and reaction processes, measurements of different physical properties, and many technological processes. However, mass spectrometers used in general chemical analyses are more robust and operate with higher mass resolution, and they are equipped with additional accessories. In material analyses, we use various techniques that enable us to determine the chemical composition of materials and their chemical states, phase structures, or structures of molecules in arbitrary matter phases. Because of this diversity, many instruments based on different physical principles and sampling residual atmospheres have been developed and used. Both solid and liquid materials are often converted to their gaseous phases and then analyzed to deduce the materials composition by mass spectrometric techniques.

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