Cluster-substrate interactions

Graphite was tised as substrate for the deposition of carbon vapor. Prior to the tube and cone studies, this substrate was studied by us carefully by STM because it may exhibit anomalotis behavior w ith unusual periodic surface structures[9,10]. In particular, the cluster-substrate interaction w as investigated IJ. At low submonolayer coverages, small clusters and islands are observed. These tend to have linear struc-tures[12j. Much higher coverages are required for the synthesis of nanotubes and nanocones. In addition, the carbon vapor has to be very hot, typically >3000°C. We note that the production of nanotubes by arc discharge occurs also at an intense heat (of the plasma in the arc) of >3000°C. 

D.Q. Yang, E. Sacher, Initial- and final-state effects on metal cluster/substrate interactions, as determined by XPS copper clusters on Dow Cyclotene and highly oriented pyrolytic gr hite. AppL Surf. Sci. 195(1-4), 187-195 (2002)... 

Reaction scheme 2 is proposed based on experimental results coming from the application of different experimental methods.The energy data was obtained by consideration of the total energy of each gas-phase species and also from each adsorbate interacting with a Cu22(14,8) cluster substrate used to model the perfect Cu(lll) surface. The geometric parameters of the transition state structures were taken from published data while details for the other structures considered, as well as the... 

In general, the good quality of the substrate is essential to analyze in detail the properties of the supported nanoclusters. In fact, as we will discuss below, the cluster-oxide interaction is such to influence the shape and the electronic structure of the deposited cluster. A deep understanding of the cluster properties needs therefore a similarly profound knowledge of the interface bonding. Furthermore, a precise knowledge of the surface structure is essential to design realistic theoretical models. 

Although the structure of the PTCDA/Ag(l 11) interface is dominated by the molecule-substrate interaction (cf. the commensurate interface structure), the interaction between molecules does play an important role for the structural details and the energetics at the interface. On the one hand, there is the attractive electrostatic interaction between molecules. Because of this interaction PTCDA molecules always cluster in two-dimensional islands. However, at surface temperatures below 150 K, these islands do not yet exhibit the familiar herringbone structure [35] since the electrostatic interaction does not exhibit sufficient directional specificity, a considerable degree of structural disorder prevails, in spite of a clear propensity of the molecules to arrange in a T-like... 

Figure 17-9 One possible model for substrate interactions with the dinuclear metal cluster. In this model, substrate binds to the Fe site, positioning the phosphate ester for in-line nucleophilic attack by a hydroxide ion coordinated to the Fe + ion.

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