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Chişinău, Moldova

Vernickaite E.,Vilnius University | Tsyntsaru N.,Vilnius University | Tsyntsaru N.,Academy str | Cesiulis H.,Vilnius University
Surface and Coatings Technology | Year: 2016

Binary Cu-W, Co-W and ternary Co-Cu-W alloy coatings were electrochemically deposited onto stainless steel substrate from a citrate-borate electrolyte under potentiostatic mode at 20 and 60. °C. The cathodic polarization, current efficiency of co-deposition, chemical composition and structure of the prepared alloys as a function of deposition potential and temperature were studied and compared to those of binary Cu-W and Co-W alloys. All deposits were of uniform thickness, without cracks and well adhered to the substrate. The cathodic current efficiency increases with the bath temperature and cathodic deposition potential increase. The polarization studies revealed that Cu-W alloy deposition starts at more negative potentials than those of Co-W and Co-Cu-W that leads to the lowest current efficiency for Cu-W (20%) in comparison with up to ~. 90% obtained for Co-Cu-W and Co-W alloys electrodeposition. Also, this results in the low W content in the Cu-W coatings (<. 6. at.%) that strongly depends on deposition potential and bath temperature. The morphology of deposited coatings depended rather on electrodeposition conditions than on W content in the alloys. X-ray diffraction analysis indicated that Cu-W alloy is a solid solution with typical Cu-type face centered cubic (fcc) lattice. Introduction of Co into this alloy resulted in the formation of additional hexagonal (hpc) Co XRD patterns for ternary Co-Cu-W alloy. © 2016. Source

Tsyntsaru N.,Academy str | Kaziukaitis G.,Vilnius University | Yang C.,Catholic University of Leuven | Cesiulis H.,Vilnius University | And 3 more authors.
Journal of Solid State Electrochemistry | Year: 2014

This study was performed in order to investigate a possibility to obtain Co-W microbumps via electrochemical routes, because this alloy recently has gained attraction as a novel barrier against copper diffusion. In order to be applied in flip-chip technology, barrier layers should be void-free and uniformly deposited on the entire area of a die to ensure high reliability and high performance of wafer bump-solder interface. To meet these requirements, a set of potentiostatic and galvanostatic electrodeposition was carried out from a citrate electrolyte, at pH 5 and at room temperature. The tests done confirm that void-free Co-W bumps with a uniform tungsten content along the bump can be obtained by potentiostatic and galvanostatic electrodeposition. Successful electrodeposition of Cu/Co-W/Sn layers with good adhesion between them and uniformity on the entire array of bumps also was obtained. The XPS data confirm that electrodeposited Co-W layers can act as a good barrier between Sn and Cu. © 2014, Springer-Verlag Berlin Heidelberg. Source

Cesiulis H.,Vilnius University | Maliar T.,Vilnius University | Tsyntsaru N.,Vilnius University | Tsyntsaru N.,Academy str | And 3 more authors.
Journal of Nanoelectronics and Optoelectronics | Year: 2014

Titanium oxide films are fabricated by Ti anodization in orthophosphoric acid-ammonium fluoride electrolytes. On the mechanically polished semi-bright Ti substrates the continuous TiO2 films are formed, whereas ordered nanoporosity is formed on the mirror-like surface of Ti substrate at temperatures of 10-20 °C in the H3PO4 electrolyte with NH4F. The photocurrents and photopotentials are affected by the amount of fluorine in the electrolyte and consequently in the deposit. Tribocorrosion tests were performed in a neutral solution, and changes of open-circuit potential (OCP) as well as electrochemical impedance spectra were recorded with/without 0.4 N load. The rapid changes of OCP can be explained by the passive film abrasion, when oxide film becomes damaged and bare Ti surface is exposed. The wear loss depends on the NH4F concentration in the solution used for TiO2 films fabrication. TiO2 films destroyed during sliding tend to restore within 300-400 s after unloading © 2014 American Scientific Publishers All rights reserved. Source

Sergentu V.,Moldova Academy of Sciences | Ursaki V.,Moldova Academy of Sciences | Sirbu L.,Academy str
Physica Status Solidi (B) Basic Research | Year: 2013

In this paper, we demonstrate that body zero frequency modes can exist at extremely low frequencies in a system of nanocylinders made of non-dissipative material. Such kind of modes is not specific to single nanocylinders, but they resemble modes inherent to photonic crystals. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Fonari A.,New Mexico Highlands University | Jradi F.M.,American University of Beirut | Fonari M.S.,Academy str | Al-Sayah M.H.,American University of Sharjah | And 4 more authors.
Journal of Molecular Structure | Year: 2011

Phenanthro[4,5-abc]phenazine-18-crown-6 chromophore (1) was synthesized, and its two polymorphic modifications were obtained by recrystallization from dichloromethane/methanol and dichloromethane/hexane solvent mixtures. Both polymorphs 1a and 1b crystallize in the same monoclinic P21/c space group, and represent conformational polymorphs, which differ by the conformation of the macrocyclic cavity. The crystal structures obtained have been compared with molecular structures computed by density functional theory (DFT). As revealed by quantum chemical calculations, both polymorphs reach different minima on potential energy surface that supports our results that different solvents template distinctive conformational isomers found in crystals. © 2011 Elsevier B.V. All rights reserved. Source

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