In Situ Real-Time Investigation of Nucleation Kinetics in Sol-Gel-Derived Functional Oxide Thin Films

Sol-gel processing is one of the most effective methods to fabricate thin films of BiFeO₃, an interesting oxide with both ferroelectric and antiferromagnetic orders at room temperature. The key to controlling the microstructure of sol-gel-derived thin films and achieving preferred functionality is to understand the nucleation and growth behavior during high temperature annealing. Researchers at the Northwestern University MRSEC have developed a versatile technique to investigate this behavior using x-ray technique combined with transmission electron microscopy. Information on the average nuclei size, distance, and spatial distribution in the BiFeO₃ film can be quantitatively determined. Intermediate phase during sintering of BiFeO₃ thin film has been successfully confirmed.

(a, b) Grazing incidence small angle x-ray scattering (GISAXS) patterns obtained from BiFeO₃ thin films deposited on SiOx/Si substrate at 250 Celsius and 350 Celsius, respectively. Nuclei size and distribution can be quantitatively obtained through fitting of the GISAXS data.
(c, d) Corresponding TEM cross-sectional images of the thin films confirming 2-dimensional nucleation and 3-dimensional nucleation mechanisms, respectively.