Alexandre Gloter

We investigate nanoscale domain engineering via epitaxial coupling in a set of SrRuO3/PbTiO3/SrRuO3 heterostructures epitaxially grown on (110)o-oriented DyScO3 substrates. The SrRuO3 layer thickness is kept at 55 unit cells, whereas the PbTiO3 layer is grown to thicknesses of 23, 45, and 90 unit cells. Through a combination of atomic force microscopy, x-ray diffraction, and high resolution scanning transmission electron microscopy studies, we find that above a certain critical thickness of the ferroelectric layer, the large structural distortions associated with the ferroelastic domains propagate through the top SrRuO3 layer, locally modifying the orientation of the orthorhombic SrRuO3 and creating a modulated structure that extends beyond the ferroelectric layer boundaries.

Charge ordering (CO) phenomena have been widely debated in strongly‐correlated electron systems mainly regarding their role in high‐temperature superconductivity. Here, the structural and charge distribution in NdNiO 2 thin films prepared with and without capping layers, and characterized by the absence and presence of CO are elucidated. The microstructural and spectroscopic analysis is done by scanning transmission electron microscopy‐electron energy loss spectroscopy (STEM‐EELS) and hard X‐ray photoemission spectroscopy (HAXPES). Capped samples show Ni 1+ , with an out‐of‐plane (o‐o‐p) lattice parameter of around 3.30 Å indicating good stabilization of the infinite‐layer structure. Bulk‐sensitive HAXPES on Ni‐2p shows weak satellite features indicating large charge‐transfer energy. The uncapped samples evidence an increase of the o‐o‐p parameter up to 3.65 Å on the thin film top with a valence toward Ni 2+ in this region. Here, 4D‐STEM demonstrates (303)‐oriented stripes which emerge from partially occupied apical oxygen. Those stripes form quasi‐2D coherent domains viewed as rods in the reciprocal space with Δq z ≈ 0.24 reciprocal lattice units (r.l.u.) extension located at Q = () and () r.l.u. The stripes associated with oxygen re‐intercalation concomitant with hole doping suggest a possible link to the previously reported CO in infinite‐layer nickelate thin films.