Growth of well aligned IrO₂ nanotubes on LiTaO₃(012) substrate

Self-assembled and well-aligned IrO₂ nanotubes have been grown on LiTaO₃ (LTO) (012) substrates via metal-organic chemical vapor deposition (MOCVD), using (methylcyclopentadienyl)(1,5-cyclooctadiene)iridium(I) as the source reagent. The surface morphology, structural, and spectroscopic properties of the as-deposited nanotubes were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and micro-Raman spectroscopy. FESEM and TEM micrographs revealed that the single-crystalline nanotubes were grown with a tilt angle of ∼35° from the normal to the substrate. The IrO ₂ nanotubes showed square cross-sections and open-end morphology with the long axis toward the [001] direction. The analysis of selected area diffraction (SAD) and XRD patterns indicated the epitaxial growth of IrO ₂ nanotubes on LTO (012) with the orientation relationship given by IrO₂(101)//LTO(012) and IrO₂[010]//LTO[100]. The probable mechanism for the formation of nanotubes has been discussed. Micro-Raman spectrum shows the red-shift and peak broadening of the IrO₂ signatures with respect to that of the bulk counterpart which may be indicative of a phonon confinement effect for these nanotubes.