Amorphous to Tetragonal Zirconia Nanostructures and Evolution of Valence and Core Regions

In this report, we study the evolution of valence band (VB) structure during a controlled amorphous to tetragonal transformation of ZrO2 core-shell nanostructures fabricated from electrospun nanofiber template (at 130, 200, and 250 °C). Shell-ZrO2 was formed with atomic layer deposition. X-ray diffraction and transmission electron microscopy are employed to unveil the transformation of amorphous to crystalline structure of ZrO2. O 1s core-level spectra indicated chemisorbed oxygen (OCh) of almost invariant fraction for the three samples. Zr 3s level suggested that the sample deposited at 130 °C has depicted a peak at relatively higher binding energy. Analyses on Zr 3d spectra indicated the presence of metallic-Zr (Zr+ζ, 0 ≤ |ζ| < 4), the fraction of which decreases with increasing template temperature. VB region is analyzed until ∼64 eV below the Fermi level (EF). The region close to EF depicted features that are dissimilar to the literature. This discrepancy is explained on the basis of the analyses from O 1s, Zr 3d, and Zr 4p levels including hybridization of orbitals from chemisorbed species. These levels were analyzed in terms of peak characteristics such as spectral position, area under the peak, etc. The results of this study would enhance the understanding of the evolution of various bands in the presence of OCh and changes to the crystallinity enabling the functionalities that are not available in the single-phase ZrO2. © 2015 American Chemical Society