High-sensitivity of initial SrO growth on the residual resistivity in epitaxial thin films of SrRuO3 on SrTiO3 (001)

The growth of SrRuO3 (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 TiO2-terminated SrTiO3 (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 x 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 approximate to 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), and miscut direction (beta), giving a volume fraction of about 92 %for t approximate to 26.6 nm and (alpha, beta) approximate to (0.14 degrees, 5 degrees). On the other hand, metallic and ferromagnetic properties were well preserved down to t approximate to 1.2 nm. Residual resistivity ratio (RRR = rho(300K)/rho(5K)) reduces from 77.1 for t approximate to 28.5 nm to 2.5 for t approximate to 1.2 nm, while rho (5K) increases from 2.5 mu Omega cm for t approximate to 28.5 nm to 131.0 mu Omega cm for t approximate to 1.2 nm. The ferromagnetic onset temperature (T-c ') of around 151 K remains nearly unchanged down to t approximate to 9.0 nm and decreases to 90 K for t approximate to 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.

Automated summary

The growth condition of initial SrO layer on TiO2-terminated SrTiO3 (STO) substrate is crucial for achieving high crystallinity and low residual resistivity in SrRuO3 (SRO) thin films. Different thicknesses of SRO films exhibit excellent crystallinity with metallic and ferromagnetic properties well preserved, while the residual resistivity ratio decreases with decreasing film thickness.