Exploring the Structural Transformation of Zirconia Films

Using a combination of experimental techniques, including Raman spectroscopy, Fourier Transform IR spectroscopy (FTIR), X-ray diffraction, atomic force microscopy (AFM) and ellipsometry, the structural transformation of a series of zirconia films were investigated. The zirconia nanoparticles (diameter of around ~4 nm) were first treated with ligands (either oleic acid or trioctylphosphine oxide), and then were spin-coated onto Si substrates. The as-grown samples were then exposed to an oxygen-plasma, and were subsequently calcined at various temperatures (300° C - 900° C). Raman, FTIR and X-ray diffraction show that the zirconia films transform from amorphous to tetragonal and monoclinic phases as a function of the calcined temperature. Using an effective medium approximation to model the ellipsometry spectra, the porosities of the zirconia films were recovered. While the porosity values decrease for both types of samples, the porosity seems to decrease faster for the samples that were capped with oleic acid. The RMS values determined from AFM measurements optimized the ellipsometry models, which included a surface-roughness layer to fit the experimental spectra.