Abstract
Herein, we describe a study of the phenomenon of field-induced electron emission from thin films deposited on flat Si substrates. Films of Mo with an effective thickness of 6–10 nm showed room-temperature low-field emissivity; a 100 nA current was extracted at macroscopic field magnitudes as low as 1.4–3.7 V/μm. This result was achieved after formation treatment of the samples by combined action of elevated temperatures (100–600 °C) and the electric field. Morphology of the films was assessed by AFM, SEM, and STM/STS methods before and after the emission tests. The images showed that forming treatment and emission experiments resulted in the appearance of numerous defects at the initially continuous and smooth films; in some regions, the Mo layer was found to consist of separate nanosized islets. Film structure reconstruction (dewetting) was apparently induced by emission-related factors, such as local heating and/or ion irradiation. These results were compared with our previous data obtained in experiments with carbon islet films of similar average thickness deposited onto identical substrates. On this basis, we suggest a novel model of emission mechanism that might be common for thin films of carbon and refractory metals. The model combines elements of the well-known patch field, multiple barriers, and thermoelectric models of low-macroscopic-field electron emission from electrically nanostructured heterogeneous materials.
Highlights
In an increasing number of applications, thermal cathodes are being replaced by cold cathodes, which have the advantages of higher energy efficiency, faster response, and easier miniaturization
In our previous works [38,39,40], we investigated low-macroscopic-field (LMF) electron emission from island carbon films on silicone substrates coated with a native oxide
To explain the observed LMF emission from such films, we proposed a model that combined elements of the known models of lateral potential variation (“patch field”) [45,52,59,60] and hot-electron emission [49,61], and it accounts for specific nanoscale thermoelectric effects in the article [62]
Summary
In an increasing number of applications, thermal cathodes are being replaced by cold cathodes, which have the advantages of higher energy efficiency, faster response, and easier miniaturization. In the vast majority of cases, such cathodes use metal needlelike tips [6,10,11], carbon fibers [3,7], or nanotubes [6,12,13] to enhance the electric field and, to reduce the required voltage. The concentration of the electric field at the high-aspect-ratio surface features implies the concentration of destructive factors such as ion sputtering, Joule heating, and ponderomotive forces. Long-term stability and lifetime remain among the key issues for cold cathodes with sharp emitting tips, which brings into attention planar or smooth-surface cold emitters as competitive options [2,6,11,14].
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