Charge injection mechanism

FIGURE 2.4.4 Comparison of different charge injection mechanisms at a biased metal-semiconductor contact (a) thermionic emission, (b) field emission (tnnneling), (c) defect assisted injection. 

Assume that our capacitor is filled by a nematic mixture with 0 well aligned along the x-axis and let the same charge injection mechanism works. Then, in a dc regime, the periodic flow will inevitably interact with the director. The maximum realignment, i.e. the deflection of the director angle 9 in the z-direction, will be... 

Results of surface studies of subatomic layers of metals formed on polymer layers (discussed in Section IV.c.2.) have shown clear evidence for chemical interactions between metal and polymer, which range from charge transfer doping for alkali metals and calcium to covalent interactions for aluminum. In this case, the tunneling model is at odds. Research on the charge injection mechanism at the interface between polymer and metals must be continued. 

To study charge injection mechanisms, we have tried to fit Richardson-Schottky thermionic emission and Fowler-Nordheim tunnelling mechanisms. We have found that under forward bias, the temperature-independent Fowler-Nordheim (FN) tunnelling mechanism is applicable, which presumes tunnelling of charge carriers directly into the bands of the semiconductor. According to the model, the current density J) is related to the applied field F) as [11,12] ... 

Traditionally, all the noncapacitive charge-injection mechanisms are grouped together into the Faradaic pathway. This includes both the reversible and irreversible chemical reactions. They are grouped together because the distinction between the two can be unclear in some instances. The reversible oxida-tion/reduction reaction plays an important role for charge injection and it is part of what gives each metal its unique electrochemical properties. 

Polythiophene and its derivatives are characterized as p-type semiconductors, and so they are expected to form a Schottky-like junction with a metal having low work function [98]. In this case the charge injection over this metal/polymer interface plays an important role. The charge injection mechanism can be studied by measuring temperature and voltage dependence of current. 

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