Microstructural analysis of doped-strontium cerate thin film membranes fabricated via polymer precursor technique

Abstract

Nanocrystalline thin film membranes of terbium (Tb)-doped strontium cerate (SrCeO 3), which is of interest in the hydrogen (H 2) separation and solid oxide fuel cells (SOFCs), was synthesized via polymer precursor technique. Continuous and dense thin film membranes of composition SrCe 0.95Tb 0.05O 3 − δ were prepared using spin-coating technique by utilizing ethylene glycol (EG)-based polymeric precursor. The polymeric precursor was deposited on silicon-based substrates, and converted to dense polycrystalline thin film ceramic membranes by sintering at relatively low temperatures. The number of spin-coating cycles and sintering temperatures were systematically varied to study their effect on the film morphology, thickness, and crystallite size within the membranes. Fourier transform infrared (FTIR) spectroscopy was utilized to study the changes in the polymer chemistry during the membrane processing. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were used to examine thermal decomposition and thermodynamics of the synthesized precursor, respectively. The scanning electron microscopy (SEM) analysis was used to study the surface morphology and estimate average particle size as a function of number of spin-coating cycles and sintering temperatures. Atomic force microscope (AFM) was utilized to determine the roughness and quality of the spin-coated films. The membrane thickness, crystal structure, and nanocrystallite size were determined using focused ion-beam (FIB) milling and X-ray diffraction (XRD) techniques. Furthermore, the surface chemistry of the thin film membranes was studied by means of X-ray photoelectron spectroscopy (XPS). This study demonstrated that by using the EG-based polymeric precursor, dense and continuous Tb-doped SrCeO 3 thin film membranes, having thicknesses in the range of 0.2–2 μm and average nanocrystallite size of 8–70 nm, can be effectively synthesized by controlling the number of spin-coating cycles and sintering temperature.