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Quantum efficiency (QE) enhancement in accelerator technology relevant to antimonide photocathodes (K2CsSb) is achieved by interfacing them with atomically thin 2D crystal layers. The enhancement occurs in a reflection mode, when a 2D crystal is placed in between the photocathodes and optically reflective substrates. Specifically, the peak QE at 405 nm (3.1 eV) increases by a relative 10%, whereas...
Quantum Efficiency Enhancement
Phototube with accelerator technology relevant antimonide photocathodes (K2CsSb) deposited on atomically thin two‐dimensional (2D) crystal layers such as graphene. Quantum efficiency enhancement occurs in a reflection mode, when a 2D crystal is placed in between the photocathodes and optically reflective substrates. More details can be found in article number 1900501...
Field emission from “nano diodes” encounter strong deviations from the tunneling barrier presupposed in Fowler Nordheim theory. Modifications to the emission barrier are modeled using a hyperbolic geometry to find trajectories along which Gamow factor is found; a quadratic equivalent potential is determined, and a shape factor method is used to evaluate the total current from a protrusion or wedge...
Under a high electrical field, field emission current may be significantly enhanced by positive ions very close to the cathode surface. In addition to distorting the potential field to both lower and thin the potential barrier, the ion can also induce resonant tunneling, which can be a major factor in the emission current. In this study, resonant tunneling behavior has been investigated using a simple...
We have considered the opportunities and challenges of fabricating a planar vacuum transistor using the edge of a single layer graphene sheet as a field emission electron source. The emission current needed to produce significant gain and power at mm-wave frequencies is roughly 100mA/mm. Simple arguments suggest such emission currents are possible.
It has been shown that field emission is an important mechanism in emerging microplasma devices. Ions formed by electron impact ionization that are very close to the cathode may bring significant enhancement to the emission current by both resonant and non-resonant processes. In this work, we numerically solve the one-dimensional Schrödinger's equation in the presence of an ion approaching the surface,...
The emittance of high brightness electron sources such as field emitters and photocathodes is increased by geometric features on the emitter surface that give rise to local field enhancement. Knowledge of the emittance is important for accelerators and electron beam devices, and particularly, the intrinsic emittance (or that portion due to the cathode), is of increasing importance because it cannot...
We report on the incorporation of a model for field emitters (FE) in the MICHELLE Particle-In-Cell (PIC) beam optics code1. The FE model is based on a Point Charge Model (PCM)2 and allows for rapid and analytical representations of tip current, variation, and emission statistics. Its usage enables determining the impact of emission variation on current characteristics and emittance. Rather than cold...
We report on the incorporation of a model of field emitters (FE) in the MICHELLE Particle-In-Cell (PIC) beam optics code. The FE model is based on a Point Charge Model (PCM) and allows for rapid and analytical representations of tip current, variation, and emission statistics. Its usage enables determining the impact of emission variation on current characteristics and emittance. Rather than cold...
Emission from an array of dissimilar field emitters are known to produce non-uniform patterns that affect space charge forces within the electron beam produced, with consequences on emittance and transit time effects. To model variation, a semi-analytical Point Charge Model (PCM) gives rapid and analytical representations of tip current, variation, and emission statistics to be used in the MICHELLE...
Secondary-electron-emission current measured from high-purity, single-crystal CVD diamond is found to increase when 3.1-eV photons are incident on the hydrogenated surface. Energy spectra indicate that the sub-gap illumination causes the band levels to shift in the bulk, thereby reducing the upwards band bending at the pinned surface.
We report on the incorporation of a model of field emitters based on a Point Charge Model (PCM)1 that allows for rapid and analytical representations of tip current, variation, and emission statistics and its implementation and usage in the MICHELLE Particle-In-Cell (PIC) code2 to model the impact of emission variation on current characteristics and emittance. Rather than cold field emission characterized...
We report on the incorporation of a model of field emitters based on a Point Charge Model (PCM) that allows for rapid and analytical representations of tip current, variation, and emission statistics and its implementation and usage in the MICHELLE Particle-In-Cell (PIC) code to model the impact of emission variation on current characteristics and emittance. Rather than cold field emission characterized...
Quantum Efficiency from photocathodes and Yield from diamond secondary emitters are affected by scattering during electron transport in bulk material. The emission distribution is required to predict how current density and emittance from these sources affect beam transport in Particle-in-Cell codes, particularly MICHELLE. Monte Carlo is used to augment a standard Three-Step-Model (TSM) based model...
We report progress in mounting small thin diamond sheets over holes in larger substrates in a manner that allows electron beam amplification. In addition to a physical mount, our bonding method must be compatible with the creation and maintenance of the negative electron affinity surface and operation at elevated temperatures. We use a transient liquid phase bonding method wherein the constituent...
A diamond current amplifier is being developed that can be biased to generate an internal electric field needed for high transport efficiency and emission gain. In the process, a bonded diamond structure has been successfully fabricated that provides mechanical support for the microns-thick diamond film and that allows for the use of processing techniques needed to fabricate the biased device. Emission...
A simple one-dimensional account of space charge in an anode-cathode (AK) gap is based on a transit time model. Two limiting cases are treated: thermionic and field emission. Each case is compared to experimental thermionic and field emission data in the literature and the correspondence is shown to be good.
How electron emission is generated from photo, secondary, field and thermionic sources affects their vacuum transport characteristics and therefore their utility for differing Vacuum Electronic applications. Complications associated with emission processes will be related to desirable features of the beams produced in terms of current density, lifetime, space charge, beam halo, emittance, and response...
There is a significant level of effort by SAIC and BWR, funded by ONR & JTO, to enhance the three dimensional (3D) finite-element (FE) electrostatic timedomain (ESTD) particle-in-cell (PIC) code MICHELLE to provide modeling and simulation of the interaction of electron emission sources in the presence of electromagnetic cavity fields. These enhancements have direct importance to the free-electron...
Electron transport through thin film semiconductors is common to both the development of semiconductor photocathodes and to secondary emission electron sources. We discuss the modeling and numerical simulation of such transport in the presence of scattering and loss mechanisms, to enable predictive estimations of energy distributions, time response, and the nature of the distribution of the emitted...
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