What is the true shape of the cluster for a given shape of the tip

Fabrication of nano-sized metallic clusters on the surfaces and the study of their catalytic properties are a hot topic in electrocatalysis, for both tailoring new catalysts and understanding the interplay between the structure and catalytic activity (including possible mesoscopic effects) in the existing catalysts. From the dreams about the „invisible" we may thus come back to earth, and ask ourselves whether the images of these clusters represent the reality. The question is motivated by often-met differences in the shapes of the clusters prescribed by STM and by transmission electron microscopy (TEM), by miraculous double clusters, etc.

A mathematical routine has been developed which relates the true shapes of the nano-sharp tip and the nano-scaled cluster and the image of the latter [17], In many cases the shape of the tip is poorly known. Thus, the solution of the inverse problem [17] suggests how to restore the shape of the tip from the image of the spherical cluster of a given radius, or by averaging images of different clusters distributed along the surface and having typical radius and a given dispersion. Such samples, calibrated by TEM, could be a tool to calibrate the tip.

Acknowledgments. The authors are thankful to U.Stimming and R.Vogel for useful discussions. The support given to M.S. by the Alexander von Humboldt Stifitung is gratefully acknowledged.

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