Junjin Jeon

Ab-initio study of interactions of gold atoms with hydroxylated MgO(001) surfaces

By employing ab-initio electronic structure calculations based on the density functional theory, we investigated the adsorption, diffusion, bonding, and electronic properties associated with the enhanced bonding of Au on hydroxylated MgO(001) surfaces. The calculations in this study show that the binding of Au on hydroxylated MgO(001) is substantially enhanced by an ionic-like interaction as compared to the case of Au on regular MgO(001). Indeed, the adsorption of Au on hydroxylated MgO surfaces is stronger than that of Au and OH on MgO(001). AuOH complexes are formed on MgO(001) surfaces via the fast surface diffusion of OH and Au. It is found that the AuOH structure is very stable against not only dissociation (i.e., it is very difficult for it to decompose back into OH and Au) but also surface diffusion (i.e., it has low surface mobility). More detailed electronic structure analysis of the charge distribution of AuOH on MgO(001) reveals that the enhanced ionic-like bonding is achieved via the polarizat...

Adsorption and Surface Diffusion of Pt Atoms on Hydroxylated MgO(001) Surfaces

Density-functional theory calculations have been used to investigate adsorption and surface dynamics of Pt atoms on MgO(001) surfaces with surface-functional hydroxyl groups. Our calculation results show that the adsorption of Pt on hydroxylated MgO(001) is considerably enhanced by interactions among Pt, OH, and MgO surface atoms. We also find that the formation of PtOH complexes instead of Pt dimers is clearly favorable. This behavior is very similar to that of Au deposition on hydroxylated MgO(001). With regard to the surface kinetics, however, the behavior is quite different. Indeed, after the formation of PtOH on MgO(001), the surface diffusion of PtOH is found to be enhanced, as compared to that of Pt on MgO(001). This behavior is in sharp contrast with the low surface mobility previously observed for AuOH on MgO(001). Finally, the reason for this difference is discussed, based on the calculated electronic structures and charge states of Pt on hydroxylated MgO(001).

Adsorption and Surface Diffusion of Au Monomers and Dimers on Strongly Correlated NiO(001) Surfaces

The adsorption and diffusion of Au monomers and dimers on strongly correlated antiferromagnetic NiO(001) were examined by density functional theory combined with the on-site Coulomb repulsion U. The preferential adsorption sites for the monomers and dimers were found to be near the surface O atoms. For surface diffusion of the Au monomer, the spin-dependent, anisotropic, and very fast diffusion was observed. In the case of dimer diffusion, isotropic hopping diffusion was observed as the lowest-energy diffusion mechanism, and the diffusion barrier was lower than the diffusion barrier of the Au dimer on MgO(001). This suggests that the Au dimer, the stable and smallest cluster, diffuses more easily on NiO(001) rather than on MgO(001). These findings provide important information for the sintering of Au clusters on NiO(001), which is essential for optimizing a catalytic process.