7/7/2023 0 Comments Epitaxial planarPLD found widespread use after it demonstrated successful growth of high-temperature superconductors, 4–6 whereas MBE owes its widespread popularity to its ability to grow “designer materials” by supplying “one atom at a time,” resulting in extremely high-quality films with the lowest defect density. 3 Nearly a century later, two disruptive vacuum deposition techniques called pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) emerged. 2 This was soon followed by thermal evaporation when Michael Faraday deposited various metals on glass to study their optical properties. The earliest vacuum deposition technique was sputtering, which was pioneered by William Robert Grove, who deposited iron oxide on a silver substrate. Vacuum deposition techniques gained popularity due to their precise control over film thickness, excellent uniformity, improved adhesion to the substrate through in situ cleaning, and lower levels of extrinsic impurities. 1 Despite this early usage, it took humanity almost five millennia to invent the first vacuum system, enabling the development of vacuum deposition techniques, which are now the basis of the semiconductor industry. Inorganic thin films have a long and fascinating history, with their first documented use occurring around 5000 years ago in ancient Greece, where they were used as gold coatings on religious artifacts. Combining these results with the recent developments in hybrid MBE, we argue that leveraging the precursor chemistry will be necessary to realize next-generation breakthroughs in the synthesis of atomically precise quantum materials. In contrast to the conventional MBE, which employs the ultra-pure Ru metal evaporated at ∼2000 ☌ as a Ru source, along with reactive ozone to obtain Ru → Ru 4+ oxidation, the use of the Ru(acac) 3 precursor significantly simplifies the MBE process by lowering the temperature for Ru sublimation (less than 200 ☌) and by eliminating the need for ozone. A superconducting transition was observed at ∼0.9 K, suggesting a low defect density and a high degree of crystallinity in these films. However, we demonstrate that a “dirty” solid precursor, ruthenium(III) acetylacetonate, can yield single-phase, epitaxial, and superconducting Sr 2RuO 4 films with the same ease and control as III–V MBE. Ultra-high purity elemental sources have long been considered a prerequisite for obtaining low impurity concentrations in compound semiconductors in the world of molecular beam epitaxy (MBE) since its inception in 1968.
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