Z. Saltyte

Magnetoresistant La1−xSrxMnO3 films by pulsed injection metal organic chemical vapor deposition: effect of deposition conditions, substrate material and film thickness

Abstract High quality epitaxial La 1− x Sr x MnO 3 films were deposited by pulsed injection metal organic chemical vapor deposition, using as precursor materials metal-2,2,6,6-tetramethyl-3,5-heptandionates dissolved in monoglyme. The influence of various deposition conditions, substrate material and film thickness on film properties was investigated. The best films were deposited on LaAlO 3 substrates at 825 °C: films exhibited a sharp semiconductor–metal transition and high magnetoresistance (∼40%) at a close-to-room temperature and in a rather low field of 1.5 T. In-situ or ex-situ high-temperature annealing in oxygen increased the temperature of semiconductor–metal transition, but decreased the magnetoresistance and the temperature coefficient of resistance. Biaxial strain imposed by the lattices’ mismatch was clearly observed in thinner La 1− x Sr x MnO 3 films on perovskite substrates. Tensile strain was present in the films on SrTiO 3 and compressive strain in the films on LaAlO 3 (and less clearly on NdGaO 3 ). Both tensile and compressive strains decreased the temperature of electric transition and the values of magnetoresistance. The strain was completely relaxed in the films more than ∼100 nm thick.

Investigation of thickness-dependent stress in PbTiO3 thin films

X-ray diffraction (XRD) and Raman spectroscopy were used to investigate stress dependence on thickness in PbTiO3 (PTO) films grown by pulsed liquid injection metalorganic chemical vapor deposition on a LaAlO3 (001) substrate (LAO). Films on sapphire substrate (R plane) were used as the polycrystalline film reference. Epitaxial PTO films with a dominant c domain structure are grown on LAO substrate, whereas the films on sapphire are polycrystalline. A detailed investigation of the PTO/LAO film microstructure by XRD gives evidence of PTO twinning. Both techniques reveal that PTO films are under tensile in-plane stresses. The study of the film thickness dependence of microstrains, grain size, volume fraction of a domains, as well as surface morphology of PTO/LAO films indicates that these parameters are clearly correlated. A change in the relaxation mechanism between 65 and 125 nm of film thickness has been evidenced. A c parameter gradient occurs throughout the film depth; it originates in stress relaxation...

Metal-organic chemical vapour deposition of mixed-conducting perovskite oxide layers on monocrystalline and porous ceramic substrates

Perovskite oxide layers, i.e. manganites La1−x(Sr,Ca)xMnO3, ferrates La1−xSrxFe1−yCoyO3, gallates La1−xSrxGa1−y(Co,Ni,Fe)yO3 of a thickness of 0.8–2 μm, were deposited by pulsed injection MOCVD (metal-organic chemical vapour deposition) on various monocrystalline and porous ceramic substrates. The layers were characterised by X-ray diffraction, scanning electron microscopy, wavelength dispersion spectroscopy and by electrical measurements of the total conductivity vs. temperature. Such oxides are known as mixed electronic–ionic conductors and are largely studied as materials for the fabrication of oxygen permeable membranes. One of the aims of this work was to estimate the suitability of the pulsed injection MOCVD technique for the preparation of dense perovskite layers for their use as membranes for oxygen.

Synthesis and characterisation of YBCO thin films grown by injection-MOCVD

Abstract Epitaxial YBCO thin films have been grown on MgO, SrTiO 3 and NdGaO 3 substrates by a new process (injection MOCVD). Droplets (few μ1) of a solution of Y, Ba and Cu β-diketonates in monoglyme are injected into an evaporator through a fast micro electro-valve driven by a computer. Growth rates more than ten times higher than those obtained by the conventional MOCVD process have been obtained in this first step of experiments (>3 μ m h −1 ). The best films obtained so far have T c >90 K and J c >3×10 6 A cm −2 .

Ferroelectric PbTiO3 Films Grown by Pulsed Liquid Injection Metalorganic Chemical Vapour Deposition

Influence of various deposition conditions (deposition temperature, partial oxygen pressure and solution composition) to the growth of ferroelectric PbTiO 3 (PTO) films by pulsed liquid injection metalorganic chemical vapour deposition (MOCVD) was examined. Films were grown on LaAlO 3 (001), SrTiO 3 (001) and sapphire (R-plane) substrates. Pb(thd) 2 and Ti(O i Pr) 2 (thd) 2 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) dissolved in toluene were used as precursors. Evolution of film composition, surface morphology and microstructure with deposition conditions were studied. Microstructure of the films was characterized by X-ray diffraction (XRD) in Bragg-Brentano and Schulz geometries and by Raman spectroscopy. Epitaxial films on perovskite substrates consisted of dominant c-axis and minor a-axis textured zones (c-domains and a-domains). The amount of a-domains in films depended mainly on deposition temperature. The twinning in a- and c-domains was observed and twinning (tilt) angles depended on deposition conditions and on substrate. Fully twinned or partially twinned films can be obtained varying deposition conditions. The best quality epitaxial films were obtained on SrTiO 3 and LaAlO 3 at 650°C. Films on sapphire were mainly polycrystalline.

