Change in work function during phase transition of Sc–O/W(100) system at high temperatures

Nakanishi, Y.; Nagatomi, T.; Takai, Yoshizo

doi:10.1016/j.apsusc.2009.05.116

Cited by 6 publications

(13 citation statements)

References 20 publications

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“…16 The proposed model explained the experimentally obtained coverages of ScO complexes in the states of ScO and Sc 2 O 3 very well. 16,17 17 The variation in the work function was well explained using the kinetics model combined with the interpretation of the reduction in the work function attributed to the formation of Sc-O electric dipoles.…”

Section: Introductionmentioning

confidence: 88%

“…12,17 The present experimental system enables AES to be performed at a high temperature of 1700 K. 12 The work function measurement can also be performed at a high temperature of 1700 K. 17 The LEED observation at 1900 K was also enabled using the LEED system developed in this study. The apparatus is equipped with a coaxial cylindrical mirror analyzer, an ion gun for sputter cleaning, a Sc evaporator, a sample holder with a heater, and a LEED system specially developed for the observation at high temperature as described below.…”

Section: Methodsmentioning

confidence: 99%

“…13,16,17 A W͑100͒ surface was cleaned by repeated sputtering using 500 eV Ar + ions of 1 A and flashing at 1900 K. The ͑2 ϫ 1͒-͑1 ϫ 2͒-Sc-O / W͑100͒ surface was prepared on the W͑100͒ surface by depositing approximately 5 ML of Sc at 1500 K in an oxygen atmosphere of 5 ϫ 10 −5 Pa. 13,16,17 A W͑100͒ surface was cleaned by repeated sputtering using 500 eV Ar + ions of 1 A and flashing at 1900 K. The ͑2 ϫ 1͒-͑1 ϫ 2͒-Sc-O / W͑100͒ surface was prepared on the W͑100͒ surface by depositing approximately 5 ML of Sc at 1500 K in an oxygen atmosphere of 5 ϫ 10 −5 Pa.…”

Section: Methodsmentioning

confidence: 99%

“…[14][15][16] The obtained AES spectra were analyzed, and a kinetics model describing surface phenomena, i.e., the oxidation, oxygen desorption, diffusion, and surface segregation of ScO complexes, during the phase transition was proposed. 17 The variation in the work function was well explained using the kinetics model combined with the interpretation of the reduction in the work function attributed to the formation of Sc-O electric dipoles. A special sample holder for the work function measurement at 1500-1700 K, where a large number of thermionic electrons are emitted, was also developed, and we succeeded in measuring in situ the work function during the phase transition.…”

Section: Introductionmentioning

confidence: 90%

“…[6][7][8][9][10][11][12][13][14][15][16][17] Previous studies have revealed that the Sc-O / W͑100͒ system has two phases at high temperature. The surface providing the excellent electron emission properties is considered to be formed only under limited preparation and operating conditions of the Sc-O / W͑100͒ emitter.…”

Section: Introductionmentioning

confidence: 99%

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In situ observation of change in surface atomic arrangement of Sc–O∕W(100) system during phase transition at high temperature

Nagatomi

Nakanishi

Takai

2010

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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In situ observation of low-energy electron diffraction (LEED) patterns during the phase transition of the Sc–O∕W(100) surface at high temperature was performed to investigate the correlation between the surface atomic arrangement, coverage of surface atoms, and work function during the phase transition. For this purpose, a LEED system enabling LEED observation at high temperatures of 1500–1900K was developed. The temperature dependence of the intensity of diffraction spots was measured, and the Debye temperatures were estimated for relevant surfaces. The changes in the intensity of diffraction spots during the phase transition were found to correlate with the changes in the coverage of surface atoms and work function. The present results revealed that surface phenomena such as surface segregation, oxidation, oxygen desorption, and diffusion of ScO complexes predominate the surface properties of the Sc–O∕W(100) system.

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Section: Introductionmentioning

confidence: 88%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 90%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

In situ observation of change in surface atomic arrangement of Sc–O∕W(100) system during phase transition at high temperature

Nagatomi

Nakanishi

Takai

2010

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Absolute work function measurement by using photoelectron spectroscopy

Kim

2021

Current Applied Physics

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Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O

2014

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In this study we employ Density Functional Theory (DFT) methods to investigate the surface energy barrier for electron emission (surface barrier) and thermodynamic stability of Ba and Ba-O species adsorption (relative to formation of bulk BaO) under conditions of high temperature (approximately 1200 K) and low pressure (approximately 10 -10 Torr) on the low index surfaces of bixbyite Sc 2 O 3 . We employ both the standard Generalized Gradient Approximation (GGA) and the hybrid HSE functional to calculate accurate surface barriers from relaxed GGA structures. The role of Ba in lowering the cathode surface barrier is investigated via adsorption of atomic Ba and Ba-O dimers, where the highest simulated dimer coverage corresponds to a single monolayer film of rocksalt BaO. The change of the surface barrier of a semiconductor due to adsorption of surface species is decomposed into two parts: a surface dipole component and doping 2 component. The dipole component is the result of charge rearrangement at the surface and is described by the electrostatic Helmholtz equation. The doping component is due to charge transfer from the surface species, which changes the Fermi level and thereby changes the surface barrier. Different initial geometries, adsorption sites, and coverages were tested for the most stable low index Sc 2 O 3 surfaces ((011) and (111)) for both atomic Ba and Ba-O dimers. The lowest surface barrier with atomic Ba on Sc 2 O 3 was found to be 2.12 eV and 2.04 eV for the (011) and (111) surfaces at 3 and 1 Ba atoms per surface unit cell (0.250 and 0.083 Ba per surface O), respectively. The lowest surface barrier for Ba-O on Sc 2 O 3 was found to be 1.21 eV on (011) for a 7 Ba-O dimer-per-unit-cell coverage (0.583 dimers per surface O). Generally, we found that Ba in its atomic form on Sc 2 O 3 surfaces is not stable relative to bulk BaO, while Ba-O dimer coverages between 3 to 7 Ba-O dimers per (011) surface unit cell (0.250 to 0.583 dimers per surface O) produce stable structures relative to bulk BaO. Ba-O dimer adsorption on Sc 2 O 3 ( 111) surfaces was found to be unstable versus BaO over the full range of coverages studied. Investigation of combined n-type doping and surface dipole modification showed that their effects interact to yield a reduction less than the two contributions would yield separately.

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Change in work function during phase transition of Sc–O/W(100) system at high temperatures

Cited by 6 publications

References 20 publications

In situ observation of change in surface atomic arrangement of Sc–O∕W(100) system during phase transition at high temperature

In situ observation of change in surface atomic arrangement of Sc–O∕W(100) system during phase transition at high temperature

Absolute work function measurement by using photoelectron spectroscopy

Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O

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Change in work function during phase transition of Sc–O/W(100) system at high temperatures

Cited by 6 publications

References 20 publications

In situ observation of change in surface atomic arrangement of Sc–O∕W(100) system during phase transition at high temperature

In situ observation of change in surface atomic arrangement of Sc–O∕W(100) system during phase transition at high temperature

Absolute work function measurement by using photoelectron spectroscopy

Electron Emission Energy Barriers and Stability of Sc2O3 with Adsorbed Ba and Ba–O

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Electron Emission Energy Barriers and Stability of Sc₂O₃ with Adsorbed Ba and Ba–O