A Microscopy Approach to Investigating the Energetics of Small Supported Metal Clusters

TL;DR

This study uses fast scanning tunneling microscopy to observe the real-time diffusion and isomerization of small metal clusters on a support, revealing how size, temperature, and defects influence their energetics and dynamics.

Contribution

It introduces a microscopy method to directly monitor the dynamical behavior of individual metal clusters and their isomerization on a support surface.

Findings

Clusters diffuse within nanomesh pores and jump between sites.

Atom and cluster diffusion are affected by defects.

Reversible isomerization occurs in situ.

Abstract

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.