Fermi level description

Figure 7.11 illustrates PEC junction response to solar illumination for both photoanodes (Fig. 7.11a) and photocathodes (Fig. 7.11b) using the quasi-Fermi level descriptions. For both configurations in Fig. 7.11, the photoelectrode is immersed in solution, and the back contact is connected by external wiring to a counter electrode also in solution. In addition, the r/a and r/c overpotentials for the OER and the HER in solution have been added to the reversible potential of the redox system to stress the minimum voltage requirement to sustain water splitting. 

For a more detailed description of the semiconductor/electrolyte interface, it is convenient to define the quasi-Fermi levels of electrons, eFyC and holes, p p,... 

T(E) spectrum. When the Fermi level EF is located between the D-HOMO and the A-LUMO resonances, a large rectification effect is observed where T(EF) reaches almost 104. At a low 100 mV bias voltage and in a forward polarity, the tunnel current intensity reached around 1 nA. The T(E) spectrum of Fig. 2b was calculated using the ESQC technique associated with a semiempirical description of the tunnel junction [110]. The full valence MO structure of the junction is taken into account in the calculation. 

On the basis of the known electronic properties of actinides (which have been discussed elsewhere in this book), theoreticians had distinguished the 5f itinerant behaviour of light actinide metals from the 5 f localized behaviour of heavy actinide metals from Am on. The crossover, presented often as a Mott transition, had been predicted to occur between Pu and Am metal, due to the localized character of the 5f state in the latter. Photoemission spectroscopy demonstrates this phenomenon directly with the observation of a 5 f multiplet away from the Fermi level. The detailed description of this peak is certainly complicated, as often happens for response of localized states in photoemission on the other hand (Fig. 17) the contrast to the emission of Pu metal is convincing. 

The ZSA phase diagram and its variants provide a satisfactory description of the overall electronic structure of stoichiometric and ordered transition-metal compounds. Within the above description, the electronic properties of transition-metal oxides are primarily determined by the values of A, and t. There have been several electron spectroscopic (photoemission) investigations in order to estimate the interaction strengths. Valence-band as well as core-level spectra have been analysed for a large number of transition-metal and rare-earth compounds. Calculations of the spectra have been performed at different levels of complexity, but generally within an Anderson impurity Hamiltonian. In the case of metallic systems, the situation is complicated by the presence of a continuum of low-energy electron-hole excitations across the Fermi level. These play an important role in the case of the rare earths and their intermetallics. This effect is particularly important for the valence-band spectra. 

The electron gas model adequately describes the conduction of electrons in metals however, it has a problem, that is, the electrons with energy near the Fermi level have wavelength values comparable to the lattice parameters of the crystal. Consequently, strong diffraction effects must be present (see below the diffraction condition (Equation 1.47). A more realistic description of the state of the electrons inside solids is necessary. This more accurate description is carried out with the help of the Bloch and Wilson band model [18],... 

Finally, Fig. 58 e may illustrate intra-3 d-band fluctuation and decay of a 3 d-valence hole in metallic Ni. This process is probably one of the essential elements in the description of the valence band photoelectron spectrum which seems to show 3 d-band narrowing, decreased splitting of the majority and minority spin bands and a pronounced shake-up structure about 6 eV below the Fermi level (see e.g.143 175) and references therein, and also Sect. 8.3.4). 

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