Multineedle Field Emission from the Ni–W Eutectic

Abstract

A composite structure consisting of an array of parallel 2 μ wires was produced by directionally solidifying the Ni–W eutectic. A multineedle field-emission cathode was then made by selectively etching and pointing the filament tips. The voltage characteristics of a simple diode constructed from this cold cathode were measured and found to follow the Fowler-Nordheim field-emission equation. At a macroscopic current density of 2×10−4A/cm2 and an electric field of 4×104V/cm a vacuum arc occurred that damaged the multineedle cathode. A field-emission microscope was constructed using a multineedle cathode to observe the emission distribution and the pattern was compared with scanning electron micrographs of the cathode before and after emission. It was concluded that the current was not uniformly distributed over the filaments and that failure was accompanied by local melting.