Fig. 3: Competitive and cooperative configurations explored by XPS and DFT.
From: In-situ monitoring of interface proximity effects in ultrathin ferroelectrics
a Pb/Ti atomic ratio at XPS emission angles (20–80)∘, higher angles displaying a higher sensitivity to the sample surface lower angles. Red and blue symbols correspond to the samples with suppressed and enhanced polarization, respectively. The error bar is based on the estimated experimental accuracy (see “Methods”). b, c Density-functional calculations of dipole moments (p) perpendicular to the bottom interface in PTO heterostructures with a Pb adatom on the surface. The polarization direction is imposed at the bottom interface to match with our experiments by fixing the dipole moment of the first u. c. in the calculation (marked as “fixed”). The atomic positions in heterostructures with (b) PbO and (c) TiO2 top-interface termination and their ionic positions are depicted on the right-hand side of the graph. d, e Sketch of the competitive and cooperative interfaces for the transient (left) “single-interface” and the persistent (right) “combined-interface” regime. The favored polarization direction at each interface is indicated with arrows and the resulting bound charges are represented with “+” and “–” signs. The additional positive charges at the top interface introduced to emulate the non-stoichiometry are shown as “⨁”.
