  Metal clusters are partway between molecular and bulk systems and thus
exhibit special physical and chemical properties. Atoms can rearrange within a
cluster to form different structural isomers. Internal degrees of freedom and
the interaction with the support - which both are dependent on cluster size -
can promote diffusion across a support. Here, we show how fast scanning
tunneling microscopy (FastSTM) can be used to investigate such dynamical
behavior of individual clusters on the example of Pdn (1<=n<=19) on a hexagonal
boron nitride nanomesh on Rh(111), in particular pertaining to minority species
and rare events. By tuning the cluster size and varying the temperature to
match the dynamics to the FastSTM frame rate, we followed steady state
diffusion of clusters and atoms inside the nanomesh pore and reversible cluster
isomerization in situ. While atoms diffuse along the rim of a pore, a small
cluster experiences a corrugation in the potential energy landscape and jumps
between six sites around the center of the pore. The atom and cluster diffusion
between pores is strongly influenced by defects.
