Lattices of Ir clusters have been grown by vapor phase deposition on graphene moirés on Ir(111). The clusters are highly ordered, spatially and thermally stable below 500 K. Their narrow size distribution is tunable from 4 to about 130 atoms. A model for cluster binding to the graphene is presented based on scanning tunneling microscopy and density functional theory. The proposed binding mechanism suggests that similar cluster lattices might be grown of materials other than Ir.PACS numbers: 68.65. Cd, 81.16.Dn, 36.40.Sx, 61.46.Bc Fabrication of regular arrays of equally sized (monodisperse) clusters on a flat substrate is a central goal for nanotechnology. Owing to their smallness, clusters differ from bulk materials in their chemical and physical properties (cf. [1]). Because these properties depend strongly on size, monodisperse cluster arrays are optimal for fundamental research and applications. Regular arrays of supported clusters are preferable to random ones, because the identical environment of each cluster (e.g. distances from their neighbors) produces a uniform response to external stimulation. Thus, in a regular array, one can use each cluster in the same way, either independently (e.g. for magnetic data storage), or by taking advantage of the coherent collective response of the array as a whole (e.g. in catalysis or for electrical transport). Recent experiments on two-dimensional regular arrays of clusters with a narrow size distribution have explored the sizedependent catalytic activity of Au-clusters [2], the magnetic properties of Co-clusters [3] and electrical transport through PbSe-clusters [4], amply demonstrating the usefulness of this approach.One route to cluster array fabrication is to deposit atoms or molecules from the vapor phase onto a "template," e.g., a substrate characterized by a periodic array of cluster nucleation sites, to which deposited particles can diffuse. Examples are large unit cell superstructures of oxide films on metal single crystals [5] or regularly spaced steps and surface reconstructions [3]. Here we demonstrate that graphene moirés on an underlying dense-packed metal lattice act as templates for exceptionally well ordered cluster lattices with remarkable properties.Experiments were performed in an ultra high vacuum, variable temperature scanning tunneling microscopy (STM) apparatus with a base pressure in the 10 −11 mbar range. Sample cleaning was accomplished by cycles of flash annealing to 1500 K and sputtering by a mass separated 1.5 keV Xe + ion beam at 1100 K. Ethylene (5 L) adsorbed at room temperature was thermally decomposed at 1450 K resulting in the formation of large graphene flakes with sizes around 1000Å covering about 30% of the sample surface (compare [6]). By continuous expo- sure of the hot surface to ethylene, samples fully covered by graphene were also prepared. Ir was subsequently evaporated from a current heated Ir-wire, with a standard deposition rate of 3.0 × 10 −3 ML/s, where 1 ML is the areal atomic density of the Ir(111) surface. Precis...

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