2. Articole

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    THE INFLUENCE OF SEMICONDUCTOR NANOPARTICLES UPON THE ACTIVITY OF MESENCHYMAL STEM CELLS
    (Springer Nature, 2020) Branişte, Tudor; Raevschi, Simion; Cobzac, Vitalie; Ababii, Polina; Pleșco, Irina; Didencu, Alexandru; Manyuk, Mihail; Nacu, Viorel; Ababii, Ivan; Tiginyanu, Ion
    In this paper, we report on the viability and proliferation of mesenchymal stem cells after exposure to different types of semiconductor nanoparticles. The nanoparticles used for the tests are based on GaN thin layers grown on commercial ZnO and ZnFe2O4 nanoparticles. Different quantities of nanoparticles incubated with mesenchymal stem cells influence the metabolic activity of cells, which was assessed by the MTT assay. The cytotoxic effect of ZnO nanoparticles on MSC was demonstrated and no harmful effect of the other materials.
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    SELF-ORGANIZED AND SELF-PROPELLED AERO-GaN WITH DUAL HYDROPHILIC-HYDROPHOBIC BEHAVIOR
    (Elsevier, 2019) Raevschi, Simion; Tiginyanu, Ion; Braniste, Tudor; Smazna, Daria; Deng, Mao; Schütt, Fabian
    Nature utilizes hydrophilic-hydrophobic biomolecular entities to perform self-organized structural and functional tasks, including the formation of cellular compartments and motion, separation of chemicals or self-healing properties in a highly energy efficient manner. So far, no inorganic artificial micro/nanostructure units are known that self-organize and mimic such functions just by adding liquid. Here we develop the first nanomaterial exhibiting hydrophobic wetting and hydrophilic dewetting. Consisting of gallium nitride nanoscopically thin membranes shaped as hollow microtetrapods, which we term aerogalnite (AGaN), the nanomaterial is extremely porous, mechanically flexible, stretchable, and exhibits hydrophilicity under tension and hydrophobicity when compressed against water. Self-assembling the AGaN tetrapods on water enabled us to develop self-healing waterproof rafts carrying liquid droplets 500-times as heavy as rafts, and to demonstrate self-propelled liquid marbles exhibiting velocity of rotation as high as 750 rot/min. The specific force of the detachment of AGaN from the water surface was experimentally determined equal to 35 mN/cm2. The new developed material aerogalnite and its peculiar characteristics are promising for applications in sensorics, microfluidic devices and microrobotics.
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    EFFECT OF p-NiO INTERLAYER ON INTERNAL QUANTUM EFFICIENCY OF p-GaN/n-ZnO LIGHT-EMITTING DEVICES
    (American Scientific Publishers, 2015) Sirkeli, Vadim; Yilmazoglu, Oktay; Küppers, Franko; Hartnagel, Hans
    We report on numerical investigations of p-GaN/n-ZnO light-emitting devices with p-NiO interlayer, and on LED design optimization which includes bandgap engineering, thickness and doping of constituent layers. The current–voltage dependences of investigated LEDs show a threshold voltage of 3.1 V and 5.4 V for the LED devices without and with presence of p-NiO interlayer, respectively. It is found that p-NiO layer act as electron blocking layer, that lead to the enhance of charge carriers confinement in active region, and to the increasing of internal quantum efficiency (IQE) of LED device up to 0.5%, that in four times higher in compare with that for original p-GaN/n-ZnO LED device.
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    EFFECT OF p-NiO AND n-ZnSe INTERLAYERS ON THE EFFICIENCY OF p-GaN/n-ZnO LIGHT-EMITTING DIODE STRUCTURES
    (IOP Publishing Ltd, 2015) Sirkeli, Vadim; Yilmazoglu, Oktay; Küppers, Franko; Hartnagel, Hans
    We report on a numerical study of the characteristics of p-GaN/n-ZnO light-emitting diodes (LEDs) with p-NiO and n-ZnSe interlayers, and on LED design optimization which includes bandgap engineering, thickness and doping of constituent layers. The current-voltage dependences of investigated LEDs show a threshold voltage of 3.1 V, 5.4 V and 5.6 V for LED devices without and with the presence of p-NiO and n-ZnSe interlayers, respectively. It is found that p-NiO, n-ZnSe and n-ZnO interlayers act as an electron blocking layer, active media layer, and electron transport layer, respectively. It is established that the insertion of both p-NiO and n-ZnSe interlayers leads to the enhancement of charge carrier-confinement in the active region and to the significant increase of internal quantum efficiency (IQE) of the LED device up to 82%, which is comparable with IQE values in order to obtain better AlGaN- and InGaN-based LEDs. It is found that the efficiency of LED devices at 100 A cm−2 is equal to 0.024, 0.09 and 16.4% of external quantum efficiency (EQE), 1.3 × 10−4, 1.6 × 10−4, and 6.4 lm W−1 of PE, and 1.3 × 10−4, 2.9 × 10−4, and 12 cd A−1 of CE for p-GaN/n-ZnO, p-GaN/p-NiO/n-ZnO, and p-GaN/p-NiO/n-ZnSe/n-ZnO LED devices, respectively.