The doping mechanism

There are two approaches to the explanation of the doping properties. One possibility is that the four-fold doping configurations 

The dopants and defects form pairs in the sense of charge compensation, but are not necessarily physically paired on adjacent sites. The pairing at independent distant sites occurs because both states interact with the electron distribution, whose thermodynamic energy is defined by the Fermi energy. There is a close relation between 

The role of the Fermi energy in the creation of defects and dopant states is shown as follows. The formation energy of a neutral donor is defined to be U. An ionized donor is created by transferring an electron from the donor level to the Fermi energy, so that the total formation energy is 

Boron doping has equivalent properties, with the formation energies given by 

Here the Fermi energy lies between the acceptor level and the defect state and electron transfer is from the defect to the acceptor. The appropriate energy level of the defect is therefore the one-electron state. 

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However, it remains to be understood how this type of doping process can induce enhancement in the electronic transport of the polymers. Indeed, the clarification of the doping mechanism of conducting polymers and of the associated electronic band evolution is of fundamental importance for the comprehension of the operational behaviour of these compounds as novel electrode materials. 

At the molecular level, studies of the doping mechanism in the poly(heterocycles) reveal that very short lived radical cations ("polarons") immediately decay (combine) to form dications ("bi-... 

Polyaniline provides the prototypical example of a chemically distinct doping mechanism [33,34], Protonation by acid-base chemistry leads to an internal redox reaction and the conversion from semiconductor (the emeraldine base) to metal (the emeraldine salt). The doping mechanism is shown schematically in Fig. II-2. The chemical structure of the semiconducting emeraldine base form of polyaniline is that of an alternating copolymer, denoted as [(1A)(2A)] , with... 

These results show that we have gone some way down the line in estabilishing what form hydrogen distribution occurs in amorphous silicon and silicon based alloys. Using the basic techniques of vibration spectroscopy and thermal evolution we can differentiate between mono-, di- and tri-hydride formations in a-Si H as well as between dilute and clustered formations. With dopant impurity atoms the picture becomes more complex where defects and included gas formations become important. Clearly this is an area for further work which would complement the recent models on the doping mechanisms. The distribution of the H atoms between the silicon and nitrogen sites in a-Si ytH determines the optical and... 

In contrast with the reaction with pyrrole, special precautions must be taken with polyaniline-coated textiles during the final washing and rinsing operation. The doping mechanism is somewhat different from the one in polypyrrole, and the counterion, e.g., chlorine orp-tolu-enesulfonic acid, can easily be partially removed by washing with water. It is therefore necessary to wash with water containing sufficient amounts of the counterion as demonstrated for polyaniline powders [63]. Because of the solubility and processibility of polyaniline... 

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