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Chişinău, Moldova

Academy str

Chişinău, Moldova
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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.

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.

Ganin E.V.,Odessa State Environmental University | Masunov A.E.,University of Central Florida | Siminel A.V.,Academy str | Fonari M.S.,Academy str
Journal of Physical Chemistry C | Year: 2013

The asymmetric isonaphthalene imide, 3-[(4-nitrophenyl)imino]-1H,3H- benzo[de]isochromen-1-one was obtained by condensation of 1,8-naphthoylchloride with p-nitroaniline in the presence of pyridine. The crystal structure and vibrational and electronic absorption spectra are reported. The emission spectrum of the crystalline phase demonstrates dual luminescence, with short and long wavelength components, while only the short wavelength component is present in chloroform solution. The geometrical and electronic structures of the ground and excited states of the molecule are investigated using density functional theory methods. Dual fluorescence is explained in terms of the excited states of different nature. The spectroscopic properties of newly synthesized compounds for possible biosensor applications are discussed. © 2013 American Chemical Society.

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.

Tsyntsaru N.,Academy str | Kavas B.,Technical University of Istanbul | Kavas B.,Ford Motor Company | Sort J.,Autonomous University of Barcelona | And 2 more authors.
Materials Chemistry and Physics | Year: 2014

The porous structure of anodic aluminium oxide (AAO) can be used in versatile applications such as a lubricant reservoir in self-lubricating systems. Such systems are subjected to biaxial loading, which can induce crack formation and propagation, ultimately leading to catastrophic mechanical failure. In this study, the mechanical and tribological behaviour of AAO, prepared from two different types of electrolytes (sulphuric and oxalic acids), are studied in detail. The electrolytic conditions are adjusted to render highly tuneable average pore diameters (between 16 and 75 nm), with porosity levels ranging from 9% to 65%. Well-ordered porous AAO are produced by two-step anodization at rather low temperatures. Mechanical properties, mainly hardness and Young's modulus, are investigated using nanoindentation. Both the porosity degree and the composition of the electrolytic baths used to prepare the AAO have an influence on the mechanical properties. Ball-on-flat configuration was used to estimate the tribological behaviour under dry conditions. No major cracks were observed by scanning electron microscopy, neither after indentation or fretting tests. In the running-in period of tribology experiments the pores were filled with debris. This was followed by the formation of a highly adherent tribolayer e a third body consisting of fine worn particles originated from both the sample and the counterbody. Pore diameter and porosity percentage are found to strongly affect hardness and Young's modulus, but they do not have a major effect on the frictional behaviour. © 2014 Elsevier B.V. All rights reserved.

Tsyntsaru N.,Academy str | Tsyntsaru N.,Catholic University of Leuven | Cesiulis H.,Vilnius University | Pellicer E.,Autonomous University of Barcelona | And 2 more authors.
Electrochimica Acta | Year: 2013

The mapping of structural, magnetic, and mechanical properties of Co-W coatings galvanostatically electrodeposited from a citrate-borate bath is investigated. The intrinsic characteristics of the coatings, such as crystallite size or tungsten content are correlated with the extrinsic growth parameters, such as pH, complexes distribution, and current density. The increase in pH from 5 to 8 results in an increase of the W content in the deposits from 2 at.% up to 36 at.% in a controlled way, and it correlates with an increase in concentration of W(VI) complexes in the bath. The crystallite size estimated from XRD patterns, decreases from 39 to 5 nm with increasing W content from 3 to 25 at.% respectively. The obtained coatings show highly tunable mechanical and magnetic properties. The hardness increases with W content from ~3 GPa up to ~13 GPa. A semi-hard ferromagnetic behavior with a coercivity of ~470 Oe along the perpendicularto- plane direction is observed for Co-W alloys containing small amounts of W in the range of ~2-3 at.%. At higher tungsten contents the coatings are magnetically softer, and the electrodeposits become nonferromagnetic beyond ~30 at.% W. Because of this combination of physical properties, electrodeposited Co-W coatings may become suitable materials for multi-scale technologies. © 2013 Elsevier Ltd. All rights reserved.

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.

Tsyntsaru N.,Academy str | Tsyntsaru N.,Vilnius University | Silkin S.,Academy str | Cesiulis H.,Vilnius University | And 3 more authors.
Electrochimica Acta | Year: 2016

Template-assisted electrodeposition of Co-rich Co-W alloys into mesoporous anodized aluminum oxide from ammonia-free solutions is investigated. The optimum deposition conditions rendering uniform filling of the pores, either by direct current (DC) or pulse current (PC) methods, are established. Contrary to the DC deposition on flat surfaces (which is kinetically controlled), the DC electrodeposition in the mesopores of the template is limited by mass transfer. Conversely, under PC mode, the Co-W electrodeposition process is controlled by kinetics at frequencies > 0.3 Hz; and by diffusion at lower frequencies. The obtained mesowires are nanocrystalline and exhibit a hexagonal closed packed (hcp) structure. The magnetic properties of selected Co-W mesowires, with variable aspect ratio, are also studied. The arrays of mesowires exhibit a semi-hard ferromagnetic behavior with coercivity values that surpass those of Co mesowires with similar dimensions. The interplay between interwire dipolar interactions, magnetocrystalline anisotropy and shape anisotropy on the overall shape of the hysteresis loops (in particular, on the coercivity and squareness ratio values, as well as on the effective magnetic easy axis direction) is investigated in a semiquantitative manner. © 2015 Elsevier Ltd.

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.

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