LaB6 single-crystal tips as an electron source of high brightness

Abstract

A LaB₆ single crystal produced at the National Institute for Research in Inorganic Materials was used as an electron source of high brightness with a commercial‐type electron probe microanalyzer (EPMA). A single‐crystal tip of 0.2 mm φ×4 mm was cut out from a mother crystal of LaB₆ obtained by discharge machining. The tip, held with Ta ribbons by electron beam welding, was mounted in a conventional tungsten hairpin filament holder which is commonly used in electron microscopes (CEM), scanning electron microscopes (SEM), and EPMA. Using this LaB₆ emitter in an electron gun of the commercial type EPMA, JAX‐3, instead of the conventional tungsten hairpin, the gun was operated under the same conditions as the tungsten hairpin: vacuum between low 10⁻⁴ and high 10⁻⁵ Torr, emission current ∼100 μA at 25 kV. It is concluded from a comparison of the scanning electron micrographs obtained with the LaB₆ emitter and the tungsten hairpin that the LaB₆ emitter can well be used instead of the conventional tungsten hairpins as an electron source of higher brightness for CEM and SEM even in such a low vacuum as ∼10⁻⁵ Torr for practical use.