Browsing by Author "Leontie, L."

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Optical Properties of III–VI Lamellar Semiconductors Doped with Cu and Cd and of Related III–VI/Native Oxide Structures
(American Scientific Publishers, 2011) Evtodiev, Silvia; Caraman, Iulia; Dmitroglo, Liliana; Leontie, L.; Nedeff, V.; Dafinei, A.; Lazar, G.; Evtodiev, I.
GaS, GaSe and GaTe are typical representatives of III–VI layered semiconductor materials, showing highly anisotropic mechanical and optical properties. At photon energies hν < E g , the anisotropy ratio for the absorption coefficients at the n = 1 excitonic peak, corresponding to E →‖C → and E →⊥C → polarizations, is α ‖/α ⊥≈15. Optical functions n e (λ) and n o (λ) of GaS and GaSe in the wavelength range 0.36–22 μm have been determined. For the photon energies hν < E g ind, these correspond to a normal dispersion and can be described by power-law wavelength dependences. By means of FTIR transmission and reflection spectroscopy in the spectral range of 1000–85 cm−1, for plan-parallel plates with thickness between several tens of nanometers and centimeters, the wavenumbers of longitudinal optical ν(LO) and transverse optical ν(TO) phonons have been determined for GaSe [ν ⊥(LO) = 254 cm−1, ν ⊥(TO) = 214 cm−1], GaS [ν ⊥(LO) = 359 cm−1, ν ⊥(TO) = 297 cm−1, ν ‖(LO) = 336 cm−1], and GaTe [ν(LO) = 164 cm−1, ν(TO) = 118 cm−1].
PREPARATION AND OPTICAL PROPERTIES OF LAMELLAR GaSe -ZnSe NANOCOMPOSITES
(2015) Caraman, M.; Untila, D.; Canțer, V.; Evtodiev, Igor; Caraman, Iu.; Susu, O.; Leontie, L.
ZnSe-GaSe nanocomposite plates photoluminescent in a photon energy range of 1.80−2.64 eV were obtained via exposing GaSe single-crystal plates to a Zn-vapor heat treatment at temperatures of 673−873 K. The photoluminescence spectrum is dominated bythe self-activated emission band of ZnSe witha maximum at 2.04 eV. The average size of the ZnSe crystallites is ~45 nm. The absorption spectrum of the composite consists of two regions characteristic of direct optical transitions in GaSe crystals with a band gap of 1.99 eV and ZnSe crystallites with aband gap of 2.56 eV at room temperature.
SYNTHESIS AND OPTICAL PROPERTIES OF Ga2O3 NANOWIRES GROWN ON GaS SUBSTRATE
(Elsevier, 2019) Leontie, L.; Sprincean, Veaceslav; Spaltu, N.; Cojocaru, A.; Susu, Ana; Lupan, Oleg; Vatavu, Elmira; Carlescu, Aurelian; Untila, Dumitru; Caraman, Iuliana; Evtodiev, Igor; Tiginyanu, Ion; Caraman, Mihail
Gallium oxide (β-Ga2O3) nanowires were synthesized by heat treatment of single crystal β-GaS plates in air. Crystal structure and composition of synthesized materials were studied by X-ray diffraction, energy dispersive X-ray spectroscopy and Raman spectroscopy. Thermal treatment of β-GaS plates at 1023 K leads to the formation of a Ga2O3 (native oxide) layer on β-GaS (0001) surface of plates. Layer thickness and size of Ga2O3 wires contained were found to depend on temperature and duration of applied heat treatment. For 1023 K and 6 h, the length of Ga2O3 wires laid in the range from units to tens of nanometers, while for 1123 K and 30 min, between 30 and 40 μm.