Spin-Polarized Carrier Injection in MOCVD-Grown YBCO/STO/LSMO Heterostructures with Underlying YBCO Layer

The oxide heterostructures composed of superconducting YBa2Cu3O7 bottom layer, the overlying ferromagnetic La 1−x Sr x MnO 3 film and SrTiO 3 as ultrathin (d ≈ 5 nm) barrier were grown heteroepitaxially onto LaAlO3 substrates by applying pulsed liquid injection metalorganic chemical vapour deposition technique. We report anomalous interface resistance increase with cooling just below superconductive transition temperature (T c ∼ = 85 K) and enhanced suppression of supercurrent of strip-like YBa 2 Cu 3 O 7 film due to spin-polarized carriers injected from the ferromagnetic manganite layer

YSZ/CeO2/YBCO heterostructures grown in-situ by pulsed injection CVD

A great improvement of YBCO film properties on YSZ substrates was obtained by a simple in-situ insertion of a thin CeO2 buffer layer between YSZ and YBCO. CeO2/YBCO hetreostructures on YSZ were deposited by a new pulsed injection CVD technique. The CeO2 buffer layer stopped Zr diffusion from the substrate into the film, improved the YBCO film epitaxy and increased Jc up to 4-5.106 A cm-2 at 77 K. The thickness of buffer layers in the range of 20-160 nm had but little influence on YBCO film properties

Thin film growth of ionic conducting membranes by PIMOCVD

[ES] En este trabajo se presentan los resultados preliminares sobre películas delgadas de YSZ obtenidas mediante la nueva técnica de MOCVD de inyección pulsada para su aplicación como electrolitos sólidos. La originalidad de esta técnica consiste en la preparación e introducción de la fase vapor que se realiza mediante la inyección pulsada de micro-gotas de la solución líquida, que contiene los precursores de los elementos a depositar, dentro de la zona de reacción. Las características de la gota: tamaño, concentración de la solución y frecuencia de inyección determinan el espesor y la micro-estructura de las capas obtenidas. Este método, además de muy reproducible, permite obtener fácilmente estructuras multicapas con bajos ritmos de crecimiento para epitaxias o con altos ritmos de crecimiento para la obtención de heteroestructuras. Se ha puesto a punto esta técnica para la obtención de capas densas de YSZ (circona estabilizada con itria), material comúnmente utilizado como electrolito sólido de alta temperatura en sondas de oxígeno, generadores de oxígeno y SOFC (pilas de combustible de estado sólido). Se pretende obtener dichos dispositivos en forma de multicapas del tipo ánodo/electrolito/cátodo. Para ello, se han depositado capas de YSZ sobre silicio para optimizar los parámetros de depósito pero también sobre sustratos porosos activos que puedan actuar como electrodo en los dispositivos anteriormente descritos.[EN] In this work, we describe the preparation of YSZ layers on porous and non-porous substrates using the Pulsed Injection MOCVD technique for solid electrolyte applications. In this technique, the vapour phase is obtained by injecting micro-droplets of the desired solution delivered from a container kept at room temperature into a heated evaporator connected to a deposition chamber. The droplet characteristics, volume, precursor concentration and injection frequency will control and determine the thickness and the microstructure of the layers. The system offers a high degree of repeatability of the liquid volume injected and thus a high reproducibility of the layers from low to high growth rates. This process has been optimised in order to obtain dense YSZ membranes to be used as solid electrolytes in SOFC, oxygen generators and oxygen sensors. Future work will consist in the preparation of anode-electrolyte-cathode multilayered devices. For this purpose, experimental parameters have been studied and optimised in order to obtain thin YSZ membranes on dense and porous substrates.Este trabajo ha sido parcialmente financiado por la red temática europea Multimetox G5RT-CT-2000-05001.Peer reviewe

Domain structure and Raman modes in PbTiO3

A comparative analysis of Raman spectra from poly-domain PbTiO3 thin films with poly-domain and single-domain PbTiO3 crystals is presented. Raman spectroscopy reveals that the profiles of A1-symmetry modes can be significantly modified by the existence of the domain structure. The possible origins of these complex profiles of the A1(LO) and A1(TO) modes are discussed. It is emphasized that analysis of stresses, domain structure and phase transitions in the PbTiO3 thin films has to be based on the E(TO) modes presenting profiles that are not affected by the domain structure.Peer Reviewe

