Frontiers in Thermionic Cathode Research

Kirkwood, David; Gross, Steven J.; Balk, T. John; Beck, Matthew J.; Booske, John H.; Busbaher, Daniel; Jacobs, Ryan; Kordesch, Martin E.; Mitsdarffer, Bryan; Morgan, Dane; Palmer, William D.; Vancil, Bernard; Yater, J.E.

doi:10.1109/ted.2018.2804484

Cited by 81 publications

(25 citation statements)

References 39 publications

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“…The work function difference between barium and tungsten is almost 2 eV, so that surface fields can play an important role in the focal point of the image when barium islands/droplets are adjacent to clean tungsten areas on the surface. There are most likely at least two barium layers adsorbed on the tungsten surface: one in direct contact with the tungsten, which was observed in [8], and a second layer that is composed of barium on barium. The barium film could be as thick as 40 layers based on the barium lattice constant.…”

Section: Resultsmentioning

confidence: 99%

“…The microscope was an Elmitec LEEM V at the Center for Functional Nanomaterials at Brookhaven National Laboratory. This microscope has been used for dewetting studies of barium and scandium on W (100) [8,[10][11][12]. The solid-solid dewetting of barium on W (112) is shown in Figure 1.…”

Section: Resultsmentioning

confidence: 99%

“…In the work shown by Zhou et al [20], similar calculations show that barium adsorption on clean tungsten is unstable relative to the Ba-oxides on W (100), W (111) and W (112). In both the experimental work [8], and in the theoretical models, W (112) is found to be an important surface. While we have observed that barium desorbs from W (100) and W (110) [10]; the W (112) single crystal that we have used for the dewetting experiment is the one with the best prepared surface.…”

Section: Introductionmentioning

confidence: 90%

“…This study was motivated by recent advances in thermionic electron emitters that highlight the structure of the emitting surface, and its composition. Barium is the key ingredient for achieving a low work function surface and high electron emission density [8].…”

Section: Introductionmentioning

confidence: 99%

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A mathematical model of solid-state dewetting of barium thin films on W(112)

Knavel

Savina

Mroz

et al. 2020

Math. Model. Nat. Phenom.

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Solid state dewetting occurs when a thin solid film is heated. The temperature of dewetting depends on the thickness of the film; dewetting can be observed in the range of 1∕3 to 1∕2 of the bulk melting temperature. While remaining solid, the film behaves in a manner similar to liquids dewetting and agglomerating to forming islands or droplets. One of the possible mechanisms is the conversion of a metastable thin film geometry into a more stable form. Heating the metastable film gives the film atoms higher mobility, and the films retract, dewetting the surface. This atomic motion can be restricted due to surface anisotropy. We present in situ emission microscopy observations of barium thin films deposited onto W(112) by thermal evaporation. From the modeling viewpoint, the evolution of the film in this system could be divided in four stages: (i) the nucleation and growth of the thin film as a simply connected region; (ii) formation of droplets/islands/hillocks; (iii) nucleation of holes; (iv) evolution of the components of the disconnected film to their equilibrium state. We present a continuum model that is qualitatively consistent with the evolution of the film observed at the initial stage of the experiment and discuss the later stages of the evolution of surface structures.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A mathematical model of solid-state dewetting of barium thin films on W(112)

Knavel

Savina

Mroz

et al. 2020

Math. Model. Nat. Phenom.

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“…At the heart of vacuum electronic devices are cathodes, including pure metal, oxide, barium tungsten, M-type, and scandate cathodes. The research and preparation technologies and emission properties of cathodes have been continuously improved [1][2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Study on Low-Temperature Emission Performance of Scandate Cathode with Micro-Blade-Type Arrays

Yin

Zhang

et al. 2019

Materials

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In order to meet the requirements of high-frequency vacuum electronic devices with small size, high current density, and low working temperature, a kind of porous tungsten scandate cathode with micro-blade-type arrays was developed. The micro-blade-type arrays were fabricated by laser engraving technology. Subsequently, the cathode was prepared by a vacuum copper removal process and impregnated with active substances at high temperature. Experimental results show that the cathode exhibits excellent low-temperature electron emission performance and that the maximum pulse electron emission current density reaches 81.18 A/cm2 at 800 °C. The cathode also shows apparent combined thermal-field emission characteristics. Further analysis shows that a high electric field strength plays an important role in the electron emission of the scandate cathode. By virtue of the electric field enhancement effect formed by the fabricated micro-blade-type arrays on the cathode surface, the prepared cathode achieves high electron emission capacity.

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Demonstration of Low Work Function Perovskite SrVO₃ Using Thermionic Electron Emission

Lin

Jacobs

Chen

et al. 2022

Adv Funct Materials

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Engineering a material's work function is of central importance for many technologies and in particular electron emitters used in high‐power vacuum electronics and thermionic energy converters. A low work function surface is typically achieved through unstable surface functional species, especially in high power thermionic electron emitter applications. Discovering and engineering new materials with intrinsic, stable low work functions obtainable without volatile surface species would mark a definitive advancement in the design of electron emitters. This work reports evidence for the existence of a low work function surface on a bulk, monolithic, electrically conductive perovskite oxide: SrVO3. After considering the patch field effect on the heterogeneous emitting surface of the bulk polycrystalline samples, this study suggests the presence of low work function (≈2 eV) emissive grains on SrVO3 surface. Emission current densities of 10–100 mA cm–2 at ≈1000 °C, comparable to commercial LaB6 thermionic cathodes, indicative of an overall effective thermionic work function of 2.3–2.7 eV are obtained. This study demonstrates that perovskites like SrVO3 may have intrinsically low work functions comparable to commercialized W‐based dispenser cathodes and suggests that, with further engineering, perovskites may represent a new class of low work function electron emitters.

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Frontiers in Thermionic Cathode Research

Cited by 81 publications

References 39 publications

A mathematical model of solid-state dewetting of barium thin films on W(112)

A mathematical model of solid-state dewetting of barium thin films on W(112)

Study on Low-Temperature Emission Performance of Scandate Cathode with Micro-Blade-Type Arrays

Demonstration of Low Work Function Perovskite SrVO₃ Using Thermionic Electron Emission

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Frontiers in Thermionic Cathode Research

Cited by 81 publications

References 39 publications

A mathematical model of solid-state dewetting of barium thin films on W(112)

A mathematical model of solid-state dewetting of barium thin films on W(112)

Study on Low-Temperature Emission Performance of Scandate Cathode with Micro-Blade-Type Arrays

Demonstration of Low Work Function Perovskite SrVO3 Using Thermionic Electron Emission

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Product

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Demonstration of Low Work Function Perovskite SrVO₃ Using Thermionic Electron Emission