Doping reversible

Other research groups have initiated studies designed to explore conductive polymer systems in the context of high-7c applications [9]. Here, such polymers offer the prospects for enhanced processibility as well as a wide range of electrical conductivities. Polymeric systems of this type can be doped reversibly from neutral, nonconductive forms (10 -10 17 cm ) to oxi-... 

Figure 15.16 Pictorial representation of lipase in GNP-doped reverse micelles.

The bipolar junction transistor (BIT) consists of tliree layers doped n-p-n or p-n-p tliat constitute tire emitter, base and collector, respectively. This stmcture can be considered as two back-to-back p-n junctions. Under nonnal operation, tire emitter-base junction is forward biased to inject minority carriers into tire base region. For example, tire n type emitter injects electrons into a p type base. The electrons in tire base, now minority carriers, diffuse tlirough tire base layer. The base-collector junction is reverse biased and its electric field sweeps tire carriers diffusing tlirough tlie base into tlie collector. The BIT operates by transport of minority carriers, but botli electrons and holes contribute to tlie overall current. 

Conductivities of polymers of technological interest such as polypyrrole and polythiophene are typically 1000 cm in the doped state, and the conductivity can be tuned by reversibly doping and undoping the polymer. Derivatives of these and other polymers have achieved even higher conductivities. 

These conjugated polymers can be chemically and electrochemically reduced and reoxidized in a reversible manner. In all cases the charges on the polymer backbone must be compensated by ions from the reaction medium which are then incorporated into the polymer lattice. The rate of the doping process is dependent on the mobiHty of these charge compensating ions into and out of the polymer matrix. 

Voltammograms of a polythiophene film showing reasonably reversible electrochemistry of both types are shown in Fig. 2.M The formal potentials (average of the anodic and cathodic peak potentials) for p- and n-doping can provide useful estimates of the energies of the polymer s valence and conduction bands and its band gap35... 

The stoichiometry of the redox reactions of conducting polymers (n and m in reactions 1 and 2) is quite variable. Under the most widely used conditions, polypyrroles and polythiophenes can be reversibly oxidized to a level of one hole per ca. 3 monomer units (i.e., a degree of oxidation, n, of ca. 0.3).7 However, this limit is dictated by the stability of the oxidized film under the conditions employed (Section V). With particularly dry and unreactive solvents, degrees of oxidation of 0.5 can be reversibly attained,37 and for poly-(4,4 -dimethoxybithiophene), a value of n = 1 has been reported.38 Although much fewer data are available for n-doping, it appears to involve similar stoichiometries [i.e., m in Eq. (2) is typically ca. 0.3].34,39"41 Polyanilines can in principle be reversibly p-doped to one... 

The same reversible appearance and disappearance of the Pt(lll)-(12xl2)-Na overlayer is shown in Figure 5.51, together with the corresponding two-dimensional Fourier-transform spectra and also in Fig. 5.52, which shows smaller areas of the sodium-free and sodium doped Pt(lll) surface. The reversible electrochemically controlled spillover/backspillover of sodium between the solid electrolyte and the Pt(lll) surface is clearly proven. 

A variety of colors, such as green, amber, and red (and infrared), can be obtained with different semiconductor materials without the need for a filter (see Ch. 13, Table 13.4). A LED (or photodiode) device may consist of multiple diodes in an array operating in the reverse-bias mode. Patterns of light showing symbols, letters, or numbers can thus be produced with different colors obtained by doping the semiconductor material by CVD or ion implantation. 

Scheme 17) [35,36]. Polymers (61) were amenable to p- and n-doping processes with good reversibility. Absorption spectra of the de-doped polymers showed that the values of A nset considerably red-shifted compared with those ob-... 

B. Bogdanovic, M. Felderhoff, S. Kaskel, A. Pommerin, K. Schlichte, F. Schiith, Reversible Storage of Hydrogen using Doped Alkali Metal Aluminum Hydrides, 2001, WO 03/053848 Al. 

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