marina tyunina - Academia.edu (original) (raw)
Papers by marina tyunina
Nanostructured Materials, 1999
Abstract The agglomeration and clustering processes occurring during pulsed laser deposition were... more Abstract The agglomeration and clustering processes occurring during pulsed laser deposition were studied by analyzing the nanometer scale surface morphology of an amorphous lead zirconate titanate deposit using scanning electron microscopy and atomic force microscopy. The surface roughening of the deposit depended on the pressure and nature of the ambient gas, as well as on the duration of deposition. The development of surface features is discussed in terms of agglomeration in the plume and the adsorption of species and surface diffusion. The power law dependence of surface roughness on the number of laser shots, observed in oxygen and in argon, is explained by the assumption of cluster generation in the plume.
Pulsed laser deposition with an off-axis geometry in a low-pressure argon ambient was used to pro... more Pulsed laser deposition with an off-axis geometry in a low-pressure argon ambient was used to produce films of nanosized silicon clusters or crystallites. Size selection was achieved by the distance of the deposit from the target. The local film structure and the crystallite size of the films were studied as a function of the distance from the target using micro-Raman spectroscopy. The nanocrystal size on the off-axis placed substrate varied in the range 1....5 nm, increasing with increasing distance from the target; this made it possible to achieve size selection of the nanocrystals. The surface morphology of the deposits was studied using scanning electron microscopy. Room temperature photoluminescence of the samples with 514.5 nm excitation was rather weak. Silicon 2p core photoelectron spectra showed the existence of a silicon dioxide layer on the surface of the nanoparticles.
Physics of the Solid State, 2010
Effect of biaxial tensile strains on optical functions and band edge transitions of ultra thin ep... more Effect of biaxial tensile strains on optical functions and band edge transitions of ultra thin epitaxial films was studied using as an example a 13 nm thick SrTiO 3 films deposited on KTaO 3 (100) single-crystal substrates. Optical functions in the 1200-200 nm spectral range were determined by spectroscopic ellipsometry technique. It was found that tensile strains result in a shift of the low energy band gap optical transitions to higher energies and decrease the refractive index in the visible region. Comparison of the optical spectra for strained SrTiO 3 films and for homoepitaxial strain-free SrTiO 3 :Cr (0.01 %at.) films deposited on SrTiO 3 (100) single crystalline substrates showed that this "blue" shift of the band gap could not be related to technological imperfections or to reduced thickness. The observed effect is connected with changes in the lowest conduction and in the top valence bands that are due to increase of the in-plane lattice constant and/or onset of polar phase in the tensile strain-induced ultra-thin epitaxial SrTiO 3 films.
Journal of Electroceramics, 2010
In epitaxial films of perovskite ferroelectrics, functionality can be controlled by size-strain-s... more In epitaxial films of perovskite ferroelectrics, functionality can be controlled by size-strain-surface effects. Experimental evidence of such a possibility is demonstrated in epitaxial heterostructures of BaTiO 3 thin films and of (Ba,Sr)TiO 3 superlattices grown by pulsed laser deposition on La 0.5 Sr 0.5 CoO 3 /MgO (001). In epitaxial BaTiO 3 films, temperature of phase transition is shown to be a function of in-plane biaxial strain and film thickness. In epitaxial (Ba,Sr)TiO 3 superlattices, the dielectric permittivity, tunability, and temperature of phase transition are shown to be a function of strain and superlattice period. The technological and principal problems limiting nanoscale engineering of ferroelectric functionality are also discussed.
Journal of Electroceramics, 2009
Several SrTiO 3 (STO) thin films without electrodes processed by pulsed laser deposition, of thic... more Several SrTiO 3 (STO) thin films without electrodes processed by pulsed laser deposition, of thicknesses down to 40 nm, were studied using infrared transmission and reflection spectroscopy. The complex dielectric responses of polar phonon modes, particularly ferroelectric soft mode, in the films were determined quantitatively. The compressed epitaxial STO films on (100) LSAT substrates show strongly stiffened phonon responses, whereas the soft mode in polycrystalline film on (0001) sapphire substrate shows a strong broadening due to grain boundaries and/or other inhomogeneities and defects. The stiffened soft mode is responsible for a much lower static permittivity in the plane of the compressed film than in the bulk samples.
