Ferroelectric oxides, featuring asymmetric or polar structures that are switchable under an external field, are required to take the form of nanoscale films in future electronic devices. However, the ferroelectricity is generally deteriorated or even vanishes when the ferroelectric films are downsized to unit cell scale. It is rather difficult to maintain and enhance the polarization in nanoscale ferroelectrics.

In a recent study published in Advanced Materials, the research team led by Prof. MA Xiuliang and Prof. ZHU Yinlian from Institute of Metal Research of Chinese Academy of Sciences found giant polarization sustainability in a series of ultrathin PbTiO₃ films scaled down to three unit-cells.

Thanks to a long-standing tradition with several decades of applying transmission electron microscopy to materials science, the research group has artificially produced a series of ultrathin PbTiO₃ films scaled down to three unit-cells grown on NdGaO₃(110) substrates with La_0.7Sr_0.3MnO₃ as bottom electrodes and found the novel phenomenon of giant polarization sustainability .

The giant enhancement of polarization in the present films is proposed to result from the charge transfer at the La_0.7Sr_0.3MnO₃/PbTiO₃ interface, as supported by the atomic mapping via aberration-corrected scanning transmission electron microscopy and by the anomalous decrease of Mn valence measured from X-ray photoelectron spectroscopy.

This study revealed the significant role of charge transfer at interfaces in improving large polarizations in ultrathin ferroelectrics and is of scientific and technological importance for the development of future electronic devices.