Interface structures, energy levels

Here r is the distance between the centers of two atoms in dimensionless units r = R/a, where R is the actual distance and a defines the effective range of the potential. Uq sets the energy scale of the pair-interaction. A number of crystal growth processes have been investigated by this type of potential, for example [28-31]. An alternative way of calculating solid-liquid interface structures on an atomic level is via classical density-functional methods [32,33]. 

Figure 11-13. Calculated current density as a limelion of bias lor two-layer hole-only structures (0.1 eV injection barrier lor holes) with a 0.0, 0.3, and 0.5 eV energy harrier for holes at the interface between the polymer layers. The upper panel is a schematic of the energy level diagram for the sttuc-turcs.

H. Ishii, K. Sugiyama, E. Ito, and K. Seki, Energy level alignment and interfacial electronic structures at organic-metal and organic-organic interfaces, Adv. Mater., 11 605-625 (1999). 

In electrode kinetics, interface reactions have been extensively modeled by electrochemists [K.J. Vetter (1967)]. Adsorption, chemisorption, dissociation, electron transfer, and tunneling may all be rate determining steps. At crystal/crystal interfaces, one expects the kinetic parameters of these steps to depend on the energy levels of the electrons (Fig. 7-4) and the particular conformation of the interface, and thus on the crystal s relative orientation. It follows then that a polycrystalline, that is, a (structurally) inhomogeneous thin film, cannot be characterized by a single rate law. 

The second important difference is that the interface potential is present at the (outer) Helmholtz layer of the semiconductor/soiution interface. The interface potential is produced by surface dipoles of surface bonds as well as surface charges due to ionic adsorption equilibria between the semiconductor surface and the solution. If the interface potential can be regulated by a change in the chemical structure of the semiconductor surface, then the semiconductor band energies can be shifted to match the energy levels of the solution species (oxidant or reductant). This is another advantage of the semiconductor system because this enables improvement of the electron transfer rate at the semiconductor/soiution interface and the energy conversion efficiency. 

Figure 6. The energy level structure for an n-semiconductor-electrolyte interface as is appropriate for electron photoemission.

Fig. 5.3. Formation of a bulk heterojunction and subsequent photoinduced electron transfer inside such a composite formed from the interpenetrating donor/acceptor network, plotted with the device structure for such a junction (a). The diagrams showing energy levels of an MDMO-PPV/PCBM system for flat band conditions (b) and under short-circuit conditions (c) do not take into account possible interfacial layers at the metal/semiconductor interface...

The mechanism of electron transfer across a liquid-liquid interface is probably quite similar to that of a homogeneous electron transfer [106, 107]. In either case, the role of changes in the oxidation state of both reactants, in their molecular structure (including valence bond deformation, breaking or formation), and in the polarization state of the solvent have to be considered. Owing to electrostatic interactions of charged reactants with polar solvent molecules, the electron energy levels of the reac-... 

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