![Research paper thumbnail of Dielectric relaxation and polar phonon softening in relaxor ferroelectric PbMg[sub 1/3]Ta[sub 2/3]O[sub 3]](https://attachments.academia-assets.com/39086310/thumbnails/1.jpg)
](Journal of Applied Physics, 2007
Relaxor ferroelectric PbMg 1/3 Ta 2/3 O3 ceramics and thin films were investigated by means of br... more Relaxor ferroelectric PbMg 1/3 Ta 2/3 O3 ceramics and thin films were investigated by means of broad-band dielectric, time-domain terahertz (THz) and Fourier-transform infrared (IR) spectroscopy in the frequency range 100 Hz -90 THz at temperatures 100 -490 K, the THz and IR spectra were studied from 20 to 900 K. Diffused and strongly temperature dependent peak in the complex permittivity is caused by a dielectric relaxation due to the dynamics of polar clusters. The relaxation appears below Burns temperature T d in the THz range, slows down on cooling through the microwave and MHz range and anomalously broadens. The shortest and longest relaxation times of the distribution of relaxation times follow Arrhenius and Vogel-Fulcher law, respectively. The degree of B-site order has only a small influence on the parameters of the dielectric relaxation and almost no influence on the phonon parameters. Below Tm ∼ =180 K the distribution of relaxation frequencies becomes broader than our experimental spectral range and frequency independent dielectric losses develop below 100 GHz in the spectra. Although the macroscopic crystal structure is cubic, IR spectra give evidence about the lower local symmetry which can be assigned to the presence of polar clusters below T d . Infrared spectra above T d still reveal more modes than predicted by selection rules in the paraelectric phase of the F m3m space group so that we suggest selection rules which take into account chemical inhomogeneity in the β"-perovskite sublattice.
Ferroelectrics, 2002
Thin films of relaxor ferroelectric lead-containing niobates (Pb B 1 m x Nb 1 m x O 3 with B = Lu... more Thin films of relaxor ferroelectric lead-containing niobates (Pb B 1 m x Nb 1 m x O 3 with B = Lu, Sc, Mg), and corresponding pseudobinary compositions with PbTiO 3 near the morpotropic phase boundary were deposited by in situ pulsed laser ablation onto a La 0.5 Sr 0.5 CoO 3 conducting oxide bottom electrode on MgO(100) and LaAlO 3 (100). Crystalline phases, epitaxial relations, crystal perfection, and chemical B-site ordering were studied by x-ray diffraction θ- 2 θ-, φ-, and y -scans. The perovskite films were pseudo-cubic and epitaxial, with (001) planes parallel to the substrate surface. At low deposition temperatures, and in thick films, also other epitaxial relations were obtained, especially on LaAlO 3 . All materials showed some degree of NaCl type (1:1) B-site ordering.
Applied Physics Letters, 2005
ABSTRACT
Nanostructured Materials, 1999
Abstract The agglomeration and clustering processes occurring during pulsed laser deposition were... more Abstract The agglomeration and clustering processes occurring during pulsed laser deposition were studied by analyzing the nanometer scale surface morphology of an amorphous lead zirconate titanate deposit using scanning electron microscopy and atomic force microscopy. The surface roughening of the deposit depended on the pressure and nature of the ambient gas, as well as on the duration of deposition. The development of surface features is discussed in terms of agglomeration in the plume and the adsorption of species and surface diffusion. The power law dependence of surface roughness on the number of laser shots, observed in oxygen and in argon, is explained by the assumption of cluster generation in the plume.
Pulsed laser deposition with an off-axis geometry in a low-pressure argon ambient was used to pro... more Pulsed laser deposition with an off-axis geometry in a low-pressure argon ambient was used to produce films of nanosized silicon clusters or crystallites. Size selection was achieved by the distance of the deposit from the target. The local film structure and the crystallite size of the films were studied as a function of the distance from the target using micro-Raman spectroscopy. The nanocrystal size on the off-axis placed substrate varied in the range 1....5 nm, increasing with increasing distance from the target; this made it possible to achieve size selection of the nanocrystals. The surface morphology of the deposits was studied using scanning electron microscopy. Room temperature photoluminescence of the samples with 514.5 nm excitation was rather weak. Silicon 2p core photoelectron spectra showed the existence of a silicon dioxide layer on the surface of the nanoparticles.
Physics of the Solid State, 2010
Effect of biaxial tensile strains on optical functions and band edge transitions of ultra thin ep... more Effect of biaxial tensile strains on optical functions and band edge transitions of ultra thin epitaxial films was studied using as an example a 13 nm thick SrTiO 3 films deposited on KTaO 3 (100) single-crystal substrates. Optical functions in the 1200-200 nm spectral range were determined by spectroscopic ellipsometry technique. It was found that tensile strains result in a shift of the low energy band gap optical transitions to higher energies and decrease the refractive index in the visible region. Comparison of the optical spectra for strained SrTiO 3 films and for homoepitaxial strain-free SrTiO 3 :Cr (0.01 %at.) films deposited on SrTiO 3 (100) single crystalline substrates showed that this "blue" shift of the band gap could not be related to technological imperfections or to reduced thickness. The observed effect is connected with changes in the lowest conduction and in the top valence bands that are due to increase of the in-plane lattice constant and/or onset of polar phase in the tensile strain-induced ultra-thin epitaxial SrTiO 3 films.
