Octahedra in Thin Films with Epitaxial Strain using ABF-STEM*

Recent studies on thin film Ca₂RuO₄ grown on LaAlO₃, NdAlO₃, and NdGaO₃ substrates show that tuning epitaxial strain can control the tilt and rotation of the RuO₆ octahedra. This leads to change in electronic properties such as the d-band bandwidth, electrical resistivity, and the metal-to-insulator transition temperature. Quantifying the exact structural distortions of RuO₆ is therefore crucial in understanding the correlation between structure modification and electronic properties. In this work we use Annular Bright Field imaging (ABF) in Scanning Transmission Electron Microscopy (STEM) to directly locate the atom positions with picometer precision. Average Ru-O-Ru bond angles are mapped layer by layer to characterize the degree of tilt relaxation and decay lengths as we move away from the strained interface. We also compare distortions of the octahedra for different epitaxially strained states.