Carrier transfer

As described above, metallic CNTs are of great interest because they possess molecular orbitals which are highly delocalised. However, metallic CNTs are very difficult to use in actual devices because they require very low temperatures to control their carrier transfer. On the contrary, even at room temperature, the nonlinear /-V jas curve and the effective gate voltage dependence have been presented by using individual semiconducting SWCNTs [29]. 

The forward current at a semiconductor-metal junction is mainly determined by a majority carrier transfer i.e. electrons for n-type, as illustrated in Fig. 1 d. In this majority carrier device the socalled thermionic emission model is applied according to which all electrons reaching the surface are transferred to the metal. In this case we have ... 

The existence of two types of mobile charge carriers in semiconductors enables us to distinguish between a majority charge carrier transferred from the electrode into the electrolyte and a minority charge carrier injected from the electrolyte into the electrode. Minority carrier injection causes significant reverse currents, but may also contribute to the total current under forward conditions. 

Dispersive transport in PVC was investigated. The results of Pfister and Griffits obtained by the transit method are shown in Fig. 6. The hole current forms at temperatures > 400 K clearly show a bend corresponding to the transit time of the holes. At lower temperature the bend is not seen and transit time definition needs special methods. The pulse form shows the broad expansion during transition to the opposite electrodes. This expansion corresponds to the dispersive transport [15]. The super-linear dependence of the transit time versus sample thickness did not hold for pure PVC. This is in disagreement with the Scher-Montroll model. There are a lot of reasons for the discrepancy. One reason may be the influence of the system dimensions. It is quite possible that polymer chains define dimension limits on charge carrier transfer. 

Photosensitivity in a PVC-Se two layer Systran is equal to the Se photosensitivity in the strong absorption region [13]. The experimental data are presented in Fig. 13. Strong dependence of the photoresponse on the electric field strength was established. For n-Se and p-Se it was explained by the dependence of the quantum yield and charge carrier transfer from the electric field respectively. 

The localization radius Rc was equal to 0.1 nm for lexan with TP A, 0.154 nm with IPC, and 0.1 nm for PVC with TP A. The strong exponential dependence of the mobility proves the charge carrier transfer between localized states, connected with doping molecules. 

Widdas, W.F. (1952). Inability of diffusion to account for placental glucose transport in the sheep and the consideration of the kinetics of a possible carrier transfer. J. Physiol. Lond. 118, 23-39. 

A. Cesnys, G. Juska and E. Montrimas, Charge Carrier Transfer at High Electric Fields in Noncrystalline Semiconductors... 

In the presence of a redox system dissolved in the electrolyte, as long as there exists an energy difference between the Fermi level of the semiconductor and the redox couple, to reach the equilibrium conditions charge-carrier transfer occurs across the semiconductor-liquid interface via the energy bands, i.e., the conduction or valence band of the semiconductor. At the equilibrium point, the Fermi level of the redox... 

Fig. 16.5 Charge-carrier transfer at large (left) and small (right) semiconductor particles in the presence of an electron donor D and an acceptor A [Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced with permission from Memming (2001)]...

These carriers transfer electrons into the electron-transport chain independently of and bypassing the NAD+/NADH couple. The main shuttle for cytoplasmic reducing equivalents is the glycerol 3-phosphate shuttle that is shown in Fig. 11-20 (page 334). 

The coenzyme biotin, a CO2 carrier, transfers CO2 in a nucleophilic acyl substitution reaction. 

This relation is identical to that derived for a pn-junction (see e.g. [89]) (solid curve in Fig. 14). It also looks similar to the current-voltage relation derived for a majority carrier transfer, as given by Eq. (42), both relations differ only by the pre-exponential factor. The first case, i.e. limitation by surface kinetics (Eq. (44)), is difficult to realize, because the majority carrier transfer becomes dominant for redox systems, the standard potential of which is located in the middle of the gap. 

In several cases it has been found that the oxidation of the redox system occurs entirely via hole transfer directly from the valence band to the reduced form of the couple. Then both processes, oxidation of the redox system and corrosion, proceed independently. This is usually not visible from measurements with an n-type electrode, because the photocurrent is entirely determined by the light intensity. As already mentioned above, p-type electrodes are more suitable, because the current is determined by majority carrier transfer (reaction rate Vf, in Fig. 21). From the thermodynamic point of view, the oxidation of Cu at GaAs is an interesting case. The corresponding current-potential curves are given in Fig. 22 [93]. The corrosion current is not changed upon addition of Cu, i.e. corrosion and redox process are completely independent. In this case, the kinetics of the direct hole transfer is obviously very fast, i.e. the redox current is considerably larger than the corrosion current. Both processes occur indepen-... 

Hot carrier transfer is most likely expected for semiconductors having high carrier mobility, low minority carrier effective mass and of high doping density [167]. The first experiments were reported by Nozik and co-workers for p-GaP and p-InP liquid junctions [168, 166]. Especially InP was a good candidate, because of its high electron mobility. The authors used p-nitrobenzene (U edox = — 0-86 V (SCE)) as an electron acceptor, because the standard potential occurs 0.44 eV above the conduction band at the interface, as shown in Fig. 36. A photocurrent was observed at potentials negative of Ue = -I- 0.15 V. 

The electron carriers in the respiratory assembly of the inner mitochondrial membrane are quinones, flavins, iron-sulfur complexes, heme groups of cytochromes, and copper ions. Electrons from NADH are transferred to the FMN prosthetic group of NADH-Q oxidoreductase (Complex I), the first of four complexes. This oxidoreductase also contains Fe-S centers. The electrons emerge in QH2, the reduced form of ubiquinone (Q). The citric acid cycle enzyme succinate dehydrogenase is a component of the succinate-Q reductase complex (Complex II), which donates electrons from FADH2 to Q to form QH2.This highly mobile hydrophobic carrier transfers its electrons to Q-cytochrome c oxidoreductase (Complex III), a complex that contains cytochromes h and c j and an Fe-S center. This complex reduces cytochrome c, a water-soluble peripheral membrane protein. Cytochrome c, like Q, is a mobile carrier of electrons, which it then transfers to cytochrome c oxidase (Complex IV). This complex contains cytochromes a and a 3 and three copper ions. A heme iron ion and a copper ion in this oxidase transfer electrons to O2, the ultimate acceptor, to form H2O. 

A) minority carrier transfer catalysis and/or surface state passivation (B) electrostatic modification (C) catalysis of multi-electron photoprocesses (refer to text). 

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