Light-Induced Metal Deposition

Accordingly, a surface state (surface radical) is formed which acts as an effective electron trap, that is. 

The OH radical is further reduced by hole injection into the valence band  

This is actually a detailed description of the current-doubling process found for the reduction of H2O2 as already discussed in Section 7.6. Since the electron transfer from the conduction band into the surface state (Eq. (11.42)) can be rather fast and the corresponding rate may be determined by the thermal velocity of electrons toward the surface, it has to be assumed that the initial chemical etching reaction (Eq. (11.41)) is even faster. 

According to this reaction mechanism, the surface radical obviously plays a key role in the etching process [125]. Other redox systems, such as Br2 and BrO , behave similarly. Kelly and co-workers have studied the corresponding reaction mechanisms in detail. They proposed a unified model which they applied for all three redox systems [127,128]. 

Selective metal deposition is of interest in several applications such as the formation of conduction patterns for integrated circuits and semiconductor devices. Instead of depositing a complete metal film and producing the pattern by selective etching, there is the interesting goal of forming the pattern directly by photodeposition. The basic concept of the procedure was already developed 25 years 

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Fig. 37. Localized tip-induced in-situ metal deposition (a) Ensemble of Ag pillars deposited on graphite (after [177]). (b) TVain of Cu dots deposited on Au (after [179]). (c) Au dots grown on p-GaAs at positive tip and with light. Size is SOOAxSOOA (after [150]).

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