2. Articole

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Author: search.filters.author.Popescu, Mihai

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    Studies of vanadium and vanadium oxide based nanocomposite structures [Articol]
    (2017) Prilepov, Vladimir; Gashin, Peter A.; Popescu, Mihai; Zalamai, Victor; Spoiala, Dorin; Ketrush, Petru; Nasedchina, Nadejda
    The results of the surface morphology studies as well as optical and electrical properties of nano-dimensional vanadium oxide composite structures deposited on various substrates- silica, glass substrates covered by conducting layer of SnO2, pure pyroceramics plates and the same covered by Al2O3, SiO2, Ta2O5 layers are presented. According to Raman spectroscopy results the thin film structure obtained on quartz corresponds to the -V2O5 orthorhombic phase. In contrast with this the Raman spectra of V2O5 films obtained on pyroceramics substrates, passivated by Al2O3, Ta2O5, SiO2 oxides, do not appear clearly marked narrow lines which indicate their amorphous character. The investigation of the optical properties of the fabricated layers in the spectral range of 200-1000 nm had revealed the presence of both allowed direct and indirect electron transitions. In the frequency range of 103-107 Hz the real Z' and imaginary Z'' part of the total impedance of pyroceramics/Al2O3/Al/V2O5/Al structure were studied. The applied direct bias leads to a considerable Z', as well as Z'' decrease. The analysis of the obtained dependencies is carried out by using the method of equivalent circuits.
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    Effect of optical coating in the thin-film system of chalcogenide glassy semiconductor-dielectric when recording the holographic optical information [Articol]
    (2015) Chirita, Arcady; Prilepov, Vladimir; Popescu, Mihai; Andries, Ion; Caraman, Mihail; Jidcov, Iurie
    In this paper we show that the possibility of obtaining the high values of efficiency of relief-phase holographic gratings formed in the photo-thermoplastic recording process holds not only due to the non-sinusoidal profile form, but also due to the effect of optical coating that appears in the two-layer system of photo-semiconductor – deformed thermoplastic. Analyzed are the conditions, under which takes place the antireflection optical coating, reducing unwanted reflections from surfaces and thereby enhancing efficiency. It is shown that by careful choice of the thicknesses and refractive indices of the layers materials the efficiency of holographic gratings can be improved by 2-5 %.