Search

This work is devoted to deposition of alumina–silica films using an innovative pulsed injection metal organic chemical vapour deposition technique and aluminium tri( iso -propoxide) (Al( i -OPr) 3 ) and tetraethoxysilane (TEOS) as precursors. The deposited aluminium silicate films have been characterised by scanning electron microscopy, infrared spectroscopy, X-ray diffractometry and capacitance–voltage ( C – V ) measurements. The investigation of the deposition at different Si/Al ratios and substrate temperatures has shown that the growth rate increases with the increase of Al( i -OPr) 3 proportion in solution and decreases as the proportion of TEOS increases. We have also shown that aluminium content in the film increases at lower deposition temperatures while silicon content increases at higher temperatures. The permittivity of the films determined from C – V measurements decreases with increasing substrate temperature. It was found that films deposited at substrate temperatures of 600 or 700 °C and with the highest Si/Al ratio have the lowest dielectric permittivity. This research should be useful for further development of MOCVD technology for the deposition of aluminosilicate-based dielectric materials with controlled dielectric permittivity.

Dense ceramic mixed ionic and electronic conducting membranes have been deposited by atmospheric spray-pyrolysis technique onto porous ceramic substrates. Perovskite oxide layers, i.e. manganites La1−xSrxMnO3, ferrites La1−xSrxFe1−y(Co,Ni)yO3, gallates La1−xSrxGa1−y(Co,Ni,Fe)yO3, cobaltites La1−xSrxCoO3 and related perovskites such as lanthanum nickelate La2NiO4 layers have been prepared. The structure, morphology and composition of the layers were characterised by XRD, SEM and WDS, respectively. Density and gas tightness of the layers were studied as a function of deposition process parameters, film thickness (from ∼0.5 to ∼3 μm) and preparation procedure. The presence of cracks and defects due to thermo-mechanical stresses applied during or after the preparation process were correlated with the membrane composition and the corresponding thermal expansion coefficient differences between substrates and membranes.

High quality epitaxial La1−xSrxMnO3 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 LaAlO3 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 La1−xSrxMnO3 films on perovskite substrates. Tensile strain was present in the films on SrTiO3 and compressive strain in the films on LaAlO3 (and less clearly on NdGaO3). 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.

The single liquid source pulsed injection MOCVD technique was used to deposit high quality heteroepitaxial structures containing YBa 2 Cu 3 O 7-x (YBCO), SrTiO 3 (STO) and La 1-x Sr x MnO 3 (LSMO) layers. Y, Cu, Sr, La, Mn thd complexes (thd-2,2,6,6-tetramethylheptane-3,5-dionate), Ba(thd) 2 (phen) 2 (phen-1,10-phenanthroline) and Ti(i-OPr) 2 (thd) 2 or Ti(i-OEt) 2 (thd) 2 were used as precursor materials and monoglyme (1,2-dimethoxyethane) as a solvent. The deposition of heterostructures was performed in situ or ex situ in a hot wall vertical MOCVD reactor. Various heteroepitaxial structures (STO/LSMO, LSMO/STO/LSMO, STO/YBCO, LSMO/YBCO, STO/LSMO/YBCO, LSMO/STO/YBCO, STO/LSMO/STO/YBCO) were grown and studied.

Biaxially textured YBa 2 Cu 3 O 7 (YBCO) thin films, yttria stabilized zirconia (YSZ) and yttria (Y 2 O 3 ), CeO 2 buffer layers were grown in situ on NiO/Ni based substrates by Pulsed Injection MOCVD (PICVD) using monoglyme solutions of β-diketonates (Cu(thd) 2 , Ba(thd) 2 , Y(thd) 3 , Ce (thd) 2 , Zr(thd) 4 ). High quality textured nickel oxide layers have been prepared by SOE (Surface Oxydation Epitaxy) following an optimized recrystallisation-oxidation process.Thin YSZ/Y 2 O 3 biaxially textured buffer layers (thickness 200nm/200 nm) were deposited in a wide range of temperature (from 600°C to 800°C). Subsequent YBCO layers (thickness 750nm) on Ni/NiO/YSZ/Y 2 O 3 were grown epitaxially (ω-scan of YBCO FWMH=5°) and exhibited critical current densities Jc ≥3.10 5 A/cm 2 with a critical temperature Tc=90K and ΔTc ≤ 1 K. The best results were obtained for deposition temperatures of 600°C for YSZ, 675°C for Y 2 O 3 and 800°C for YBCO.

YBa 2 Cu 3 O 7-x (YBCO) and La 1-x Sr x MnO 3 (LSMO) layers were grown by single liquid source pulsed injection MOCVD technique in hot wall vertical MOCVD reactors. Y, Ba, Cu, Sr, La, Mn thd complexes (thd -2,2,6,6-tetramethylheptane-3,5-dionate) were used as precursor materials and monoglyme (1,2-dimethoxyethane) as a solvent. The influence of deposition temperature and thickness on the properties of films on LaAlO 3 and MgO substrates was studied. Thin YBCO layers deposited at 825 °C on LaAlO 3 substrates exhibited epitaxial quality, sharp superconducting transition (∼0.2 K) and a high critical current density (= 4MA/cm 2 at 77 K). Films on MgO substrates were of lower quality, Epitaxial LSMO films were deposited on various substrates, and the tensile or compressive strains and their influence on the film properties was obvous in thinner films on LaAlO 3 and SrTiO 3 substrates.

Bilayers composed from a YSZ or CeO 2 buffer layer and a YBCO film were in situ grown on monocrystalline sapphire, MgO. silicon, vicinally polished sapphire and MgO substrates by single source pulsed injection CVD. Zr. Ce. Y. Ba and Cu 2,2,6,6-tetramethyl-3,5-heptandionates dissolved in organic solvent were used for film deposition. CeO 2 /YBCO bilayers on sapphire were grown epitaxially and exhibited critical current densities up to 10 6 A/cm 2 at 77 K. YSZ and CeO 2 buffer layers on MgO substrates did not improved the properties of YBCO layers compared with YBCO films deposited directly on MgO surface; however, interesting microstructural properties of these heterostructures were found. Homogeneous YSZ films were also deposited on large Si substrates (3 inches in diameter).

Epitaxial YBa 2 Cu 3 O 7 layers with 45° in-plane orientation have been grown by Injection CVD on MgO substrates polished off-axis to within 1.4–1.9° of the [100] direction. This new single-source CVD process is based on computer-controlled injection of precise microdoses of a metal–organic precursor solution into a CVD reactor. A wide range of solution compositions was tested to investigate compositional effects on phase purity, surface morphology, texturing and superconducting properties of the prepared films. The highest quality films with pure 45° texture had a smooth surface, zero resistance T c ( R =0) of 88–89 K, and critical current density J c (77 K) above 10 6 A/cm 2 .