X-ray Photoelectron Spectra Studies Research Articles

Observation of Electrical Conductivity During XPS Analysis of Organic Oils

Under the conditions of x-ray photoelectron spectra (XPS) analysis organic liquids appear to behave as electrical conductors. Here we report x-ray photoelectron spectra for pentaphenylether and pentaphenyltrimethyltrisiloxane oils at room temperature. These materials are commercially available as diffusion pump fluids (Santovac 5 and DC705, respectively). Their room temperature vapor pressures are ∼2 × 10−8 Pa and they can be studied by XPS without hazard to the spectrometer vacuum system. Both materials were investigated as relatively thick liquid films (∼10 μm, as determined by weighing) on a piece of silicon wafer. A solid organic film of this thickness would be expected to be an XPS insulator. The oil films on silicon required no external charge compensation and gave high resolution C 1s spectra with the first component of the envelope very close to 285 eV binding energy. Measured binding energies closely followed a bias voltage applied to the silicon wafer. Oil films thicker than 10 μm behaved as XPS insulators. Insulating behavior was also observed on cooling the samples by passing liquid nitrogen through the spectrometer manipulator during analysis. The explanation of these phenomena is not yet clear but the apparent electrical conductivity allows XPS study of low vapor pressure organic liquids in a straightforward way, without charging effects.

A theoretical study of x-ray photoelectron spectra of model molecules for polymethylmethacrylate

We explore the usefulness of the delta self-consistent-field (ΔSCF) approximation in connection with high-resolution x-ray photoelectron spectra for component and structural analysis of organic compounds. Results for core electron binding energy shifts for model molecules of the polymethylmethacrylate polymer are presented. A previously devised method for proper self-consistent-field solutions for core hole states in molecules is evaluated. The results indicate that chemical shifts can be obtained within a few tenths of an eV. A discussion is presented on the inherent errors in the ΔSCF approximation, the proper corrections for zero-point vibrational energies, and the role of relaxation of core orbitals.

Anionic conduction in lead oxyfluoride glasses

The DC conductivity, F1s X-ray photoelectron spectra (XPS), Al K α fluorescence spectra (XFS) and Raman spectra have been studied for the glasses in the systems B 2O 3PbOPbF 2 and B 2O 3PbOPbF 2AlF 3. The conductivity increases by several orders of magnitude and the activation energy decreases linearly with the PbF 2 content for both the ternary and the quaternary glasses. Such a change has been proposed to be due to the contribution of F − ions to the conduction. The F1s XPS study shows the presence of three kinds of F − ions, such as those bonded to B, Al and Pb atoms in the glasses. The decrease in the conductivity upon the addition of AlF 3 is attributed to the formation of AlF bonds. The Raman and Al K α XFS study shows that the glasses are comprised of discrete and polymerized three-coordinated borate units and six-coordinated Al atoms.

Theoretical study of X-ray photoelectron spectra of mono- and polycrystalline samples

X-ray photoelectron emission intensity from mono- and polycrystalline samples has been studied theoretically. In case of polycrystals the spectrum shape of valence photoelectrons is defined by the photoionization cross-sections and the partial densities of states of electrons with symmetry of different types. For single crystals the expression is more complicated. In case of Si theoretical spectra from polycrystals coincide practically with those from single crystals while in case of Cu there is some appreciable difference in the spectrum shape.

Theoretical study of X-ray photoelectron spectra of BN and SiC crystals

The tight-binding method has been used to calculate the density of states and X-ray photoelectron spectra of valence electrons in BN and SiC cubic crystals. It is shown that s- and p-states of atoms of various components contribute differently to the spectrum.