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Kovalev A.I.,Surface Phenomena Researches Group | Wainstein D.L.,Surface Phenomena Researches Group | Rashkovskiy A.Y.,National University of Science and Technology "MISIS" | Gago R.,CSIC - Institute of Materials Science | And 3 more authors.
Journal of Nanomaterials | Year: 2015

Transformations of the electronic structure in thin silver layers in metal-dielectric (TiAlN/Ag) multilayer nanocomposite were investigated by a set of electron spectroscopy techniques. Localization of the electronic states in the valence band and reduction of electron concentration in the conduction band was observed. This led to decreasing metallic properties of silver in the thin films. A critical layer thickness of 23.5 nm associated with the development of quantum effects was determined by X-ray photoelectron spectroscopy. Scanning Auger electron microscopy of characteristic energy losses provided images of plasmon localization in the Ag layers. The nonuniformity of plasmon intensities distribution near the metal-nitride interfaces was assessed experimentally. © 2015 A. I. Kovalev et al.

Fox-Rabinovich G.,McMaster University | Kovalev A.,Surface Phenomena Researches Group | Aguirre M.H.,University of Zaragoza | Yamamoto K.,Kobe Steel | And 9 more authors.
Applied Surface Science | Year: 2014

The evolution of the self-organization process where dissipative structures are formed under the extreme frictional conditions associated with high performance dry machining of hardened steels has been studied in detail. The emphasis was on the progressive studies of surface transformations within multilayer and monolayer TiAlCrSiYN-based PVD coatings during the running-in stage of wear when self-organization process occurs. The coating layer was characterized by high resolution electron energy-loss spectroscopy (HREELS). It is shown that the nano-multilayer coating possesses higher non-equilibrium structure in comparison to the monolayer. Comprehensive studies of the tribo-films (dissipative structures) formed on the friction surface were made using a number of advanced surface characterization techniques such as X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure (XANES). The data obtained for the tribo-films was combined with the detailed TEM studies of the structural and phase transformations within the underlying coating layer. This data was related to the micro-mechanical characteristics of the coating layer and its wear resistance. It was demonstrated that the evolution of the self-organization process is strongly controlled by the characteristics of the tribo-films formed at different stages of the wear process. Within running-in stage (after length of cut of 15 m) fully protective mullite tribo-films predominantly form on the surface of nano-multilayer coating, establishing a functional hierarchy within the layer of tribo-films. This reduces entropy production during friction and leads to significant surface damage reduction and wear rate stabilization. In contrast, in a monolayer coating with a lower structural complexity, a variety of protective and non-protective tribo-films form during the running-in stage, which cannot fully protect the surface. Therefore the wear rate on the monolayer is not stabilized and its wear resistance is lower. The results obtained show that it is possible to control tribo-films evolution during self-organization by means of increase in structural complexity and the non-equilibrium state of the surface engineered layer with simultaneous tuning of its integrative behaviour. © 2014 Elsevier B.V. All rights reserved.

Kovalev A.I.,Surface Phenomena Researches Group | Wainstein D.L.,Surface Phenomena Researches Group | Rashkovskiy A.Yu.,Surface Phenomena Researches Group | Osherov A.,Ben - Gurion University of the Negev | Golan Y.,Ben - Gurion University of the Negev
Surface and Interface Analysis | Year: 2010

Crystals of PbS with different sizes were obtained by chemical deposition from aqueous solution (chemical bath deposition technique) onto undoped Si (100) substrate. The morphology and size of crystals were analyzed by high resolution scanning electron microscopy. The fine structure of Pb 4f and S 2p photoelectron lines was measured by X-ray photoelectron spectroscopy with monochromatic Al Kα source (hv = 1486.6 eV). The phenomenon of size shift, i.e. growth of binding energies for both donor Pb 4f and acceptor S 2p photoelectron lines with decreasing nanocrystals' size, was found and quantified as a function of nanocrystals' size. The size shift values of the Pb 4f 5/2 and 4f7/2 lines were determined for nanocrystals with a size from 20 to 250 nm. The interband and intraband electronic transitions were investigated by high resolution electron energy losses spectroscopy. It was shown that width and spatial anisotropy of the band gap depend on the size of PbS nanocrystals. The dependence of size shift from nanocrystals' size, the nature of this phenomenon, and a role of changes in fine structure of electronic states near the band gap are discussed in the report. Copyright © 2010 John Wiley & Sons, Ltd.

Kovalev A.,Surface Phenomena Researches Group | Wainstein D.,Surface Phenomena Researches Group | Rashkovskiy A.,Surface Phenomena Researches Group
Surface and Interface Analysis | Year: 2010

In accordance with high-resolution transmission electron microscopy (HRTEM), (Ti34Al66)N/Cu physical vapour deposition (PVD) composite coating had a nanolaminated structure with 20 nm (Ti 34Al66)N and 2.0-5.0 nm fine grain recrystallized Cu layers. It was unexpectedly found that the coatings under investigation had a lower thermal conductivity coefficient of 25 to 450° C compared to the TiAlN single layer coating. The physical basis of thermo-barrier protective features of copper nanolayers was explained based on XPS and high-resolution electron energy losses spectroscopy (HREELS) data. The temperature dependence of the phonons and conducting electron vibrations was investigated for Cu bulk, (TiAl)N upper layer, and the intermediate Cu one. In comparison with Cu bulk reference sample, the intermediate Cu layers of complex PVD coating were characterized by the following features: size-dependent shift of Cu 2p3/2 binding energy, reduced plasmon losses and acoustic mode phonon vibrations amplitudes, and increased intensities of the optical mode vibrations. These features of phonon and plasmon oscillations in the crystal lattice of Cu nanolayers do not completely explain the anomalies of the thermal conductivity of the (TiAl)N/Cu PVD coating. The thermal barrier properties of Cu nanolayers can be primarily attributed to the mirror effect or reflecting of the heat flux from the surface by metal layer with high concentration of conducting electrons. Copyright © 2010 John Wiley & Sons, Ltd.

Kovalev A.,Surface Phenomena Researches Group | Wainstein D.,Surface Phenomena Researches Group | Rashkovskiy A.,Surface Phenomena Researches Group | Fox-Rabinovich G.,McMaster University | And 3 more authors.
Surface and Interface Analysis | Year: 2010

Nanostructured single-layer TiAlCrSiYN and multilayer TiAlCrSiYN/TiAlCrN coatings were deposited by a hybrid physical vapor deposition (PVD) coater with a plasma-enhanced type arc source. Yttrium was added as a surfactant element to stabilize the nanostructure of the coating. The paper reports on the X-ray photoelectron spectroscopy(XPS) and analysis of the extended energy loss fine structure(EELFS) spectroscopy studies of the electronic and atomic structure of tribofilms formed on the surface of cutting tools during high-speed machining of hardened tool steels. It was shown by electron spectroscopy investigations that two types of tribofilms form on the surface of cutting tools. The first type is sapphire-like (Al - O) and mullite-like (Al - Si - O) films with high protective ability. The second type has an amorphous-like structure and a high density of dangling bonds enhancing their lubrication properties at elevated temperatures. This unique combination of thermal-barrier and frictional characteristics of these tribofilms allows the cutting tool to stand high-speed cutting conditions and achieve reliable tool life. A more intensive generation of mullite-like tribofilms was observed in the single-layer coating in contrast to the multilayer one, where generation of the sapphire-like component prevailed. Most probably, the nanostructuring of the coating increases the interface and grain boundary diffusion and activates the formation of a high-temperature tribo-oxide. Copyright © 2010 John Wiley & Sons, Ltd.

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