Solid Source Metal-Organic MBE of Atomically Smooth IrO₂ Films

Experimental realization of novel quantum phenomena in Iridium-based complex oxides has been challenging due to the difficulty in synthesizing atomically precise films owing to low vapor pressure, and difficulty in oxidation of Ir. Using a novel solid-source metal-organic MBE approach employing Ir(acac)₃, a solid metal-organic precursor for Ir and a rf-plasma source for oxygen, we demonstrate atomically controlled growth of single crystalline, phase-pure, epitaxial IrO₂ films on TiO₂ and r-Al₂O₃ substrates. Atomically smooth films with root mean square (rms) roughness of ~ 3-4 Å in Atomic Force Microscopy were obtained regardless of substrate’s orientation. All films exhibit streaky Reflection High-Energy Electron Diffraction (RHEED) patterns consistent with smooth film morphology. Thickness dependent strain relaxation accompanied by a broadening of the X-Ray Diffraction film rocking curve was observed in the films. Temperature-dependent electrical transport measurements revealed metallic behaviour down to 1.8 K with room temperature resistivity of ~ 70 μΩ-cm in 12 nm IrO₂ film/TiO₂ (110) comparable to bulk single crystals. Further, we also discuss correlation between growth conditions, strain relaxation, dimensionality and magneto-transport properties in IrO₂ films.