Surface compositions of hexaborides at high temperatures

Abstract
The surface compositions of (La,M) B6‐type hexaborides are investigated at high temperatures using Auger electron spectroscopy. Above 1000 °C, La atoms become more enriched in the surface layer than in the bulk. Surface composition approaches that of LaB6 above 1400 °C. Above 1400 °C, the hexaboride surface maintains constant composition during long‐term operation. The surface layer, in which La is more enriched than other metals, is estimated to be 2 or 3 nm thick. This enrichment may be due to the fact that the metals of higher vapor pressures evaporate faster than lanthanum.