Metallic and Composite Micropoint Cathodes: Aging Effect and Electronic and Spatial Characteristics

Abstract

Composite micro-emitters consisting of a tungsten core coated with different dielectric materials were prepared. Various properties of these emitters were measured, including the current-voltage (IV) characteristics and spatial current distributions. We compared coated and uncoated tips and determined differences between both types. It could be proven that coated emitters are superior to uncoated ones in terms of the current stability and the emission current obtained for the same applied voltages. After these samples have been stored under atmospheric conditions for a period of 10 to 20 years from the first time being characterized, they were tested again. The IV characteristics and spatial current distributions in addition to stability measurements were recorded. Various similarities as well as some differences compared to the initial characterization have been found. It is interesting to note that after one and a half decades these composite emitters are still functioning effectively without being subjected to field desorption processes. The dielectric layers built on the tungsten cores were still in shape and stable. Some theoretical analysis of the tip properties and their change during storage time is included. Particular attention is paid to the deviations from the ideal Fowler-Nordheim (FN) behavior as well as the related slope and intercept correction factors.

Keywords: Field electron emission; Coated tips; Aging effects.