2. Articole

Permanent URI for this collectionhttps://msuir.usm.md/handle/123456789/47

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Start date: 2020End date: 2021

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    PLASTIC DEFORMATION AND MICROHARDNESS OF Pb 1-xYbxTe SINGLE CRYSTALS UNDER QUASI-STATIC AND SCLEROMETRIC INDENTATION
    (2021) Grabco, Daria; Nicorici, Valentina; Topal, Daria; Pârțac, Constantin; Șichimaca, Olga
    In this work, the microhardness and specificity of deformation of Pb 1-xYbxTe single crystals by quasi-static and sclerometric indentation are studied. It is shown that these crystals are distinguished by high plasticity and low microhardness both under indentation and under the movement of the indenter. An opinion is expressed that the mechanism of crystal structure compaction is involved in mass transfer during the formation of an imprint, along with the dislocation mechanism. Crystals have low sclerometric anisotropy of hardness along different crystallographic directions on the (001) plane, which is typical for crystals of a cubic system. The jump-like mechanism of the deformation process during the movement of the indenter, which is characteristic of crystals of different types, is confirmed.
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    AERO-Ga2O3 NANOMATERIAL ELECTROMAGNETICALLY TRANSPARENT FROM MICROWAVES TO TERAHERTZ FOR INTERNET OF THINGS APPLICATIONS
    (2020) Braniște, Tudor; Dragoman, Mircea; Jucov, Serghei; Aldrigo, Martino; Ciobanu, Vladimir; Iordănescu, Sergiu; Alîabîeva, Liudmila; Fumagalli, Francesco; Ceccone, Giacomo; Raevschi, Simion; Schűtt, Fabian; Adelung, Rainer; Colpo, Pascal; Gorșunov, Boris; Tighineanu, Ion
    In this paper, fabrication of a new material is reported, the so-called Aero-Ga2O3 or Aerogallox, which represents an ultra-porous and ultra-lightweight three-dimensional architecture made from interconnected microtubes of gallium oxide with nanometer thin walls. The material is fabricated using epitaxial growth of an ultrathin layer of gallium nitride on zinc oxide microtetrapods fabricated using epitaxial growth of an ultrathin layer of gallium nitride on zinc oxide microtetrapods followed by decomposition of sacrificial ZnO and oxidation of GaN which according to the results of X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) characterizations, is transformed gradually in β-Ga2O3 with almost stoichiometric composition. The investigations show that the developed ultra-porous Aerogallox exhibits extremely low reflectivity and high transmissivity in an ultrabroadband electromagnetic spectrum ranging from X-band (8–12 GHz) to several terahertz which opens possibilities for quite new applications of gallium oxide, previously not anticipated.
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    SELF-PROPELLED AERO-GaN BASED LIQUID MARBLES EXHIBITING PULSED ROTATION ON THE WATER SURFACE
    (2021) Braniște, Tudor; Ciobanu, Vladimir; Schűtt, Fabian; Mimura, Hidenori; Raevschi, Simion; Adelung, Rainer; Pugno, Nicola M.; Tighineanu, Ion
    We report on self-propelled rotating liquid marbles fabricated using droplets of alcoholic solution encapsulated in hollow microtetrapods of GaN with hydrophilic free ends of their arms and hydrophobic lateral walls. Apart from stationary rotation, elongated-spheroid-like liquid marbles were found, for the first time, to exhibit pulsed rotation on water surfaces characterized by a threshold speed of rotation, which increased with the weight of the liquid marble while the frequency of pulses proved to decrease. To throw light upon the unusual behavior of the developed self-propelled liquid marbles, we propose a model which takes into account skimming of the liquid marbles over the water surface similar to that inherent to flying water lily beetle and the so-called helicopter effect, causing a liquid marble to rise above the level of the water surface when rotating.
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    AERO-ZNS ARCHITECTURES WITH DUAL HYDROPHILIC–HYDROPHOBIC PROPERTIES FOR MICROFLUIDIC APPLICATIONS
    (2020) Pleșco, Irina; Braniște, Tudor; Wolff, Niklas; Gorceac, Leonid; Duppel, Viola; Cinic, Boris; Mishra, Yogendra Kumar; Sarua, Andrei; Adelung, Rainer; Kienle, Lorenz; Tighineanu, Ion
    Here, we report on a new aero-material, called aero-ZnS, representing self-organized architectures made of ZnS hollow micro-tetrapod struc- tures with nanoscale thin walls. The fabrication process is based on the hydride vapor phase epitaxy of CdS on sacrificial micro-tetrapods of ZnO with simultaneous or subsequent transformation of CdS into ZnS and removal of the sacrificial ZnO crystals. The nanostructure of the obtained ZnS hollow micro-tetrapods exhibits the polytypic intergrowth of wurtzite- and sphalerite-type phases perpendicular to their close packed planes. The inner surface of the micro-tetrapod walls preserves oxygen sites, as demonstrated by imaging based on electron energy- loss filtering. The self-organized aero-ZnS architecture proves to be hydrophilic under tension and hydrophobic when compressed against water. Self-propelled liquid marbles assembled using ZnS hollow micro-tetrapod structures are demonstrated.
