Raman scattering characterization of well-aligned RuO₂ and IrO₂ nanocrystals

Raman spectroscopy (RS) has been used as a technique for the characterization of well-aligned IrO₂ and RuO₂ nanocrystals (NCs) grown on a number of different oriented substrates under various conditions. The IrO₂ and RuO₂ NCs were grown via metalorganic chemical vapor deposition and reactive magnetron sputtering. The relative intensity of the three strongest Raman-active modes, namely, the A _1g, B_2g and E_g modes, depends on the orientation of NCs and has been used to determine the preferred growth direction of the NCs. The redshifts and asymmetric linewidth broadening of the Raman features of IrO₂ and RuO₂ NCs with respect to that of their bulk counterparts were analyzed by a modified spatial correlation (MSC) model, which includes a factor of stress-induced shift. The MSC model showed that the effects of stress and nanometric size could be separated in analyzing the observed Raman features. The usefulness of experimental RS together with the MSC model analysis as a structural and residual stress characterization technique for NCs has been demonstrated.