A novel method on single crystallization of h-BN coated tungsten tip using to a point electron source

Abstract

A point electron source is desired to improve performance of high-brightness electron beam instruments. Poly-crystalline tungsten (W) manufactured by electrochemical etching has been practically utilized as a field emission electron source. We have discovered a novel method on growing up single-crystallization at the top of poly-crystalline W needle coated with hexagonal boron nitride (h-BN), by supplying high electric field. Field emission characteristics of the single-crystalline W tips were measured and showed extremely sharp apexes. The emission current from the single-crystalline W tip was measured to exceed 0.1 mA. Field emission microscope (FEM) and transmission electron microscope (TEM) images of the single-crystalline W tip were observed. The FEM image showed significantly electron emission from the crystallographical facets of single-crystalline W tip. The TEM image also showed atomic structure of single-crystalline W with six hold symmetry. Furthermore, electron beam diffraction (EBD) pattern of the single-crystalline W tip was obtained to show <110> facet. From these results, the present novel method for formation of single-crystalline W tip would be expected as a key technology to realize a point electron source, which makes it possible to improve performance of electron beam instruments, especially for developing tiny X-ray tubes of medical or industrial use, as well as to product cantilevers of scanning probe microscopes.