High-Temperature Observation of Tungsten Cathode by Field Emission Microscope

Abstract

Emission patterns of tungsten single crystal were observed at high temperature by using Müller-type field emission microscope having an oil diffusion pump and a rotary pump. As a result, we could obtain two kinds of patterns, namely, “high-temperature pattern” which appeared after heat treatment at temperatures higher than 2200°K, and “low-temperature pattern” which appeared after heat treatment at temperatures lower than 2200°K. Introducing a small quantity of oxygen, it was confirmed that the high-temperature pattern was due to carbon-adsorbed surface. As for the low-temperature pattern which has six-fold symmetry, it was conjectured from a few considerations of the experimental results that it might be a pattern of tungsten carbide.