Band energy position

The prediction of which semiconductor materials are suitable as electrodes for a given photoelectrolysis reaction would be straightforward if the energy position of the bands at the electrode surface remained fixed with respect to the solution redox levels and independent of the redox species in the solution. Gerischer... 

Fig. 5.10 Relative band edge diagram for FeS2 and the energy position of some electron donor species. The thermodynamic reactions corresponding to corrosion processes at the anodic and cathodic sides are indicated as decomposition potentials due to holes, fip dec, and to electrons, n,dec> respectively. r]c and are the cathodic and anodic overpotentials, respectively, for the decomposition reaction of pyiite crystals in acid medium. (Reproduced from [159], Copyright 2009, with permission from Elsevier)...

Fig. 5.13 Energy level diagram comparing the surface band edge positions of SnS and the energies corresponding to selected redox couples and corrosion reactions involving the semiconductor. (Reproduced from [198])...

In general, semicontinuum models explain the band maximum position rather well. GJ calculate the energy at maximum absorption as 0.9 and 2.0 eV respectively for eam and eh, which compare reasonably well with the experimental values, 0.8 and 1.7 eV respectively. 

There are further possible advantages from the use of P.E. spectroscopy in the elucidation of the electronic structure of coordination compounds, and information not otherwise available or only indirectly available may thus come to light. The energy position of ionization bands of nonbonding orbitals, such as 6 s2 in (T1(I),... 

Irradiation of a CCI4 solution sample of the polymer at the wavelength of the higher energy, positive, CD extremum resulted in the spectral bleaching of all CD and UV bands. On the other hand, irradiation at the longer... 

The position of the intervalence band is measured by the mean band energy E ... 

Once electronic equilibrium is established, the surface and the volume of the semiconductor have a common Fermi level, i.e., the same electrochemical potential (depicted by the horizontal line FF in Fig. 22). However, owing to the bending of the bands the position of the Fermi level in the energy spectrum of the crystal (its position relative to the energy bands) will, generally speaking, depend on the distance from the surface. We shall characterize the position of the Fermi level by its distance from the top of the valence band, denoted by e+. Evidently, + = We intro-... 

Fig. 4 Illustration of valence and conduction band edge positions of anatase at pH 0 and IM° reduction potential energy region for Au, Ag, Hg, Cr, Cu, and Fe. Energy scale takes vacuum as zero. See text for details.

In open shell metals, these empty states can be d- or f-states somewhat hybridized with band states (see Chap. A). In a metal, these states may be pulled down into the conduction band (as a virtual state, see Chap. A) in a compound, presenting a ligand valence band (insulator or semiconductor), they may be pulled down to an energy position coinciding with or very near to this valence band (as a true impurity level). The two possible final states (Eqs. 22 a and 22 b) explain the occurrence of a split response one of the crystal band electrons occupies either the outer hole level P (Eq. 22 a) or the more bandlike hole B " (Eq. 22 b). 

According to our energy conditions of Fig. 7, materials suitable for hole injection must have a relative high energy position of the valence band edge. From Fig. 12 we learn that this is the case for GaP, and CdSe. CdS could be a candidate but it is not available as fi-type material. Besides -GaP only fi-SiC (band gap 3 eV) 7> has been used for the study of hole injection from excited dye molecules. 

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