Coverage-Dependent Adsorption of X Clusters (X=Pt-Au, Au-Au) on the Defect-Free (3×2) TiO<sub>2</sub>(110) Surface

Abstract

Based on spin-polarized density functional theory and generalized gradient approximation(DFT-GGA) calculations,the coverage-dependent adsorption of X bimetallic clusters(X=Pt-Au,Au-Au) on the(3 × 2) TiO2(110) surface has been investigated utilizing periodic supercell models in the absence of oxygen vacancy sites.Only the ground-state structures corresponding to the given coverage patterns(θ= 1/6-1 ML) for X clusters are discussed in this work.The unambiguous results reveal that the adsorption energies increase with coverage up to 1/2 ML and then decrease except for when saturated coverage is reached.According to the interaction with X clusters,it is more feasible at all coverage levels to create a monolayer film of Pt-Au bimetallic clusters on the TiO2(110) surface than it is to create a monolayer of AuAu clusters,even though the adsorption energy of the Pt-Au/TiO2 adsorption system is smaller in comparison with that of the Au-Au/TiO2 system.Importantly,especially for the half and saturated coverages,there is a broadening of X peaks overlapping with the TiO2 state ranging from-3.0 eV to the Fermi level,suggesting a strong interaction between the surface and bimetallic cluster.Also of particular interest is the adsorptive mechanism where the X-TiO2 interaction is the main driving force at the initial stage of the adsorption process,whereas the X-X interaction controls the process as the coverage increases.