Hole states, delocalization

The opposite case, i.e., when the band width is much larger than the hopping matrix element, can be seen in Figure 2.5 for the unoccupied As states of adsorbed on Ag. This has been measured using XAS of Ar adsorbed on Ag, since Ar using the Z + 1 approximation becomes as an effect of the final core hole state [28]. We can directly see that the As level has become a broad asymmetric resonance. The adatom resonance has a tail towards lower energies with clear cut-off at the Fermi level. The 45 level mainly interacts with the delocalized unoccupied Ag sp electrons. Most of the 45 resonance is unoccupied which indicates that charge transfer has occurred from the adatom to the substrate. 

The BSFs in GaN do not introduce localized states in the band gap, but can be considered as a thin zinc-blend (ZB) layer embedded in the wurtzite (W) matrix. The theory predicts that this polytypic QW has a type 11 band alignment with a conduction band offset of about 270 meV [55]. The D1 emission can be described as a recombination of electrons confined in the ZB region with holes residing in the W barrier. At low temperatures, the holes are expected to be localized in a triangular potential notch formed in the barrier because of the discontinuity of the spontaneous polarization across the ZB-W interface [55]. Thus, the emission occurs between separately localized but closely spaced electrons and holes. At higher temperatures, the holes become delocalized and the emission is attributed to a recombination between electrons still localized in ZB QW and holes are attracted to them by Coulomb interaction. This... 

Solid mixed ionic-electronic conductors (MIECs) exhibit both ionic and electronic (electron-hole) conductivity. Naturally, in any material there are in principle nonzero electronic and ionic conductivities (a i, a,). It is customary to limit the use of the term MIEC to those materials in which a, and 0, 1 do not differ by more than two orders of magnitude. It is also customary to use the term MIEC if a, and Ogi are not too low (o, a i 10 S/cm). Obviously, there are no strict rules. There are processes where the minority carriers play an important role despite the fact that 0,70 1 exceeds those limits and a, aj,i< 10 S/cm. In MIECs, ion transport normally occurs via interstitial sites or by hopping into a vacant site or a more complex combination based on interstitial and vacant sites, and electronic (electron/hole) conductivity occurs via delocalized states in the conduction/valence band or via localized states by a thermally assisted hopping mechanism. With respect to their properties, MIECs have found wide applications in solid oxide fuel cells, batteries, smart windows, selective membranes, sensors, catalysis, and so on. 

How then, can one recover some quantity that scales with the local charge on the metal atoms if their valence electrons are inherently delocalized Beyond the asymmetric lineshape of the metal 2p3/2 peak, there is also a distinct satellite structure seen in the spectra for CoP and elemental Co. From reflection electron energy loss spectroscopy (REELS), we have determined that this satellite structure originates from plasmon loss events (instead of a two-core-hole final state effect as previously thought [67,68]) in which exiting photoelectrons lose some of their energy to valence electrons of atoms near the surface of the solid [58]. The intensity of these satellite peaks (relative to the main peak) is weaker in CoP than in elemental Co. This implies that the Co atoms have fewer valence electrons in CoP than in elemental Co, that is, they are definitely cationic, notwithstanding the lack of a BE shift. For the other compounds in the MP (M = Cr, Mn, Fe) series, the satellite structure is probably too weak to be observed, but solid solutions Coi -xMxl> and CoAs i yPv do show this feature (vide infra) [60,61]. 

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