Doping reaction

Polythiophene films can be electrochemically cycled from the neutral to the conducting state with coulombic efficiencies in excess of 95% [443], with little evidence of decomposition of the material up to + 1.4 V vs. SCE in acetonitrile [37, 54, 56, 396,400] (the 3-methyl derivative being particularly stable [396]), but unlike polypyrrole, polythiophene can be both p- and n-doped, although the n-doped material has a lower maximum conductivity [444], Cyclic voltammetry shows two sets of peaks corresponding to the p- and n-doping reactions, with E° values at approximately + 1.1 V and — 1.4 V respectively (vs. an Ag+/Ag reference electrode)... 

The situation can be illustrated with respect to the acceptor-doped perovskite structure SrZrC>3, with Y3+ substituted for Zr4+ to give compositions SrZrj YVC>3-0.5.V The doping reaction can be written ... 

Oxygen is also a dopant for polyacetylene, but on exposure the conductivity rises to a maximum then rapidly declines as oxidation of the polymer backbone occurs, as shown in Fig. 21. We have no data on the diffusion coefficient as the process is rapid and is masked by the reaction of oxygen with the polymer. The kinetics are first-order, implying that the doping reaction is rapid, goes to less than 1 mol%, and is then followed by irreversible oxidation of the polymer. Based on the observa-... 

Phosphorus. For the predeposition of phosphorus, the predominant species in the gas phase is P2Os. The doping reaction with P205 is shown in equation 7. 

Eqs. (6.69) and (6.70) are the doping reactions related to the gas-phase and solid-phase concentrations of silicon and phosphorus. The square root law applies to the gas-phase arsenic concentration provided that and are regular (i.e. independent of arsenic concentration). However, the law only applies to the solid-phase concentrations (Eq. (6.70)) if, in addition, is also constant. The variation of the arsenic distribution coefficient with rf power and gas concentration (Fig. 5.4) explains the deviations from the doping law for the solid phase which are shown in Fig. 5.17. The phosphorus distribution coefficient has a much weaker dependence on the rf power and gas concentration, so... 

Previous work on KxCm showed the need for a variety of characterization techniques for these highly air sensitive materials. These included in situ conductivity, Raman spectroscopy, microwave absorption, and dc susceptibility. In this study, as well, all doping reactions and measurements were carried out using sealed tubes. C60 was purified by chromatography of fullerite on oc-tadecylsilanised silica with toluene-isopropanol eluent, and dried at 160°C under vacuum. 

The doping reaction is the same as that which occurs during the polymerization process, and the dedoping reaction is the reverse process. Many of the side reactions that can occur during polymerization can also be a problem during doping, particularly those involving overoxidation. 

Doping by FeCls is usually carried out in nitromethane solution. The anion species is identified by Fe Mossbauer spectroscopy and the extended X-ray absorption fine structure (EXAFS) di7 FeCU. The doping reaction involves dissociation of FeCb in nitromethane (16a) followed by oxidation of polyacetylene by FqC 2 (16b). Thus, the overall doping reaction can be written as equation (16c). 

In their ASF5 vapour doping studies, Hasslin et al. [33] find the intercalation spacing to depend on the vapour pressure. A possible explanation for this is that some neutral species (AsFs or AsFj) remain in the lattice. The stoichiometry, therefore, may correspond to (CH)(AsF5)v, rather than (CH)(AsF( ). Both neutron and synchrotron x-ray diffraction have been used for kinetic investigations of this and other doping reactions a survey has been given by Riekel [148]. 

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