Heteroepitaxial growth of oxides via solution chemical techniques

An all-alkoxide solution chemistry utilizing methoxyethoxide-metal complexes in 2-methoxyethanol was developed to deposit epitaxial thin-films of metal oxides on single-crystal oxide and textured metal substrates. The speciation within these solutions was studied using Nuclear Magnetic Resonance (NMR) spectroscopy. Film precursor gels were studied using IR spectroscopy and thermal analysis. Approximate temperature ranges for film crystallization were determined from powders prepared from the film coating solutions. Film structure was determined using X-ray diffraction and film morphology was studied using scanning electron microscopy (SEM), and atomic force microscopy (AFM).

A number of technologically interesting systems were prepared using this general technique. Bismuth-containing ferroelectric materials of the general formula (Sr or Ba)Bi₂(Nb or Ta)₂O₉, were synthesized. Films were deposited on polycrystalline silver, (100) strontium titanate, and (100) lanthanum aluminate single-crystal oxide substrates by spin coating techniques. Excellent epitaxy was achieved on the oxide substrates.

Several systems which may be used for buffer layers for superconducting thin-films were synthesized. Rare earth gallates and rare-earth aluminates (where Ln = La, Pr, Nd, Gd, Y) were synthesized. The crystallization of powders under reducing and oxidizing conditions, deposition of polycrystalline films on silver substrates, deposition of epitaxial films on single crystal oxide substrates using solution deposition was studied. In addition, rare-earth aluminates were deposited on roll-textured nickel using spin-coating and dip-coating techniques. Tetragonal perovskites in the general form ABCO₄ (where A = Sr; B = La or Pr; C = Al or Ga) were prepared on single crystal oxide substrates. Chemical solution epitaxy was used to deposit films of rare-earth oxides (Ln = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) on roll-textured nickel.

Superconducting thin-films of yttrium barium copper oxide (YBCO) were grown on several solution-deposited buffer layers. The high critical currents and transition temperatures of the YBCO thin-films were measured and found satisfactory, thus demonstrating the viability of the technique.