Transfer doping

N.D. Lang, Ph. Avouris, Carbon-Atom Wires Charge-Transfer Doping, Voltage Drop, and the Effect of Distortions, Phys. Rev. Lett. 84 (2000) 358. 

The emeraldine salt, (II-7), can also be obtained directly from leucoemeraldine by charge transfer doping, with reactions analogous to (II-1) and (II-3). Thus, the doping of polyaniline has been described as two-dimensional in a space where one axis describes the charge transfer chemistry and the second, orthogonal axis describes the acid/base (protonation) chemistry [37]. 

To a large extent, current interest in solid-state polymerization of monoacetylenes derives from the observation of interesting electrical, magnetic, and optical phenomena in polyacetylene, (CH)j (45), a pEutially crystalline material unstable to ambient conditions typically synthesized by Ziegler-Natta techniques. The fundamental study of (CH), and its electron-transferred ( doped ) forms has been retarded by the lack of fully ordered materials. Ftilly ordered polyacetylenes are also of interest because it is conceivable that their crystal structures could allow significant interchain interactions, a situation precluded in most PDA by side chains. 

Again, with respect to the last two points, surface oxidation might result in effective charge-transfer doping even at room temperature and thereby enhancing the density of free carriers and the effective mobility. 

Two striking effects are observed in Fig. 10. One is the large decrease in the resistivity of the layered material relative to the nonlayered material for large Ls. The low resistivity (10 2 cm) persists even for relatively thick a-Si H layers (1200 A) and is of n-type conductivity from the sign of the thermoelectric power. The decrease in resistivity has been ascribed to transfer doping by the a-SiNjj H layers (Tiedje and Abeles, 1984). The other noteworthy effect in Fig. 10 is the large increase in resistivity when is reduced below 40 A. It... 

We will discuss the transfer doping effect first. 

The new transfer doping mechanism produces conductive material with a lower density of gap states than phosphorus-doped material of comparable resistivity, where the substitutional dopant always introduces extra defect states. Evidence for the lower density of defects comes from the magnitude of the low energy shoulder in the photoconductivity response spectrum shown in Fig. 14, where the absorption of the layered material at photon energies below 1.4 eV is more than an order of magnitude lower than the phosphorus-doped material of comparable dark resistivity. Furthermore, the photoconductivity of the transfer-doped material is large (10 Q cm ) compared with the photoconductivity achievable in heavily P-doped material under similar illumination. 

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. 

Polk BJ, Potje-Kamloth K, Josowicz M, Janata J (2002) Role of protonic tmd chaige transfer doping in solid-state poly-aniUne. J Phys Chem 106 11457-11462... 

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