Template controlled growth

The fabrication of such a system can be accomplished only by nanofabrication, and different routes can be imagined in this context. We will focus in the following section on the template-controlled growth of metal clusters on thin oxide films, which has proven to give excellent results in terms of low complexity. This approach has been successfully employed for metal-on-metal systems (for a comprehensive review see [6]) and has recently been extended to metal growth on oxide films. 

A more detailed picture of the temperature dependence of the growth is given in Figure 2.4, where the island density is plotted as a function of temperature. It can be seen that only in the temperature range from 207 to 288 K the growth is perfectly template controlled and the number of islands matches the number of available nucleation sites. This illustrates the importance of kinetic control for the creation of ordered model catalysts by a template-controlled process. Obviously, there has to be a subtle balance between the adatom mobility on the surface and the density of template sites (traps) to allow a template-controlled growth. We will show more examples of this phenomenon below. 

That not only an increased interaction energy at the traps can be responsible for a template-controlled growth but also an anisotropy of the surface diffusion... 

Before we discuss the template-controlled growth of model catalysts in more detail, we will have to consider a few aspects of STM imaging of these systems. This will be crucial for the characterization of the model catalyst surfaces. 

Finally, we should address the question of the influence of substrate temperature - thus kinetics - on the template-controlled growth on surfaces. It is quite obvious from the example of the particles in a box (Fig. 1) that temperature strongly influences the structures formed. On the one hand it has to be low enough to allow for the adsorption of the building blocks on the surface (Fig. lb), on the other hand it has to be high enough to provide a sufficient mobility of the entities on the surface in order to avoid a mere hit-and-stick (random) adsorption (Fig. Ic). In that sense the structures formed on surfaces by a template-controlled process will be subject to strong kinetic effects and temperature control will be an important factor (see Sects. 3 and 4). 

Table 1 Overview of template-controlled growth on metallic substrates ...

Furthermore, the moir pattern found for FeO thin films on Pt(l 11) has been used as a template for the growth of nanopatterned Fe layers [198]. This effect is believed to be due to the strain relief in the oxide layer resulting in domains with fee and hep stacking. Thus, the same mechanism as found for similarly reconstructed metal surfaces should be responsible for the template-controlled growth on metal film templates. Table 2 summarizes the results obtained for the template-controlled growth on the surfaces discussed in Sect. 4. 

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