Field emission characteristics of a small number of carbon fiber emitters

Wilkin W Tang,Donald A Shiffler,John R Harris,Matthew Lacour,Tim Knowles,Kevin L Jensen,Ken Golby

doi:10.1063/1.4962921

Abstract

This paper reports an experiment that studies the emission characteristics of small number of field emitters. The experiment consists of nine carbon fibers in a square configuration. Experimental results show that the emission characteristics depend strongly on the separation between each emitter, providing evidence of the electric field screening effects. Our results indicate that as the separation between the emitters decreases, the emission current for a given voltage also decreases. The authors compare the experimental results to four carbon fiber emitters in a linear and square configurations as well as to two carbon fiber emitters in a paired array. Voltage-current traces show that the turn-on voltage is always larger for the nine carbon fiber emitters as compared to the two and four emitters in linear configurations, and approximately identical to the four emitters in a square configuration. The observations and analysis reported here, based on Fowler-Nordheim field emission theory, suggest the electric field screening effect depends critically on the number of emitters, the separation between them, and their overall geometric configuration.

Highlights

Field emission cathodes continue to be of high research interest due to their wide array of applications, ranging from field emission displays, to x-ray tubes, to both low and high power microwave devices.[1,2,3,4,5,6,7] Their ability to provide high current density with low voltage and high pulse repetition rate constitute attractive attributes
Our configuration allows a simple experimental configuration for isolating the electric field screening from other effects, such as work function variation
The experimental results show that the four fibers at the corner of the nine-fibers array dominate the emission, and produce I-V curves that are nearly identical to the four-fiber square array configuration

Summary

Introduction

Field emission cathodes continue to be of high research interest due to their wide array of applications, ranging from field emission displays, to x-ray tubes, to both low and high power microwave devices.[1,2,3,4,5,6,7] Their ability to provide high current density with low voltage and high pulse repetition rate constitute attractive attributes. The proximity of the individual field emitters results in electric field screening which influences the amount of current that can be liberated from the cathode surface as well as the relationship between the macroscopically applied field and the emitted current. Such effects figure prominently in many previous studies.[8,9,10,11,12] past experiments involve large arrays that contains thousands of emitters,[11,12] often complicating an analysis of screening and field enhancement effects except in a statistical nature. In previous work, we explored the emission characteristics of two- and four-fiber arrays of carbon emitters in a carefully prepared, simple geometry.[13,14,15,16,17,18,19] Our configuration allows a much more pristine and straightforward experimental geometry for isolating and interpreting the electric field screening from other effects such as work function variation across the cathode surface or statistical inhomogeneities in the geometry of the individual emitters that comprise the array

Methods

Results

Conclusion