Total pressure measurement down to 10−12 Pa without electron stimulated desorption ion errors

Abstract

In order to measure a total pressure as low as 10−12 Pa, the avoidance of electron stimulated desorption (ESD) ion errors is more important than the x-ray limit, because even if we can contrive to reduce ESD ions in a gauge, we do not know what fraction the ESD ion error makes in the measured pressure value. This is the largest defect in the reliability of the measurements. Therefore, the development of the ion spectroscopy gauge which avoids ESD ion errors, was recalled with a historical review of the limiting processes in a hot-cathode gauge. The most advanced ion spectroscopy gauge was constructed with a fine platinum alloy spherical grid ion source, immersed in a copper block with stainless steel flanges. Gas phase ions were effectively separated from ESD ions by the actions of electron space charge in the grid and a hemispherical 180° ion energy analyzer. The x-ray limit of the advanced gauge was approximately 2.5×10−13 Pa, and the outgassing rate of 2×10−9 Pa ℓ/s (about 1/100 that of an ordinary nude Bayard–Alpert gauge) was achieved.