Bonding Fermi energy

For a semiconductor like Ge, the pattern of electronic interaction between the surface and an adsorbate is more complex than that for a metal. Semiconductors possess a forbidden gap between the filled band (valence band) and the conduction band. Fig. 6a shows the energy levels for a semiconductor where Er represents the energy of the top of the valence band, Ec the bottom of the conduction band, and Ey is the Fermi energy level. The clean Ge surface is characterized by the presence of unfilled orbitals which trap electrons from the bulk, and the free bonds give rise to a space-charge layer S and hence a substantial dipole moment. Furthermore, an appreciable field is produced inside the semiconductor, as distinct from a metal, and positive charges may be distributed over several hundred A. 

Fig. 8.11 (a) The energy bands of La about the equilibrium atomic volume Q0 and the corresponding d band occupancy, A/d. of La and Lu. d, t, and b label the centre of gravity, the top and bottom of the d band respectively is the bottom of the NFE sp band, and F is the Fermi energy, (b) The relative d bond energies in units of the d bandwidth, W, of hep (full curve). La structure type (dashed curve), and Sm structure type (dot-dashed curve) with respect to fee as a function of the d band occupancy /Vd. The resulting stable structures for the ideal and a non-ideal axial ratio are also shown. (From Duthie and Pettifor (1977).)... 

X directions. These directions were chosen because they represent the directions of maximum jt and o bonding. Inspection of this figure shows that the pd-hybridization is strongly localized in the A3 and A2-bands, while the Fermi energy DOS is the result of the bonding characterized by the comparatively flat A4 and A5-bands. 

Fig. 10.1. One-dimensional metal model of interacting 2/ z-electrons in polymer chain from C-C- bonds of equal length [9] (a) the configurations of chain with repeat union (a). 2/jz-electrons are indicated by black dots (b) energy band scheme for 2/ z-electrons EF Fermi energy.

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