Cristina Vasiliu

Institutul National de Cercetari Economice (INCE), Bucureşti, Hunedoara, Romania

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Publications (20)21.93 Total impact

  • Journal of Organometallic Chemistry 11/2013; · 2.00 Impact Factor
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    ABSTRACT: Thin films of ferrocene carboxaldehyde, also known as cyclopentadienyl(formylcyclopentadienyl)iron, were grown on silicon and glass substrates by matrix-assisted pulsed laser evaporation technique, using a Nd:YAG device operating at 266 nm (4ω). Spectroscopic-ellipsometry, Fourier transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy investigations revealed that the films are homogeneous in thickness, with dense morphology and without cracks, low surface roughness (∼11 nm), and no significant chemical damage. Second harmonic generation capabilities of the thin films were evidenced by using a femtosecond Ti:sapphire laser.
    Applied Surface Science 01/2013; · 2.54 Impact Factor
  • Optoelectronics And Advanced Materials – Rapid Communications. 01/2010; 4(10):1620-1623.
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    ABSTRACT: The paper reports a study on lithium phosphate glasses, containing calcium or magnesium and ferric/ferrous oxides. Iron oxides provide high chemical stability against water and enhance the glass capacity to embed different chemical compounds. The wet synthesis method provides an enhanced homogeneity of the glass batch and improves the optical quality of the glass samples. FTIR and Raman spectroscopy revealed the network former role of P2O5 as well as the modifier/former role of iron. The vibration mode shifted at 1250 cm-1 is attributed to the iron that enters into the phosphate network, forming Fe-O-P bonds instead of P-O-P bonds.
    Optoelectronics and Advanced Materials, Rapid Communications. 01/2010; 4(9):1301-1303.
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    ABSTRACT: Thin films based on two different metal–organic systems are developed by MAPLE and their nonlinear optical applications are explored. A complex of o,o′-dihydroxy azobenzene with Cu2+ cation is found to organize as a non-central symmetric crystallite. A simple protocol is developed for the in situ fabrication of highly monodisperse copper-complex nanoparticles in a polymer film matrix of polyacrylic acid. The thin films were deposited on quartz substrates by MAPLE (matrix assisted pulsed laser evaporation) using a Nd:YAG laser working at 355 nm. Atomic force microscopy (AFM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and optical second harmonic generation (SHG) were performed on the samples. The optical limiting capability of the nanoparticle-embedded polymer film is investigated.
    Applied Surface Science 01/2009; 255(10):5480-5485. · 2.54 Impact Factor
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    ABSTRACT: Thin films of [Cd{SSi(O–But)3}(S2CNEt2)]2, precursor for semiconducting CdS layers, were deposited on silicon substrates by Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. Structural analysis of the obtained films by Fourier transform infrared spectroscopy (FTIR) confirmed the viability of the procedure. After the deposition of the coordination complex, the layers are manufactured by appropriate thermal treatment of the system (thin film and substrate), according to the thermal analysis of the compound. Surface morphology of the thin films was investigated by atomic force microscopy (AFM) and spectroscopic-ellipsometry (SE) measurements.
    Applied Surface Science 01/2009; 255(15):6786-6789. · 2.54 Impact Factor
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    ABSTRACT: Thin films of complex oxides have been obtained by pulsed-laser deposition (PLD) from glass targets belonging to the system Li(2)O-Al(2)O(3)-P(2)O(5)-(RE)(2)O(3), with RE = Nd, Pr, Er. The films were deposited on quartz, silicon and ITO/glass substrates using a F(2) laser (lambda = 157 nm, iota approximate to 20 ns) for ablation in vacuum. The structural, morphological and optical properties of the oxide films were investigated through IR and UV-VIS spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Spectroscopic Ellipsometry. The laser wavelength was found to be the key parameter to obtain thin films with very smooth surface. In this way new possibilities are opened to grow multilayer structures for photonic applications. (C) 2008 Elsevier B. V. All rights reserved.
