Synthesis science of SrRuO3 and CaRuO3 epitaxial films with high residual resistivity ratios

Abstract

Epitaxial SrRuO3 and CaRuO3 films were grown under an excess flux of elemental ruthenium in an adsorption-controlled regime by molecular-beam epitaxy (MBE), where the excess volatile RuOx (x = 2 or 3) desorbs from the growth front leaving behind a single-phase film. By growing in this regime, we were able to achieve SrRuO3 and CaRuO3 films with residual resistivity ratios (ρ300 K/ρ4 K) of 76 and 75, respectively. A combined phase stability diagram based on the thermodynamics of MBE (TOMBE) growth, termed a TOMBE diagram, is employed to provide improved guidance for the growth of complex materials by MBE.

Epitaxial Oxides on Semiconductors: From Fundamentals to New Devices

“…In a recent work, high‐quality SRO films were demonstrated on STO‐templated Si . Wang et al optimized the SRO crystalline quality by implementing a self‐limiting growth window . The growth conditions required for obtaining high quality SRO include high temperatures and high oxygen reactivity, which result in a thin amorphous SiO x layer at the STO/Si interface (Figure a).…”

“…SRO/STO/Si structures showing a) close‐ups on the STO/Si (left) and SRO/STO (right) interfaces, b) resistivity–temperature curve showing a high residual resistivity ratio indicative of high quality SRO films. Reproduced under the terms and conditions of the Creative Commons Attribution license . Copyright 2018, The Authors, published by AIP Publishing LLC YBCO/STO/Si structure showing c) the entire stack (inset shows a close‐up of the YBCO/STO interface) and d) resistivity–temperature curves showing the critical superconducting temperature in comparison to YBCO grown on STO substrates (insets shows a close‐up of the transition region).…”

“…In a recent work, high‐quality SRO films were demonstrated on STO‐templated Si . Wang et al optimized the SRO crystalline quality by implementing a self‐limiting growth window .…”

Electronic and vibrational signatures of ruthenium vacancies in Sr2RuO4 thin films

“…Despite the fundamental interest and potential applications, the growth of high quality ruthenate thin films has proven to be very challenging due to the nature of ruthenium and its oxides 10,[14][15][16][17][18][19] . In fact, the high volatility of ruthenium oxides (RuO x=2,3,4 ) leads to ruthenium deficiency, as shown in numerous reports 14,15,[20][21][22][23] . The ruthenium deficiency increases the resistivity and reduces the Curie temperature of SrRuO 3 and is detrimental to superconductivity in Sr 2 RuO 4 .…”

“…Superconductivity in Sr 2 RuO 4 is extremely sensitive to defects, such as nonmagnetic impurities and lattice imperfections and thus it requires high quality samples 24,25 . In order to overcome the volatility of ruthenium oxides, some of us have recently used an adsorption-controlled growth technique to synthesize ruthenate thin films showing superconductivity and unprecedentedly high residual resistivity ratios, defined as the ratio of the resistivities at 300 and 4K 14,15 . Related results have also been reported by other groups where the growth of Sr 2 RuO 4 films was carried out by means of molecular beam epitaxy 16,18 .…”