Photo-excitation Fermi level

FIGURE 22.35 Electronic energy diagrams for a metal electrode in contact with an n-type metal oxide (a) prior to contact, (b) posterior to contact, and (c) with photoexcitation peF = quasi-Fermi level for photo-excited holes in oxide and eQx = Fermi level of oxygen reaction. 

The additional enhancement provided by coadsorbed halide ions on a colloidal silver surface has been pointed out [401]. As an explanation, morphological changes effected by the strongly adsorbed anions have been invoked. The photo-driven CT that is assumed to proceed from filled metal states near the Fermi level of the metal to the first and second excited state in the case of pyrazine adsorbed on polycrystalline gold has been invoked as the cause for the breakdown of Raman selection rules upon adsorption (i.e. the activation of originally Raman-forbidden vibrational modes) [314]. 

On the other hand, good agreement with the de Haas-van Alphen measurements on UPdj (Ubachs et al. 1986) is only obtained by treating the f electrons as core states (Norman et al. 1987), whilst photo-emission results show that there is no f-electron density at the Fermi level in this compound (Baer et al. 1980). It is significant that UPdj is the only actinide metal in which well defined crystal-field excitations have been observed by neutron spectroscopy (Shamir et al. 1978, Murray and Buyers 1980, Buyers and Holden 1985). All these results indicate that the uranium ions in UPdj have a localised f configuration and behave more like stable lanthanide ions. 

The photoelectrochemical reactions are driven by photo excited electron-hole pair. The potential of Fermi level of the photoelectrode under photo excitation is similar to the potential of electron on cotmter electrode. 

Fig. 2. Principle of the photo-electronic effect the excitation and relaxation processes are shown indicating schematically the different binding states with the Fermi energy 0%) as the reference level (=0). The valence band energy is Ey followed by a discrete level of El and the core level Er after [7]...

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