Clusters supported by solid substrates are prime candidates
for
heterogeneous catalysis and can be prepared in various ways. While
mass-selected soft-landing methods are often used for the generation
of monodisperse particles, self-assembly typically leads to a range
of different cluster sizes. Here we show by scanning tunneling microscopy
measurements that in the initial stages of growth, Mn forms trimers
on a close-packed hexagonal Ir surface, providing a route for self-organized
monodisperse cluster formation on an isotropic metallic surface. For
an increasing amount of Mn, first a phase with reconstructed monolayer
islands is formed, until at full coverage a pseudomorphic Mn phase
evolves, which is the most densely packed one of the three different
observed Mn phases on Ir(111). The magnetic state of both the reconstructed
islands and the pseudomorphic film is found to be the prototypical
antiferromagnetic Néel state with a 120° spin rotation
between all nearest neighbors in the hexagonal layer.