Field emission studies of the lanthanum hexaboride/tungsten system

Kanitkar, P L; Dharmadhikari, C. V.; Joag, Dilip S.; Shukla, V N

doi:10.1088/0022-3727/9/14/001

Cited by 13 publications

(6 citation statements)

References 8 publications

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“…at ≈2.0 eV [9]. However, in practical applications, a number of alloys and compounds, such as thoriated tungsten [10][11][12][13] and lanthanum hexaboride [14,15], are used because they offer relatively low work functions (≈2.5 eV) in combination with much better chemical and thermal stabilities. It has also been known since the 1930s [16,17] that it is possible to create surfaces with work functions lower than those of any elemental, bulk materials by using coatings with thicknesses on the order of a monolayer.…”

Section: Introductionmentioning

confidence: 99%

An orbital-overlap model for minimal work functions of cesiated metal surfaces

Chou

Voss

Bargatin

et al. 2012

J. Phys.: Condens. Matter

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We introduce a model for the effect of cesium adsorbates on the work function of transition metal surfaces. The model builds on the classical point-dipole equation by adding exponential terms that characterize the degree of orbital overlap between the 6s states of neighboring cesium adsorbates and its effect on the strength and orientation of electric dipoles along the adsorbate-substrate interface. The new model improves upon earlier models in terms of agreement with the work function-coverage curves obtained via first-principles calculations based on density functional theory (DFT). All the cesiated metal surfaces have optimal coverages between 0.6 to 0.8 monolayers (ML), in accordance with experimental data. All the cesiated tungsten surfaces we have considered are shown to have minimum work functions (MWF) lower than most cesiated metals, also in accordance with experiments.

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Section: Introductionmentioning

confidence: 99%

An orbital-overlap model for minimal work functions of cesiated metal surfaces

Chou

Voss

Bargatin

et al. 2012

J. Phys.: Condens. Matter

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“…The most commonly used materials for low work function applications that are chemically and thermally stable are compounds like lanthanum hexaboride 12 , 13 and thoriated tungsten. 14 − 17 However, their work functions (∼2.5 eV) are not low enough for efficient collectors in thermionic converters.…”

mentioning

confidence: 99%

“…The most commonly used materials for low work function applications that are chemically and thermally stable are compounds like lanthanum hexaboride , and thoriated tungsten. − However, their work functions (∼2.5 eV) are not low enough for efficient collectors in thermionic converters. Instead, submonolayer coatings of alkali metals (most commonly cesium) on substrate surfaces result in work functions that are much lower than the work function of either substrate or coating individually.…”

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confidence: 99%

Surface Photovoltage-Induced Ultralow Work Function Material for Thermionic Energy Converters

et al. 2019

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Low work function materials are essential for efficient thermionic energy converters (TECs), electronics, and electron emission devices. Much effort has been put into finding thermally stable material combinations that exhibit low work functions. Submonolayer coatings of alkali metals have proven to significantly reduce the work function; however, a work function less than 1 eV has not been reached. We report a record-low work function of 0.70 eV by inducing a surface photovoltage (SPV) in an n-type semiconductor with an alkali metal coating. Ultraviolet photoelectron spectroscopy indicates a work function of 1.06 eV for cesium/oxygen-activated GaAs consistent with density functional theory model predictions. By illuminating with a 532 nm laser we induce an additional shift down to 0.70 eV due to the SPV. Further, we apply the SPV to the collector of an experimental TEC and demonstrate an I – V curve shift consistent with the collector work function reduction. This method opens an avenue toward efficient TECs and next-generation electron emission devices.

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“…The most commonly used materials for low work function applications that are chemically and thermally stable are compounds like lanthanum hexaboride [ 16,17 ] and thoriated tungsten [ 18–21 ] with a work function around 2.5 eV. For thermionic converters, extremely low work functions are required, which are achieved by sub‐monolayer coatings of alkali metals (most commonly cesium) on metal surfaces.…”

Section: Introductionmentioning

confidence: 99%

Discovery of Stable Surfaces with Extreme Work Functions by High‐Throughput Density Functional Theory and Machine Learning

Schindler,

Antoniuk,

Cheon

et al. 2024

Adv Funct Materials

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The work function is the key surface property that determines the energy required to extract an electron from the surface of a material. This property is crucial for thermionic energy conversion, band alignment in heterostructures, and electron emission devices. This work presents a high‐throughput workflow using density functional theory (DFT) to calculate the work function and cleavage energy of 33,631 slabs (58,332 work functions) that are created from 3,716 bulk materials. The number of calculated surface properties surpasses the previously largest database by a factor of ≈27. Several surfaces with an ultra‐low (<2 eV) and ultra‐high (>7 eV) work function are identified. Specifically, the (100)‐Ba‐O surface of BaMoO3 and the (001)‐F surface of Ag2F have record‐low (1.25 eV) and record‐high (9.06 eV) steady‐state work functions. Based on this database a physics‐based approach to featurize surfaces is utilized to predict the work function. The random forest model achieves a test mean absolute error (MAE) of 0.09 eV, comparable to the accuracy of DFT. This surrogate model enables rapid predictions of the work function (≈ 105 faster than DFT) across a vast chemical space and facilitates the discovery of material surfaces with extreme work functions for energy conversion and electronic device applications.

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Field emission studies of the lanthanum hexaboride/tungsten system

Cited by 13 publications

References 8 publications

An orbital-overlap model for minimal work functions of cesiated metal surfaces

An orbital-overlap model for minimal work functions of cesiated metal surfaces

Surface Photovoltage-Induced Ultralow Work Function Material for Thermionic Energy Converters

Discovery of Stable Surfaces with Extreme Work Functions by High‐Throughput Density Functional Theory and Machine Learning

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