A Study of Scandia-Doped Pressed Cathodes

Wang, Jinshu; Liu, Wei; Li, Lili; Wang, Yanchun; Wang, Yiman; Zhou, Meiling

doi:10.1109/ted.2009.2015423

Cited by 38 publications

(27 citation statements)

References 13 publications

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“…2 Scandate cathodes, which have the capability of providing high current densities at an operating temperature lower than that of Ba-type dispenser cathodes, have attracted much attention since their discovery by Figner 3 in 1967. [9][10][11][12] High current densities are routinely demonstrated and the cathode shows potential for application in terahertz vacuum electron sources in the future. For this reason, several types of scandate cathodes, including impregnated, mixed matrix, pressed top-layer, and thin-film top-layer, were developed mainly by Philips ͑the Netherlands͒ and Hitachi ͑Japan͒.…”

Section: Introductionmentioning

confidence: 99%

“…4,5 In the 1990s pulsed laser deposition technology was studied for scandate cathode fabrication at Philips Research Laboratories ͑Ger-many͒ and BEVRI ͑China͒. 12 In both cases, the sol-gel process is adopted for doping Scandium oxide and other compounds into tungsten. 6 However, the CRT industry declined before scandate cathodes could be applied in industry.…”

Section: Introductionmentioning

confidence: 99%

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Emission mechanism of high current density scandia-doped dispenser cathodes

Wang¹,

Wang²,

Liu³

et al. 2011

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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High current, high current density field emitter array cathodes Emission uniformity enhancement between microfabricated tips in cold cathode arrays High current density field emission from arrays of carbon nanotubes and diamond-clad Si tipsThe emission mechanism of scandia-doped dispenser ͑SDD͒ cathodes is characterized based on systematic investigation of microstructure, surface behavior, evaporation, and emission. High current density SDD cathodes have been developed in recent years to meet the requirements of advanced vacuum electron devices. Space charge limited current densities of over 100 A / cm 2 have been reliably reached at a temperature of 950°C b . SDD cathodes are composed of a tungsten matrix with submicron structure and uniformly dispersed materials containing Sc, Ba, Ca, Al, and O as nanosized particulates in the matrix. The authors conclude that the copious electron emission from this cathode type results from a layer of Ba-Sc-O on W formed after activation on top of the matrix. This layer is about 100 nm thick and maintains a stable composition over its lifespan. Its emission can be explained in terms of a semiconductor layer with characteristics that differ from a metal-like emission model. The Ba-Sc-O layer is formed by codiffusion of Sc, Ba, and O ͑generated inside the W-matrix͒ to the surface of the W-matrix during activation. Furthermore, this layer guarantees a low evaporation rate of emission-relevant materials and thus enables a longer lifespan. A. Structure features of SDD cathodesUp to now, two types of SDD cathodes have been developed. They are the scandia-doped impregnated ͑SDI͒ cathodes and the scandia-doped pressed ͑SDP͒ cathodes. The SDI cathodes have a porous matrix fabricated by calcining, a͒ Electronic Wang et al.: Emission mechanism of high current density scandia-doped dispenser cathodes 04E106-2 04E106-2 Wang et al.: Emission mechanism of high current density scandia-doped dispenser cathodes 04E106-7 04E106-7 JVST B -Microelectronics and Nanometer Structures Redistribution subject to AVS license or copyright; see http://scitation.aip.org/termsconditions. Download to IP: 84.88.136.149 On: Tue, 02 Dec 2014 08:38:57 Wang et al.: Emission mechanism of high current density scandia-doped dispenser cathodes 04E106-8 04E106-8

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Emission mechanism of high current density scandia-doped dispenser cathodes

Wang¹,

Wang²,

Liu³

et al. 2011

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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“…It can be seen that cathode surface is composed of Ba, Sc, O, and W. The calculated atomic ratio of Ba:Sc:O is 1.7:1:2.3 at the cathode surface. It is reported in [20] and [21] that the SDI cathode can provide high emission property when the cathode surface is covered by a multilayer of active substances with the optimal Ba:Sc:O concentration ratio in the range of (1.5-2.0):1:(2-3). After proper activation, the Ba:Sc:O concentration ratio of this cathode drops into such a range.…”

Section: Electron Emission Property Of Sdi/sd Cathodementioning

confidence: 99%

A Study of Scandia-Doped-Impregnated Cathode Fabricated by Spray Drying Method

Wang

Cui

Liu

et al. 2015

IEEE Trans. Electron Devices

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Scandia-doped-impregnated (SDI) cathodes were fabricated with scandia-doped tungsten powders using spray drying (SD) combined with two-step reduction in hydrogen atmosphere. The temperature-programmed reduction results show that the addition of Sc 2 O 3 leads to a decrease of the reduction temperature of scandia-doped tungsten oxide powders. Using the obtained scandia-doped tungsten powders with homogenous distribution of nanosized scandia, a submicrometer porous matrix cathode composed of tungsten grains with active substances distributing uniformly around these grains has been obtained. For cathodes with the above matrices and impregnated with 411 or 612 Ba, Ca aluminates (named SDI/SD-411 or SDI/SD-612 cathodes, respectively) and space charge limited current densities of ∼72.5 A/cm 2 have been reliably reached at 900°C b . After proper activation, the cathode surface is covered by a Ba-Sc-O active substance layer with preferable atomic ratios, leading to its good emission property. The average evaporation rate of 8.45 × 10 −9 gcm −2 s −1 at 1150°C b for SDI/SD-612 cathode is the lowest one among Ba-W, W/Re/Os-M, SG-411 (the scandia-doped cathode fabricated by sol-gel method with impregnating 411 aluminates), and SDI/SD-612 cathodes.Index Terms-Evaporation behavior, scandate cathode, thermionic emission.

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“…Moreover, using sol-gel technique instead of ball-milling method for the fabrication of cathode enhances the emission properties of it. Wang et al [8] technique and ball-milling method. They reported that the emission properties of cathode synthesized by sol-gel technique were better than that of cathode produced through ball-milling method.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of Nanocrystalline Electron Emissive Materials with Homogenous Composition in Nanoscale

Shiran¹,

Hadianfard²,

Shiezadeh³

2013

IJCEA

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Abstract-In this research, specific stoichiometric mixture of nanocrystalline barium carbonate, calcium carbonate, and aluminum oxide was fabricated by using the sol-gel combustion method. This mixture is used as emissive materials on impregnated cathodes which make up high power vacuum microwave tubes such as klystrons. Composition uniformity and particle size of emissive materials affect the electron emission properties of impregnated cathodes. In this study, dry gel and heat treated powder at 500 °C are investigated by thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The results show that dry gel combusts at 260 °C , and that during combustion transforms from an amorphous phase to a nanocrystalline phase. The average crystallite size of the powders which is calculated by Debye-Scherrer's method based on the XRD patterns is under 45 nm. The results of SEM and EDX of powder after heat treatment at 500 °C show that the particle size of powder is under 100 nm, and the chemical composition of emissive material is uniform at nanoscale.Index Terms-Dispenser cathode, emissive material, nanopowder, sol-gel combustion synthesis.

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A Study of Scandia-Doped Pressed Cathodes

Cited by 38 publications

References 13 publications

Emission mechanism of high current density scandia-doped dispenser cathodes

Emission mechanism of high current density scandia-doped dispenser cathodes

A Study of Scandia-Doped-Impregnated Cathode Fabricated by Spray Drying Method

Synthesis of Nanocrystalline Electron Emissive Materials with Homogenous Composition in Nanoscale

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