Giant Ferroelectric Polarization in Ultrathin Ferroelectrics via Boundary‐Condition Engineering

Abstract

Tailoring and enhancing the functional properties of materials at reduced dimension is critical for continuous advancement of modern electronic devices. Here, the discovery of local surface induced giant spontaneous polarization in ultrathin BiFeO ferroelectric films is reported. Using aberration-corrected scanning transmission electron microscopy, it is found that the spontaneous polarization in a 2 nm-thick ultrathin BiFeO film is abnormally increased up to ≈90-100 µC cm in the out-of-plane direction and a peculiar rumpled nanodomain structure with very large variation in c/a ratios, which is analogous to morphotropic phase boundaries (MPBs), is formed. By a combination of density functional theory and phase-field calculations, it is shown that it is the unique single atomic Bi O layer at the surface that leads to the enhanced polarization and appearance of the MPB-like nanodomain structure. This finding clearly demonstrates a novel route to the enhanced functional properties in the material system with reduced dimension via engineering the surface boundary conditions.

Superior polarization retention through engineered domain wall pinning

“…1c, the high-angle XRD θ−2θ scan exhibits only (00 l) peaks yielding an out-of-plane (OOP) lattice parameter c = 4.67 Å. The broad peak at 30.4°has been suggested to be a tetragonal β-Bi 2 O 3 phase, which can impose a net compressive strain on BFO and thus stabilize the T' phase (without forming relaxed R' phase striations) at thicknesses well over 60 nm 45,49 . High-angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) was used to study the defect structure in these samples at the atomic scale ( Fig.…”

Structural, magnetic, and ferroelectric properties of T-like cobalt-doped BiFeO3 thin films

“…This effect is ascribed to the presence of a strain-stabilizing Bi 2 O 3 phase. 35,40 More specifically, it has recently been found that fine tuning of growth conditions can favour the formation of "stacking fault" like nanoregions in our T films: these regions appear to help maintain the strain required for T BFO up to larger thicknesses. To determine the structural symmetry, XRD RSMs around the (103) and (113) reflections [Figs.…”

Defect-Induced Hedgehog Polarization States in Multiferroics

“…On the other hand, recent observation of a strong interaction between ferroelectric polarization and built-in fields induced by charged impurity defects embedded in the ferroelectric matrix suggests that these defects may be used as nano-building-blocks that can provide a strong electrostatic driven force for stabilization of complex domain structures 13,14 . For example, it has been shown that nanoscale planar charged defects in BiFeO 3 thin films can induce novel head-tohead mixed-phase polarization structures 13 .…”