Direct evidence for ferroelectric polar distortion in ultrathin lead titanate perovskite films

TL;DR

This study provides direct experimental evidence of ferroelectric polar distortion in ultrathin lead titanate films, showing that ferroelectricity persists down to just three unit cells without a dead layer at the surface.

Contribution

It combines X-ray photoelectron diffraction and ab-initio calculations to directly demonstrate ferroelectricity in ultrathin PbTiO3 films, advancing understanding of nanoscale ferroelectricity.

Findings

Ferroelectric polar distortion observed in films as thin as 3 unit cells

No evidence of a paraelectric dead layer at the surface

Non-centrosymmetry confirmed in ultrathin films

Abstract

X-ray photoelectron diffraction is used to directly probe the intra-cell polar atomic distortion and tetragonality associated with ferroelectricity in ultrathin epitaxial PbTiO3 films. Our measurements, combined with ab-initio calculations, unambiguously demonstrate non-centro-symmetry in films a few unit cells thick, imply that films as thin as 3 unit cells still preserve a ferroelectric polar distortion, and also show that there is no thick paraelectric dead layer at the surface.