Doping band structure

DOS analysis shows that both Ni and B character dominate the region around Ef, as also predicted by band structures. Doping by Co, Fe, or Ru causes a broadening (lattice disorder) and weakening (dilution effect) of the Ni-dominated peak which correlates reasonably well with the experimentally observed depression of Tc. A simple rigid-band+dilution model works adequately for low doping levels, but is inadequate for... 

The electronic band structure of a neutral polyacetylene is characterized by an empty band gap, like in other intrinsic semiconductors. Defect sites (solitons, polarons, bipolarons) can be regarded as electronic states within the band gap. The conduction in low-doped poly acetylene is attributed mainly to the transport of solitons within and between chains, as described by the intersoliton-hopping model (IHM) . Polarons and bipolarons are important charge carriers at higher doping levels and with polymers other than polyacetylene. 

Semiconductor electrodes seem to be attractive and promising materials for carbon dioxide reduction to highly reduced products such as methanol and methane, in contrast to many metal electrodes at which formic acid or CO is the major reduction product. This potential utility of semiconductor materials is due to their band structure (especially the conduction band level, where multielectron transfer may be achieved)76 and chemical properties (e.g., C02 is well known to adsorb onto metal oxides and/ or noble metal-doped metal oxides to become more active states77-81). Recently, several reports dealing with C02 reduction at n-type semiconductors in the dark have appeared, as described below. 

The authors also calculated the band structure expected for the fully oxidised form, taken as 33% doping or 2 charges per 6 rings, and the result is depicted in Figure 3.72(c). Continued removal of the states from the valence and conduction bands widens the gap to 3,56eV, with the two intense absorptions in the gap observed in the optical spectra now accounted for by the presence of wide bipolaron bands. The authors stated that, on the basis of other workers calculations, the lowest energy absorption should have the most intense oscillator strength, as is indeed observed. 

In doped semiconductors, the band structure is not so well known as in metals, and a prevision about carrier-phonon decoupling is difficult. 

Figure 4 Schematic band structures for (a) a regular n-stack (b) a Peierls distorted n-stack and (c) a Peierls distorted n-stack after p-type doping...

V. L. Bonch-Bruevich, Effect of Heavy Doping on the Semiconductor Band Structure Donald Long, Energy Band Structures of Mixed Crystals of III-V Compounds Laura M. Roth and Petros N. Argyres, Magnetic Quantum Effects... 

P. Barta, P. Dannetun, S. Stafstrom, M. Zagorska, and A. Pron, Temperature evolution of the electronic band structure of the undoped and doped regioregular analog of poly(3-alkylthio-phenes) a spectroscopic and theoretical study, J. Chem. Phys., 100 1731-1741, 1994. 

At this time, the fastest growing area in the field of nanophysics is in the studies of buckyballs and nanotubes. After the discovery [33] of the Qo molecule, many properties of the molecule and solids formed from the molecule were explored. The doped C6o crystals showed interesting behavior, including superconductivity. [34] The standard model, including the GW quasiparticle theory, was used [35] successfully to explore the energy band structure, and the superconducting properties appear to be consistent with the BCS theory. [36]... 

It is reported that the band structure of ZnS doped with transition metal ions is remarkably different from that of pure ZnS crystal. Due to the effect of the doped ions, the quantum yield for the photoluminescence of samples can be increased. The fact is that because more and more electron-holes are excited and irradiative recombination is enhanced. Our calculation is in good correspondence with this explanation. When the ZnS (110) surface is doped with metal ions, these ions will produce surface state to occupy the valence band and the conduction band. These surface states can also accept or donate electrons from bulk ZnS. Thus, it will lead to the improvements of the photoluminescence property and surface reactivity of ZnS. 

The occurrence of bipolaronic states in the polymer chains promotes optical absorption prior to the n-n gap transitions. In fact, referring to the example (9.30) of the band structure of doped heterocyclic polymers, transitions may occur from the valence band to the bipolaronic levels. These intergap transitions are revealed by changes in the optical absorptions, as shown by Fig. 9.8 which illustrates the typical case of the spectral evolution of polydithienothiophene upon electrochemical doping (Danieli et al., 1985). 

The evolution of the band structure - and thus of the doping process -may be conveniently monitored by detecting in situ the optical absorption during the electrochemical process, by placing the cell directly into the spectrophotometer (Danieli et al, 1985). 

Since the band structure which develops upon doping induces changes not only in the conductivity but also in the optical absorption (see Fig. 9.8), conducting polymers may be exploited for electrochromic displays, which are optical devices with marked colour transitions. An example is illustrated diagramatically in Fig. 9.18. 

V. L. Bonch-Bruevich, Effect of Heavy Doping on the Semiconductor Band Structure... 

N. K. Dutta, Radiative Transitions in GaAs and Other III-V Compounds R. K. Ahrenkiel, Minority-Carrier Lifetime in III-V Semiconductors T. Furuta, High Field Minority Electron Transport in p-GaAs M. S. Lundstrom, Minority-Carrier Transport in III-V Semiconductors R A. Abram, Elfects of Heavy Doping and High Excitation on the Band Structure of GaAs D. Yevick and W. Bardyszewski, An Introduction to Non-Equilibrium Many-Body Analyses of Optical Processes in III-V Semiconductors... 

Figure 1 Schematic band structures for pure and doped BaBiOs and...

Nd2CuC>4, 70,112 band structure schematic, 717 electron doping, 431ff interrelationships of T, T, T structures, 320... 

FIGURE 6.15 Band structure of graphite doped with (a) an electron donor and (b) an electron acceptor. 

Fig. 2.15 Suggested band structure for WSe3 doped with Nb.

Conjugated conducting polymers consist of a backbone of resonance-stabilized aromatic molecules. Most frequently, the charged and typically planar oxidized form possesses a delocalized -electron band structure and is doped with counteranions (p-doping). The band gap (defined as the onset of the tt-tt transition) between the valence band and the conduction band is considered responsible for the intrinsic optical properties. Investigations of the mechanism have revealed that the charge transport is based on the formation of radical cations delocalized over several monomer units, called polarons [27]. 

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