Hybrid atomic structure of the Schmid cluster Au-55(PPh3)(12)Cl-6 resolved by aberration-corrected STEM

We have investigated the atomic structure of the Au-55(PPh3)(12)Cl-6 Schmid cluster by using aberration-corrected scanning transmission electron microscopy (STEM) combined with multislice simulation of STEM images. Atom counting was employed, with size-selected clusters as mass standards, to fractionate the correct cluster size in the image analysis. Systematic structure analysis shows that a hybrid structure, predicted by density functional theory, best matches nearly half the clusters observed. Most other clusters are amorphous. We believe our conclusions are consistent with all the previous, apparently contradictory structural studies of the Schmid cluster.