Experimental determination of the energy difference between competing isomers of deposited, size-selected gold nanoclusters
The structure and dynamics of nano-systems are controlled by the multi-dimensional potential energy surface (PES), which describes its free energy as a function of configuration. There have been considerable theoretical efforts to determine the ground-state structures and energy differences between competing isomers of nanosytems in general and of nano clusters in particular. Gold clusters have received much theoretical attention due to the role of structure in the catalytic performance. What is needed now is an experimental handle on key parameters of the PES. Understanding the energy difference between structural isomers is important not only for the design of well-defined materials but also for understanding how these materials will work in situ. For example, if a particular structural isomer is unstable, exposure to high temperatures is likely to drive it towards the ground state (i.e. annealing), altering (for better or worse) the characteristics of the system. Such behavior is likely to be relevant to the applications of nanoparticles, which include catalysis, drug delivery and chemical sensing.
The authors have obtained the energy difference between the most abundant structural isomers of magic number Au561 clusters, the decahedron and face-centred-cubic (fcc) structures, from the equilibrium proportions of the isomers. These are measured by atomic-resolution scanning transmission electron microscopy, with an ultra-stable heating stage, as a function of temperature (125–500 °C). The publication shows clearly the benefits of DENSsolutions heating technology which provides not only ultra high mechanical and thermal stability but also across temperature control across the entire temperature range.