High-sensitivity of initial SrO growth on the residual resistivity in epitaxial thin films of SrRuO $$_3$$ 3 on SrTiO $$_3$$ 3 (001)

Abstract

Abstract The growth of SrRuO $$_3$$ 3 (SRO) thin film with high-crystallinity and low residual resistivity (RR) is essential to explore its intrinsic properties. Here, utilizing the adsorption-controlled growth technique, the growth condition of initial SrO layer on TiO $$_2$$ 2 -terminated SrTiO $$_3$$ 3 (STO) (001) substrate was found to be crucial for achieving a low RR in the resulting SRO film grown afterward. The optimized initial SrO layer shows a c(2 $$\times $$ × 2) superstructure that was characterized by electron diffraction, and a series of SRO films with different thicknesses (ts) were then grown. The resulting SRO films exhibit excellent crystallinity with orthorhombic-phase down to $$t \approx $$ t ≈ 4.3 nm, which was confirmed by high resolution X-ray measurements. From X-ray azimuthal scan across SRO orthorhombic (02 ± 1) reflections, we uncover four structural domains with a dominant domain of orthorhombic SRO [001] along cubic STO [010] direction. The dominant domain population depends on t, STO miscut angle ( $$\alpha $$ α ), and miscut direction ( $$\beta $$ β ), giving a volume fraction of about 92 $$\%$$ % for $$t \approx $$ t ≈ 26.6 nm and $$(\alpha , \beta ) \approx $$ ( α , β ) ≈ (0.14 $$^{\mathrm{o}}$$ o , 5 $$^{\mathrm{o}}$$ o ). On the other hand, metallic and ferromagnetic properties were well preserved down to t $$\approx $$ ≈ 1.2 nm. Residual resistivity ratio (RRR = $$\rho ({\mathrm{300 K}})$$ ρ ( 300 K ) / $$\rho ({\mathrm{5K}})$$ ρ ( 5 K ) ) reduces from 77.1 for t $$\approx $$ ≈ 28.5 nm to 2.5 for t $$\approx $$ ≈ 1.2 nm, while $$\rho ({\mathrm{5K}})$$ ρ ( 5 K ) increases from 2.5 $$\upmu \Omega $$ μ Ω cm for t $$\approx $$ ≈ 28.5 nm to 131.0 $$\upmu \Omega $$ μ Ω cm for t $$\approx $$ ≈ 1.2 nm. The ferromagnetic onset temperature ( $$T'_{\mathrm{c}}$$ T c ′ ) of around 151 K remains nearly unchanged down to t $$\approx $$ ≈ 9.0 nm and decreases to 90 K for t $$\approx $$ ≈ 1.2 nm. Our finding thus provides a practical guideline to achieve high crystallinity and low RR in ultra-thin SRO films by simply adjusting the growth of initial SrO layer.