Dynamics of laser-induced phase switching in GeTe films

Phase switching in GeTe thin films (grown using a modified metal organic chemical vapor deposition system) upon pulsed femtosecond and nanosecond laser irradiation has been studied. Two in situ methods, i.e., optical microscopy and real-time reflectivity measurements, have been used in order to compare the optical response before and after phase change and to follow the phase change dynamics with a time resolution close to 400 ps. The results show that cycling is possible under irradiation with both fs and ns pulses using single pulses for amorphization and multiple pulses for crystallization. The use of ns pulses favors the crystalline-to-amorphous phase transformation, with a characteristic transformation time of ∼15 ns. The presence of the liquid phase was identified and temporally resolved, featuring a well-defined transient reflectivity state, in between those of the crystalline and amorphous phases. We have also studied the role of material configuration in the phase change dynamics and the mechanisms involved in the re-crystallization process. © 2011 American Institute of Physics.This work has been partially supported by the EU project CHEMAPH (IST-027561) and by the Spanish Ministry of Education and Science (Project TEC 2008-01183).Peer Reviewe

Atmospheric pressure chemical vapour deposition and characterisation of crystalline InTaO4, InNbO4 and InVO4 coatings

7 páginas, 6 figuras.-- et al.The possibilities to grow crystalline complex InTaO4, InNbO4 and InVO4 coatings as well as single oxide layers In2O3, Ta2O5, Nb2O5, and VOx were investigated using aerosol assisted atmospheric pressure chemical vapour deposition technique. Indium(III) and niobium(IV) tetramethylheptanedionates, tantalum(V) tetraethoxyacethylacetonate and vanadium(III) acethylacetonate were used as precursors, monoglyme and toluene as solvents. The influence of deposition conditions and solution composition on elemental and phase compositions of layers was studied. Indium tantalate layers containing pure monoclinic InTaO4 phase were obtained ex-situ, i.e., after high-temperature (800 °C) annealing of layers grown at lower temperature (500 °C). Films containing pure orthorhombic indium vanadate or monoclinic indium niobate phase may be prepared using both in-situ (600 °C) or ex-situ (deposition at 400 °C, annealing at 800 °C) approaches. Under optimised deposition conditions and solution compositions, Ni-doped InVO4 and InTaO4 films were also deposited and their photocatalytic activity was tested.This work was partially supported by the Lithuanian State Science and Studies Foundation.Peer reviewe

Spin-Polarized Carrier Injection in MOCVD-Grown YBCO/STO/LSMO Heterostructures with Underlying YBCO Layer

The oxide heterostructures composed of superconducting YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ bottom layer, the overlying ferromagnetic La$\text{}_{1-x}$Sr$\text{}_{x}$MnO$\text{}_{3}$ film and SrTiO$\text{}_{3}$ as ultrathin (d≈5 nm) barrier were grown heteroepitaxially onto LaAlO $\text{}_{3}$ substrates by applying pulsed liquid injection metalorganic chemical vapour deposition technique. We report anomalous interface resistance increase with cooling just below superconductive transition temperature (T$\text{}_{c}$≅85 K) and enhanced suppression of supercurrent of strip-like YBa$\text{}_{2}$Cu$\text{}_{3}$O$\text{}_{7}$ film due to spin-polarized carriers injected from the ferromagnetic manganite layer

Effect of pulsed laser irradiation on the structure of GeTe films deposited by metal organic chemical vapor deposition: A Raman spectroscopy study

Phase changes between amorphous and crystallized states were induced by laser irradiation with nanosecond pulses in Gex Tey films grown by metal organic chemical vapor deposition. The different phases were obtained by adjusting the pulse energy and could be distinguished by their different optical reflectivities. The corresponding structural changes were studied by Raman spectroscopy, showing marked differences for the two phases. A clear correlation is found between optical reflectivity levels, crystallographic state and the evolution of Ge-Ge, Te-Te, and Ge-Te Raman bands. © 2009 American Institute of Physics.This work was partially supported by the European Project CHEMAPH, FP6, under Grant No. N 027561.Peer Reviewe

Deposition of Oxide Layers by Computer Controlled"Injection-LPCVD"

A new process for stable generation of precursor's vapour pressure for CVD thin layers synthesis is experimented. The vapour pressure is controlled by sequential computer-driven injection of precise micro amounts of liquid in an evaporator, where flash volatilization occurs. During deposition, the precursors are maintained at room temperature under inert gases in an hermetically closed vessel : even thermally unstable precursors may be used. The results reported here are focused on the OMCVD deposition of Ta2O5. The growth rate increases up to 11µm/h at 650°C (amorphous layers), and decreases above (crystallized layers). In a second part, we demonstrate the feasibility of Ta2O5/SiO2 multilayers using two injectors