Transformation of polycrystalline tungsten to monocrystalline tungsten W(100) and its potential application in Schottky emitters

Abstract

The electron sources in electron microscopes and electron lithography machines often consist of small diameter W(100) wires, etched to form a sharp tip. The electron emission is facilitated by the Schottky effect, thus the name Schottky emitter. The authors are investigating the feasibility of arrays of such electron emitters for the use in multibeam lithography. This, however, would require large pieces of W(100) which are not easily available. The concept of dc Joule heating for the crystallographic transformation is utilized to convert polycrystalline tungsten to W(100) for the fabrication of the Schottky emitters. A miniature Schottky emitter fabricated by wire electrical discharge machining was heated by dc and the crystallographic orientation was subsequently determined by electron diffraction. The x-ray diffraction measurement on another sample of tungsten filament, heated by similar method, confirms the above results. The concept will be extended for the fabrication of a prototype multibeam source for parallel electron beam lithography.