Deposition of small Cu, Ag and Au particles on reduced SiO2

In this work, the adsorption of Mn (M: Cu, Ag, Au; n=1-3) particles on the ≡Si-O· defect of a SiO2 surface is studied in the framework of density functional theory. A charge transfer from the metal particle to the support is observed following the sequence: Cu≈Ag>Au. This is in agreement with the greater ionization potential of the latter metal. The M1-Mn−1OSi≡ and Mn-OSi≡ interactions of nucleation and adhesion processes, respectively, were analyzed from an energetic point of view. The strongest interaction is obtained always between two open-shell systems. When the comparison is performed among the metals, the bond strength of the M-M interaction follows the order: Cu≈Au>Ag. The deep position of Ag d-levels in the energy scale could explain the relatively weak Ag-Ag interaction. If the M-oxide interaction is considered, this order in the bond strength was observed: Cu>Ag>Au. The strong adhesion for Cu could be ascribed to the greater charge transfer to the support and to a strong Cu(d)-O(p) interaction. On the other hand, for Au the charge transfer to the support is relatively small, while for Ag the Ag(d)-O(p) interaction is relatively weak due to the more localized Ag(d) band.