Electronic Structure of Twisted SrTiO₃ Moiré Bicrystals and Membranes

Twisted oxide Moiré bicrystals, created by stacking and twisting 3D materials at specific angles, present a novel platform for nanomaterial design, significantly altering their electronic, magnetic, and ferroic properties through the formation of Moiré patterns. In this study, we conducted proof-of-principle x-ray imaging and spectroscopic studies of ultrathin SrTiO₃ membranes and twisted Moiré bicrystals using standing-wave x-ray photoelectron spectroscopy (SW-XPS) and x-ray photoelectron emission microscopy (XPEEM). By establishing a standing-wave x-ray field within the sample, we achieved angstrom-level depth resolution and sub-50 nm lateral resolution. Our SW-XPS results confirm the high quality of the twisted SrTiO₃ membranes, with Ti 2p spectra verifying the Ti⁴⁺ valence state. Element-specific XPEEM imaging further revealed nanoscale features and defects. Polarization-dependent x-ray absorption spectroscopy (XAS) at the Ti L_2,3 and O K edges provided insights into orbital polarization and hybridization between Ti 3d and O 2p states. These findings demonstrate the feasibility of advanced, non-destructive synchrotron-based x-ray techniques for characterizing oxide membranes and Moiré bicrystals, offering depth-resolved insights into chemical and electronic states, as well as emergent phenomena at buried interfaces.