Density of states at the Fermi level

Flowever, when the metal can be detected directly (mainly Pt), it is possible to relate the form of the NMR spectmm to the dispersion of the metal and to calculate the electron density of states at the Fermi level. 

This restriction, however, could be circumvented by the doped CNT with either Lewis acid or base [32-36], since such doping, even to semiconductive CNT could enhance the density of states at the Fermi level as well as bring about the metallic property. Appearance of metallic conductivity in helical CNT by such doping process would be of interest in that it could make molecular solenoid of nanometer size [37]. 

In the nonrelativistic limit (at c = 10 °) the band contribution to the total energy does not depend on the SDW polarization. This is apparent from Table 2 in which the numerical values of Eb for a four-atom unit cell are listed. The table also gives the values of the Fermi energy Ep and the density of states at the Fermi level N Ef). 

Both Ir02 and Ru02 are metallic oxides with high density of states at the Fermi level. In this respect they are very similar to metals. On the other hand the fact that backspillover 08 ions originating from YSZ can migrate (backspillover) enormous (mm) atomic distances on their surface, as proven experimentally by Comninellis and coworkers, is not at all obvious. 

For undoped a-Si H the (Tauc) energy gap is around 1.6-1.7 eV, and the density of states at the Fermi level is typically lO eV cm , less than one dangling bond defect per 10 Si atoms. The Fermi level in n-type doped a-Si H moves from midgap to approximately 0.15 eV from the conduction band edge, and in / -type material to approximately 0.3 eV from the valence band edge [32, 86]. 

Very useful information concerning the surface of emersed electrodes, however, can be deduced from UPS spectra directly, like the electronic density of states at the Fermi level, the position of the valence band with respect to the Fermi level or possible band gap states. The valence band of UPD metals might help to explain the respective optical data (see Sections 3.2.1 and 3.2.5). 

In reference to the latter question, we have obtained UPS data on polycrystalline samples of NaMo406, but not on single crystals. These measurements indicate a relatively high density of states at the Fermi level, which is in agreement with the low resistivity and metallic character of the material. 

Figure 3.18 shows a series of UPS spectra obtained from an Ru(001) substrate on which small amounts of Ag or Au have been evaporated. The spectrum of the clean Ru(001) substrate, being a d-metal, exhibits a high density of states at the Fermi level. The Ru 4d band is seen to extend to about 5 eV below the Fermi level Silver and gold, on the other hand, are s-metals, with a low density of states at the Fermi level, as illustrated by the spectrum of the thick layers (top spectra of Fig. 3.18). The d-band falls between 4 and 8 eV below the Fermi level. The other...

Our XPS results on AU55 can also be examined to decide whether metallic shielding is present. The presence of a finite density of states at the Fermi level in AU55 was clearly detected in our XPS valence band spectrum, as indicated by the arrow in Fig. 10. This presence can be considered as an indication of metallic character in a cluster, even though this view has been questioned [74, 152,157]. In addition, the near full bulk value of the valence band splitting of AU55 is also... 

The shape and splitting of the XPS Au5d band in the 55 atom cluster material, with its insulating jacket of ligands, reproduces nicely the basic shape of the 5d band of bulk gold, including a clearly visible density of states at the Fermi level. 

The density of states at the Fermi-level N(pp) is responsible for many electronic properties, e.g. the electronic contribution to the low-temperature specific heat of a solid, and the Pauli paramagnetic moment of conduction electrons. The specific heat contribution may be written as ... 

Table 7. The density of states at the Fermi level and the Stoner product in some NaCl-structure binary compounds of actinides...

The f-band width was found to be about 5 eV in Ac, about 3 eV for Th-Np and around 2 eV for Pu. In Am it is down to 1 eV. The Stoner parameter, was calculated to be about 0.5 eV and almost constant throughout the series. At Am, however, the product I N(Ef) of the Stoner parameter and the f-density of states at the Fermi level exceeds one and spontaneous spin polarization occurs in the band calculation. Since Am has about 6.2 f-electrons and the moment saturates, this leads to an almost filled spin-up band and an empty spin-down band. The result is that the f-pressure all but vanishes leading to a large jump in atomic volume - in agreement with experiment. This has been interpreted as Mott-localization of the f-electrons at Am and the f-electrons of all actinides heavier than Am are Mott-localized. The trend in their atomic volumes is then similar to those of the rare earths. 

Classical BCS theory dictated that superconductors with the highest Tc s would not be thermodynamically stable phases. Softening the phonons would raise Tc but would ultimately lead to structural instabilities. Increasing the density of states at the Fermi level would raise Tc but would eventually lead to an electronic instability. 

It is beyond the scope of this text to describe the mechanism for charge transfer in the high-temperature superconductors. While there is still a great deal of discussion on the applicability of BCS theory (cf. Section 6.1.1.3) to HTSC materials, it is safe to say that many of the principles still apply—for example, density of states at the Fermi level. The interested reader should refer to existing literature [3,4] for more information on the strucmre and theory of copper oxide superconductors. 

Thus, the shape of the band energy difference curves in Fig. 6.16(a) can be understood in terms of the relative behaviour of the densities of states in the middle panel. In particular, from eqn (6.111), the stationary points in the upper curve correspond to band occupancies for which A F vanishes in panel (c). Moreover, whether the stationary point is a local maximum or minimum depends on the relative values of the density of states at the Fermi level through eqn (6.113). Thus, the bcc-fcc energy difference curve has a minimum around N = 1.6 where the bcc density of states is lowest, whereas the hcp-fcc curve has a minimum around N = 1.9, where the hep density of states is lowest. The fee structure is most stable around N = 1, where A F fts 0, and the fee density of states is lowest. 

As in previous sections, we introduce the Mott -factor, though here we must define it as being proportional to the density of states at the Fermi level, and normalized so that... 

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