The influence of core hole relaxation on the main-line intensities in X-ray photoelectron spectra

The main photoelectron line spectroscopic factors that are currently used in photoelectron spectroscopy for quantitative analysis are calculated for a broad set of atoms. General trends of the behaviour of the spectroscopic factors of core atomic levels are discussed. The influence of the spectroscopic factors on the main line intensities and on concentrations of the elements, that are obtained using X-ray photoelectron spectra, is analysed.     

The effects of the lithium intercalation on the X-ray photoelectron spectra of NiPS3

Summary A detailed XPS study of the lithium-intercalated NiPS₃ specimens was performed at the 2p, 3p, 3s core levels of the nickel atoms and at the 2p core levels of the sulphur and phosphorous atoms for various lithium contents. Comparison of the Ni 2p, 3p and 3s XPS spectra corresponding to NiPS₃ and Li _x NiPS₃ systems shows some evident trends. In particular, a shift of the Ni main line towards lower binding energies, a decrease in the intensity of the Ni 3p, 2p satellite structures and a change in the full width at half maximum of the Ni 3s band with lithium content are observed. All these findings suggest a change in the 3d electron configuration for high lithium concentrations. As regards the cluster (P₂S₆)⁴⁻, with the addition of lithium, a P 2p main line shift towards higher binding energies is noted, while the S 2p peak shifts towards lower binding energies. These results are discussed in comparison with previous physical measurements concerning the nickel reduction process and the related electronic modifications. The authors of this paper have agreed to not receive the proofs for correction.     

The effects of elastic backscattering on the Auger or X-ray photoelectron spectra of solids

Simple attempts to understand the background on the low energy side of a spectral Auger or photoemission peak picture the electron as undergoing multiples of a typical loss according to a Poisson process with a mean distance λ. This model ignores elastic backscattering effects, and leads to the rather unrealistic situation in which the multiple loss peaks have the same intensity as the no loss peak. Here we have considered two related one-dimensional models which include backscattering and which allow exact solution. We find that, in general, losses follow a non-Poisson distribution governed by a characteristic distance Λ which includes both elastic and inelastic effects. However, contrary to the approximate results of Tougaard and Sigmund, the same value of Λ operates for electrons at all depths and so exponential attenuation is predicted. This modified (non-Poisson) distribution then leads to a background which decays with energy E from the peak as $\text{E}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>2</mtext>}}$ for large E and which varies approximately logarithmically closer to the peak, results which are in agreement with Tougaard and Sigmund and in support of the experimental work of Tougaard and Ignatiev.     

X-ray photoelectron spectra of hexavalent iron

Binding energies of Fe 3p and Fe 2p electrons for K₂FeO₄ were measured and compared with those for γ-FeOOH, α-Fe₂O₃, and for metallic iron.     

Many-body effects in the X-ray photoelectron spectra of magnetic chalcogenide chromium spinels

The many-electron excitations in magnetic chalcogenide spinels have been studied by X-ray photoelectron spectroscopy. Strong exchange splitting and asymmetry of 2p spectra of chromium and iron in Fe_0.25Cu_0.75Cr₂Se₄ ferrimagnet is found. The main characteristics of many-body interactions are determined and a mechanism determining the intensities of split lines is proposed.     

X-ray photoelectron spectra of cobalt compounds

The X-ray photoelectron spectra of a variety of cobalt(II) and cobalt(III) complexes have been investigated. Intense satellite lines were observed for the 2p, 3s and 3p peaks in the case of the high spin cobalt(II) compounds, but not for low spin cobalt(III) complexes. The satellites of the 2p levels are best explained as arising from shake-up processes, whereas those of the 3s and 3p levels are thought to arise largely from multiplet (exchange) splitting of the levels. Multiplet splitting of the 2p level is small and responsible for an increase in the doublet separation of the 2p_1/2, 2p_3/2 spin-orbit levels of the high spin cobalt(II) compounds. The chemical shifts for cobalt differ for the 2p, 3s and 3p levels of the high spin cobalt(II) compounds. Those of the 2p and 3p levels of diamagnetic cobalt(III) and low spin cobalt(II) complexes are equal. The difference in the case of the high spin cobalt(II) compounds is thought to be due to the presence of unpaired 3d electrons.     

Relative intensities in X-ray photoelectron spectra

An experimental determination of the relative intensities of X-ray photoelectron lines corresponding to the inner levels of elements with Z ? 20, and calculations of the total photo-ionization cross-sections for all shells of these elements with the Hartree—Fock—Slater potential are reported. The experimental and theoretical values agree well for the 1s levels while marked discrepancies are revealed for the 2p levels. The theoretical values of the cross sections for the atomic valence levels are used to calculate the relative intensities of molecular levels in CF₄, BF₄^?, BeF₄^2?, LiF, NO₃^?, CO₃^2?, CO, N₂, CO₂, H₂O and C₄H₅N. The results of the calculations agree satisfactorily with experiment.     

