Direct observation of dynamic events of Au clusters on MgO(100) by HAADF-STEM

摘要

Direct atomic imaging of ultrasmall nanoclusters in three-dimension is challenging, not only because of the low signal to noise ratio, but also of the cluster-probe interaction that is often uncharacterized. Here, we report a study of Au nanoclusters (～3 nm) supported on MgO(100) surface using aberration-corrected scanning transmission electron microscopy. By applying the model-based method on successively acquired images, the number of atoms in the projected atomic columns of a cluster was analyzed, allowing for the reconstruction of its 3D structures. It is found that the total number of atoms within the cluster fluctuated under the intense electron beam and the cluster became strongly elongated along the e-beam illumination direction. This study highlights the importance of atom counting with single atom sensitivity. The reported approach is particularly useful in dealing with practical difficulties associated with the characterization of ultrasmall clusters.