Nickel Fermi level

Ni(lOO), using multiple scattering cluster calculations, and conclude that sulphur increases the antibonding nature of the 5o and In orbitals, thereby reducing the interaction of CO with the surface. Its influence at the Fermi level is small. For Li, on the other hand, there is increased occupancy of the 2n orbital which lies near the nickel Fermi level. 

Calculated band structures of aU these compounds feature the fermi level above a density-of-state peak that is consistent with the 3d bands for nickel. The [BN]" anion in CaNi(BN) compromises an electronic situation with a filled 3(7 (HOMO) level that is B-N anti-bonding (Fig. 8.13). Any additional electron will... 

Fig. 10 Electrochemical energy level model for orbital mediated tunneling. Ap and Ac are the gas-and crystalline-phase electron affinities, 1/2(SCE) is the electrochemical potential referenced to the saturated calomel electrode, and provides the solution-phase electron affinity. Ev, is the Fermi level of the substrate (Au here). The corresponding positions in the OMT spectrum are shown by Ar and A0 and correspond to the electron affinity and ionization potential of the adsorbate film modified by interaction with the supporting metal, At. The spectrum is that of nickel(II) tetraphenyl-porphyrin on Au (111). (Reprinted with permission from [26])...

The fact that evaporated potassium arrives at the surface as a neutral atom, whereas in real life it is applied as KOH, is not a real drawback, because atomically dispersed potassium is almost a K+ ion. The reason is that alkali metals have a low ionization potential (see Table A.3). Consequently, they tend to charge positively on many metal surfaces, as explained in the Appendix. A density-of-state calculation of a potassium atom adsorbed on the model metal jellium (see Appendix) reveals that the 4s orbital of adsorbed K, occupied with one electron in the free atom, falls largely above the Fermi level of the metal, such that it is about 80% empty. Thus adsorbed potassium is present as K, with 8close to one [35]. Calculations with a more realistic substrate such as nickel show a similar result. The K 4s orbital shifts largely above the Fermi level of the substrate and potassium becomes positive [36], Table 9.2 shows the charge of K on several metals. 

In the case of nickel electrodes on which the passive film is a p-f pe nickel oxide (NiO), the energy gap ( 0.2 eV) between the valence band edge and the Fermi level at the flat band potential is small so that the transpassivation potential Etp is relatively close to the flat band potential as in Fig. 11-13. 

By choosing the three metals, copper, nickel, and gold, two of them (Cu and Au) with low density of states close to the Fermi level E ) and one (Ni) with a high electron density of states close to E, the significance of the density of states concept could be explored 74). 

Fig. 6. Variation of Fermi level Ef in nickel oxide as a function of temperature, nature, and concentration of additions to nickel oxide (ref. 55).

Nature of Active Sites. There is no apparent correlation between the increase of catalytic activity and a modification of the electronic structure of nickel oxide, since the electrical properties of both catalysts are identical. It is probable that local modifications of the nickel oxide surface are responsible for the change of its activity and of the reaction mechanism. It should be possible to associate these structural modification with local modifications of the height of the Fermi level, but it would be difficult to explain the results by the electronic theory of catalysis which considers only collective electrons or holes. A discussion based only on the influence of surface defects seems, therefore, to be more straightforward. 

If the active metal becomes highly diluted the minimum polarity model leads to the virtual bound-state model (127, 128, 129). This model has also been applied to highly diluted Ni-Cu alloys (121a). The nickel d-states are then found to form not a common band with the copper d-states but narrow virtual levels between the copper d-states and the Fermi level. The levels are in resonance with the s,p-band of the metal. 

Deren et al. (271) have reported compensation behavior in the oxidation of carbon monoxide on nickel oxide containing various amounts of chromium oxide the effect is attributed to the modification of the Fermi level at... 

Fig. 84. Schematic density of states curve for f.c.c. nickel, where n(E) for 48 band is enlarged by a factor of ten. The Fermi level Ef is 5 eV above the bottom of the 48 band. Efb for Mn, Fe, and Co are also indicated.

D. N. Mcllroy, Nickel Doping of Boron-Carbon Alloy Films and Corresponding Fermi Level Shifts, Journal of Vacuum Science Technology, V0I.AI5, 1997, pp.854-859. 

Figure 2 also shows a d-band, arising from the four nickel atoms with d electrons explicitly included, extending downward from about -0.5 a.u. for the clean surface, adsorbed CH and coadsorbed CH and H cases. In a Ni atom, for this basis, the average d orbital energy is -0.44 a.u., a value close to the Hartree-Fock result. Photoemission measurements position the d ionization peaks of nickel near the Fermi level, a result also obtained by most density functional treatments of nickel clusters. Application of Koopmans theorem would therefore suggest that the present d-ionization... 

In all chemisorption cluster investigations the Gaussian level broadening parameter a was fixed at 0.3 eV. At least for our nickel clusters this seems a reasonable choice as orbitals near the Fermi levels are of similar spatial character. The results shown in Table II below support this view. 

A cluster density of states of Niia, literally (not just formally) broadened by 0.2 eV, is presented in Figure 2a for the icosahedral geometry near the equilibrium structure. The general features are roughly similar to that derived from a spin-polarized band structure calculation of bulk nickel. Near the Fermi level a very high density of states of the minority spin is found, the d band of the... 

In 1948 Verwey and his co-workers (88) established that lithium ions incorporated into nickel oxide produced an equivalent number of Ni + ions and so enhanced the electrical conductivity. Later, from measurements of the Seebeck effect, Parravano (89) confirmed that in the presence of lithium the Fermi level of nickel oxide is indeed depressed in accordance with the increased concentration of positive holes. For trivalent additions, Hauffe and Block (90) have shown that the incorporation of small amounts of Cr + ions decreases the conductivity of nickel oxide one infers accordingly that the hole concentration is decreased and that the Fermi level is raised. This is therefore an attractive situation with which to examine the influence of the height of the Fermi level on catalytic activity. The most appropriate n-type oxide for analogous studies is zinc oxide. 

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