    Applied Surface Science 01/2009; 255(10):5295-5298. · 2.54 Impact Factor
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    ABSTRACT: Thin films of phosphate glasses were prepared by pulsed laser deposition in oxygen atmosphere on ITO-coated glass and silicon substrates respectively, using a Nd:YAG laser (266 nm). The targets were Li2O–Al2O3–P2O5 bulk glasses doped with Pr and Nd. Infrared transmission-, energy dispersive X-ray- and X-ray photoemission spectroscopy investigations carried out on targets as well as on the deposited films proved a satisfactory compositions transfer on both substrates. Scanning electron microscopy and atomic force microscopy show continuous films with glassy spheres. Processes where substrates were positioned perpendicularly to targets produced discontinuous drops free films.
    Journal of Materials Science Materials in Electronics 01/2009; 20:286-289. · 1.49 Impact Factor
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    ABSTRACT: This work aims at establishing the influence of different phosphor-precursors on the electrical properties of 90%SiO2-10%P2O5 (%mol) thin films prepared by sol-gel method from triethylphosphate, triethylphosphite and phosphoric acid precursors. Glass and respectively ITO-coated glass were used as substrates. The films were annealed at 200 °C and respectively 500 °C. For all selected precursors the results show that the conduction in the phosphate glass films decreases with increasing annealing temperature, giving thus evidence of a reduced release- and transfer-activity of protons within the films. The activation energy of the conduction process takes values in the range 0.033-0.04 eV. The correlation between the electrical properties and optical and structural data is also discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 01/2008; 5(10):3392-3396.
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    ABSTRACT: The investigated ecological glasses with no toxic compounds, such as BaO, PbO, As2O3, As2O5, fluorine, CdS and CdSe in their composition are located in ternary and quaternary oxide systems: ZnO-SiO2-TiO2 and SiO2-R′2O- R″O-R‴O2, where R′ is Na or K, R″ is Ca or Mg and R‴ is Zr or Ti. The first system contains P2O 5, ZnO and TiO2 in order to obtain opal glasses, without fluorine compounds. The second system replaces the barium oxide and lead oxide with potassium, magnesium, zirconium and titanium oxides, for materials like lead free crystals. The raw materials can be replaced by silicate or borosilicate glass waste. The advantages of borosilicate glass waste are: bringing valuable components into recipes (B2O3, CaO, Al2O3), saving raw materials and energy, creating an ecological environment The characteristic temperatures (vitreous transition point, low and high annealing points, softening point) and the thermal expansion coefficient of the glass are presented. The FTIR and Raman spectroscopy provided structural data, such as characteristic vibration maxima for silicon and titanium oxide, and revealed the role of zinc oxide in the vitreous network. The refraction index and UV-VIS transmission are discussed.
    Advanced Materials Research 01/2008; 39-40:667-670.
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    ABSTRACT: Spectroscopy results of aluminophosphate glasses doped with transition metal (TM) ions (Cr and/or Mn) are reported. Li2O-BaO-Al2O3-La2O3-P2O5 (CrO3-MnO2), Li2O-BaO-Al2O3-La2O3-P2O5 (CrO3-MnO2) and Li2O-Na2O-BaO-Al2O3-La2O3-P2O5 (CrO3-MnO2) glasses have been prepared. Ultraviolet-vis, Raman and photoluminescence spectroscopies have been used to investigate the structural and optical properties of the doped glasses. Optical transmission in the ultraviolet-vis range was used to study the oxidation states of the TM ions and the redox equilibria of the transition ion pairs in the aluminophosphate glasses as well as their coordination with oxygen ion ligands (O2−). Aluminophosphate glasses doped with Mn-Cr ions show absorption peaks at 650 and 680 nm, which are characteristic of Cr3+ ions. The absorption peak at about 450 nm reveals the presence of both Cr3+ and Mn2+ ions. Raman peaks at about 700 and 1200 cm−1, obtained by 325 and 514·5 nm laser excitation, were assigned to the P-O-P symmetrical stretching mode and to the PO2 symmetrical stretching mode, respectively. The fluorescence peak obtained by 514˙5 nm laser excitation is localised at about 600 nm for Mn-doped samples and is due to Mn2+ ions in octahedral coordination. Glass samples containing Cr and Cr-Mn ion pairs exhibit fluorescence emission at about 800 nm due to Cr3+ ions in octahedral and tetrahedral symmetry; no Mn fluorescence was seen in these glasses. The effect of the mixed alkali ions on the spectra of these glass doped with transition ion pairs was also investigated. An increase in the sodium/lithium content results in a nonlinear shift of the ultraviolet transmission edge and improves the fluorescence intensity of the Cr-Mn-doped glass samples.
