Anomalous Schottky Effect

Hansen, L. K.

doi:10.1063/1.1708068

Cited by 16 publications

(11 citation statements)

References 3 publications

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“…But, in fact, the enhancement factor as conventionally defined for an old-style metal field emitter is not strictly independent of field, either. Real field emitters, that expose facets with different values of local work-function, are surrounded by a system of so-called "patch fields" 11,29 . Consider such an emitter mounted on one face of a parallel-plate arrangement.…”

Section: B Theoretical Discussionmentioning

confidence: 99%

The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

Peng

et al. 2008

Journal of Applied Physics

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A 1 µm long, field emitting, (5,5) single-walled, carbon nanotube (SWCNT) closed with a fullerene cap, and a similar open nanotube with hydrogen-atom termination, have been simulated using the MNDO (Modified Neglect of Diatomic Overlap) quantum-mechanical method. Both contain about 80 000 atoms. It is found that field penetration and band-bending, and various forms of chemically and electrically induced apex dipole, play roles. Field penetration may help to explain electroluminescence associated with field emitting carbon nanotubes. Charge-density oscillations, induced by the hydrogen adsorption, are also found. Many of the effects can be related to known effects that occur with metallic or semiconductor field emitters; this helps both to explain the effects and to unify our knowledge about field electron emitters. However, it is currently unclear how best to treat correlation-and-exchange effects when defining the CNT emission barrier. A new form of definition for the field enhancement factor (FEF) is used. Predicted FEF values for these SWCNTs are significantly less than values predicted by simple classical formulae. The FEF for the closed SWCNT decreases with applied field; the FEF for the H-terminated open SWCNT is less than the FEF for the closed SWCNT, but increases with applied field. Physical explanations for this behavior are proposed. Curved Fowler-Nordheim plots are predicted. Overall, the predicted field emission performance of the H-terminated open SWCNT is slightly better than that of the closed SWCNT, essentially because a C-H dipole is formed that reduces the height of the tunnelling barrier. In general, the physics of a charged SWCNT seems more complex than hitherto realised.

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Section: B Theoretical Discussionmentioning

confidence: 99%

The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

Peng

et al. 2008

Journal of Applied Physics

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“…When different parts ("patches") of an emitter surface have different work functions, a system of electrostatic patch fields [6,7] exists outside the surface, strongest near the patch edges.…”

Section: Work-function Theory and Patch Fieldsmentioning

confidence: 99%

“…When all energy-states in energy range dε n dε p are taken as fully occupied, the supply density is constant in energy-space and equal to the Sommerfeld supply density z S given by [12] z S = 4πem e /h P 3 ≈ 1.618311 × 10 14 A m -2 eV -2 , (7) where m e is the electron mass in free space and h P is Planck's constant. This is a fundamental statistical-mechanical result that is exactly equivalent to assuming that "the density of electron states is constant in phase-space", but is a better starting point for emission theory.…”

Section: H Elements Of Free-electron Theorymentioning

confidence: 99%

“…(6) The symbol f has a unique definition, whereas, historically, the symbol y has had several related (slightly different) meanings. (7) The concept of "scaled barrier field" is, in principle, more general than the Nordheim-parameter concept, and can be extended (when suitably modified in detail) to apply both to general modeling barriers and to real physical barriers. (8) The parameter f seems likely to prove more generally useful than y.…”

Section: Why Change From Using the Nordheim Parmeter Y ?mentioning

confidence: 99%

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Field electron emission theory (October 2016)

Forbes

2016

2016 Young Researchers in Vacuum Micro/Nano Electronics (VMNE-YR)

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“…A number of previous works have studied the interplay of a heterogeneous cathode surface on the resulting thermionic emission, and have sought to connect the smooth TL-FSCL transition to the spatial distribution of work function values. The theory of the anomalous Schottky effect [46] studied the contribution of the patch field effect (electrostatic potential nonuniformity on the cathode surface based on local work function values) and the Schottky barrier lowering effect on the smoothness of the TL-FSCL transition in J − V curves. Studies on space charge effects [39,40,47,48] reveal the contribution of 3-D space charge fields on the smooth transition in J − T curves.…”

Section: Introductionmentioning

confidence: 99%

Physics-based Model for Nonuniform Thermionic Electron Emission from Polycrystalline Cathodes

Chen¹,

Jacobs²,

Petillo³

et al. 2021

Preprint

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A new physics-based model is developed that predicts the emitted current from thermionic emission that accurately spans from the temperature-limited (TL) to the full-space-charge-limited (FSCL) regions. Experimental observations of thermionic electron emission demonstrate a smooth transition between TL and FSCL regions of the emitted-current-density-versus-temperature (J − T ) (Miram) curve and the emitted-current-density-versus-voltage (J − V ) curve. Knowledge of the temperature and shape of the TL-FSCL transition is important in evaluating the thermionic electron emission performance of cathodes, including predicting the lifetime. However, there have been no firstprinciples physics-based models that can predict the smooth TL-FSCL transition region for real thermionic cathodes without applying physically difficult to justify a priori assumptions or empirical phenomenological equations. Previous work detailing the nonuniform thermionic emission found that the effects of 3-D space charge, patch fields (electrostatic potential nonuniformity on the cathode surface based on local work function values), and Schottky barrier lowering can lead to a smooth TL-FSCL transition region from a model thermionic cathode surface with a checkerboard spatial distribution of work function values. In this work, we construct a physics-based nonuniform emission model for commercial dispenser cathodes for the first time. This emission model is obtained by incorporating the cathode surface grain orientation via electron backscatter diffraction (EBSD) and the facet-orientation-specific work function values from density functional theory (DFT) calculations. The model enables construction of two-dimensional emitted current density maps of the cathode surface and corresponding J − T and J − V curves. The predicted emission curves show excellent agreement with experiment, not only in TL and FSCL regions but, crucially, also in the TL-FSCL transition region. This model provides a method to predict the thermionic emission from the microstructure of a commercial cathode, and improves the understanding on the relationship between thermionic emission and cathode microstructure, which is beneficial to the design of vacuum electronic devices.

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Anomalous Schottky Effect

Cited by 16 publications

References 3 publications

The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

The roles of apex dipoles and field penetration in the physics of charged, field emitting, single-walled carbon nanotubes

Field electron emission theory (October 2016)

Physics-based Model for Nonuniform Thermionic Electron Emission from Polycrystalline Cathodes

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