2. Articole
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Item CRYSTALLINE STRUCTURE, SURFACE MORPHOLOGY AND OPTICAL PROPERTIES OF NANOLAMELLAR COMPOSITES OBTAINED BY INTERCALATION OF InSe WITH Cd(2015) Untila, Dumitru; Caraman, Iuliana; Evtodiev, Igor; Canțer, Valeriu; Spalatu, Nicolae; Leontie, Liviu; Dmitroglo, Liliana; Luchian, EfimiaA material composed of InSe and CdSe crystallites was obtained by heat treatment at 753K of InSe single crystalline plates in Cd vapour for 3÷24 hours. The average diameters of CdSe and InSe crystallites determined from diffraction lines analysis are respectively equal to 20 nm and 22 nm. The photoluminescence spectra at 300K and 80K of composite decompose well into two Gaussian curves, one is in good correlation with the photoluminescence of CdSe crystals and the other is shifted to higher energies than the width of the band gap of CdSe crystals.Item RESONANT TERAHERTZ LIGHT ABSORPTION BY VIRTUE OF TUNABLE HYBRID INTERFACE PHONON–PLASMON MODES IN SEMICONDUCTOR NANOSHELLSN(MDPI, 2019) Nika, Denis; Fomin, Vladimir; Devreese, Josef; Pokatilov, Evghenii; Tempere, JacquesMetallic nanoshells have proven to be particularly versatile, with applications in biomedical imaging and surface-enhanced Raman spectroscopy. Here, we theoretically demonstrate that hybrid phonon-plasmon modes in semiconductor nanoshells offer similar advantages in the terahertz regime. We show that, depending on tm,n,nhe doping of the semiconductor shells, terahertz light absorption in these nanostructures can be resonantly enhanced due to the strong coupling between interface plasmons and phonons. A threefold to fourfold increase in the absorption peak intensity was achieved at specific values of electron concentration. Doping, as well as adapting the nanoshell radius, allowed for fine-tuning of the absorption peak frequencies.Item ANISOTROPY OF THE EXCITON PROCESSES IN GaSe CRYSTALS WITH LOW S AND TE CONCENTRATIONS(American Scientific Publishers, 2009) Evtodiev, IgorThe anisotropy of the excitonical processes in the GaSe crystals and GaSe with small quantities of GaS(GaSe0.99S0.01) crystals has been studied through the optical specters (SO) and through the photoluminescence (PL) from the perpendicular surface on the symmetry axis C6 (E⊥C polarization) and from the flat surface parallel with the C6axis (E∥C and E⊥C polarization). The edge of the fundamental band of the GaSe crystals as well as of the GaSe0.99S0.01 and GaSe0.99Te0.01 crystals is formed at T = 78 K of the direct excitons' band. The width of the free excitons' band is determined by the processes of interaction between the excitons and optical and acoustic phonons. Phonons with energy of 17 meV and 27 meV participate to the formation of the edge towards small energies of the excitonic band in the GaSe crystals. The average energy of the phonons that participate to the formation of the excitonic absorbtion band in the GaSe crystals with small concentrations of S and Te equals 17 meV. Due to the mechanism of interaction of the excitons and phonons the integral absorption coefficient for the studied crystals (polarized E⊥C) is in small increase once with the temperature whilst the integral absorption coefficient in the maximum of the direct excitons' band. The n = 1 state is in diminution. For example, for the GaSe0.99Te0.01 crystals, α increases from 2700 at T = 78 K to 2025 cm−1 at 220 K. The edge towards small energies of the free excitons' band in the GaSe crystals and GaSe crystals with small quantities of S and Te is in a great concordance with Toyozowa's theory. The constant of interaction between the free excitons with phonons with an average energy of 135 cm−1 equals 0.9. Using the spectral characteristic of the reflection coefficient from the surface parallel to the C6 axis, there has been determined the refraction index placed in the center of the excitons n = 1 which equals 2.62 for GaSe and 2.58 and 2.55 respectively for the GaSe0.99S0.01 and GaSe0.99Te0.01 crystals. The shifting of the reflection specters towards big energies like ∼10 meV in a E⊥C polarization comparing to E∥C is determined by the difference of the oscillators' strength in these polarizations. The PL at T = 78 K specters from the surface parallel with the C6 axis (polarized E∥C) confirm the difference between the forces of the excitons' oscillators in the E∥C and E⊥C polarization. The intensity of PL bands, at the (001) surface as well as at the (100) surface depends on the excitation intensity by a function of a I = Ln force towards the emission bands of the direct and indirect free excitons the force factor is overlinear, and for the impurity nature bands it represents ∼0.5. The parameters that determine the width of the bands of excitonic PL is determined, considering the strong concentration of the structural faults at the (100) surface of the GaSe and GaSe0.99Te0.01 and GaSe0.99S0.01 GaSe crystals. Out of the spectral analysis I(L) the nature of the impurity bands has been determined, and from the PL specter structure there has been determined the energy of the accepting level which equals 93 meV from the maximum of the valence band of the GaSe crystals. Out of the analysis of the PL specter in a E∥C and E⊥C polarization (the (100) surface) it was stated that the process of emissional annihilation of the indirect excitons in the E∥C polarization takes place once with the emission of the phonons of a 38 meV energy whilst at the E⊥C polarization there are emitted phonons with an energy of 17 meV. GaSe with small concentrations of GaS and GaTe leads to the forming of a considerable concentration of localizing centers of the direct excitons and at the same time to the shifting towards small and big energies of the excitonic emission band (state n = 1) comparing to the GaSe crystals with a stoikiometric composition.Item DISPOZITIVE FOTOVOLTAICE PE BAZA FTALOCIANINEI DE CUPRU FABRICATE PRIN METODA VOLUMULUI CVASIÎNCHIS(CEP USM, 2016) Duca, Dumitru; Potlog, TamaraÎn cadrul acestui studiu au fost cercetate proprietăţile fizice ale straturilor subţiri de ftalocianină de cupru (CuPc) depuse în vid prin metoda volumului cvasiînchis, dar şi a dispozitivelor fotovoltaice pe baza acestora. A fost studiată influenţa tratării termice asupra structurii şi proprietăţilor optice ale straturilor CuPc utilizând metoda difracţiei de raze X şi spectroscopia optică (transmitanţa, reflectanţa). Au fost fabricate structurile ITO/CuPc/Al şi ITO/PEDOT:PSS/CuPc/Al şi studiate proprietăţile fotoelectrice ale acestora. S-a constatat ca utilizarea stratului de PEDOT:PSS îmbunătăţeşte parametrii fotovoltaici, în special tensiunea de circuit deschis.Item OPTICAL PROPERTIES OF COMPOUNDS WITH SUBMICRON POINTS OBTAINED THROUGH Ga2S3 INTERCALATION WITH Cd(Universitatea de Stat „Alecu Russo“ din Bălţi, 2012) Racoveț, O.; Evtodiev, I.; Caraman, Iu.; Rotaru, I.; Lazăr, G.Luminescence and optical absorption spectra of Ga2S3 single crystals were investigated at temperatures of 78 K and 293 K. Optical band gap is equal to 3.27 eV and 3.457 eV at 293 K and 78 K respectively. Luminescence spectrum of single crystal lamellas at temperature of 78K consists of three bands with peaks at 2.04 eV, 1.84 eV and 1.66 eV.Native structural defects form deep recombination and electronic capture levels localized within the Ga2S3 band gap.