Using “dirty” precursors to develop ultra-clean crystals

Five thousand years after the first known use of inorganic thin films as gold coatings on religious objects in ancient Greece, vacuum film deposition techniques have become a foundation for the modern semiconductor industry. Among them, molecular beam epitaxy (MBE) is especially relevant to emerging microelectronic applications, such as quantum computing, because it can produce high-quality films with low defect densities.

But conventional MBE methods, which involve evaporating pure elemental sources within an ultra-high vacuum chamber and depositing them onto a substrate, pose formidable challenges: elemental sources are difficult to extract and expensive to purify, and many have high melting points that complicate their evaporation.

Choudhary et al. proposed an alternative approach by replacing the pure elemental sources with so-called “dirty” organometallic precursors, which have lower melting points and are more cost-effective.

“By utilizing these innovative precursors, we could successfully grow highly pure strontium ruthenate films demonstrating superconductivity,” said author Rashmi Choudhary. “The use of organometallic precursors that are labeled as ‘dirty’ because they contain elements that can act as impurities, in fact, offers a variety of advantages that conventional MBE method simply do not.”

The key advantage was that the organometallic precursors enabled the researchers to replace the source of oxygen from ozone to oxygen plasma, which makes their technique safer and simpler than conventional methodology.

“Our work now firmly establishes that the textbooks describing MBE largely as a research tool need to be rewritten,” said author Bharat Jalan. “The recent technical and scientific advancements have made the MBE a highly modular, reproducible, and commercially viable approach.”

Source: “Growing clean crystals from dirty precursors: Solid-source metal-organic molecular beam epitaxy growth of superconducting Sr₂RuO₄ films,” by Rashmi Choudhary, Zhaoyu Liu, Jiaqi Cai, Xiaodong Xu, Jiun-Haw Chu, and Bharat Jalan, APL Materials (2023). The article can be accessed at http://doi.org./10.1063/5.0150893 .