Modification of the Chemisorption Properties of Epitaxial Delafossite CuFeO2 Thin Films by Substituting Fe for Ga in the Crystal Structure
Films of CuFeO2 and CuFe0.75Ga0.25O2 were grown over sapphire substrates in high vacuum using a pulsed laser deposition technique. The films grew with rhombohedral delafossite structure and highly epitaxial in the c-direction. Samples were characterized by X-ray diffraction, Raman spectroscopy and atomic force microscopy. Surface of the films were inspected with X-ray and UV photoelectron spectroscopy. Adsorption of CO2 and H2O was studied by a thermal program desorption technique. In both films Cu and Fe were exposed at the surface–gas interface. X-ray photoelectron data indicated that CO2 adsorbs preferentially at Cu sites forming a similar coordination to CuCO3. The energy for desorption of CO2 and H2O was estimated to be 30 kcal mol−1 (1.3 eV atom−1) for CuFeO2 and 36 kcal mol−1 (1.6 eV mol−1) for CuFe0.75Ga0.25O2. UV photoelectron spectroscopy showed that the valence band of the CuFeO2 delafossite oxides is modified with the substitution of Fe by Ga in the crystal lattice. The semiconductor band gap of CuFeO2 delafossite oxides also increased from 1.2 to 1.5 eV due to the substitution of Fe by Ga in the crystal lattice.
KeywordsThin films Copper delafossite oxides Thermal desorption Carbon dioxide Water Electron spectroscopy Pulsed laser deposition
Work at PUC was supported by FONDECyT 1130372 and Anillo ACT1409. Support from the American Chemical Society (PRF #56642-ND10) is also acknowledged. Thanks are due to WVU Shared Research Facilities. Thanks are due to M J Retamal for AFM images.