Quantifying the orientation dependence of diffraction contrast on magnetic STEM-DPC imaging of freestanding oxide thin-film

Abstract

Scanning Transmission Electron Microscopy–Differential Phase Contrast (STEM-DPC) is a well-established nanoscale resolution technique for imaging internal magnetic and electric fields in materials. However, imaging crystalline materials is made difficult due to diffraction effects, which distort the bright-field disk and can obscure the medium-range magnetic and electric field contrasts. In this study, we employ monocrystalline regions of freestanding La0.67⁢Sr0.33⁢MnO3 (LSMO) thin films to systematically investigate the influence of diffraction contrast on magnetic imaging using four-dimensional STEM-DPC. This was done by tilting the sample across orientations with different amounts of diffractive scattering and processing the data using two data processing algorithms: center of-mass and phase correlation. The proximity of the orientation to a systematic row is the most important cause of diffraction contrast whereas proximity to a zone axis had a low effect. Our experiments demonstrate only small tilt adjustments are necessary to mitigate the diffraction contrast, with 𝑥 and 𝑦 tilts of about 0.5° sufficient to reduce calculated noise in the STEM-DPC image up to 95%. Phase correlation often gives lower noise but is less robust at higher diffractive scattering compared to center of mass. To avoid the obstructive effects of diffraction contrast, systematic rows must be avoided and processing algorithms must be carefully chosen.