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    Wyświetlanie 1-8 z 8
    Tytuł:
    Effect of $Fe^{2+} (Fe^{3+})$ Doping on Structural Properties οf $CeO_2$ Nanocrystals
    Autorzy:
    Radović, M.
    Dohčević-Mitrović, Z.
    Paunović, N.
    Šćepanović, M.
    Matović, B.
    Popović, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1807838.pdf
    Data publikacji:
    2009-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    61.72.uj
    78.30.-j
    75.50.Tt
    Opis:
    We have measured the Raman scattering and magnetization of pure and $Fe^{2+}(Fe^{3+})$ doped $CeO_2$ nanopowders at room temperature. The Raman scattering spectra revealed the existence of $CeO_2$ fluorite cubic structure for all investigated samples. The Raman active mode at about 600 $cm^{-1}$, seen in all samples, can be ascribed to the $CeO_2$ intrinsic oxygen vacancies. Additional Raman modes at 720 $cm^{-1}$, 1320 $cm^{-1}$ and 1600 $cm^{-1}$, which appear in the spectra of doped samples, can be assigned to maghemite $(γ-Fe_2O_3)$ cation deficient structure, to $2ω_{LO}$ IR-allowed overtone and two magnon structure, respectively. This implies that our powders are composed of mixed valence states and have defective structure. Presence of oxygen defect states and magnetic ions can be responsible for the observed ferromagnetism at room temperature in both pure and Fe doped samples.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 1; 84-87
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Anharmonicity Effects in Nanocrystals Studied by Raman Scattering Spectroscopy
    Autorzy:
    Dohčević-Mitrović, Z.
    Popović, Z.
    Šćepanović, M.
    Powiązania:
    https://bibliotekanauki.pl/articles/1807800.pdf
    Data publikacji:
    2009-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    63.22.-m
    78.67.Bf
    78.30.-j
    61.72.uj
    Opis:
    Phonon-phonon interactions were investigated in various nanocrystalline powders like anatase $TiO_{2-δ}$, pure $CeO_{2-δ}$ and ceria doped with Nd(Gd) analyzing temperature dependent Raman spectra of these systems. Phonon confinement model based on size, inhomogeneous strain and anharmonic effects was used to properly describe the evident changes present in the Raman spectra of pure and doped ceria nanocrystalline samples. In small particles of pure and doped ceria nanocrystals, when size effects have minor impact on Raman modes, four phonon anharmonic processes prevail under the three-phonon ones. When nanopowdered particles are grown enough size effects provoke changes of the anharmonic interactions when three-phonon coupling prevails over the four-phonon anharmonic processes. In nanocrystalline anatase $TiO_2$ evident blueshift of the most prominent $E_g$ Raman mode probably originates from dominant four-phonon anharmonic interactions.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 1; 36-41
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Hydrothermal Synthesis of $CeO_{2}$ and $Ce_{0.9}Fe_{0.1}O_{2}$ Nanocrystals
    Autorzy:
    Radović, M.
    Dohčević-Mitrović, Z.
    Golubović, A.
    Matović, B.
    Šćepanović, M.
    Popović, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1795617.pdf
    Data publikacji:
    2009-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.16.Be
    61.05.C-
    78.30.-j
    78.67.Bf
    Opis:
    Pure and 10 mol% $Fe^{3+}$ doped $CeO_2$ nanocrystals were synthesized by hydrothermal method using two different basic solutions ($NH_4OH$ and NaOH). All the samples were calcinated at 140°C and 200°C. The characterization of crystalline structure, vibrational and optical properties was performed using X-ray diffraction, Raman spectroscopy and spectroscopic ellipsometry. The obtained results showed that the Fe-doped samples are solid solutions with different size of nanocrystals, very dependent on the synthesis temperature and type of basic solution. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas doping provokes a small decrease of optical absorption edge in comparison with pure ceria.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 4; 614-617
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Use of Phonon Confinement Model in Simulation οf Raman Spectra of Nanostructured Materials
    Autorzy:
    Grujić-Brojčin, M.
