Thermal electron emission from saline hydrides deposited on a metal surface

• Published in: Applied surface science 1999-05, Vol.146 (1), p.101-104
• Main Authors: Kawano, H, Serizawa, N, Tanaka, A, Zhu, Y
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron and ion emission by liquids and solids; impact phenomena; Exact sciences and technology; Metals. Metallurgy; Oxygen adsorption; Physics; Saline hydride; Thermal decomposition; Thermal electron emission; Thermionic emission; Work function
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/S0169-4332(99)00042-2

To study the thermionic property of saline hydride (NaH, LiH, CaH 2 or SrH 2), its powder (∼3 mg) was deposited in the central part (∼0.03 cm 2) of a boat-type molybdenum ribbon, and the thermal electron current (∼10 −9–10 −3 A) from each hydride was measured as a function of sample temperature (∼600–900 K), elapsed time (0–10 h), or pressure (∼10 −6–10 −4 Torr) of H 2 or O 2 introduced at a residual gas pressure of ∼10 −7 Torr, thereby yielding the following results. (1) Thermal decomposition such as LiH (solid)→Li (solid)+H 2 (gas)/2 created those active spots (mainly composed of Li) with low work function ( φ). (2) After activation above ∼700 K for several hours, φ's of LiH, CaH 2, and SrH 2 were 3.1, 5.0, and 7.3 eV, respectively. (3) The active spots were destroyed by introduced H 2 or O 2 according to the deactivation reaction such as Ca+H 2→CaH 2 or Ca+O 2/2→CaO, thereby increasing φ by up to ∼0.5 eV. (4) NaH was thermally so unstable that φ could not be determined. (5) CaH 2 was most stable in current and longest in durability, safely recommended to be the best thermal electron source material among the hydrides.