    Glass Technology - European Journal of Glass Science and Technology Part A. 09/2007; 48(5):247-251.
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    ABSTRACT: Thin films of complex oxides have been deposited by pulsed laser ablation, starting from glass targets. Glass oxide targets were prepared by a non-conventional wet method and consisted of a matrix having the composition: Li 2O, BaO, Al 2O 3, La 2O 3 and P 2O 5, respectively, non-doped and doped with Nd 2O 3. The films were deposited on silicon substrates using the fourth harmonic of a Nd:YAG laser (266 nm), in an oxygen background atmosphere. The influence of the deposition parameters on the morphological and optical properties of the oxide films was particularly investigated. IR absorption spectroscopy, optical microscopy, X-ray diffraction and atomic force microscopy were used to characterize the targets and the deposited thin films.
    Applied Surface Science 07/2007; 253(19):8278-8281. · 2.54 Impact Factor
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    ABSTRACT: A series of Er(III) six-coordinated complexes with the general formulae [Er(LH)3] of the tridentate ligands (LH2) were obtained for the metal to ligand ratio 1/3. Chelates prototype complexes based on azo-derivatives and Schiff bases as ligands were characterized by elemental analyses and FTIR methods. Luminescence properties and the antenna effect of the organic ligands were investigated. The aim of syntheses and characterization of these multifunctional materials was to use them as fiber amplifiers in optoelectronic devices.
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    ABSTRACT: Polyaniline (PAni) has important electro-conductive properties, high absorbance in microwave range and it is also frequently used in gas sensors because of its capability to convert chemical interactions into electrical signals. The methods of obtaining polyaniline in the form of thin films and/or nanostructures are complicated and request special physical and chemical treatments, both on the substrate surface and for the polymer itself.In this paper we applied matrix assisted pulsed lased evaporation (MAPLE) for obtaining thin films and nanostructures of polyaniline. In MAPLE, the target consisting of the material (usually 0.2–3 wt%) dissolved in a solvent is frozen and it is evaporated using a laser. In our case polyaniline–emeraldine salt (PAni–ES) was dissolved in xylene or toluene, frozen in liquid nitrogen and was used as target. The third and the fourth harmonics of a Nd–YAG laser (λ = 355 nm and 266 nm) were used as laser sources. The obtained films have been characterized by atomic force microscopy, dielectric spectroscopy and Fourier transform infrared spectroscopy. The influence of the solvent type and of the laser parameters (wavelengths and fluence) on the polyaniline structures composition and properties has been investigated.
    Applied Surface Science 01/2007; 253(19):7711-7714. · 2.54 Impact Factor
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    ABSTRACT: Phosphosilicate films with 90%SiO2-10%P2O5 molar composition, derived from tetraethoxysilane as SiO2 precursor and triethylphosphate, triethylphosphite or phosphoric acid as P2O5 precursors were prepared using the sol-gel method. The films were deposited on glass and ITO coated glass supports. The influence of the type of P2O5 precursor, type of substrate and of the thermal treatment (200, 300 and 500°C) on their structure and properties was studied. By spectroellipsometric and XPS measurements the high vaporization of the phosphorous during the densification of the films by thermal treatment was noticed when alkoxide were used, underlying that the mentioned precursors are not recommended for thin phosphosilicate films preparation. The phosphoric acid that forms chemical bond with silica network during the sol-gel process lead to better incorporation of P in the silica network as compared to the P-alkoxides.
