Change in work function during phase transition of Sc–O/W(1 0 0) system at high temperatures

Abstract

The change in work function during the phase transition of a Sc–O/W(1 0 0) system at high temperatures of 1500–1700 K was investigated in order to elucidate the mechanism of the decrease in the work function of a (1 × 1)-Sc–O/W(1 0 0) surface. For the measurement of the work function using a secondary electron method at high temperatures, a sample holder was uniquely designed in order to suppress contributions of a large number of thermionic electrons emitted from a low-work-function surface. The obtained work function revealed that the change in work function strongly correlates with the coverage of Sc–O complexes, the stoichiometry of which is Sc 1O 1. The higher the coverage of ScO is, the lower the work function is, suggesting that the work function of the (1 × 1)-Sc–O/W(1 0 0) surface is reduced by the formation of ScO electric dipoles. Furthermore, the decrease in work function was modeled in combination with a previously reported kinetic model describing surface phenomena, i.e., the oxidation, oxygen desorption, diffusion and surface segregation of Sc–O complexes, during the phase transition of the Sc–O/W(1 0 0) surface at high temperatures. It was confirmed that the proposed model can explain the experimentally obtained change in work function very well. The value of the dipole moment of a ScO electric dipole was determined to be 2.7 × 10 −30 C m.