Mott model

Figure 8.09. Density of states for amorphous semiconductors, (a) The CFO model, showing tailing of states causing overlap, (b) The Davis-Mott model, showing a band of compensated levels near the middle of the gap. (c) The Marshall-Owen model, (d) A real glass with defect states (After Nagels, 1979).

The understanding of the basic mechanism of photolysis of silver halide is incomplete yet vital for the planning and interpretation of experiments. This fact is illustrated by the ramifications inherent in the contemporary discussions of the latent image in silver halide. There are the conventional Gurney-Mott mechanism (1) and the thermodynamic model ((5,9). We have described the Gurney-Mott model. The thermodynamic view envisages nucleation of a supersaturated concentration of silver atoms in silver halide as induced by light. Obviously the effect of external variables is quite different in the two mechanisms. 

Fig. 5.3 Electronic structures of metal and organic when the metal and organic are (a) separated (b) under contact obeying Schottky-Mott model (c) under contact obeying the If aligned approach. The electronic structures of metal/polymer interface are shown in (d).

Devices in molecular electronics typically have a multilayered structure. An understanding of processes at the interfaces between different layers is imperative to achieve high efficiency of the devices. It is often necessary to know how electronic levels of different organic layers are located with respect to each other. In the simple Shottky-Mott model, two different organic layers share the common vacuum level. However, in a number of experimental studies this picture has been shown to be not correct [1]. Usually, an additional potential is present at the interface, shifting the vacuum level (VL) of one material with respect to the other. This additional potential at the donor/acceptor interface is caused by an interfacial dipole layer [1]. 

In fact, there are still some uncertainties about the applicability of Schottky-Mott model to 0/0 heterojunctions. For example, it is not clear whether the energy-level alignment is controlled only by the constituents of the heterojunction and is independent of the substrates and the formation sequence of the junction. In this chapter, we also discuss the electronic structures of some representative 0/0 heterojunctions and investigate the substrate effects on the energy-level alignment. In Section 6.7, we address the implications of the aforementioned for the design of ambipolar OFETs and stacked OLEDs. 

The energies E, Eg, E, and E have the same meaning as in the Davis and Mott model. A band of localized acceptor states lies below and a band of donor states above the gap center. In the cases shown, the acceptors are nearly compensated by the donors. As T is increased Ep moves toward the gap center. 

For the Davis-Mott Model E = E (or Eg). /z(E) drops sharply below E. so that In a more general case the tunnel probabiUty (contained in... 

Figure 5.32 compares the screening potential obtained from a band model such as shown in Figure 5.3 with that predicted by the Davis-Mott model shown in Figure 5.4. In both cases an interface potential U(0) = 1 eV was assumed and a dielectric constant k = 16. Letting tails of localized states in the first model drop exponentially toward Ep as...

The interface between the quasi-metal PEDOT PSS and organic semiconductors has been investigated in numerous experiments. As illustrated in Figure 14.16, the energy barrier for hole injection (AE) is not simply determined by the difference between the PEDOT PSS work function (4>) and the ionization potential (/ ) of the semiconductor as predicted by the Schottky-Mott model dipole layer formation at the interface will lead to a vacuum level shift A [158-161]. 

The kinetic growth equation predicted by the Cabrerra-Mott model has the form... 

The pH dependence of oxide formation, not directly predicted by the Cabrerra-Mott model, was explained with the Eo term in Eq. (10), using the dependence ... 

The generally accepted model for passive film growth, illustrated in Fig. 3-14, is of field-assisted film formation, which is essentially a modified Cabrera-Mott model originally established for gaseous oxidation and the formation of thin oxide films in a gas at low temperature (Cabrera and Mott, 1948-1949 Fehlner and Mott, 1970). This classical theory describes the growth, in the direction perpendicular to the surface, of an oxide layer completely covering the substrate surface, by a hopping mechanism. The... 

The rate law derived from the Cabrera-Mott model is as follows... 

Fig. 15. Space charge potential distribution across solid AgCl-aqueous solution interface, a) from Grimley-Mott model, b) from adsorption of negative ions, (c) total effect of (a) and (b).

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