X-ray diffraction analysis of the surface acoustic wave propagation in langatate crystal

X-ray diffraction on a langatate crystal (La₃Ga_5.5Ta_0.5O₁₄, LGT) modulated by a Λ=12 μm Rayleigh surface acoustic wave (SAW) was studied in a double axis X-ray diffractometer scheme at the BESSY synchrotron radiation source. SAW propagation in the crystal causes sinusoidal modulation of the crystal lattice and the appearance of diffraction satellites on the rocking curves, with their number, angular positions, and intensities depending on the wavelength and amplitude of acoustic vibrations of the crystal lattice. Strong absorption of X-ray radiation in LGT enables the observation of the diffraction spectra extinction at certain SAW amplitudes. X-ray diffraction spectra analysis makes it possible to determine SAW amplitudes and wavelengths, to measure the power flow angles, and investigate the diffraction divergence in acoustic beam in LGT.     

Laser crystallization for large-area electronics

Laser crystallization is reviewed for the purpose of fabrication of polycrystalline silicon thin film transistors (poly-Si TFTs). Laser-induced rapid heating is important for formation of crystalline films with a low thermal budget. Reduction of electrically active defects located at grain boundaries is essential for improving electrical properties of poly-Si films and achieving poly-Si TFTs with high performances. The internal film stress is attractive to increase the carrier mobility. Recent developments in laser crystallization methods with pulsed and continuous-wave lasers are also reviewed. Control of heat flow results in crystalline grain growth in the lateral direction, which is important for fabrication of large crystalline grains. We also report an annealing method using a high-power infrared semiconductor laser. High-power lasers will be attractive for rapid formation of crystalline films over a large area and activation of silicon with impurity atoms.     

Real-time X-ray diffraction measurements of structural dynamics and polymorphism in diindenoperylene growth

We investigate the temperature-dependent polymorphs in diindenoperylene (DIP) thin films on sapphire and silicon oxide substrates using in situ X-ray scattering. On both substrates the DIP unit cell is very similar to the high-temperature phase of bulk crystals, with the substrate stabilising this structure well below the temperature where a phase transition to a low-temperature phase is observed in the bulk. Lowering the substrate temperature for DIP growth leads to a change in molecular orientation and an additional polymorph appears, with both these effects being more pronounced on sapphire as compared to silicon oxide. Using real-time reciprocal-space mapping we observe an expansion of the in-plane unit cell during DIP growth, which may be due to changes in molecular orientation as well as strain in the first monolayers. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorized users.     

Structural characteristics of a single-crystalline Sr<Subscript>0.75</Subscript>Ba<Subscript>0.25</Subscript>NbO<Subscript>3</Subscript> electro-optic material

Sr_0.75Ba_0.25NbO₃ (SBN-75) has the tungsten-bronze structure with a tetragonal unit cell and exhibits electro-optic properties that are important for sensors. Due to its quaternary nature, its structural uniformity, integrity, and homogeneity become important for these applications. In this paper, we present high-resolution X-ray diffraction studies of the crystalline quality and lattice parameter variation across the surface of single crystals of SBN-75. Using rocking curves, topographs, and point-wise measurements of lattice parameters, we show that these crystals have a high degree of crystalline quality and microscopic homogeneity for any electro-optic application.     

Growth and characterization of L-Alanine-doped Zinc Thiourea Chloride single crystal (ZTC)

Single crystal of L-Alanine-doped Zinc Thiourea Chloride (ZTC) was grown by slow evaporation technique. L-Alanine was added in saturated ZTC solution by molar percent. The second-harmonic generation efficiency was studied by Kurtz and Perry powder SHG test for 1, 2, and 3 mole% L-Alanine-doped ZTC and compared with pure ZTC. We observed enhancement in the SHG efficiency of L-Alanine-doped ZTC. Higher enhancement was observed for 3 mole% L-Alanine-doped ZTC. Incorporation of L-Alanine in the crystal was confirmed by energy dispersive X-ray analysis (EDAX). The Fourier transform infrared spectroscopy (FTIR) qualitatively confirms the presence of all the functional groups. The unit cell parameters and crystal structure were determined by single crystal X-ray diffraction. The UV-visible absorption spectra of L-Alanine-doped ZTC show excellent transmittance from 300 nm to 1100 nm. The thermal stability of the grown crystal was also studied by thermo-gravimetric analysis (TGA).     

