restgasanalyse

Restgasanalyse, known in English as residual gas analysis (RGA), is a mass spectrometric technique used to identify and monitor gases present in high-vacuum systems. It provides qualitative information about the composition of residual gases and, with calibration, semi-quantitative estimates of their partial pressures.

The technique works by drawing a small sample from the vacuum environment into a mass spectrometer, where residual gas molecules are ionized by electron impact, producing fragments that are separated by mass-to-charge ratio and detected. The resulting spectrum shows peaks at characteristic m/z values corresponding to species present; however, many molecules fragment into multiple ions, which can complicate direct identification. Some RGAs employ alternative ionization methods or data-processing approaches to aid interpretation.

RGAs use vacuum-compatible mass spectrometers, typically quadrupole analyzers, connected to the chamber through a small orifice and protected by differential pumping. They can provide continuous monitoring or time-resolved measurements during processes such as thin-film deposition. The peak intensities give semi-quantitative information about partial pressures, but accurate quantification requires calibration and knowledge of fragmentation patterns for each species.

Applications include monitoring vacuum quality, outgassing rates, process contamination, leak detection, and characterization of surface films and contaminants. Limitations include spectral overlap of peaks at certain m/z values, reliance on calibration for quantitative results, fragmentation ambiguities, and insensitivity to non-ionizable neutrals. Overall, restgasanalyse is a practical tool for diagnosing and optimizing vacuum systems and related processes.