Rare-earth monosulfides as durable and efficient cold cathodes

TL;DR

This paper demonstrates the successful deposition and characterization of lanthanum monosulfide thin films as durable, low work function cold cathodes with high emission current densities, using various substrates and advanced techniques.

Contribution

It introduces a novel method for depositing LaS thin films with low work function properties and explores their application as efficient cold cathodes.

Findings

LaS thin films have a work function of about 1 eV.

Achieved emission current densities up to 50 A/cm2.

Successfully grew LaS on different substrates and produced nanostructures.

Abstract

In their rocksalt structure, rare-earth monosulfides offer a more stable alternative to alkali metals to attain low or negative electron affinity when deposited on various III-V and II-VI semiconductor surfaces. In this article, we first describe the successful deposition of Lanthanum Monosulfide via pulsed laser deposition on Si and MgO substrates and alumina templates. These thin films have been characterized by X-ray diffraction, atomic force microscopy, high resolution transmission electron microscopy, ellipsometry, Raman spectroscopy, ultraviolet photoelectron spectroscopy and Kelvin probe measurements. For both LaS/Si and LaS/MgO thin films, the effective work function of the submicron thick thin films was determined to be about 1 eV from field emission measurements using the Scanning Anode Field Emission Microscopy technique. The physical reasons for these highly desirable low work function properties were explained using a patchwork field emission model of the emitting surface. In this model, nanocrystals of low work function materials having a <100> orientation perpendicular to the surface and outcropping it are surrounded by a matrix of amorphous materials with higher work function. To date, LaS thin films have been used successfully as cold cathode emitters with measured emitted current densities as high as 50 A/cm2. Finally, we describe the successful growth of LaS thin films on InP substrates and, more recently, the production of LaS nanoballs and nanoclusters using Pulsed Laser Ablation.