| Using density-functional theory within the generalized gradient approximation we investigated atomic and electronic structures of noble and alkali metal adatoms adsorption on (?)-Ag surface. Our results show that the adsorption behaviors of the metal adatoms are closely related to their atomic size. For single adatom such as Ag Au, Cu or Li with small atomic radius they can immerse into the substrate Ag layer, while Na or K with large atomic radius adsorbs on the surface. Both noble and alkali adatoms adsorption, irrespective incorporation into or on the surface, may induce the atomic structure changes of the substrate Ag layer significantly and reduce the average Ag-Ag distance. The most stable configures of the adsorption systems are three noble or alkali adatoms in the unit cell. The three adatoms may incorporate into the LT or ST sites dependent on their atomic radii. For the electronic properties, we find that the almost empty two-dimensional free-electron-like band s1 and its band folding s1* of the original surface band s1 of the (?)-Ag split into two bands with a gap opening at the surface Brillouin zone (SBZ) boundary with an adatom adsorption. The two surface bands are gradually moved downwards and the bonding surface state s1 is gradually filled with an increase of coverage. The s1 band is fully occupied with the largest band gap～0.25 eV between the s1 and s1* bands at the critical coverage 0.14 ML (three adatoms in the (?)-Ag unit cell), which corresponds to the most stable adsorption phase. Though the adsorption configurations are different, both the noble and alkali adatom adsorptions give rise to similar electronic structures at low coverages, indicating a free-electron-like character of the adsorption surfaces.
|
PDF Full Text Request