Journal of Electroceramics, 2010
In epitaxial films of perovskite ferroelectrics, functionality can be controlled by size-strain-s... more In epitaxial films of perovskite ferroelectrics, functionality can be controlled by size-strain-surface effects. Experimental evidence of such a possibility is demonstrated in epitaxial heterostructures of BaTiO 3 thin films and of (Ba,Sr)TiO 3 superlattices grown by pulsed laser deposition on La 0.5 Sr 0.5 CoO 3 /MgO (001). In epitaxial BaTiO 3 films, temperature of phase transition is shown to be a function of in-plane biaxial strain and film thickness. In epitaxial (Ba,Sr)TiO 3 superlattices, the dielectric permittivity, tunability, and temperature of phase transition are shown to be a function of strain and superlattice period. The technological and principal problems limiting nanoscale engineering of ferroelectric functionality are also discussed.
Journal of Electroceramics, 2009
Several SrTiO 3 (STO) thin films without electrodes processed by pulsed laser deposition, of thic... more Several SrTiO 3 (STO) thin films without electrodes processed by pulsed laser deposition, of thicknesses down to 40 nm, were studied using infrared transmission and reflection spectroscopy. The complex dielectric responses of polar phonon modes, particularly ferroelectric soft mode, in the films were determined quantitatively. The compressed epitaxial STO films on (100) LSAT substrates show strongly stiffened phonon responses, whereas the soft mode in polycrystalline film on (0001) sapphire substrate shows a strong broadening due to grain boundaries and/or other inhomogeneities and defects. The stiffened soft mode is responsible for a much lower static permittivity in the plane of the compressed film than in the bulk samples.
Journal of Applied Physics, 2007
Relaxor ferroelectric PbMg 1/3 Ta 2/3 O3 ceramics and thin films were investigated by means of br... more Relaxor ferroelectric PbMg 1/3 Ta 2/3 O3 ceramics and thin films were investigated by means of broad-band dielectric, time-domain terahertz (THz) and Fourier-transform infrared (IR) spectroscopy in the frequency range 100 Hz -90 THz at temperatures 100 -490 K, the THz and IR spectra were studied from 20 to 900 K. Diffused and strongly temperature dependent peak in the complex permittivity is caused by a dielectric relaxation due to the dynamics of polar clusters. The relaxation appears below Burns temperature T d in the THz range, slows down on cooling through the microwave and MHz range and anomalously broadens. The shortest and longest relaxation times of the distribution of relaxation times follow Arrhenius and Vogel-Fulcher law, respectively. The degree of B-site order has only a small influence on the parameters of the dielectric relaxation and almost no influence on the phonon parameters. Below Tm ∼ =180 K the distribution of relaxation frequencies becomes broader than our experimental spectral range and frequency independent dielectric losses develop below 100 GHz in the spectra. Although the macroscopic crystal structure is cubic, IR spectra give evidence about the lower local symmetry which can be assigned to the presence of polar clusters below T d . Infrared spectra above T d still reveal more modes than predicted by selection rules in the paraelectric phase of the F m3m space group so that we suggest selection rules which take into account chemical inhomogeneity in the β"-perovskite sublattice.
Ferroelectrics, 2002
Thin films of relaxor ferroelectric lead-containing niobates (Pb B 1 m x Nb 1 m x O 3 with B = Lu... more Thin films of relaxor ferroelectric lead-containing niobates (Pb B 1 m x Nb 1 m x O 3 with B = Lu, Sc, Mg), and corresponding pseudobinary compositions with PbTiO 3 near the morpotropic phase boundary were deposited by in situ pulsed laser ablation onto a La 0.5 Sr 0.5 CoO 3 conducting oxide bottom electrode on MgO(100) and LaAlO 3 (100). Crystalline phases, epitaxial relations, crystal perfection, and chemical B-site ordering were studied by x-ray diffraction θ- 2 θ-, φ-, and y -scans. The perovskite films were pseudo-cubic and epitaxial, with (001) planes parallel to the substrate surface. At low deposition temperatures, and in thick films, also other epitaxial relations were obtained, especially on LaAlO 3 . All materials showed some degree of NaCl type (1:1) B-site ordering.
Applied Physics Letters, 2005
ABSTRACT