Ligand-stabilized Au 55 clusters have been observed by scanning probe microscopy upon thermal decomposition on top of graphite and mica substrates. On highly oriented pyrolitic graphite as well as on mica the ligand shell exhibits a thermal decomposition at a temperature of about 390 K. This temperature well matches data obtained on cluster solutions and pallets. The ligand decomposition results under ultrahigh vacuum conditions in the formation of naked Au clusters. The in situ needle sensor studies show that, due to the high cluster mobility at elevated temperatures, bigger spherical Au aggregates are formed on the graphite substrate. In contrast, on the mica substrate, the naked Au clusters aggregate to form small uniform islands that are stable up to temperatures of more than 700 K. Bigger Au aggregates could only be formed upon pushing the clusters by the microscope's probe at elevated temperatures. The significant difference in the cluster decomposition and aggregation processes on graphite and mica is attributed to the influence of a strong cluster-substrate interaction, which is solely present for mica.
Amorphous C-Ni superlattice films designed as normal-incidence reflector for 5 nm have been grown on quartz substrates by magnetron sputter deposition in Ar discharge. An extended set of characterization techniques has been applied: Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM) in order to characterize the growth conditions. ThM measurements revealed information about the evolution of smoothness and the uniformity of the multilayer structure function of the distance to the substrate. A new DSP-controlled AFM system has been involved in investigating the surface topography of the final surface of the multilayer structure as well as the substrate. A detailed analysis of AFM topographic images is presented. Special attention has been paid to an important parameter for such niirrors, the surface roughness, for nanometric and micrometric areas, involving AFM tips with different radius of curvatute. Roughness analysis as well as the implication of the different radius curvature tips used in AFM-contact experiments are presented together with the power spectral density function calculation.
Thin films of ligand-stabilized Au55 clusters deposited on Au (111)-oriented thin films have been investigated by noncontact atomic force microscopy and spectroscopy. The properties of the clusters with a diameter of about 2nm have been investigated by force spectroscopy performed above individual clusters. The interaction force and dissipated energy were deduced from the obtained data. The conservative component of the interaction between tip and individual Au55 cluster is given by an interplay between the interactions of the tip apex with the ligand shell and with the gold core. In contrast, only the ligand shell contributes to the dissipative interaction.
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