Work Function of Oxide
Ultrathin Films on the Ag(100)
Surface
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Abstract
Theoretical calculations of the work function of monolayer
(ML)
and bilayer (BL) oxide films on the Ag(100) surface are reported and
analyzed as a function of the nature of the oxide for first-row transition
metals. The contributions due to charge compression, charge transfer
and rumpling are singled out. It is found that the presence of empty
d-orbitals in the oxide metal can entail a charge flow from the Ag(100)
surface to the oxide film which counteracts the decrease in the work
function due to charge compression. This flow can also depend on the
thickness of the film and be reduced in passing from ML to BL systems.
A regular trend is observed along first-row transition metals, exhibiting
a maximum for CuO, in which the charge flow to the oxide is so strong
as to reverse the direction of rumpling. A simple protocol to estimate
separately the contribution due to charge compression is discussed,
and the difference between the work function of the bare metal surface
and a Pauling-like electronegativity of the free oxide slabs is used
as a descriptor quantity to predict the direction of charge transfer