Growing clean crystals from “dirty” precursors in MBE

Growth of high-purity compound semiconductors via molecular beam epitaxy (MBE) has traditionally relied on ultra-high-purity elemental sources. The fear of impurities from source getting incorporated into the film has, in part, led to this practice. However, our work challenges this age-old wisdom by demonstrating successful growth of superconducting Sr₂RuO₄ films using a “dirty” organometallic precursor for Ru. We grew 100 nm thick (001) Sr₂RuO₄ films on (001) LSAT substrates, which are phase-pure, single-crystalline, fully coherent, and superconducting at 0.85 K. Unlike conventional MBE, which requires high-temperature evaporation (>2000˚C) of ultra-pure Ru metal and ozone for oxidizing Ru, our ruthenium acetylacetonate precursor allowed lower-temperature Ru sublimation (<200˚C) and oxidized without ozone. This marks the first successful realization of superconducting Sr₂RuO₄ films via ozone-free MBE. Combining our results with recent advances in hybrid-MBE, we emphasize the importance of precursor chemistry for advancing synthesis of atomically precise quantum materials.