Metal-insulator transition in epitaxial thin films of BaRuO3

Abstract

Highly conductive BaRuO3 thin films have been grown heteroepitaxially on (100) LaAlO3 substrate using pulsed laser deposition technique over temperature range varying from 600°C to 775°C. Atomic force microscopy, scanning tunneling microscopy and x-ray diffraction (XRD) reveal that the films are well textured and are c-axis oriented with an in-plane epitaxial relationship of ⟨010⟩⟨100⟩BaRuO3//⟨110⟩LaAlO3. The resistivity of the films has been found to be a strong function of substrate temperature during film deposition. Both metallic and semiconducting behaviour has been observed in films deposited at 700°C or above. However, films deposited at lower temperature show only metallic behaviour as seen in bulk BaRuO3. XRD studies showed that the films deposited at lower temperature (600°C), exhibit poor crystallinity, while films deposited at 700–775°C are much better crystallized, and have enlarged unit cells but have a conductivity that decreases with increasing temperature (at least a low temperatures). We believe that the substitution of the small Ru cations by larger Ba cations and grain boundary scattering could be the main possible causes of these interesting conductive properties. This unique phenomenon, which is not observed in bulk, may provide new features useful in the fabrication of novel electronic devices.