AVS 49th International Symposium
    Vacuum Technology Tuesday Sessions
       Session VT-TuA

Paper VT-TuA5
Quantification of Mass Spectra in Experiments with Deuterium

Tuesday, November 5, 2002, 3:20 pm, Room C-104

Session: Vacuum System Architecture and Specialized Analytical Techniques
Presenter: B. Zajec, Institute of Surface Engineering and Optoelectronics, Slovenia
Authors: B. Zajec, Institute of Surface Engineering and Optoelectronics, Slovenia
V. Nemanic, Institute of Surface Engineering and Optoelectronics, Slovenia
M. Zumer, Institute of Surface Engineering and Optoelectronics, Slovenia
Correspondent: Click to Email
For monitoring the interaction of gaseous hydrogen with surfaces or bulk materials, deuterium is frequently applied as a tracer gas for the quadrupole mass spectrometer (QMS) analysis. In fast and steady processes, the major peak at mass number 4 is frequently a good indicator of deuterium involved reactions while peaks at mass numbers 2 and 3 may be neglected. In slow and transient processes, the weak peaks at mass numbers 2, 3 and 4 must be considered for a quantitative analysis. Tracing reactions where deuterium molecules dissociate is troublesome since the mass number 2 overlaps with the hydrogen background. The problem to eliminate the QMS artefacts is usually solved by calibration of the instrument with a suitable low deuterium flux, but any further resolution of the background hydrogen originated from the chamber surfaces is very inaccurate. We present the results of a calibration procedure of two QMS mounted on a well outgassed UHV system, realised in a specific way. Each of the QMS was pumped in line but could be also separated from the system by a valve. A constant deuterium or hydrogen inflow was set from 10@super -8@ mbar l s@super -1@ to 10@super -6@ mbar l s@super -1@ by observing the pressure rise in the chamber by means of a calibrated capacitance manometer. The calibration of both QMS was taken in the dynamic mode for both gases. Further on, the spectra of deuterium accumulated in the UHV system for a defined period of time were compared to the calibration spectra. From the difference, we could resolve the extent of mass numbers 2 and 3 produced in the QMS from the contribution of the deuterium participated in surface reactions at the chamber wall. It was thus shown that after admittance of pure deuterium into the UHV chamber at 10@super -4@ mbar, its exchange with the adsorbed hydrogen led in some hours to a noticeable changed proportion of mass numbers 2, 3 and 4. This could not be predicted from the low background outgassing rate.