Surface atoms in Sc–O/W(100) system as Schottky emitter at high temperature

Tsujita, Takuji; Iida, Shin‐ichi; Nagatomi, T.; Takai, Yoshizo

doi:10.1016/j.susc.2003.10.008

Cited by 15 publications

(11 citation statements)

References 18 publications

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“…Previous studies [4][5][6][7][8][9][10][11][12][13] have revealed that the Sc-O/W(1 0 0) surface has two phases with surface atomic arrangements of the (1 Â 1) and (2 Â 1)-(1 Â 2) structures at high temperature. The (2 Â 1)-(1 Â 2)-Sc-O/W(1 0 0) surface is formed by heating at 1500 K in oxygen atmosphere.…”

Section: Introductionmentioning

confidence: 99%

“…In this regard, the authors have been involved in the surface characterization of the Sc-O/W(1 0 0) system using Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and work function measurement at high temperature [4][5][6][7][8][9][10][11][12][13]. Previous studies [4][5][6][7][8][9][10][11][12][13] have revealed that the Sc-O/W(1 0 0) surface has two phases with surface atomic arrangements of the (1 Â 1) and (2 Â 1)-(1 Â 2) structures at high temperature.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Kinetics of surface atoms during phase transition of Sc–O/W(100) system at high temperature studied by Auger electron spectroscopy

Nakanishi¹,

Nagatomi²,

Takai³

2008

Surface Science

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Kinetics of surface atoms during phase transition of Sc–O/W(100) system at high temperature studied by Auger electron spectroscopy

Nakanishi¹,

Nagatomi²,

Takai³

2008

Surface Science

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“…There have been numerous attempts to describe the physics behind the enhanced emission of scandate cathode systems. These theories include the formation of Sc-O dipole layers on the W surface which lower the work function, 19,20 a semiconductor model whereby an applied potential lowers the emission barrier near the Sc 2 O 3 surface, 21 and Ba-Sc-O surface complexes that also act to reduce the work function. [22][23][24] Although numerous theories currently exist, it is important to note that an unequivocal fundamental physical understanding of enhanced emission from Sc 2 O 3 is still missing.…”

Section: Introductionmentioning

confidence: 99%

Intrinsic defects and conduction characteristics of Sc2O3in thermionic cathode systems

2012

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Recent experimental observations indicate that bulk Sc 2 O 3 (~200 nm thick), an insulator at room temperature and pressure, must act as a good electronic conductor during thermionic cathode operation, leading to the observed high emitted current densities and overall superior emission properties over conventional thermionic emitters which do not contain Sc 2 O 3 . Here, we employ ab initio methods using both semilocal and hybrid functionals to calculate the intrinsic defect energetics of Sc and O vacancies and interstitials and their effects on the electronic properties of Sc 2 O 3 in an effort to explain the good conduction of Sc 2 O 3 observed in experiment. The defect energetics were used in an equilibrium defect model to calculate the concentrations of defects and their compensating electron and hole concentrations at equilibrium. Overall, our results indicate that the conductivity of Sc 2 O 3 solely due to the presence of intrinsic defects in the cathode operating environment is unlikely to be high enough to maintain the magnitude of emitted current densities obtained from experiment, and that presence of impurities are necessary to raise the conductivity of Sc 2 O 3 to a high enough value to explain the current densities observed in experiment. The necessary minimum impurity concentration to impart sufficient electronic conduction is very small (approximately 7.5x10 -3 ppm) and is probably present in all experiments.

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“…The surface structure is still close to the p 2 ð 1 -p 1 ð 2 structure. In contrast to the change in the surface composition and atomic arrangement upon heating at ¾1600 K, it has been confirmed already that the properties of the Sc-O/W(100) surface prepared at ¾1500 K (step (iv)) are very stable against further heating at ¾1500 K. 10,12 These results revealed that the surface properties of the Sc-O/W(100) system are significantly different between those prepared by heating at ¾1500 and at ¾1600 K. Note that the heating treatment at ¾1600 K following step (v) revealed that the p-p intensities of the AES spectra and the LEED pattern show no significant changes with further heating at ¾1600 K for ¾60 min.…”

Section: Resultsmentioning

confidence: 91%

Self‐recovery function of p(1×1)‐Sc‐O/W(100) system used as Schottky emitter

Iida

Nagatomi

Takai

2005

Surface & Interface Analysis

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The effects of heating temperature for the preparation of an Sc-O/W(100) surface were investigated. Surface properties of the Sc-O/W(100) surface prepared by heating at ∼1600 and ∼1700 K were significantly different from those prepared at ∼1500 K, which is the operating temperature of the Sc-O/W(100) emitter. By heating at ∼1700 K the p(1×1) structure formed by Sc-O complexes was confirmed, whereas the p(2×1)-p(1×2) double-domain structure was obtained by heating at ∼1500 K. The surface properties prepared by heating at ∼1700 K were found to be very stable, and the surface has a self-recovery function against residual gas ion sputtering at the operating temperature of the emitter. The present results strongly suggested that pretreatment of the Sc-O/W(100) emitter by heating at ∼1700 K and device operation at ∼1500 K result in high reproducibility of the superior electron emission property of the Sc-O/W(100) emitter.

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Surface atoms in Sc–O/W(100) system as Schottky emitter at high temperature

Cited by 15 publications

References 18 publications

Kinetics of surface atoms during phase transition of Sc–O/W(100) system at high temperature studied by Auger electron spectroscopy

Kinetics of surface atoms during phase transition of Sc–O/W(100) system at high temperature studied by Auger electron spectroscopy

Intrinsic defects and conduction characteristics of Sc2O3in thermionic cathode systems

Self‐recovery function of p(1×1)‐Sc‐O/W(100) system used as Schottky emitter

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