A. Teiserskis

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.

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 .

Nondestructive Material Homogeneity Characterization by Millimeter Waves

Millimeter wave bridge technique for nondestructive material homogeneity characterization is described. The idea of this technique is the local excitation of millimeter waves in testing material and the measurement of the transmitted amplitude and phase in it different places. Some results of the homogeneity measurements for the dielectric substrates are presented.

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.