Novel synthesis approach for “stubborn” metals and metal oxides

Abstract

Advances in physical vapor deposition techniques have led to a myriad of quantum materials and technological breakthroughs, affecting all areas of nanoscience and nanotechnology which rely on the innovation in synthesis. Despite this, one area that remains challenging is the synthesis of atomically precise complex metal oxide thin films and heterostructures containing “stubborn” elements that are not only nontrivial to evaporate/sublimate but also hard to oxidize. Here, we report a simple yet atomically controlled synthesis approach that bridges this gap. Using platinum and ruthenium as examples, we show that both the low vapor pressure and the difficulty in oxidizing a “stubborn” element can be addressed by using a solid metal-organic compound with significantly higher vapor pressure and with the added benefits of being in a preoxidized state along with excellent thermal and air stability. We demonstrate the synthesis of high-quality single crystalline, epitaxial Pt, and RuO2 films, resulting in a record high residual resistivity ratio (=27) in Pt films and low residual resistivity, ∼6 μΩ·cm, in RuO2 films. We further demonstrate, using SrRuO3 as an example, the viability of this approach for more complex materials with the same ease and control that has been largely responsible for the success of the molecular beam epitaxy of III-V semiconductors. Our approach is a major step forward in the synthesis science of “stubborn” materials, which have been of significant interest to the materials science and the condensed matter physics community.

Adsorption-Controlled Growth and Magnetism in Epitaxial SrRuO3 Films

“…The SrRuO 3 thin films were grown on SrTiO 3 (001) substrates (Shinkosha Co., Japan, and Crystec GmbH, Germany) in an EVO 50 MBE system (Scienta Omicron, Germany) using solid source metal–organic molecular beam epitaxy described elsewhere . The substrates were heated to temperatures ( T sub ) of ∼700–800 °C and cleaned for 20 min before the start of film growth with an inductively coupled radio-frequency oxygen plasma (Mantis, UK) operated at 300 W and at an oxygen pressure of ∼8 × 10 –6 Torr.…”

“…In this article, we demonstrate the adsorption-controlled growth of SrRuO 3 films using the sublimation of a solid metal–organic precursor, Ru­(acac) 3 , in a technique called solid source metal–organic molecular beam epitaxy (SSMOMBE) described elsewhere. , The metal–organic precursor contains pre-oxidized Ru and can be sublimed at T < 200 °C in an effusion cell as opposed to ∼2000 °C required to evaporate the elemental Ru source in electron-beam assisted MBE. By harnessing the property of adsorption-controlled growth and carefully controlling the growth parameters in SSMOMBE, we interpret the origins of the changes in the anomalous Hall resistance as a function of cation stoichiometry and film thickness.…”

Solid-source metal–organic molecular beam epitaxy of epitaxial RuO2

“…RuO2 films were grown using the solid source MOMBE approach which has been described in more detail elsewhere. 25 Here, an effusion cell source temperature of 100°C was used for Ru(acac)3 and oxygen was supplied with a radio-frequency inductively coupled plasma source. An oxygen background pressure of ~ 10 -6 -10 -5 Torr was used.…”

“…In this paper, we demonstrate a novel solid source metal-organic molecular beam epitaxy (MOMBE) approach using a detailed RuO2 growth study that addresses these synthesis issues by using a solid metal-organic precursor as the metal Ru source. 25 This allows for supplying a "preoxidized" metal with orders of magnitude higher vapor pressure than the elemental metal at a particular temperature.…”

Correlated Quantum Phenomena of Spin–Orbit Coupled Perovskite Oxide Heterostructures: Cases of SrRuO3 and SrIrO3 Based Artificial Superlattices

“…More recently, solid source metal‐organic molecular beam epitaxy has been suggested to obtain low vapor pressures and low source temperatures, which is more stable and cheaper compared with other oxide molecular beam epitaxies. [ 57 ] Finally, atomic layer deposition has also proven to be useful in depositing oxide thin films, although the realization of perovskite oxide superlattices has yet to be demonstrated.…”