Valence level spectra

The presence of N2O at 80 K was confirmed in foiu ways first by determining a difference spectrum between 80 and 120 K (when it desorbed). Two N(ls) peaks (Fig. 10) (one at 402 eV and the other at 406 eV) and one 0(1 s) peak (at 531 eV) were lost on warming the intensities of the N(ls) peaks were identical. Second, the difference spectrum was shown to be identical with N2O molecularly adsorbed at 80 K on a Cu(lll) surface. Third, a mass spectrum analysis of the gas phase on warming from 80 K showed the presence of N2O and last, helium-induced valence-level spectra at 80 K were consistent with a NO-N2O mixed adlayer (44, 45). 

Fig. 15. Valence level spectra of isomeric polybutyl acrylates excited be Mgjtaj 2 radiation...

Before we proceed to discuss the valence spectrum in greater detail, it is very instructive first to consider the Is deep core level spectrum, which is not complicated by the presence of several overlapping satellite spectra and therefore gives direct information about the ionic excitation level structure. If the core level spectrum is experimentally available, this may then be of great help for interpreting valence level spectra. 

Ae/untreated PE. Based on the C Is level and valence level spectra, no evidence of Ag interaction with untreated PE was found. Several depositions were done, and in all cases no changes in the shape or peak positions were found. This is consistent with the poor adhesion for Ag on untreated PE. The results for Ag depositions on argon-plasma-treated PE were similar, except for slight changes in the valence level spectra which will be discussed below. 

The valence level spectra are shown in Figure 4. Even at coverages of less than a monolayer, the valence band spectrum is dominated by the Ag 4d band between 3-8 eV. This band directly overlaps the region of the C-H band of the untreated PE and the region where the O 2p lone pair orbitals occur for oxygen-plasma-modified PE (5). TTte two peaks comprising the C-C band (predominately C 2s character) of the PE substrate are evident in all spectra at 13.2 eV and 18.8 eV. The Ag 4d band for... 

The valence level spectra are shown in Figure 8. The valence level spectrum for clean PET consists of five main bands of which the most important are the bands between 3-10 eV. The highest occupied valence level (3-4 eV) should have significant contribution from the re electrons in the phenyl ring and are not resolvable as a separate band. The bands between 4-10 eV have significant contributions from... 

Figure 3.13. UPS valence level spectra for the gas phase thiophene (a) the condensed phase thiophene (b) bithio-phenc (c) terthiophene (d), and undoped poly(3-methylthio-phene) on Pt (e), as excited with the He(II) resonance line (40.8 eV). (Reprinted with permission from ref 117, Am. Inst. Phys.)...

The present experimental data show similarities with those of previous workers [12,34] but new features appear, which we will discuss in the light of the results from the calculations. Considering first the valence level spectra (Fig. 2b), the growth of bandgap peaks with respect to inserted proton concentration involves two distinct peaks instead of the singular features previously observed. Moreover, the appearance of both peaks may be... 

Figure 6, Valence level spectra for evaporated silver on PS after removal of the PS conttibution for the low coverages. The coverages are given in atoms/cm. The bulk spcctium is for a 600 nm thick coating. The dashed line denotes the Fermi edge.

Figure 7. Valence level spectra for approximately 2x10 atoms/cm silver on and plasma-lieaied PE after removal of the PE contribution.

Figure 9. Valence level spectra for evaporated silver on PPS after removal of the pp ...

X-Ray photoelectron spectroscopy (XPS) or ESCA is another routine analytical technique whose application to CPs is best illustrated by examples. Wide-spectrum XPS is a simple tool for elemental analysis, useful, e.g., to see the presence of an atom belonging to a particular dopant to verify doping. Higher resolution (core-level) XPS is typically useful for determining oxidation states of a central heteroatom, e.g. the N-atom in poly(aromatic amines), hence elucidating the redox state of the polymer or at least of the central heteroatom. Finally, valence-level spectra, at very low energies, have been said to be usable for estimation of density of states, although their accuracy is questionable. 

From XPS core valence levels spectra, the C-S bond appears very similar in both (di)phenyl sulfide and poly-p-phenylene sulfide. The S lone pair of PPS interacts with the ir electronic aromatic system and the C-S bond has some double character, as observed in aromatic sulfides or disulfides So, there is in the polymer a... 

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... 

Fig. 48. Experimental valence level ESCA spectrum for C0124). Ionic excitation levels (top of picture) inferred from the core hole spectrum in Fig. 47...

The XPS valence band spectrum of an electroactive polymer/dopant complex can be understood in terms of the known valence band spectra of the monomer and the dopant. Thus, the valence band spectroscopy confirms the core-level results by identifying the monomer and dopant species [15]. 

Core levels of all elements except hydrogen can be detected using an X-ray source. Valence bands can be obtained using a UV source. Core level binding energies are characteristic of the atom and the valence band spectrum of an adsorbed molecule is usually characteristic of the molecule. The spectra of adsorbed CO and C6H6 resemble the gas... 

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