Methods of Doping

In electrochemical doping the reduction or oxidation of the polymer is caused by electric current, and the counterion is drawn into the system from the electrolyte solution with an electric field. This method is applicable to a large number of doping ions. Even anions of protonic acids can be used, because in electrochemical doping protonation of the thiophene chain does not occur [75,76], since the positive ions (e.g. H, Na ) move towards the counter-electrode in the electrochemical cell. Tourillon [55] discusses the use of CF3S03 anions in polythiophenes, and Nilsson et al [77] have has used dodecylbenzene sulfonate anions for the doping of P3HT. 

In vapor phase doping, the polymer is exposed to a gaseous dopant, typically a Lewis acid halide, that can take part in the charge transfer reaction. For instance iodine, I2, forms 

I3 and I5 ions in the doping process. The obtainable conductivity depends on the vapor pressure and doping time, as demonstrated by Satoh et al, [78]. Other dopants used in vapor phase doping with good results include BF3, ASF5 and SbFs. 

Self-doping has also been studied with poly(3-alkylsulfonate-thiophenes) [7-9]. The self-doped polythiophenes have a SO3H group at the end of the alkyl side chain. However, in order to obtain good conductivities, the charge transfer reaction has to be driven electrochemically to remove the cation (H+ or Na+) of the sulfonic acid out of the polymer. Otherwise this kind of self-doped polythiophenes have a very low conductivity in the dried state due to the protonation of the thiophene rings [75]. 

As discussed by Han et al [76], protonic acids are not suitable dopants for PTs or P3ATs, although the optical and mechanical properties of P3ATs, mixed with protonic acids, to some extent resemble those of doped PTs. The reason is the protonation of the thiophene rings, which prevents the conduction of the electric current, in analogy with the case of the self-doped polymers. 

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Methods of Doping Dye Molecules into Silica Nanoparticles. 234... 

Method of doping (exposure of LB film 763 to iodine vapor, immersion of LB films in aqueous KI3 solution, or anodic oxidation of LB films deposited on indium tin oxide glass) determined properties of the films. Lateral [Pg.165]

The properties of the wide band-gap semiconductor SiC have been extensively studied by HFEPR because knowledge of the defect states is needed for its application in high power and radiation resistant devices. (The main method of doping SiC is by ion implantation that inevitably also introduces defects into the lattice.) The primary defects that can be produced are vacancies, interstitials and anti-sites. In contrast to silicon the primary defects in SiC seem to be stable at and even far above room temperature. 

In recent years, the electronics industry has made increasing use of ion imptamaiion as a method of doping semiconductors. Since rhe number of ions implanted is determined hy the charge transferred to the substrate and Iheir depth distribution hy the incident energy, ion implantation has improved the controllability and reproducibility of certain semiconductor device processing operations. Also, ion implantation processes do not... 

Understanding the role of cafalysf promofers is not a simple matter. Confusion in the interpretation of promofer effects has resulted because different groups have reported contrasting results for the same promoters. The effects of promofers on vanadium phosphate performance was summarized by Ballarini ef al. (8) (Table 1). As illustrated by the work by Sananes-Schulz et al. (196), the catalyst preparation method can alter the effect of the promoter, as can the method of doping. Hutchings and... 

Figure II-1 Schematic summary of methods of doping conjugated polymers, with applications and related chemical and physical phenomena.

The occurrence of etch rate reduction on highly boron doped materials appears to be independent of doping methods, whether by solid-source diffusion, epitaxial growth, or ion implantation. However, the boron concentration at which significant reduction occurs is different for different methods of doping. The critical boron concentration for etch rate reduction to occur is affected by the defect density in different doped materials. It is found that for similar boron concentrations the amount of etch rate reduction in KOH solutions decreases with increasing defect densityIn... 

Several methods of doping were tested, using 2 mol% La203 (calculated with respect to final alumina) or 4 mol % BaO, both added as nitrates. No signiftcant differences were observed between adding dopant to the solution of aluminium sulphate before cooling or to solid aluminium sulphate after drying (see below). 

The "classical" method of doping involves the redox doping, i. e. chemical or electrochemical partial oxidation ("p-doping"), or partial reduction ("n-doping") of the K backbone of the polymer,. More recently, non-redox doping which neither adds nor removes electrons from the polymer backbone has been discovered. 

The results of the Fe-M6Bbauer spectroscopy prove that doping does not destroy the bridged structure. Isomer shifts and quadrupole splittings of chemically and electrochemically doped compounds show nearly identical values as found for PcFe(pyz)2 and [PcFe(pyz)] . The oxidation therefore does not take place at orbitals which are centered at the metal atom. Other authors describe an oxidation of the central Fe -ion [73,102], however their methods of doping [PcFe(pyz)] are different from that described above. 

An interesting method of doping, that of heat treatment, has been applied mainly to ladder-type CPs such as BBL. Wang et al. [128] found tliat previously wet-spun and mildly stretched BBL, when subjected to a heat treatment of 50 C increments lasting... 

Wang and Herron [76] have also, demonstrated another new method of doping PVK. By synthesizing small cadmium sulphide clusters (diameter ca 16 A) inside a PVK layer the authors have demonstrated that the resultant composite is capable of generating charges efficiently upon irradiation. In such a composite the semiconductor cluster acts as a sensitizer for the photogeneration of carriers and the polymer serves as carrier transporting medium. The quantum yield 0 and a thermalized separation distance of electron-hole pairs ro were found to be 0.16 and 26 A respectively. The approach can probably be extended to include other semiconductor nanoclusters and to develop a novel class Pf photoconductive materials. 

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