In-situ transmission electron microscopy crystallization studies of sol-gel-derived barium titanate thin films

Barium titanate (BaTiO3) thin films that were derived from methoxypropoxide precursors were deposited onto (100) Si, Pt/Ti/SiO2/(100) Si, and molecular-beam-epitaxy-grown (MBE-grown) (100) BaTiO3 on (100) Si substrates by spin coating. The crystallization behavior of the amorphous-gel films was characterized using in-situ transmission electron microscopy heating experiments, glancing-angle X-ray diffraction, and differential thermal analysis/thermogravimetric analysis. Amorphous-gel films crystallized at a temperature of similar to 600 degrees C to an intermediate nanoscale (5-10 nm) barium titanium carbonate phase, presumably BaTiO2CO3, that subsequently transformed to nanocrystalline (20-60 nn) BaTiO3. Random nucleation in the bulk of the gel film was observed on all substrates, In addition, oriented growth of BaTiO3 was concurrently observed on MBE-grown BaTiO3 on (100) Si. High-temperature decomposition of the intermediate carbonate phase contributed to nanometer-scale residual porosity in the films. High concentrations of water of hydrolysis inhibited the formation of the intermediate carbonate phase; however, these sols precipitated and were not suitable for spin coating.