N. V. Lyanguzov

Amplification of raman scattering by localized plasmons in silver nanoparticles on the surface of zinc oxide nanorods

The magnetron sputtering of Ag nanoparticles onto ZnO nanorod arrays is studied. The lateral faces of the nanorods are coated with nanoparticles at a much lower density as compared to the flat faces at comparable sputtering times. The silver density is high on the edges of the lateral faces of the nanorods. The plasmon absorption in the synthesized arrays of nanorods coated with individual Ag nanoparticles is maximal at 450–500 nm. The appearance of local plasmon excitations increases the intensity of the multiphonon processes with the participation of ZnO polar modes in Raman spectra. The cross section of resonance Raman scattering for A1(LO) phonon overtones increases with the equivalent Ag film thickness.

Ferroelectric superlattice based on barium–strontium titanate solid solutions

A superlattice of the composition Ba0.8Sr0.2TiO3/Ba0.4Sr0.6TiO3 has been grown by rf cathode sputtering on a MgO(001) substrate. The unit cell parameters of the superlattice layers along the normal to the substrate, modulation period, and orientation relationships between the film and the substrate have been determined using X-ray diffraction. Based on the temperature dependences of the polarized Raman spectra, it has been revealed that the frequency of soft mode E(TO) increases from 79 to 97 cm–1 in the temperature range of 80–350 K. It has been found that there are no characteristic indications of a sequence of phase transitions, which take place in bulk samples of barium–strontium titanate solid solutions of identical compositions, and the transition from the ferroelectric to paraelectric phase in the superlattice occurs at a temperature of ∼350 K.

Raman spectra of polycrystalline bismuth titanate nanotubes

The Raman spectra of bismuth titanate Bi4Ti3O12 nanotubes synthesized by the template method on an Al2O3 membrane have been studied. The samples prepared represent an array of oriented ∼50-μm-long nanotubes with coalescing smooth walls. The nanotube wall thickness is varied from 20 to 50 nm, and the nanotube inside diameter is about 200 nm. The Raman spectra of the nanotubes demonstrate a broadening of the lines corresponding to the stretching and bending vibrations of TiO6 octahedra. In the low-frequency spectral range corresponding to vibrations of Bi ions with respect to the oxygen octahedra, a transformation due to strong mechanical stresses generated during the formation of the nanotubes has been observed.

Direct transition from the rhombohedral ferroelectric to the paraelectric phase in a (Ba,Sr)TiO3 thin film on a (111)MgO substrate

A heteroepitaxial (200 nm thick) (BST) thin film was deposited on a (111)MgO substrate using rf sputtering. X-ray diffraction examinations confirmed epitaxial growth and rhombohedral symmetry of the film ( and ) at room temperature. Polarized Raman spectra of the film were studied in the temperature range from 100 to 420 K. In contrast to a BST thin film grown on (001)MgO, the observed linear temperature dependence of the squared soft mode frequency suggests the displacive character of the ferroelectric-paraelectric phase transition in a BST thin film on (111)MgO.

Use of various growth catalysts for laser sputtering of ZnO micro- and nanorods

Pulsed laser deposition and various catalysts are used to fabricate ZnO micro- and nanorods at temperatures close to the optimum temperature for each catalyst. A comparative analysis of the optical and structural properties of the rods shows that, as the temperature of growth on Al2O3(11–20) substrates decreases, the internal stresses in the rods decrease, which improves their structure and optical properties. This effect is not observed for GaN/Si substrates because of the high stresses induced by the difference in the lattice parameters. An increase in the synthesis temperature leads to an increase in the lattice strains and the concentration of point defects, the relaxation of selection rules, and the appearance of numerous phonon A1(LO) overtones. The lattice strains calculated from unit cell parameter a and the shift in the phonon A1(LO) frequency agree qualitatively. The study of the photoluminescence of the rods shows that a decrease in the synthesis temperature decreases the imperfection of the ZnO rods and improves their optical properties for UV applications.

Negative magnetoresistance of (1–x)La0.7Sr0.3MnO3/x(GeO2, Li4P2O7) composite ceramics

Ceramics of (1–x)La0.7Sr0.3MnO3/x(GeO2) and (1–x)La0.7Sr0.3MnO3/x(Li4P2O7) compositions with x = 0.1–0.3 have been synthesized that possess high absolute values of isotropic negative magnetoresistance MR at room temperature. In a composite containing 20 mass % GeO2 as the barrier component, the negative magnetoresistance reaches MR = 15% in a magnetic field of 18 kOe, while an analogous composite with Li4P2O7 under identical conditions has MR = 16%.

Specific features of the dielectric spectrum of CaCu3Ti4O12 in the low-frequency range

The dielectric spectra of CaCu3Ti4O12 ceramics with giant values of the dielectric constant have been presented. The spectrum exhibits Debye dispersion with an activation energy of 0.075 eV in the high-frequency range of 106–107 Hz, and a characteristic plateau has been seen in the frequency dependence of the dielectric constant in the range of 104–105 Hz. A considerable increase in the loss factor ɛ″ has been observed in the low-frequency part of the spectrum and a capacitive-to-inductive impedance transition has been revealed in some samples at a frequency below 10−2 Hz. The causes of this transition have been discussed.

Positive magnetoresistance of La0.7Sr0.3MnO3/C Composites at room temperature

Two-phase composites xLa0.7Sr0.3MnO3/(100–x)C (x = 5–85 mass %) have been synthesized. The magnetoresistive properties of these materials in magnetic fields from 0 to 15 kOe have been investigated. It has been shown that, at room temperature, the positive isotropic magnetoresistance for samples with x = 50–60 mass % reaches 15%.

Specific features of optical phonons in raman spectra of an array of vertical ZnO microrods on silicon

The polarized Raman spectra of an array of vertical zinc oxide microrods prepared by the carbothermal synthesis on a Si(001) substrate have been investigated. The length and diameter of the rods are 9 ± 0.5 μm and 210 ± 50 nm, respectively. X-ray diffraction studies have confirmed the mutual crystallographic orientation [001]ZnO ‖ [001]Si in the direction normal to the substrate plane. In the Raman spectra of the rods, there are modes forbidden by selection rules for the single crystal: the A1(TO) E2high and modes in the scattering geometry