    Šćepanović, M.
    Dohcević-Mitrović, Z.
    Popović, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1807810.pdf
    Data publikacji:
    2009-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.07.Wx
    78.30.-j
    63.22.-m
    07.05.Tp
    Opis:
    The simulation of the Raman spectra of nanostructured materials, where the effects of frequency shift and asymmetric broadening of the Raman modes play an important role, can be very useful in systematic characterization of these materials. Use of phonon confinement model for calculating Raman spectra of different nanomaterials is considered both from the viewpoint of different confinement function and the confinement strength, as well as the dimensionality of the confinement model. The phonon dispersion relations and the choice of their approximation are also studied. The influence of particle size distribution on the shape of the calculated spectra is discussed and contributions of Gaussian and asymmetric Gaussian distribution are compared. The effects of average and inhomogeneous strain on the behavior of simulated Raman spectra are also discussed. The results of the phonon confinement model are compared to the experimental spectra of $CeO_2$ and anatase $TiO_2$ nanopowders.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 1; 51-54
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Raman Scattering from ZnSe Nanolayers
    Autorzy:
    Nesheva, D.
    Šćepanović, M.
    Aškrabić, S.
    Levi, Z.
    Bineva, I.
    Popović, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1807824.pdf
    Data publikacji:
    2009-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.15.Ef
    81.05.Dz
    78.30.-j
    68.55.-a
    Opis:
    A series of ZnSe single layers having thickness between 30 nm and 1 μm was deposited on c-Si and glass substrates at room substrate temperature. Thermal evaporation of ZnSe powder in high vacuum has been applied. Moreover, $SiO_x$/ZnSe periodic multilayers prepared by the same deposition technique and having ZnSe layer thickness of 2 and 4 nm have been studied. Raman spectra were measured at 295 K, using the 442 nm line of a He-Cd laser as well as different lines of the $Ar^+$ or $Ar^+//Kr^+$ lasers. The observed Raman features have been related to multiple optical phonon (1LO to 4LO) light scattering and connected with the existence of randomly oriented crystalline ZnSe grains in both ZnSe single layers and ZnSe layers of the multilayers. Relatively large line width ( ≈ 15 $cm^{-1}$) of the 1LO band has been observed and related to lattice distortion in the crystalline grains and existence of amorphous phase in the layers thinner than 100 nm. The Raman spectra measured on both ZnSe single layers and $SiO_x$/ZnSe multilayers using the 488 nm line with a gradually increased laser beam power indicate an increased crystallinity at high irradiation levels.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 1; 75-77
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Low-Frequency Raman Spectroscopy of Pure and La-Doped $TiO_2$ Nanopowders Synthesized by Sol-Gel Method
    Autorzy:
    Šćepanović, M.
    Aškrabić, S.
    Grujić-Brojčin, M.
    Golubović, A.
    Dohčević-Mitrović, Z.
    Kremenović, A.
    Popović, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1807845.pdf
    Data publikacji:
    2009-07
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.20.Fw
    81.07.Wx
    78.30.-j
    63.22.-m
    Opis:
    Pure and La-doped titania $(TiO_2)$ nanopowders are synthesized by sol-gel technology. The crystallite sizes determined by X-ray diffraction measurements range from 10 to 15 nm. Dependence of structural and morphological characteristics of nanopowders on synthesis conditions and $La^{3+}$ content is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of $TiO_2$. Additional Raman modes of extremely low intensity can be related to the presence of a small amount of brookite amorphous phase in nanopowders, which is in accordance with the results of X-ray diffraction analysis. The particle size distribution in TiO_2 nanopowders was estimated from the low frequency Raman spectra, using the fact that the phonon modes in nanosized $TiO_2$ observed in the low frequency region (ω <40 $cm^{-1}$) can be well described by the elastic continuum model, assuming that nanoparticles are of perfect spherical shape and isotropic. The nanosized particle distribution obtained by this method is used for the calculation of the frequency and shape of the most intensive $E_g$ Raman mode in anatase $TiO_2$ by the phonon confinement model. The calculated broadening of this mode, associated with the particle size distribution, coincides well with the characteristics of $E_g$ mode observed in measured Raman spectra of $TiO_2$ nanopowders. This confirms the Raman spectroscopy method as a powerful tool for determination of particle size distribution in nanosized materials.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 1; 99-102
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Characterization of La-Doped $TiO_2$ Nanopowders by Raman Spectroscopy
    Autorzy:
    Šćepanović, M.