Femtosecond hard X-ray plasma sources with a kilohertz repetition rate

Laser-driven plasma sources of femtosecond hard X-ray pulses have found widespread application in ultrafast X-ray diffraction. The recent development of plasma sources working at kilohertz repetition rates has allowed for diffraction experiments with strongly improved sensitivity, now revealing subtle fully reversible changes of the geometry of crystal lattices. We provide a brief review of this development and present a novel plasma source with an optimized mechanical and optical design, providing a high flux of several 10¹⁰ photons/s at the Cu-Kα energy of 8.04 keV and a pulse duration of ≤300 fs. First experiments, including the generation of Debye–Scherrer diffraction patterns from Si powder, demonstrate the high performance of this source.     

On the competiting role of mean-field and residual interactions in flow observables

Theoretical analyses of heavy-ion reactions are performed in the framework of the semi-classical Landau-Vlasov approach. The incident energies are investigated in the range from intermediate to low energy regimes, where transverse collective motion has been experimentally evidenced. The influence of the equation of state (E.O.S.) parameters on various collective observables is studied in relation with the action of the residual interactions. From the sensitivity to both aspects, and taking into account the experimental biases limitations, our investigation indicates that E.O.S. signatures should be more expected at energies below 100 MeV per nucleon.     

Energy dependence of collective flow of neutrons and protons in197Au+197Au collisions

We investigate the beam energy dependence of neutron and proton squeeze-out in collisions of¹⁹⁷Au+¹⁹⁷Au atE/A=400—800 MeV. The azimuthal anisotropy that describes the enhanced emission of mid-rapidity neutrons perpendicular to the reaction plane rises strongly with the transverse momentum of the neutrons. This dependence of the azimuthal anisotropy follows a universal curve — independent of beam energy — if the neutron momenta are measured in fractions of the projectile momentum per mass unit. Analogously, the kinetic energy spectra of mid-rapidity neutrons exhibit a universal behaviour as a function of the kinetic energy of the projectile. The members of the FOPI-collaboration: J.P. Alard, Z. Basrak, N. Bastid, I.M. Belayev, M. Bini, R. Bock, A. Buta, R. aplar, C. Cerruti, N. Cindro, J.P. Coffin, M. Crouau, P. Dupieux, J. Erö, Z.G. Fan, P. Fintz, Z. Fodor, R. Freifelder, L. Fraysse, S. Frolov, A. Gobbi, Y. Grigorian, G. Guillaume, N. Herrmann, K.D. Hildenbrand, S. Hölbling, O. Houari, S.C. Jeong, M. Jorio, F. Jundt, J. Kecskemeti, P. Koncz, Y. Korchagin, R. Kotte, M. Krämer, C. Kuhn, I. Legrand, A. Lebedev, C. Maguire, V. Manko, T. Matulewicz, G. Mgebrishvili, J. Mösner, D. Moisa, G. Montarou, P. Morel, W. Neubert, A. Olmi, G. Pasquali, D. Pelte, M. Petrovici, G. Poggi, F. Rami, W. Reisdorf, A. Sadchikov, D. Schüll, Z. Seres, B. Sikora, V. Simion, S. Smolyankin, U. Sodan, N. Taccetti, K. Teh, R. Tezkratt, M. Trzaska, M.A. Vasiliev, P. Wagner, J.P. Wessels, T. Wienold, Z. Wilhelmi, D. Wohlfarth, A.V. Zhilin.     

Growth of AgInSe<Subscript>2</Subscript> on Si(100) substrate by thermal evaporation technique

AgInSe₂ films were prepared by a thermal evaporation technique onto Si(100) substrates at a pressure of 10⁻⁵ mbar. Structural and optical properties of films deposited at 300 and 473 K have been investigated. The film composition was studied by energy dispersive analysis through X-rays. X-ray diffraction patterns indicate that AgInSe₂ films have chalcopyrite structure with strong preferred orientation in the (112) direction. Average vertical crystallite size of 25 nm was observed. The optical energy gaps of 1.20 and 1.90 eV were obtained due to the fundamental absorption edge and a transition originating from crystal field splitting, respectively. Field emission scanning electron microscopy shows loosely packed grains of spherical symmetry with some facets.     

