Atomic Structures of Pt Nanoclusters Supported on Graphene Grown on Pt(111)

Atomic structures of Pt nanoclusters on graphene/Pt(111) were investigated with various techniques to probe the surface under ultrahigh-vacuum conditions and with calculations based on density-functional theory. Monolayer graphene was grown on thermal decomposition of ethylene on Pt(111) at 950 K and Pt clusters on the deposition of Pt vapor onto graphene/Pt(111) at 300 K. The graphene had two predominant domains: one had a small angle of rotation between the graphene and the underlying Pt lattice, structurally commensurate with the Pt(111) lattice (G_0°), and the other was rotated about 30° with respect to the Pt lattice (G_30°). G_0° had a slightly corrugated structure, involving tetrahedral hybridization, and a stronger adsorption on Pt(111); in contrast, G_30° was flat and weakly bound to Pt(111) via a van der Waals interaction. The grown Pt clusters were structurally ordered, having a face-centered cubic phase and growing in a (111) orientation, whereas they had correspondingly disparate nucleation modes and rotational configurations on the two major graphene domains. On G_0°, the clusters were smaller and had a narrow size distribution and greater cluster density; they were structurally commensurate with the G_0° lattice (with their [-110] (or [0-11]) axes along direction [1-100] of G_0°). In contrast, on G_30°, the clusters were larger and had an evidently broader size distribution and smaller cluster density; they preferred to rotate by 30° relative to the underlying G_30° lattice. The former is attributed to a strong Pt-G_0° interaction, whereas the latter is only partly attributed to a weak Pt-G_30° interaction; the preferential rotation of Pt clusters on G_30° is governed not only by the graphene lattice, but largely by an indirect interaction between the Pt substrate and the clusters, likely through the charge transferred from the Pt substrate to graphene.