Abstract
An axial emission ionization gauge with an electrode construction similar to that of J. Z. Chen and C. D. Suen (An axial-emission ultrahigh vacuum gauge. J. Vac. Sci. & Technol. 20 (1), 88-91 (1982)) was studied experimentally with respect to its applicability as a calibration gauge for use in the UHV range. The optimum operation parameters were determined experimentally. At these values of the operation parameters the sensitivity is smaller than that in the publication of Chen and Suen. In contrast with the ionization gauge of the extractor type, the sensitivity of the modified axial emission gauge depends only very weakly on the electron current and pressure, so that its application as calibration gauge in the UHV region seems possible from this point of view. In the low-pressure region, the influence of gas exposure on the pressure reading was studied for a gauge with a molybdenum anode and one with a platinum anode. In both cases the electron-stimulated desorption (ESD) caused errors in the pressure reading. If a platinum anode was used, the influence of hydrogen was larger than that of oxygen. In the case of a molybdenum anode, the influence of oxygen was larger than that of hydrogen. This behavior is accounted for by the greater adsorption of hydrogen on platinum. The experiments on the ESD demonstrate that the axial emission gauge has a somewhat lower collection efficiency for ESD ions generated on the anode surface than for those generated by electron impact in the space surrounded by the grid. This is in conformity with some calculations of ion trajectories performed with the program SIMION.
