Adsorption of small Au clusters on MgO and MgO/Mo: the role of oxygen vacancies and the Mo-support

We report a systematic density functional theory investigation of adsorption of small Au n ( n =1–6) clusters on ideal and defected MgO(100) single crystal surfaces and Mo(100) supported thin MgO(100) films. As a model defect, we consider a neutral surface oxygen vacancy ( F s ). Optimal adsorption geometries and energies, cluster formation energies and cluster charges are discussed and compared in detail over four different substrates. For a given cluster size, the adsorption energy among these substrates increases in the order MgO, F s /MgO, MgO/Mo and F s /MgO/Mo. While cluster growth by association of atoms from gas phase is exothermic on all the substrates, cluster growth by diffusion and aggregation of pre-adsorbed Au atoms is an endothermic process for Au 1 →Au 2 , Au 3 →Au 4 and Au 5 →Au 6 on MgO/Mo and Au 2 →Au 3 and Au 5 →Au 6 on F s /MgO/Mo. The adsorbed clusters are close to neutral on MgO, but adopt a significant anionic charge on other supports with the increasing order: MgO/Mo, F s /MgO and F s /MgO/Mo. The adsorption strength thus correlates with the amount of negative charge transferred from the substrate to gold.