Growth and characterization of well aligned densely packedIrO2 nanocrystals on sapphire via reactive sputtering

Abstract

Well aligned densely packed IrO2 nanocrystals (NCs) have been grown on sapphire (SA) substrates with differentorientations by reactive magnetron sputtering using an Ir metal target. The surfacemorphology, structural and spectroscopic properties of the as-deposited NCs werecharacterized using field-emission scanning electron microscopy (FESEM), x-ray diffraction(XRD), x-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. FESEMmicrographs reveal that NCs with parallel in-plane alignment were gown on SA(001),vertically aligned NCs were grown on SA(100), while the NCs on SA(012) and SA(110)contained, respectively, single- and double-aligned directions with a tilt angle of∼35° from the normal to the substrates. The XRD results indicate that the NCs are(100), (001), and (101) oriented on SA(001), SA(001), and SA(012)/SA(110)substrates, respectively. A strong substrate effect on the alignment of theIrO2 NCs growth has been demonstrated and the probable mechanism forthe formation of these NCs has been discussed. XPS analyses showthe coexistence of higher oxidation states of iridium in the as-grownIrO2 NCs.The Raman spectra show the red-shift and asymmetric peak broadening with a low frequency tail ofthe IrO2 signatures with respect to that of the bulk counterpart, which are attributed to both thesize and residual stress effects.