X-ray and UV photoelectron spectra of the metal sesquioxides

He(I,II) and MgKα valence region photoelectron spectra of polycrystalline Ti₂O₃, V₂O₃, Cr₂O₃, Mn₂O₃, Fe₂O₃ and Rh₂O₃ have been recorded. The method of sample preparation employed gave rise to UV-PE spectra which are significantly different from those previously reported. While clear changes are observed in the spectra accompanying the semiconductor-to-metal transition of V₂O₃ at 150 K, there is no apparent modification of the Ti₂O₃ spectra accompanying its second order transition at 500 K. The remaining first row transition metal sesquioxides exhibit spectra indicative of localised 3d electrons.     

Exact nondipole Kramers-Henneberger form of the light-atom hamiltonian: an application to atomic stabilization and photoelectron energy spectra

The exact nondipole minimal-coupling Hamiltonian for an atom interacting with an explicitly time- and space-dependent laser field is transformed into the rest frame of a classical free electron in the laser field, i.e., into the Kramers-Henneberger frame. The new form of the Hamiltonian is used to study nondipole effects in the high-intensity, high-frequency regime. Fully three-dimensional nondipole ab initio wave packet calculations show that the ionization probability may decrease for increasing field strength. We identify a unique signature for the onset of this dynamical stabilization effect in the photoelectron spectrum.     

The influence of electron scattering on the lineshape of auger and photoelectron spectra

A simplified model of Auger and photoelectron scattering in solids is presented. Within the framework of the model the relation between the distribution of backscattered primary electrons and Auger photoelectron distribution is obtained in terms of the geometric factor and the density of inelastic electron scattering probability. The new algorithm of spectrum background subtraction is formulated and applied to process the X-ray photoelectron and Auger spectra for a series of oxygen, fluorine, and copper compounds. It is shown that the method accuracy for the peak area measurements is better than 10%.     

X-ray photoelectron spectra and structure of iron polynuclear complexes

Iron trimethylacetate complexes with different ligands have been investigated by X-ray photoelectron spectroscopy (XPS). The Fe 2p, Fe 3p, C 1s, O 1s, and N 1s spectra obtained at successive replacement of the Fe-O coordination bonds with Fe-N bonds have been analyzed. A satellite component is found in the spectra of iron trimethylacetate complexes, which is indicative of the high-spin state of Fe^II and Fe^III iron atoms. The XPS data made it possible to determine the degree of covalence of the metal-ligand bonding and reveal two nonequivalent states for iron atoms.     

Repeatable intensity calibration of an X-ray photoelectron spectrometer

Ten years ago, NPL developed an infrastructure for calibrating the intensity response functions of electron spectrometers for Auger electron and for X-ray photoelectron spectroscopies. Two software systems were developed: one for Auger electron spectrometers or for Auger electron and X-ray photoelectron spectrometers combined, and one for X-ray photoelectron spectrometers on their own; the latter being applied if no suitable electron gun is available. The system for Auger electron and X-ray photoelectron spectrometers combined has been used regularly to calibrate the Metrology Spectrometer II at NPL and experience shows that this gives an instrumental intensity consistency of 0.4% over 10 years. Evaluations have not previously been reported at this level. The system for Auger electron and X-ray photoelectron spectrometers combined is used here in preference to the system solely for X-ray photoelectron spectrometers since it is more robust to the sample condition and can be used over a wider energy range. These issues, and how observed variations in the instrument intensity response may arise, are explained.     

X-ray photoelectron spectra of halogens in coordination compounds

X-ray photoelectron data on C12p energies for more than 200 coordination compounds of transition metals have been analysed. The effects of the central atom, other ligands, and the geometrical location of the chlorine atom on the C12p energy have been considered and certain regularities have been observed. The data on Br3d and F1s lines in coordination compounds have also been considered.     

Surface sensitivity and angular dependence of X-ray photoelectron spectra

By using an ultra-high vacuum X-ray photoelectron spectrometer designed specifically for surface studies, the surface sensitivity (ratio of surface to volume signal) of the technique was found to be enhanced by approximately one order of magnitude at low angles of electron emission measured from the surface plane. While the $\text{Mo(3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$) peak intensity from a clean polycrystalline target of molybdenum was independent of angle, the $\text{Cs(3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$) intensity from an adsorbed cesium layer on molybdenum increased and the $\text{Mo(3d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$) signal from the molybdenum substrate decreased as the angle of emission was decreased. A model is presented to account for the angular dependence and it is proposed that the angular dependence of spectral intensities can be used to differentiate surface from bulk species.     

The effect of transition probability on the shape of X-ray photoelectron spectra of diamond and silicon

X-ray photoelectron spectra of valence bands in diamond and silicon have been calculated. It is shown that the probability of electron excitation from s-states is higher than that from p-states. The density of the electron states in the valence band of these crystals differs markedly from the energy distribution of photoelectrons.     

Satellite phenomena in the X-ray photoelectron spectra of lanthanide trihydroxides

Using the direct CI method perturbation corrections to the Koopmans ionization energies have been obtained up to order 10 for the molecules CN^? and H₂O. The results are compared with those from the fully converged CI and B_k-type calculations. The convergence of the perturbation series is found to be quite slow although substantial improvement is possible using a variation-perturbation method.