Effect of caesium adsorption on the emission properties of (110) and (100) molybdenum surfaces

DOI: 10.62564/M4-SS2353

Sviatoslav Smolnik¹, Mykola Shevchenko¹, Iryna Galstian¹, Yevheniy Tsapko¹, Evgen Len<sup>1,2

1</sup>G. V. Kurdyumov Institute For Metal Physics, N.A.S. Of Ukraine
²Kyiv Academic University, M.E.S. and N.A.S. Of Ukraine


Improving the emission properties of refractory metals electrodes of thermionic converters (TECs) and emission electronics devices is a challenging but important task [1]. Optimization of the electron work function (φ) for the electrodes’ surfaces and the back current from the anode to the cathode, i.e., the reduction of the electron reflection coefficient (K) from anode, in particular due to the presence of adsorbates (in our case, caesium) on its surface, is one of the main aspects of this task’s solution. To understand the emission properties formation in refractory metals, it is important to obtain their atomically clean surfaces and to study these properties on them. In the present work, the influence of caesium adsorption on the work function of atomically clean surfaces (110) and (100) of Mo single crystal obtained by high-temperature annealing and on the reflection of electrons from them is considered. To control the state of the surface and measure φ the methods of total current spectroscopy I(U) and contact difference of potentials, correspondingly, are used. Dependences of coefficient K on adsorbed caesium concentration (n) were determined from the experimental current-voltage characteristics (CVC) in the region of the first maximum, which corresponds to slow electrons with energies of 1-2 eV. It is shown that the electron reflection coefficient from the anode takes the largest value (0.42) for a pure (Cs-free) Mo (110) face, and for a similar Mo (100) face it acquires the smallest value (0.05). Formation of Cs monolayer on both investigated surfaces (at n ≥ 6.2·1014 at/cm2) leads to the levelling of the difference between different faces and to attainment of saturation for K (~0.21).

Keywords
refractory metals, emission properties, molybdenum single crystal, adsorption of caesium, work function

Acknowledgments
This work was supported by the project No. 0123U102275 of the National Academy of Sciences of Ukraine.

References
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