    Journal of Sol-Gel Science and Technology 11/2006; 40(2):325-333. · 1.66 Impact Factor
  • Revista de Chimie -Bucharest- Original Edition- 01/2006; · 0.54 Impact Factor
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    ABSTRACT: Aluminophosphate glasses doped with CdSxSe1-x have been produced by a wet nonconventional method that provides a better homogeneity of the glass matrix. The glass samples belong to the oxide systems: Li2O–BaO–Al2O3–La2O3–SiO2–P2O5 and Li2O–Na2O–BaO–Al2O3–La2O3–SiO2–P2O5. The band gaps of the doped samples were determined by UV-VIS-NIR transmission spectroscopy, using the dependence of the absorption coefficient on photon energy. Structural investigations on semiconductor doped glasses were performed by infrared absorption and Raman spectroscopy. Infrared absorption spectra revealed structural units of the phosphate glass matrix. Raman spectra obtained by excitation with 458 and 514 nm revealed CdS0·696Se0·304 peaks and by excitation with 325 nm, revealed the phosphate matrix bonds. Transmission electron microscopy, selected area electron diffraction (SAED) and fluorescence spectroscopy were used to investigate the semiconductor doped glasses. SAED patterns allowed the calculation of the composition and consequently the band gap of the CdSSe crystallites embedded in the glass matrix. A strong CdSSe fluorescence was observed, indicating well ordered crystallites with a molar fraction of S and Se close to 0·5 as intended.
    Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B. 11/2005; 46(6):553-558.
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    ABSTRACT: Aluminophosphate glasses doped with Fe, Mn, and Cr have been obtained by a wet non-conventional method. Structural information was provided by IR absorption spectra in the range 2000-500 cm -1 . The optical behaviour (transmission and refractive index) of the samples has been studied by UV-VIS-NIR spectroscopy. The Fe valence state and the local coordination were also analysed via 57 Fe Mossbauer spectroscopy, whose data revealed the redox equilib-rium in the Fe-doped glasses according to the redox potentials of the transition ions.
    Reviews on advanced materials science 01/2005; 10:367-374. · 1.02 Impact Factor
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    ABSTRACT: Summary form only given. We present a review of the research carried out during the past six months by groups from Romania, Victoria University of Wellington, New Zealand, and Universite de Provence, Marseille, France, with the aim to fabricate photonic materials within the framework of the COST ACTION P11. Novel aluminophosphate glasses doped with semiconductors (CdSSe) have been produced, whose transmission in the visible and Raman spectra have been investigated. We have noticed that transmission edge and the spectra shape depend on the crystallites' dimensions. The fluorescence is relatively narrow (0.12-0.15 eV) suggesting reasonably well-ordered crystallites with reasonably uniform diameters. Another attempt of the groups to find a way of producing quasi-periodic, at this stage, features, in amorphous materials, consists of annealing studies on amorphous GaN thin films (150 nm) on silicon. The annealing processes have been carried out using the hot stage of an electronic microscope (SEM), so that real time observation has been possible. Following the annealing, the GaN films have developed hemispherical structures uniformly distributed over the entire surface of the sample. Apparently, those structures are denser than the surrounding film, and EDX analysis shows that they conserved the initial composition of the film. At the necked eye the colour of the sample changed from blue to yellow.
    Transparent Optical Networks, 2004. Proceedings of 2004 6th International Conference on; 08/2004
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    ABSTRACT: Vanadium and vanadium-cerium oxide gels and films obtained by the sol-gel method have been widely studied, due to their catalytic, electrochemical, electronic and ionic properties, a result of their ability to form combinations in more than one valent state. V and V-Ce oxide powders were prepared by sol-gel method in the presence and absence of polyols. An organic alkoxide precursor was used to obtain V 2 O 5 , while in case of the binary product, the alkoxide preparation route was compared with an aqueous one. The powders were characterized by transmision electron microscopy (TEM), infrared spectroscopy, X-ray diffraction and by thermal analysis. The obtained V 2 O 5 powders crystallized in the micrometric range. In case of the binary product, the CeO 2 addition led to a nanometric quasi-crystallised product.