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    CRYSTALLINITY AND OPTICAL PROPERTIES OF β-Ga2O3/Ga2S3 LAYERED STRUCTURE OBTAINED BY THERMAL ANNEALING OF Ga2S3 SEMICONDUCTOR
    (2021) Sprincean, Veaceslav; Lupan, Oleg; Caraman, Iuliana; Untila, Dumitru; Postica, Vasile; Cojocaru, Ala; Gapeeva, Anna; Palachi, Leonid; Adeling, Rainer; Tiginyanu, Ion; Caraman, Mihail
    In this work, the β-Ga2O3 nanostructures were obtained by thermal annealing in air of β-Ga2S3 single crystals at relatively high temperatures of 970 K, 1070 K and 1170 K for 6 h. The structural, morphological, chemical and optical properties of β-Ga2O3–β-Ga2S3 layered composites grown at different temperatures were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) as well as photoluminescence spectroscopy (PL) and Raman spectroscopy. The results show that the properties of obtained β-Ga2O3–β-Ga2S3 composites were strongly influenced by the thermal annealing tem- perature. The XRD and Raman analyses confirmed the high crystalline quality of the formed β-Ga2O3 nano- structures. The absorption edge of the oxide is due to direct optical transitions. The optical bandwidth was estimated to be approximately 4.34-4.41 eV, depending on the annealing temperature. Annealing of the β-Ga2S3 monocrystals at a higher temperature of 1170 K showed the complete conversion of the surface to β-Ga2O3. These results demonstrate the possibility to grow high quality β-Ga2O3–β-Ga2S3 layered composites and β-Ga2O3 nanostructures in large quantities for various applications such as gas sensing, non-toxic biomedical imaging, nonlinear optical, as well as power device applications. Micro and nanocrystallites present on the surface of the Ga2O3 layer contribute to a diffusion of the incident light which leads to an increase of the absorption rate allowing thus to reduce the thickness of the Ga2O3 layer, in which the generation of unbalanced charge carriers takes place. By decreasing the Ga2O3 layer thickness in such layered composites, the efficiency of photovoltaic cells based on such junctions can be increased.
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    THERMAL TRANSPORT EVOLUTION DUE TO NANOSTRUCTURAL TRANSFORMATIONS IN GA-DOPED INDIUM-TIN-OXIDE THIN FILMS
    (2021) Cocemasov, Alexandr; Brinzari, Vladimir; Jeong, Do-Gyeom; Korotcenkov, Ghenadii; Lee, Jong S.; Nika, Denis L.
    We report on a comprehensive theoretical and experimental investigation of thermal con- ductivity in indium-tin-oxide (ITO) thin films with various Ga concentrations (0–30 at. %) deposited by spray pyrolysis technique. X-ray diffraction (XRD) and scanning electron microscopy have shown a structural transformation in the range 15–20 at. % Ga from the nanocrystalline to the amorphous phase. Room temperature femtosecond time domain thermoreflectance measurements showed nonlinear decrease of thermal conductivity in the range 2.0–0.5 Wm−1 K−1 depending on Ga doping level. It was found from a comparison between density functional theory calculations and XRD data that Ga atoms substitute In atoms in the ITO nanocrystals retaining Ia-3 space group symmetry. The calculated phonon dispersion relations revealed that Ga doping leads to the appearance of hybridized metal atom vibrations with avoided-crossing behavior. These hybridized vibrations possess shortened mean free paths and are the main reason behind the thermal conductivity drop in nanocrystalline phase. An evolution from propagative to diffusive phonon thermal transport in ITO:Ga with 15–20 at. % of Ga was established. The suppressed thermal conductivity of ITO:Ga thin films deposited by spray pyrolysis may be crucial for their thermoelectric applications.
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    SINTEZA ȘI CARACTERISTICA STRUCTURALĂ A DOI CLUSTERI HEXANUCLEARI {Fe6} ÎN BAZA LIGANZILOR PIVALAT ȘI N,N,N´,N´-TETRAKIS (2-HIDROXIETIL)ETILENEDIAMINĂ
    (CEP USM, 2021-04-22) Podgorîi, Daniel
    Ultrasonic treatment of 3-oxo trinuclear [Fe3O(piv)6(H2O)3](piv)·Hpiv pivalate clusters and N,N,N´,N´-tetrakis(2-hydroxyethyl)ethylenediamine ligand (H4teed) in acetonitrile solution gave a hexanuclear [Fe6O2(piv)8(Hteed)2] (1) cluster. The use in the same reaction sodium azide yielded another hexanuclear [Fe6O2(piv)6(Hteed)2(N3)2] (2) cluster. Compounds 1 and 2 have been characterized by X-ray crystallography and IR spectroscopy.
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    ON THE STABILITY OF EQUILIBRIUM STATES OF THE DYNAMICAL SYSTEMS IN CRITICAL CASES
    (Elsevier, 2021) Barsuk, Alexandr A.; Paladi, Florentin
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    FOTODETECTOR PE HETEROJONCȚIUNE DIN FOSFURĂ DE INDIU
    (CEP USM, 2020) Gorceac, Leonid; Botnariuc, Vasile; Coval, Andrei; Vatavu, Sergiu; Cinic, Boris; Raevschi, Simion; Rotaru, Corneliu