    Aškrabić, S.
    Berec, V.
    Golubović, A.
    Dohčević-Mitrović, Z.
    Kremenović, A.
    Popović, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1808047.pdf
    Data publikacji:
    2009-04
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.20.Fw
    81.07.Wx
    78.30.-j
    07.05.Tp
    Opis:
    Titanium dioxide $(TiO_2)$ nanopowders doped with 0.65, 1, 2, 3 and 4 wt.% of lanthanum ions $(La^{3+})$ were synthesized by sol-gel technology. Dependence of structural and morphological characteristics of nanopowders on $La^{3+}$ content and synthesis conditions is investigated by the Raman spectroscopy. Very intensive modes observed in the Raman spectra of all nanopowder samples are assigned to anatase phase of $TiO_2$. Additional Raman modes of extremely low intensity can be related to the presence of certain amount of highly disordered brookite phase in nanopowders. Dependence of the intensity ratio of the Raman modes which originate from anatase and brookite on doping conditions is specially analyzed. In order to estimate the variation of nanocrystallite size with dopant content, shift and asymmetrical broadening of the most intensive $E_g$ Raman mode of anatase are analyzed by phonon confinement model. The obtained results are compared with the results of X-ray diffraction spectroscopy. Special attention is dedicated to the changes in the Raman spectra of pure and La-doped $TiO_2$ nanopowders observed after high temperature treatment.
    Źródło:
    Acta Physica Polonica A; 2009, 115, 4; 771-774
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Characterization of ZnSe Nanolayers by Spectroscopic Ellipsometry
    Autorzy:
    Šćepanović, M.
    Grujić-Brojčin, M.
    Nesheva, D.
    Levi, Z.
    Bineva, I.
    Popović, Z.
    Powiązania:
    https://bibliotekanauki.pl/articles/1795712.pdf
    Data publikacji:
    2009-10
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    81.07.-b
    81.15.-z
    81.05.Dz
    78.30.-j
    07.60.Fs
    68.55.-a
    Opis:
    Single layers of ZnSe with thicknesses of 30, 40, 50, 70 and 100 nm are deposited at room substrate temperature by thermal evaporation of ZnSe powder in vacuum. The layers surface morphology has been investigated by atomic force microscopy. Structural characterization by the Raman scattering measurement revealed the existence of randomly oriented crystalline ZnSe particles in all layers, and the presence of amorphous phase in layers thinner than 100 nm. The ellipsometric measurements were performed in the range from 1.5 to 5 eV at room temperature in air. To interpret the experimental results, the Bruggeman effective medium approximation of dielectric function of ZnSe layers has been used, representing the layers as different mixtures of crystalline ZnSe (c-ZnSe), amorphous ZnSe (a-ZnSe), and voids. The assumption of polycrystalline ZnSe layers modeled as mixture of porous c-ZnSe (with volume fraction of voids ≈ 0.17) and a-ZnSe gives the best fit of ellipsometric experimental data. Single layer thicknesses similar to those expected from preparation conditions have been obtained by this fitting procedure. It has been also found that decrease in the layer thickness causes an increase of the volume fraction of a-ZnSe. Thus, c-ZnSe/a-ZnSe ratio, porosity and layer thickness obtained by spectroscopic ellipsometry, provides useful information about crystallinity and micro-/nanostructure of ZnSe nanolayers.
    Źródło:
    Acta Physica Polonica A; 2009, 116, 4; 708-711
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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