Structural characterization of TiO2-Cr2O3 nanolaminates grown by atomic layer deposition

TiO2-Cr2O3 nanolaminates were atomic layer deposited on (012)-oriented sapphire and (100)-oriented silicon. The thickness of the alternating layers in the eight-layer laminates grown was close to 10 nm. The laminates were characterised by cross-sectional high-resolution TEM, high-resolution SEM, AFM, reflection high-energy electron diffraction, and micro-Raman spectroscopy. Highly oriented growth of the laminate on sapphire and its growth with very little preferred orientation on silicon were revealed. The laminate grown on sapphire had, along with better crystallinity, more exactly defined and more planar interphase boundaries. The diffuseness of the boundaries increased with the layer distance from the substrate. The crystalline phase of titania was rutile in the laminate grown on sapphire and anatase in the laminate grown on silicon, while the crystalline phase of chromia had an eskolaite structure. In the laminate grown on sapphire, titania contained numerous twins, and the compressively strained chromia had in this case a more perfect structure.