Effect of deposition conditions on the stoichiometry and structural properties of LiNbO3 thin films deposited by MOCVD

Epitaxial LiNbO3 thin films were deposited on C-sapphire substrates by pulsed injection metal organic chemical vapor deposition and atmospheric pressure metal organic chemical vapor deposition. The effect of deposition conditions, such as the ratio of Li/Nb precursors in solution and the deposition pressure, on the phase composition, Li nonstoichiometry, texture, epitaxial quality, residual stresses and formation of twins in LiNbO3 films was studied by means of X-ray diffraction and Raman spectroscopy. It was found that the deposition pressure played an important role in the incorporation of Li2O in the film and the formation of in-plane and out-of-plane twins.

Raman Spectroscopy and X-ray Diffraction Studies of Stress Effects in PbTiO 3 Thin Films

The evolution of domain structure and in-plane and out-of-plane lattice parameters in PbTiO3 (PTO) films on SrTiO3 (STO), LaAlO3 (LAO) and MgO substrates was studied as a function of film thickness and temperature by X-ray diffraction (XRD). Microstrains and average grain sizes were determined in several crystallographic directions for films of different thicknesses using a Williamson-Hall and Langford analysis. Stress relaxation with film thickness was observed in different domains by Raman spectroscopy and greatly influences lattice parameters. Specific contributions of a-and c-domains on Raman spectra were analyzed and correlated to domains fraction. The high temperature structural phase transition was followed by Raman spectroscopy, showing that the transition depends on the nature of stress.

YBCO films on buffered Ni RABiT substrates by pulsed injection MOCVD

Abstract Biaxially textured buffer layers and YBa 2 Cu 3 O 7 (YBCO) films were grown on NiO/Ni based substrates by pulsed injection MOCVD. High quality biaxially textured NiO layers have been prepared following an optimised recrystallisation–oxidation process. The yttria stabilized zirconia (YSZ) and its combination with CeO 2 and/or Y 2 O 3 were investigated in the role of buffer layers for YBCO. Thin biaxially textured buffer layers were deposited in a temperature range from 600 to 800 °C. The best superconducting properties correspond to the Ni/NiO/YSZ/Y 2 O 3 /YBCO architecture: YBCO layers were grown epitaxially and exhibited a critical temperature T c ∼90 K ( ΔT c ⩽1 K) and critical current densities J c ⩾5×10 5 A/cm 2 at 77 K.

Properties of Al-doped ZnO films grown by atmospheric pressure MOCVD on different orientation sapphire substrates

ABSTRACT Al-doped ZnO films were grown on different orientation sapphire substrates (sapphire-R, C, M, A) at 400–600 °C via the atmospheric pressure aerosol-assisted MOCVD technique. The influence of deposition temperature and orientation of sapphire substrate on the microstructure, electrical and optical properties of ZnO-Al films was investigated. Epitaxial films grown on sapphire-R substrates exhibited the best electrical properties: carrier mobility was 50–60 cm2 V−1 s−1, resistivity <10−3 Ω cm. The conditions of post-deposition treatment of films (gas atmosphere during film cooling after deposition, ex-situ annealing) had a marked influence on the electrical properties of films.

On the possibility to grow zinc oxide-based transparent conducting oxide films by hot-wire chemical vapor deposition

Hot-wire chemical vapor deposition (HW-CVD) was applied to grow zinc oxide (ZnO)-based transparent conducting oxide (TCO) films. Indium (In)-doped ZnO films were deposited using a cold wall pulsed liquid injection CVD system with three nichrome wires installed at a distance of 2 cm from the substrate holder. The wires were heated by an AC current in the range of 0–10 A. Zn and In 2,2,6,6-tetramethyl-3,5-heptanedionates dissolved in 1,2-dimethoxyethane were used as precursors. The hot wires had a marked effect on the growth rates of ZnO, In-doped ZnO, and In2O3 films; at a current of 6–10 A, growth rates were increased by a factor of ≈10–20 compared with those of traditional CVD at the same substrate temperature (400 °C). In-doped ZnO films with thickness of ≈150 nm deposited on sapphire-R grown at a wire current of 9 A exhibited a resistivity of ≈2 × 10−3 Ωcm and transparency of >90% in the visible spectral range. These initial results reveal the potential of HW-CVD for the growth of TCOs.