Chemically derivatized semiconductor

Highlights of research results from the chemical derivatization of n-type semiconductors with (1,1 -ferrocenediyl)dimethylsilane, , and its dichloro analogue, II, and from the derivatization of p-type semiconductors with N,N -bis[3-trimethoxysilyl)-propyl]-4,4 -bipyridinium dibromide, III are presented. Research shows that molecular derivatization with II can be used to suppress photo-anodic corrosion of n-type Si derivatization of p-type Si with III can be used to improve photoreduction kinetics for horseheart ferricyto-chrome c derivatization of p-type Si with III followed by incorporation of Pt(0) improves photoelectrochemical H2 production efficiency. Strongly interacting reagents can alter semicon-ductor/electrolyte interface energetics and surface state distributions as illustrated by n-type WS2/I-interactions and by differing etch procedures for n-type CdTe. 

Dyes such as erythrosin B [172], eosin [173-177], rose bengal [178,179], rhodamines [180-185], cresyl violet [186-191], thionine [192], chlorophyll a and b [193-198], chlorophyllin [197,199], anthracene-9-carboxylate [200,201], perylene [202,203] 8-hydroxyquinoline [204], porphyrins [205], phthalocyanines [206,207], transition metal cyanides [208,209], Ru(bpy)32+ and its analogs [83,170,210-218], cyanines [169,219-226], squaraines [55,227-230], and phe-nylfluorone [231] which have high extinction coefficients in the visible, are often employed to extend the photoresponse of the semiconductor in photoelectro-chemical systems. Visible light sensitization of platinized Ti02 photocatalyst by surface-coated polymers derivatized with ruthenium tris(bipyridyl) complex has also been attempted [232,233]. Because the singlet excited state of these dyes is short lived it becomes essential to adsorb them on the semiconductor surface with... 

The second important feature of a metal-semiconductor composite approach is that the metal can function as a template for chemical or electrochemical deriva-tization to afford a film comprising of molecular redox-semiconductor (or even semiconductor-semiconductor) contacts. Figure 34 generically illustrates the occlusion electrosynthesis approach for preparing M-TiO composite films and a subsequent derivatization with ferri/ferrocyanide to afford the corresponding metal hexacyanoferrate (MHCF)-Ti02 counterparts [424]. 

The main problem "in the field is the lack of semiconductor materials that exhibit high conversion efficiency and long term stability. However, one very promising approach involves the chemical modification or derivatization of the semiconductor surface to enhance photo-stability and catalytic activity. This approach is interesting in that it represents a common intersection with the current directions of photochemical approaches to solar energy conversion (61). In the latter, systems are being studied that involve semiconductor particles as catalysts to help drive the photochemical redox reactions. These semiconductors act as electron pools to facilitate the redox chemistry and catalyze the desired reactions. 

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