Semiconductor electron-transfer processes

Duonghung D, Ramsden J, Gratzel M (1982) Dynamics of interfacial electron-transfer processes in colloidal semiconductor systems. J Am Chem Soc 104 2977-2985... 

Tang, J. and Marcus, R. A. (2005) Diffusion-controlled electron transfer processes and power-law statistics of fluorescence intermittency of nanoparticles. Phys. Rev. Lett, 95, 107401-1-107401-4 Tang, J. and Marcus, R. A. (2005) Mechanisms of fluorescence blinking in semiconductor nanocrystal quantum dots./. Chem. Phys., 123,054704-1-054704-12. 

Between 0.20 and 0.30 V, a decay of the initial photocurrent and a negative overshoot after interrupting the illumination are developed. This behavior resembles the responses observed at semiconductor-electrolyte interfaces in the presence of surface recombination of photoinduced charges [133-135] but at a longer time scale. These features are in fact related to the back-electron-transfer processes within the interfacial ion pair schematically depicted in Fig. 11. 

Gratzel, M. (1982) Artificial photosynthesis, light-driven electron transfer processes in organized molecular assemblies and colloidal semiconductors. Pure. Appl. Chem, 54, 2369-82. 

It is well known that the flotation of sulphides is an electrochemical process, and the adsorption of collectors on the surface of mineral results from the electrons transfer between the mineral surface and the oxidation-reduction composition in the pulp. According to the electrochemical principles and the semiconductor energy band theories, we know that this kind of electron transfer process is decided by electronic structure of the mineral surface and oxidation-reduction activity of the reagent. In this chapter, the flotation mechanism and electron transferring mechanism between a mineral and a reagent will be discussed in the light of the quantum chemistry calculation and the density fimction theory (DFT) as tools. 

Boroda YG, Voth GA (1996) A theory of adiabatic electron transfer processes across the semiconductor-electrolyte interface. J Chem Phys 106 6168-6183... 

The net result of a photochemical redox reaction often gives very little information on the quantum yield of the primary electron transfer reaction since this is in many cases compensated by reverse electron transfer between the primary reaction products. This is equally so in homogeneous as well as in heterogeneous reactions. While the reverse process in homogeneous reactions can only by suppressed by consecutive irreversible chemical steps, one has a chance of preventing the reverse reaction in heterogeneous electron transfer processes by applying suitable electric fields. We shall see that this can best be done with semiconductor or insulator electrodes and that there it is possible to study photochemical primary processes with the help of such electrochemical techniques 5-G>7>. 

Figure 12 Schematic representation of thermodynamic and kinetic parameters influencing interfacial electron-transfer processes between the semiconductor and an adsorbed redox specie.

It is interesting to estimate the maximum number of atoms which may be chemisorbed by an electron transfer process, in terms of the fraction of surface sites covered, 0max, and of the relative concentration of free electrons to the total number of atomic sites, n, on a semiconductor. Following the treatment of Weisz (24) we obtain, with 4.6 A as a typical size of a surface site ... 

Fig. 4.1 Photoinduced electron transfer processes in a semiconductor/solution system. C.B. conduction band, V.B. valence band.

One of the major questions that remains to be answered is the detailed mechanism of charge transfer. For redox couples which lie in the gap of the semiconductor, isoenergetic electron transfer would require the existence of an appropriate surface state. While such states have been postulated, little direct evidence of their existence is available. An alternate possibility is an inelastic (non-isoenergetic) electron transfer process such as is commonly observed in solid state dev ices.(18)... 

The Role of Interface States in Electron-Transfer Processes at Photoexcited Semiconductor Electrodes... 

Figure 1. Schematic of various electron transfer processes between semiconductor carriers at the surface and electrolyte and surface states...

Interfacial Electron Transfer Processes at Modified Semiconductor Surfaces... 

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