Novel MBE Approach for Highly Conducting Epitaxial RuO₂ Films

A fascinating consequence of electron correlation is the emergence of a wide range of quantum phases including superconductivity in perovskite oxides such as cuprates and ruthenates. In particular, ruthenates are difficult to grow in molecular beam epitaxy (MBE) due to the ultra-low vapor pressures of Ru. Additionally, Ru has high electronegativity which further makes it difficult for achieving complete oxidation, Ru to Ru⁴⁺ states under standard MBE conditions. The former issue has been dealt by supplying Ru using an e-beam source whereas the latter oxidation issue is addressed by using highly reactive ozone. However, the use of e-beam and ozone has adverse consequences on the stability of Ru beam-flux, which is critical for obtaining electronic-grade materials. Here we show a new hybrid MBE approach that circumvents these issues by supplying a metal-organic compound containing Ru for the growth of RuO₂. Highly perfect RuO₂ films as evident from rocking curve and electrical measurements were obtained down to a substrate temperature of 300°C. Bulk-like room temperature resistivity of 35 μΩcm was achieved for films of only 10 nm. The effect on the electrical properties of film thickness, orientation, strain, and defects such as oxygen vacancies will be discussed.