Catalytic growth models

However, it is unclear what the growth mechanisms are because no Si feedstock was fed in the gas form, which is required for the tip-growth model to work. In the following, we will discuss the composition and growth mechanisms of the nanowires made in this work, and show that the Co nanoparticles may play a dual-catalytic role by helping form gaseous silicon species and catalyze the growth of Si-based nanowires. 

A schematic of the proposed growth model is shown in Fig. 10.23. In this model, Co nanoparticles play a dual catalytic role. On the one hand, they catalyze silane formation by reacting first with silicon to form Co silicides, and then react with hydrogen to form silane while being reduced to Co metal. The second role of Co nanoparticles is their classic catalytic ability of making nanowires by first dissolving the silane and precipitating out Si nanowires. 

Fig. 10.2.13 Growth model of SWNTs based on the root growth" on the surface of a catalytic particle.

Two proposals have been made for the mechanism of oxidation of apoferritin-bound Fe. In the crystal growth model, the bulk of the Fe is oxidized to Fe(0)(0H) on the surface of the growing crystallite." " It is initiated at catalytic sites on the interior surface of the protein. There is evidence that the mechanism of iron uptake by ferritin changes after the initial uptake. Initial uptake occurs more effectively with O2 as the oxidizing agent, but in the latter stages O2 and KIO3 are equally effective. 

Figure 2.4 Three typical growth models for the catalytic synthesis of nanosilica, (a) VLS = vapor-liquid-solid ...

As in other fields of nanosdence, the application of STM techniques to the study of ultrathin oxide layers has opened up a new era of oxide materials research. New emergent phenomena of structure, stoichiometry, and associated physical and chemical properties have been observed and new oxide phases, hitherto unknown in the form of bulk material, have been deteded in nanolayer form and have been elucidated with the help of the STM. Some of these oxide nanolayers are and will be of paramount interest to the field of advanced catalysis, as active and passive layers in catalytic model studies, on the one hand, and perhaps even as components in real nanocatalytic applications, on the other hand. We have illustrated with the help of prototypical examples the growth and the structural variety of oxide nanolayers on metal surfaces as seen from the perspective of the STM. The selection of the particular oxide systems presented here refleds in part their relevance in catalysis and is also related to our own scientific experience. 

Growth Mechanisms. Growth mechanisms have been investigated, andsev-eral theories have been proposed. There are two general models that are used to explain catalytic synthesis of nanowires or nanotubes. The first is called tip growth, in which... 

In addition, these thin films have been important in studies of electron transfer, relevant for catalytic systems [64], molecular recognition [65], biomaterial interfaces [66], cell growth [67], crystallization [68], adhesion [69], and many other aspects [70]. SAMs provide ideal model systems, because fine control of surface functional group concentration is possible by preparing mixed SAM systems of two or more compounds, evenly distributed over the surface [71, 72], as two- or... 

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