STM INVESTIGATIONS ON COMPACT AU55 CLUSTER PELLETS

We have investigated the topography and the local electronic structure of compact Au55 cluster pellets by scanning tunnelling microscopy (STM) at room temperature. Surface topography and differential conductivity (partial derivative I/partial derivative V) were measured simultaneously. Additionally, I(V) curves were taken at particular locations on the surface. The topographies generally show largely ideally arranged individual clusters, while also a few agglomerates of several clusters could be observed. The surfaces exhibit a nearly homogeneous differential conductivity, whereby some clusters produce a striking ''overshoot''. I(V) curves for various probe-sample separations show a strong dependence on the tunnelling impedance and are highly non-linear for large probe-sample separations.