Home – Home – Jornals – Advanced Search

By UPS spectroscopy of vapor, XPS spectroscopy of the condensed phase, and quantum chemical methods the adducts of tris -b-diketonates Eu(асас)₃Phen and Eu(hfас)₃Phen are studied. The electronic structure and features of the nature of chemical bonds in the adducts are established. The geometric structure of the studied compounds in the gas phase is determined. A procedure is developed that helps to assign the bands in gas-phase HeI photoelectron spectra and also in the valence band of the XPS spectra. Quantum chemical calculations (DFT) make it possible to find the regular changes in the electronic structure of the chelate complexes depending on ligand fluorination, to study the effect of a 1,10-phenanthroline molecule on the electronic structure of the chelate rings, and also to analyze the electronic effects caused by trifluoromethyl substitution for methyl groups in the ligand.

X-ray photoelectron spectroscopy and quantum chemistry methods are used to study Nd(tol)₃ and Nd(сor)₃ carboxylate complexes and their adducts with 1,10-phenanthroline (Nd(tol)₃Phen and Nd(сor)₃Phen₂). The electronic structure and specific features of the nature of chemical bonds are studied, as well as the effect of 1,10-phenanthroline on the electronic structure of the adduct. We propose the band assignment of the valence band of the XPS spectra of all compounds.

A series of Ni- and/or Cu-containing coatings formed by plasma electrolytic oxidation on aluminum and titanium are examined by X-ray photoelectron spectroscopy. Binding energies of core electrons, elemental composition, chemical state of elements, and features of the structural organization of the surface and near-surface layers of the coatings are determined. A combination of the data collected indicates similar regularities of the composition and significant distinctions in the structure of the coatings formed. It is shown that the coatings formed on titanium are characterized by a considerably higher phosphorus concentration, and correspondingly, phosphates, unlike the coatings formed on aluminum, in which base metal and 3 d element (Ni or Cu) oxides are dominant. In both cases, Cu is mainly concentrated in the surface layers of the coatings whereas Ni is mainly concentrated in the near-surface layers.

Mineral valleriite of the Talnakh deposit, which consists of alternating copper-iron sulfide layers and brucite-like layers of magnesium-aluminium hydroxide is studied for the first time by XPS at photon excitation energies ranging from 1.253 keV to 6 keV and CuL FeL, SL, AlL, MgK, and OK edge TEY XANES using synchrotron radiation. The comparison of the XPS and XANES spectra of valleriite and chalcopyrite, in particular, demonstrates that in the sulfide layers of valleriite, Cu⁺ and Fe³⁺ are in a tetrahedral coordination, however, a local positive charge on both cations is slightly lower than that in chalcopyrite, apparently, due to a structure disorder. The concentration of oxygen-bound iron decreases with an increase in the depth of the analyzed layer even after ion etching; probably, Fe does not enter into the brucite-like layer, but mainly forms its own surface structures.

XPS, Pb L ₃ and Cu K EXAFS, solid state NMR, and EPR techniques are used to study insoluble products formed in the interaction of aqueous solutions of lead(II) nitrate and copper (II) sulfate with potassium n -butylxanthogenate (PX). The XPS spectra of lead xanthogenates with the composition PbX₂ are similar to those of PX, and interatomic distances of 0.279 nm suggest a nearly ionic character of Pb-S bonds. In copper xanthogenate precipitating together with dixanthogene (approximately 15 wt.%), the Cu(I)-S bond length is smaller (0.229 nm), and copper coordination number of 2.9 in a composite with dixanthogene increases to 3.3 after its removal by washing with acetone. The XPS spectra indicate the covalent character of the bond and non-equivalence of xanthogenate radicals. Solid state ¹H and ¹³C NMR spectra as well as the actual absence of metal lines under the measurement conditions demonstrate strong disordering of the structure of xanthogenates, which is stronger for PbX₂ and weakest in CuX after the removal of dixanthogene. EPR reveals sulfur-containing radicals and Cu²⁺ in CuX, however, their amounts are insignificant and decrease after the washing with acetone. The results of the work are significant for the understanding of the reactivity of xanthogenates, in particular, under the conditions of flotation beneficiation of base metal ores.

The states of components of highly efficient Pt/CeO₂ catalysts for low-temperature oxidation of carbon monoxide are studied in detail by X-ray photoelectron spectroscopy (XPS). Using the precise calibration of the spectra relative to the internal standard and the fitting of Ce3d and Pt4f spectra by elementary doublets, we found the features of the platinum interaction with the ceria lattice. It is shown that when the co-deposition technique is used, depending on the quality of stock solutions, it is possible to obtain both homogeneous solid solutions of platinum in the ceria lattice and solutions containing polyatomic platinum associates of the (PtO)_m type. It is found that when homogeneous PtCeO_x solid solutions are stored in air at room temperature, the homogeneous solutions slowly pass into the state of solutions with platinum associates. Mechanical mixtures of metallic platinum and ceria nanoparticles, synthesized by laser ablation, were also investigated in the course of their annealing in the air. The results obtained from the Pt4f spectra completely confirm the specific features of the interaction of platinum with ceria.

The regularities of the electron energy dissipation found in the subsurface atomic layer are valid in the bulk of a solid, too. On the example of model graphite-based materials it is shown that energy losses in X-ray photoelectron spectra agree with the calculated valence electron excitation spectra in analogous unit cells. The control of conjugate electron transitions opens the way to gain new data on the geometry, character, and order of bonding between atoms in the sample by the conventional electron spectroscopy and quantum chemistry methods.

The electronic structure of hexanuclear Mn(II,III) pivalate complexes with tetrahydrofuran and isonicotinamide are studied by X-ray photoelectron spectroscopy and X-ray emission spectroscopy. It is shown that when isonicotinamide substitutes for tetrahydrofuran the spin state of manganese ions is retained, and the electron density increases on the manganese and oxygen atoms of the [Mn₆(O)₂Piv₁₀] core.

X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), and near edge X-ray absorption fine structure (NEXAFS) spectroscopy are used for in situ studies of the electronic structure of lithiated natural graphite produced by thermal deposition of lithium upon graphite in a vacuum. By XPS and NEXAFS spectroscopy it is found that lithium vapor thermal deposition results in the formation of a lithiated graphite surface layer and a change in its electronic structure. Based on the quantum chemical simulation of the experimental СK_α XES spectrum of lithiated graphite, it is found that lithium atoms are located mostly on the edges of graphite crystallites. Atomic force microscopy reveals that the size of natural graphite flakes varies from 50 nm to 200 nm.

The electronic structure and functional composition of the products of graphite oxide (GO) interaction with concentrated sulfuric acid (H₂SO₄) depending on the oxygen content in the precursor and the treatment temperature are studied. X-ray photoelectron spectroscopy measuring the near-edge Xray absorption fine structure at the CK edge, and infrared spectroscopy are used to show the reduction of the π-electron system of graphene planes at a temperature of 200° C. Aggregation of oxygen groups in GO containing more than 40 % of oxygen causes the formation of vacancy defects in the planes with oxygen groups at the edges. When the GO treatment temperature rises to 280°C, the oxidation of the basal plane π-regions occurs. The results can be the basis to control the functional composition, vacancy number and size in graphite materials.