On the correctness of estimates on (n,e)-amplitude and neutron polarizability from total cross sections of Bi and Pb

The explanation of a discrepancy in the(n, e)-scattering amplitude values obtained by the Garching and Dubna groups from the data on the scattering length and total cross sections for Bi was suggested. It is also shown that the methods of derivation of the neutron polarizability coefficient used by these groups have incorrectnesses leading to additional uncertainties of neutron polarizability evaluations.     

Strain relaxation of CdTe films growing on lattice-mismatched substrates

We have deposited CdTe films by laser-assisted epitaxy approach and investigated the influence of substrate and film thickness on the film properties. Grown on Si(001), GaAs(001), and quartz substrates; the CdTe films exhibit preferential orientation along the cubic CdTe(111) direction. When the films are thin (<500 nm), a blueshift of the band gap and splitting of valence bands were observed. These results are attributed to the existence of residual strains induced by mismatch of the film lattice constant with that of the substrate, and by their difference in thermal expansion coefficients. The bulk band-gap energy of 1.5 eV was achieved on the surface of thick CdTe films grown on Si(001) substrate, indicating that strain was almost completely relaxed in this case. Our results demonstrate that by a proper selection of substrate and film thickness it is possible to grow film semiconductors with band gap approaching those of bulk crystals.     

Dye-sensitized solar cells based on TiO2 nanotube/porous layer mixed morphology

Titania porous layer has been fabricated on titania nanotubes for dye sensitized solar cells and the photovoltaic performance of solar cells with mixed morphology has been investigated. The porous layer results in a similar improvement in the short circuit current density to conventional TiCl₄ treatment, although the mechanisms responsible for the observed increase in the efficiency are different. This enables further improvements of the photovoltaic performance by combining the TiCl₄ treatment and porous layer deposition, so that the efficiency in the case of ∼5 μm long tubes increases on average from ∼1.6 to ∼2.2%.     

Nanocomposites of magnetic cobalt nanoparticles and cellulose

Polymeric matrices with stabilized metallic nanoparticles constitute an important class of nanostructured materials, because polymer technology allows fabrication of components with various electronic, magnetic and mechanical properties. The porous cellulose matrix has been shown to be a useful support material for platinum, palladium, silver, copper and nickel nanoparticles. In the present study, nanosized cobalt particles with enhanced magnetic properties were made by chemical reduction within a microcrystalline cellulose (MCC) matrix. Two different chemical reducers, NaBH₄ and NaH₂PO₂, were used, and the so-formed nanoparticles were characterized with X-ray absorption spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. These experimental techniques were used to gain insight into the effect of different synthesis routes on structural properties of the nanoparticles. Magnetic properties of the nanoparticles were studied using a vibrating sample magnetometer. Particles made via the NaBH₄ reduction were amorphous Co-B or Co oxide composites with diminished ferromagnetic behaviour and particles made via the NaH₂PO₂ reduction were well-ordered ferromagnetic hcp cobalt nanocrystals.     

Square-pyramidal iron coordination modules as potential spin switches for the chemisorption on gold

Octahedral iron(II) complexes of a unique pyridine-derived tetrapodal pentadentate polyamine ligand, 2,6-C₅H₃N(CMe[CH₂NH₂]₂)₂, show temperature-dependent spin crossover (SCO) depending on the nature of a sixth monodentate ligand L (imidazol or pyridine derivative). For L = 1-methylimidazol, the redox behaviour of the complex, as determined by cyclic voltammetry, suggests an accompanying ligand exchange. Pyridine-4-thiol and the disulphides: 4-(2-methyldisulphanyl)pyridine, 4-(2-hexadecyldisulphanyl)pyridine and 1,2-bis([pyridine-4-yl]methyl)disulphane, were studied as mono-dentate ligands L, with a view to enable chemisorption of iron(II) complexes on a gold surface. In the case of pyridine-4-thiol, the participation of the thiolate functional group in iron coordination is difficult to suppress, whereas the disulphides enter into yet unrecorded redox chemistry with iron(II), yielding a di-iron(III) complex containing a persulphide bridge (S ₂²⁻).     

Propagation of cylindrical shock waves in a rotating atmosphere under the action of monochromatic radiation

Summary  A model of cylindrical shock waves is discussed in a non-uniform rotating atmosphere under the action of monochromatic radiation. We have assumed that the radiation flux moves through a rotating gas with constant intensity and the energy is absorbed only behind the shock wave which moves in opposite direction to the radiation flux.     

