Noble and alkali adatoms on a –Ag surface: a first-principles study

Abstract

Using first-principles calculations, we present a comprehensive study on the atomicand electronic structures of metal adatoms (noble metals Ag, Au, Cu and alkalimetals Li, Na, K) adsorbed on a –Ag (hereafter -Ag) surface. We found that adsorption of noble and alkali adatoms can inducesignificant structural changes in the topmost Ag layer. The most striking andinteresting results are the immersion of the noble and Li adatoms into the substrateAg layer and the finding of the most stable configurations with three adatomsincorporating into or being adsorbed on the surface dependent on their atomic radii.We also found that the almost empty two-dimensional free-electron-like bands1 and its band foldings1* of the originalsurface band s1 of the -Ag surface split into a gap at the surface Brillouin zone (SBZ) boundary withadsorption of an adatom. The two surface bands gradually move downwards and thes1 band is gradually filled with an increase of coverage. Thes1 band is fully occupied with the largest band gap ∼ 0.25 eV betweenthe s1 and s1* bands at the critical coverage of 0.14 monolayers (ML) [three adatoms in a –Ag (hereafter -Ag) unit cell], which corresponds to the most stable adsorption phase. Although theadsorption configurations are different, both the noble and alkali adatom adsorptions giverise to similar electronic structures at low coverages, indicating a free-electron-likecharacter of the adsorption surfaces.