Field penetration into amorphous‐carbon films: consequences for field‐induced electron emission

Abstract

The phenomenon of low-macroscopic-field (LMF) electron emission is sometimes exhibited by thin films of non-metallic materials. Both wide-band-gap semiconductors and hopping conductors such as amorphous carbon exhibit this phenomenon, and its origin has been under discussion for some years. This paper first uses a simple theory to discuss field penetration into hopping conductors with a high density of localised states near the charge-neutrality level. This theory is physically similar to widely used existing theories, in that it assumes continuous charge distributions and uses the one-dimensional Poisson's equation. The theory suggests that little field penetration occurs, and that models of LMF emission based on uniform barrier lowering are not viable. Unexpected self-consistency difficulties are also created for some types of local-field-enhancement model. A re-assessment of the validity of this simple field-penetration theory suggests the following. Contrary to a basic assumption of this type of theory, the granularity of the screening charge distribution is a dominant feature of the physics associated with LMF emission from nanoscale-sized emission sites on thin films of hopping conductors. The authors think that the screening is carried out by discrete charges in localised states, although details are not clear. This conclusion is potentially very far-reaching. In particular, new forms of field-penetration theory may be required before definitive decisions can be made about the self-consistency of some models of local field enhancement.

Автоэмиссионная Шахматрая Структура На Основе Алмазографитовых Кластеров

“…Увеличение эмиссии, которой формально соответствует понижение РВ до порядков долей eV, до сих пор строго не объяснено. Обзор возможных теорий дан в [11], где также предложе-на теория проникновения поля в полупроводниковый материал соответствующей углеродной фазы эмиттера. В работе [10] указанный эффект объяснен резонансным туннелированием в результате размерного квантования при образовании уровней размерного квантования, сов-падающих с уровнем Ферми.…”

“…Он создает изображение −q ′ = −kq в точке z ′ = c − h, которым можно ограничиться в случае большой толщины пластины (c ≫ h). Для строгого учета обоих электродов достаточно построить потенциал этих двух зарядов на основе приведенных выше формул, например (11). Этот потенциал действует в области z > c. В области z < c заряд воспринимается как его изображение q ′′ = 2εq/(ε + 1) = (1 − k)q в точке его расположения.…”

Dimensional Quantization and the Resonance Concept of the Low-Threshold Field Emission

“…In numerous recent experiments, see for instance [1][2][3][4][5][6][7][8], extremely low-threshold field emission from the carbon nano-clusters was observed for electric fields (10 4 − 10 5 V/cm). This is a surprisingly strong effect, because the field initiating a noticeable emission from these materials is 2-3 orders less than the field required for the field-emission from the traditional metals and semiconductors.…”

“…This is a surprisingly strong effect, because the field initiating a noticeable emission from these materials is 2-3 orders less than the field required for the field-emission from the traditional metals and semiconductors. Despite the obviously unusual nature of the effect, numerous authors, see for instance [6,8], have attempted to explain the low-threshold phenomenon trivially with use of the classical Fowler-Nordheim machinery, based on the enhancing of the field at the micro-protrusions. They assume that the local field F s near the emitting center is calculated as F 0 = γF 0 , where γ is the field enhancement coefficient, defined by the micro-geometry, and F 0 is the field of the equivalent flat capacitor.…”

Resonance scattering across the superlattice barrier and the dimensional quantization

“…In numerous recent experiments, see for instance [1][2][3][4][5][6][7] extremely low-threshold field emission from metallic cathodes under carbon deposit was observed for electric fields (10 4 − 10 5 V /cm). This is a surprisingly strong effect, because the field initiating a noticeable emission (10 −10 − 10 −9 A) from these materials is by 2-3 orders of magnitude less than the field required for the field-emission from the traditional metals and semiconductors.…”