In-situ water signal calibration method for thermal desorption spectroscopy

• Novel method based on deuterium desorption from self-damaged tungsten. • Diffusing deuterium reacts with tungsten oxide layer, forming HDO and D 2 O. • Quantification of deuterium content with 3 He Nuclear Reaction Analysis. • Calibration factor for water agrees with tabulated values. • Method allows in situ quantification of water desorption without setup modification. A method is presented that allows to quantify water desorption in a thermal desorption spectroscopy (TDS) setup in-situ. It is based on deuterium (D) desorption from D-containing tungsten covered with a thin, electro-chemically grown tungsten oxide layer. The method is based on the fact that diffusing deuterium is known to react with amorphous tungsten oxide, forming HDO and D 2 O. A stable deuterium reservoir underneath the oxide is accomplished by MeV tungsten ion irradiation to create a so-called self-damaged tungsten layer that is loaded with deuterium with a low-temperature plasma prior to oxidation. The total deuterium amount in the sample is determined with 3 He Nuclear Reaction Analysis ( 3 He-NRA) before the TDS measurement. Detecting all deuterium-containing molecules desorbing during TDS and closing the particle balance with the known total deuterium amount from 3 He-NRA, the calibration factor for water can be determined. The calibration factor is found to be close to the one of e.g. deuterium or hydrogen. It agrees with tabulated values but contradicts the usual assumption that water cannot be treated in a quantitative manner in TDS because it is highly likely to stick to surfaces and thus would be lost on the way to the mass spectrometer. The result suggests that this general assumption is not always applicable. At least for the case where the gas flow does not consist solely of water but is a mixture of water and hydrogen molecules, quantification is still possible. Because the method simply relies on the desorption of gases from a sample of typical size it can be applied to any existing TDS setup without modifying the latter. However, care must be taken for TDS systems were the sample environment is undefined and water signals stem not from the sample under investigation alone but from undefined outgassing of the surrounding materials.