Abstract
We review the results of the synthesis ofIrO2 nanocrystals (NCs) on different substrates via metal-organic chemical vapour deposition(MOCVD) using (MeCp)(COD)Ir as the source reagent. The surface morphology,structural and spectroscopic properties of the as-deposited NCs were characterizedusing field emission scanning electron microscopy (FESEM), transmission electronmicroscopy (TEM), selected-area electron diffractometry (SAD), x-ray diffractometry(XRD), x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The rolesof different substrates for the formation of various textures of nanocrystallineIrO2 are studied. Several one-dimensional (1D) nanostructures have evolved bydecreasing the degree of interface instability. The morphological evolution occursfrom triangular/wedged nanorods via incomplete/scrolled nanotubes to squarenanotubes and square nanorods (NRs), with increasing morphological stability.The results show that the three-dimensional (3D) grains composing traditionalfilm belong to the most stable form as compared to all the 1D NCs, and thesequential shape evolution has been found to be highly correlated to a morphologicalphase diagram based on the growth kinetics. In addition, area selective growth ofIrO2 NRs has been demonstrated on sapphire(012) and sapphire(100) substrates which consist of patternedSiO2 as the nongrowth surface. The initial growth ofIrO2 nuclei is studied. Selectivity, rod orientation, and other morphological features of thenanorod forest can find their origins in the nucleation behaviour during initial growth. XPSanalyses show the coexistence of higher oxidation states of iridium in the as-grownIrO2 NCs. The usefulness of the experimental Raman scattering together with the modified spatialcorrelation (MSC) model analysis as a residual stress and structural characterization technique for1D IrO2 NCs has been demonstrated. The field emission properties of the vertically alignedIrO2 NRs are studied and demonstrated as a high-performance and robust field emitter materialowing to its low work function, low resistivity and excellent stability against oxygen.
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