Epitaxial RuO₂ and IrO₂ films by pulsed laser deposition on TiO₂(110)

We present a systematic growth study of epitaxial RuO₂(110) and IrO₂(110) on TiO₂(110) substrates by pulsed laser deposition. We describe the main challenges encountered in the growth process, such as a deteriorating material flux due to laser induced target metallization or the delicate balance of under- vs over-oxidation of the 'stubborn' Ru and Ir metals. We identify growth temperatures and oxygen partial pressures of 700 K, 1× 10⁻³ mbar for RuO₂ and 770 K, 5× 10⁻⁴ mbar for IrO₂ to optimally balance between metal oxidation and particle mobility during nucleation. In contrast to IrO₂, RuO₂ exhibits layer-by-layer growth up to 5 unit cells if grown at high deposition rates. At low deposition rates, the large lattice mismatch between film and substrate fosters initial 3D island growth and cluster formation. In analogy to reports for RuO₂ based on physical vapor deposition, we find these islands to eventually merge and growth to continue in a step flow mode, resulting in highly crystalline, flat, stoichiometric films of RuO₂(110) (up to 30 nm thickness) and IrO₂(110) (up to 13 nm thickness) with well defined line defects.