Absorption measurements in InSe:Ho single crystal under an electric field

InSe:Ho single crystal was grown by Bridgman-Stockberger method. Electric field effects on the absorption measurements have been investigated as a function of temperature in InSe:Ho single crystal. The absorption edge shifted towards longer wavelengths and a decrease of intensity in absorption spectra occurred under an electric field of 7.5 kV/cm. Using absorption measurements, steepness parameter and Urbach energy were calculated under electric field. Applied electric field caused an increase in the Urbach energy. At 10 K and 320 K, the first exciton energies were calculated as 1.322 and 1.301 eV for zero voltage and 1.245 and 1.232 eV for applied electric field, respectively.     

Growth and magneto-optical properties of LiTb(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript> crystal

Lithium terbium molybdate (LiTb(MoO₄)₂) single crystal was grown by the Czochralski method. The lattice parameters of the crystal were determined by X-ray diffraction analysis. The absorption coefficient and the Faraday rotation spectrum (B=1.07 T) were investigated at wavelengths of 400–1500 nm at room temperature. Verdet constants of LiTb(MoO₄)₂ crystal at 532-, 633- and 1064-nm wavelengths were measured by the extinction method. The results show that LiTb(MoO₄)₂ crystal has a larger magneto-optical figure of merit than that of terbium gallium garnet at wavelengths of 600–1500 nm.     

Structure and impedance spectroscopy of Pr1? x Sr x Fe0.8Co0.2O3? δ ( x =0.1, 0.2, 0.3) thin films grown by laser ablation

Polycrystalline samples of Pr_1−x Sr _x Fe_0.8Co_0.2 O_3−δ (x=0.1, 0.2, 0.3) (PSFC) were prepared by the combustion synthesis route at 1200°C. The structure of the polycrystalline powders was analysed with X-ray powder diffraction data. The X-ray diffraction (XRD) patterns were indexed as the orthoferrite similar to that of PrFeO₃ having a single-phase orthorhombic perovskite structure (Pbnm). Pr_1−x Sr _x Fe_0.8Co_0.2O_3−δ (x=0.1, 0.2, 0.3) films have been deposited on yttria-stabilized zirconia (YSZ) single-crystal substrates at 700°C by pulsed laser deposition (PLD) for application to thin film solid oxide fuel cell cathodes. The structure of the films was analysed by XRD, scanning electron microscopy (SEM) and atomic force microscopy (AFM). All films are polycrystalline with a marked texture and present pyramidal grains in the surface with different size distributions. Electrochemical impedance spectroscopy (EIS) measurements of PSFC/YSZ single crystal/PSFC test cells were conducted. The Pr_0.7Sr_0.3Fe_0.8Co_0.2O_3−δ film at 850°C presents a lower area specific resistance (ASR) value, 1.65 Ω cm², followed by the Pr_0.8Sr_0.2Fe_0.8Co_0.2O_3−δ (2.29 Ω cm² at 850°C) and the Pr_0.9Sr_0.1Fe_0.8Co_0.2O_3−δ films (5.45 Ω cm² at 850°C).     

Solidification velocity in liquid silicon during excimer laser crystallization

Excimer laser crystallization (ELC) is commonly employed to fabricate low-temperature polycrystalline silicon. A time-resolved in-situ optical system with nanosecond response time is developed to monitor and record the phase transformation process during ELC. The average solidification velocity of liquid silicon (liquid Si) is investigated from the optical spectra recorded by a fast oscilloscope. It is found that the average solidification velocities of liquid Si in the partial-melting and complete-melting regimes are fundamentally different. In the partial-melting regime, the average solidification velocity decreases with increasing excimer laser energy density; while in the complete-melting regime, it increases abruptly due to the presence of deeply supercooled liquid Si.     

The sublimation growth of AlN fibers: transformations in?morphology & fiber direction

The growth of AlN fibers using sublimation method was investigated in the temperature range from 1600 °C to 2000 °C. Large-scale AlN fibers are obtained with diameters from 100 nm to 50 μm and lengths up to several millimeters. The fiber morphology and growth direction are characterized by X-ray diffraction (XRD), field emission scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman scattering. The fibers change from wire-like to prism-like in morphology and increase in diameter as rising temperatures, accompanying a transformation in axial direction from [10 ] to [0001]. The transformation in the growth direction is discussed in terms of AlN structure and supersaturation of AlN gas species. These results provide useful information for controlling the growth of large-scale AlN fibers.