The transport of H adatoms across oxide supports plays an important role in many catalytic reactions. We investigate the dynamics of H/Fe3O4(001) between 295 and 382 K. By scanning tunneling microscopy at frame rates of up to 19.6 fps, we observe the thermally activated switching of H between two O atoms on neighboring Fe rows. This switching rate changes in proximity to a defect, explained by density functional theory as a distortion in the Fe-O lattice shortening the diffusion path. Quantitative analysis yields an apparent activation barrier of .9 ± . eV on a pristine surface. The present work highlights the importance of local techniques in the study of atomic-scale dynamics at defective surfaces such as oxide supports.

Magnetite surface defect dynamics followed by fast scanning tunneling microscopy and surface X-ray diffraction.

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 supportwhich both are dependent on cluster sizecan 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.

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