Nanoscale Design of High-Quality Epitaxial Aurivillius Thin Films

Abstract

Efforts for the integration of ferroelectric materials in nonvolatile, low energy consuming memories have so far been focused on perovskite oxide materials. Their down-scaling for nanodevices is, however, hindered by finite-size effects, and alternative materials offering more robust polar properties are required. Layered ferroelectrics of the Aurivillius phase have since emerged as promising candidates with robust polarization at subunit-cell thicknesses. Their controlled growth in the epitaxial thin film form has unfortunately remained elusive. Here, we demonstrate the stabilization of the coalescent layer-by-layer growth mode of the Bi n+1 Fe n−3 Ti 3 O 3n+3 (BFTO) Aurivillius family homologues. We define the growth conditions for high-quality, single-crystalline thin films exhibiting ferroelectricity from the first half-unit-cell. We demonstrate the process to be effective for several homologous Aurivillius compositions, which highlights its general applicability. Our work thus provides the systematic framework for the integration of high-quality epitaxial layered ferroelectrics into oxide electronics.

Control of Layering in Aurivillius Phase Nanocomposite Thin Films and Influence on Ferromagnetism and Optical Absorption

“…Furthermore, from a practical point of view, common pressure sensors and gas flow controls are sensitive and precise enough to ensure almost continuous fine-tuning of Λ and c . In agreement with our findings, Gradauskaite et al recently reported on stabilizing layer-by-layer growth modes in PLD for Bi m +1 Fe m –3 Ti 3 O 3 m +3 Aurivillius phase thin films and were able to adjust m from 4 up to 8 by increasing the laser fluence and background pressure …”

“…Furthermore, from a practical point of view, common pressure sensors and gas flow controls are sensitive and precise enough to ensure almost continuous fine-tuning of Λ and c. In agreement with our findings, Gradauskaite et al recently reported on stabilizing layer-by-layer growth modes in PLD for Bi m+1 Fe m−3 Ti 3 O 3m+3 Aurivillius phase thin films and were able to adjust m from 4 up to 8 by increasing the laser fluence and background pressure. 19 Keeping in perspective the aforementioned analysis, we are now in a position to address the underlying reasons for the observed dependencies, that is, which physical processes are adjusted when tuning these process parameters? It is known that the formation of oxide nanostructures can be governed by diffusion-limited processes during the growth.…”

Improved polarization and endurance in ferroelectric Hf0.5Zr0.5O2 films on SrTiO3(110)

“…Note that the lateral PFM shows a maximum response when the cantilever lies perpendicular to the polar axis of the film. 24 The film grown on LSMO/STO(110) shows similar vertical and in-plane contrasts (Fig. 1d and e).…”

Ferroelectric Domain Engineering Using Structural Defect Ordering

“…Let us now investigate OPB formation in our ultrathin BFTO n = 4 films. The films of the Aurivillius phase are grown using PLD with reflection high-energy electron diffraction (RHEED) monitoring to ensure the subunit-cell thickness accuracy. , The excellent epitaxial lattice matching between the BFTO and NGO (001) (henceforth crystallographic indices correspond to the orthorhombic u.c. notation) substrate results in films that are single-crystalline and uniaxially polarized along the [010] substrate direction ( a -axis of BFTO). , We use APT to image a 5-u.c.-thick BFTO film.…”

“…The films of the Aurivillius phase are grown using PLD with reflection high-energy electron diffraction (RHEED) monitoring to ensure the subunit-cell thickness accuracy. , The excellent epitaxial lattice matching between the BFTO and NGO (001) (henceforth crystallographic indices correspond to the orthorhombic u.c. notation) substrate results in films that are single-crystalline and uniaxially polarized along the [010] substrate direction ( a -axis of BFTO). , We use APT to image a 5-u.c.-thick BFTO film. The APT measurement allows three-dimensional reconstruction of the chemical composition on the atomic length scale and helps locating structural defects and their propagation within the volume .…”