The growth and characterization of well aligned RuO2 nanorods on sapphire substrates

Self-assembled and well aligned RuO2 nanorods (NRs) have been grown on sapphire (SA) substrates via metal-organic chemical vapour deposition (MOCVD), using bis(ethylcyclopentadienyl)ruthenium as the source reagent. The surface morphology, structural, and spectroscopic properties of the as deposited NRs were characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected-area electron diffractometry (SAD), x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and micro-Raman spectroscopy. FESEM micrographs reveal that vertically aligned nanorods (NRs) were grown on SA(100), while the NRs on the SA(012) were grown with a tilt angle of similar to35degrees from the normal to the substrates. TEM and SAD measurements showed that the RuO2 NRs with square cross-section have the long axis directed along the [001] direction. The XRD results indicate that the RuO2 NRs are (002) oriented on SA(100) and (101) oriented on SA(012) substrates. A strong substrate effect on the alignment of the RuO2 NRs growth has been demonstrated and the probable mechanism for the formation of these NRs has been discussed. XP spectra show the coexistence of higher oxidation state of ruthenium in the as-grown RuO2 NRs. Micro-Raman spectra show the red shift and peak broadening of the RuO2 signatures with respect to that of the bulk counterpart which may be indicative of a phonon confinement effect for these NRs.