Density of valence states

The most direcdy measurable feature of the electronic band structure, the valence band photoelectron spectrum, involves the density-of-valence-states (DOVS), or p(e), which is obtained from the electronic band structure using the standard definition,... 

Some of the theoretical models used vary in each of the studies reported. These models were discussed in chapter 2, and the results are presented in each individual case below. In some cases, however, a detailed interpretation of the experimental UPS spectra requires the support of calculated density-of-valence-states (DOVS) curves. For that purpose, the valence effective Hamiltonian (VEH) method, which has been shown to provide accurate distributions of valence states for polymers and molecules, is used12-14. Even though it cannot be used for metal-containing systems (since the VEH potentials are not defined for metal atoms), the VEH approach is nevertheless of interest to determine the nature of the electronic wavefunctions (molecular orbitals) associated with a given UPS feature in the pristine polymer. 

A detailed analysis of the UPS spectra of pristine P3HT, (where H = hexyl) based on the results of VEH quantum-chemical calculations of the density-of-valence-states, the DOVS, has been presented previously27. For the present purposes, the UPS results on P3HT and P30T are the same the differences in the length of the aliphatic side... 

Fig. 3.10. Evolution of the local density of valence states on various sites on Pd particles containing 3,871 atoms, calculated in the tight-binding approximation (from [40])...

The density of valence states of crystalline Te2.ooBro.75Io.2s was determined 54) by UV and X-ray photoemission experiments and compared with the density of valaice states of elemental tellurium The results are given in Figs. 26a-c. 

Figure 3.24 UPS spectra (upper curve), PIES spectra (medium curve) for thin film of PT without annealing, and calculated density of valence states (bottom curve, calculated by a DFT method with B3LYP/6-31C basis set on PT with 12 repeated thiophene ring units the longer...

Calculations of the density of valence states in AS2S3, As2Se3 and As2Te3 have recently been reported [905]. 

Similarly, the number of holes, denoted by pdT), will be equal to the integral over all valence states of the density of valence states gv( ) multiplied by one minus the Fermi occupation number ... 

Three of the most direct and readily comprehensible measures of the electronic structure of a molecular system are optical absorption spectroscopy and the two branched of photoelectron spectroscopy, known as ultraviolet and X-ray photoelectron spectroscopy, or UPS and XPS. The XPS of polymers [51], the UPS of polymers [52], as well as both the XPS and UPS of conducting polymers [53] have been reviewed recently. The reader is referred to the literature for further details. It should be relatively obvious from the figures presented below, however, how the calculated band structure, the density-of-valence-states (DOVs) derived therefrom, and the corresponding experimental valence band spectra can be compared with one another. 

B) dehydrogenated and (C) plasma oxidized. Notice the different scaling of the spectra and the difference in energy and intensity of the low energy cut-off. Spectrum (A) is that of an NEA surface, whereas (B) and (C) correspond to surfaces with PEA [62]. (b) Schematic explanation for (a). On the left, the photoexcitation process leads to the emission of primary electrons that yield a replica of the occupied density of valence states in the kinetic energy distribution of... 

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