Epitaxial integration of improper ferroelectric h-YMnO$_3$ thin films in heterostructures

TL;DR

This paper demonstrates improved epitaxial growth techniques for improper ferroelectric YMnO₃ thin films, enabling high-quality heterostructures with potential applications in multiferroic devices.

Contribution

It introduces novel growth methods combining substrate annealing and low-energy PLD to produce ultralow roughness YMnO₃ films without misoriented inclusions or dislocations.

Findings

Achieved two-dimensional growth mode of YMnO₃ on YSZ with ultralow roughness.

Inserted sacrificial manganite layer to produce lattice-relaxed, dislocation-free films.

Established a template for fabricating multiferroic heterostructures with improved structural quality.

Abstract

We report on multiple fundamental qualitative improvements in the growth of improper ferroelectric hexagonal YMnO$_3$ (YMO) thin films and heterostructures by pulsed laser deposition (PLD). By a combination of pre-growth substrate annealing and low-energy-fluence PLD, we obtain a two-dimensional growth mode of the YMO films on yttria-stabilized zirconia (YSZ) with ultralow roughness and devoid of misoriented nanocrystalline inclusions. By inserting a sacrificial manganite layer capped with conducting indium-tin oxide between the substrate and the final film, the latter is grown in a fully lattice-relaxed mode and, thus, without any misfit dislocations while maintaining the extraordinary flatness of the films grown directly on pre-annealed YSZ. This provides a template for the fabrication of heterostructures based on hexagonal manganites as promising class of multiferroics with improper room-temperature ferroelectricity and the implementation of these into technologically relevant epitaxial metal|ferroelectric-type multilayers.