Core XPS spectra

Accurate Density-Functional Calculation of Core XPS Spectra Simulating Chemisorption and Intermolecular Effects on Real Systems ... 

Accurate Density-Functional Calculation of Core XPS Spectra... 

Accurate density-functional calculation of core XPS spectra simulating chemisorption and intermolecular effects on real systems... 

X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), is described in section Bl.25,2.1. The most connnonly employed x-rays are the Mg Ka (1253.6 eV) and the A1 Ka (1486.6 eV) lines, which are produced from a standard x-ray tube. Peaks are seen in XPS spectra that correspond to the bound core-level electrons in the material. The intensity of each peak is proportional to the abundance of the emitting atoms in the near-surface region, while the precise binding energy of each peak depends on the chemical oxidation state and local enviromnent of the emitting atoms. The Perkin-Elmer XPS handbook contains sample spectra of each element and bindmg energies for certain compounds [58]. 

Figure 5-19. N(ls) XPS core level spectra of emeraldine base adsorbed on ITO. The top most spectrum corresponds to ultra-thin Him (in the mono layer regime) while the bottom spectrum corresponds to thick film.

The XPS S(2p) core level spectra recorded during the stepwise deposition of copper onto poly(3-hcxyllhiophenc), or P3HT [88] are shown in Figure 5-17. The S(2p) spectrum at the lop correspond to the pristine system. On increasim copper... 

Figure 1. XPS 4f core level spectra for glass 76101 containing...

Figure 2. 4f core level spectra for glass I (Table I) demonstrating the strong tendency of the Pu + ions to reduce in the XPS spectrometer. Spectra (a) through (e) are short (10 min) sequential runs showing accumulative reduction of Pu + to Pu +. 

On the other hand, the XPS data near the Fermi level provide us the valuable information about the band structures of nanoparticles. XPS spectra near the Fermi level of the PVP-protected Pd nanoparticles, Pd-core/ Ni-shell (Ni/Pd = 15/561, 38/561) bimetallic nanoparticles, and bulk Ni powder were investigated by Teranishi et al. [126]. The XPS spectra of the nanoparticles become close to the spectral profile of bulk Ni, as the amount of the deposited Ni increases. The change of the XPS spectrum near the Fermi level, i.e., the density of states, may be related to the variation of the band or molecular orbit structure. Therefore, the band structures of the Pd/Ni nanoparticles at Ni/Pd >38/561 are close to that of the bulk Ni, which greatly influence the magnetic property of the Pd/Ni nanoparticles. 

PtRu nanoparticles can be prepared by w/o reverse micro-emulsions of water/Triton X-lOO/propanol-2/cyclo-hexane [105]. The bimetallic nanoparticles were characterized by XPS and other techniques. The XPS analysis revealed the presence of Pt and Ru metal as well as some oxide of ruthenium. Hills et al. [169] studied preparation of Pt/Ru bimetallic nanoparticles via a seeded reductive condensation of one metal precursor onto pre-supported nanoparticles of a second metal. XPS and other analytical data indicated that the preparation method provided fully alloyed bimetallic nanoparticles instead of core/shell structure. AgAu and AuCu bimetallic nanoparticles of various compositions with diameters ca. 3 nm, prepared in chloroform, exhibited characteristic XPS spectra of alloy structures [84]. 

Figure 8. Valence band XPS (a) and UPS (b) spectra of silver islands on native oxide covered Si(l 0 0) during bombardment with 1 keV Ar" ions. Substrate related contributions are removed. Numbers at each spectra stand for the Ag/Si ratio determined from the appropriate XPS core level spectra. The uppermost curve is the spectrum of polycrystalline bulk Ag. (Reprinted from Ref [146], 1998, with permission from Elsevier.)...

As it can be observed in Table 13.1, Ir supported over pure oxides exhibited low acidity, but Ir supported on mixed Nb20s-Si02 displayed an important enhancement in the surface acidity with surface coverage by niobia increases. Binding energies (BE) of core-level electrons and metal surface composition were obtained from XP spectra. The BE values of Si 2p, Ti 2p3/2, Nb 3ds/2 were 103.4, 458.5 and 123 eV respectively, which are exactly the expected values considering the presence of oxides of Si (IV), Ti (IV) and Nb (V). With regard to Ir 4f7/2 core level, a... 

To determine the BEs (Eq. 1) of different electrons in the atom by XPS, one measures the KE of the ejected electrons, knowing the excitation energy, hv, and the work function, electronic structure of the solid, consisting of both localized core states (core line spectra) and delocalized valence states (valence band spectra) can be mapped. The information is element-specific, quantitative, and chemically sensitive. Core line spectra consist of discrete peaks representing orbital BE values, which depend on the chemical environment of a particular element, and whose intensity depends on the concentration of the element. Valence band spectra consist of electronic states associated with bonding interactions between the... 

Fig. 4 Survey spectrum of sputter-cleaned Hf metal containing 3% Zr impurity, with all visible core-line peaks labelled, collected using a monochromatic A1 Ka X-ray source (1486.7 eV). The stepped background hatched), found in all XPS spectra, arises from photoelectrons that lose KE by inelastic electron scattering as they travel through the surface and into vacuum...

An attractive feature of applying XPS to study these skutterudites is that the valence states of all atoms can be accessed during the same experiment. As in the study of the MnP-type compounds, these types of investigations also provide insight into bonding character and its relation to electronegativity differences. This information is obtained by analysing both core-line and valence band XPS spectra. 

Fig. 28 Comparison of RE 3d XPS spectra for a LaFe4Pi2 and CeFe4Pi2 with b LaP, CeF3, and CeF4. The 3d5/2 (A) and 3d3/2 core lines (B), and satellite peaks (A, S ) are marked. Reprinted with permission from [110]. Copyright the American Chemical Society...

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