Patterning enhanced tetragonality in $\mathrm{Bi}\mathrm{Fe}{\mathrm{O}}_{3}$ thin films with effective negative pressure by helium implantation

Patterning enhanced tetragonality in $Bi Fe O_{3}$ thin films with effective negative pressure by helium implantation

C. Toulouse, J. Fischer, S. Farokhipoor, L. Yedra, F. Carlà, A. Jarnac, E. Elkaim, P. Fertey, J.-N. Audinot, T. Wirtz, B. Noheda, V. Garcia, S. Fusil, I. Peral Alonso, M. Guennou, and J. Kreisel

Phys. Rev. Materials 5, 024404 – Published 9 February 2021

Abstract

Helium implantation in epitaxial thin films is a way to control the out-of-plane deformation independently from the in-plane strain controlled by epitaxy. In particular, implantation by means of a helium microscope allows for local implantation and patterning down to the nanometer resolution, which is of interest for device applications. We present here a study of bismuth ferrite ( ${BiFeO}_{3}$ ) films where strain was patterned locally by helium implantation. Our combined Raman, x-ray diffraction, and transmission electron microscopy (TEM) study shows that the implantation causes an elongation of the ${BiFeO}_{3}$ unit cell and ultimately a transition towards the so-called supertetragonal polymorph via states with mixed phases. In addition, TEM reveals the onset of amorphization at a threshold dose that does not seem to impede the overall increase in tetragonality. The phase transition from the R-like to T-like ${BiFeO}_{3}$ appears as first-order in character, with regions of phase coexistence and abrupt changes in lattice parameters.

Received 22 September 2020
Accepted 11 January 2021

DOI:https://doi.org/10.1103/PhysRevMaterials.5.024404

Physics Subject Headings (PhySH)

Epitaxial strain Structural phase transition

Multiferroics Perovskites Thin films

Grazing-incidence X-ray diffraction Ion implantation Raman spectroscopy Transmission electron microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

C. Toulouse ^1,2,*, J. Fischer ³, S. Farokhipoor⁴, L. Yedra⁵, F. Carlà ^6,7, A. Jarnac ⁸, E. Elkaim⁸, P. Fertey ⁸, J.-N. Audinot ², T. Wirtz ², B. Noheda ⁴, V. Garcia³, S. Fusil³, I. Peral Alonso¹, M. Guennou ¹, and J. Kreisel ¹

¹Department of Physics and Materials Science, University of Luxembourg, 41 rue du Brill, L-4422 Belvaux, Luxembourg
²Materials Research and Technology Department, Luxembourg Institute of Science and Technology, 41 rue du Brill, L-4422 Belvaux, Luxembourg
³Unité Mixte de Physique, CNRS, Thales, Université Paris-Saclay, F-91767 Palaiseau, France
⁴Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, NL-9747AG Groningen, The Netherlands
⁵Laboratoire Structures, Propriétés et Modélisation des Solides (UMR CNRS 8580) and Laboratoire Mécanique des Sols, Structures et Matériaux (UMR CNRS 8579), CentraleSupélec, Universite Paris Saclay, F-91192 Gif-sur-Yvette Cedex, France
⁶European Synchrotron Radiation Facility, 71 Avenue des Martyrs, F-38000 Grenoble, France
⁷Diamond Light Source Ltd., Didcot OX11 0DE, United Kingdom
⁸Synchrotron SOLEIL, L'Orme des Merisiers, F-91190 Saint-Aubin, Gif-sur-Yvette, France

^*Present address: Department of Physics and Materials Science, University of Luxembourg, LIST-Belvaux site, 41 rue du Brill, L-4422 Belvaux, Luxembourg; Corresponding author: constance.toulouse@uni.lu

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Vol. 5, Iss. 2 — February 2021

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Figure 1
Schematic representations of (a) compressive and (b) tensile epitaxial strain and of (c) the out-of-plane negative pressure induced by helium implantation. TRIM simulations (see “Experimental details” section for details) of (d) the helium-ion distribution and (e) the implantation depth profile of 6 keV helium ions inside $Bi Fe O_{3} (70 nm) / Sr Ru O_{3} (5 nm) / / Sr Ti O_{3}$ with an incident angle of $49^{\circ}$ . (f) Secondary electron images (SEM-HIM) of patterned ${BiFeO}_{3}$ films with various sizes of implanted regions.
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Figure 2
(a) Raman spectra performed on different regions of the ${BiFeO}_{3} / / {SrTiO}_{3}$ film. The underlying intense signal of ${SrTiO}_{3}$ is dominant, but some ${BiFeO}_{3}$ phonon modes can be singled out. The inset shows these phonon modes, with a baseline substraction. The colored regions and dotted lines are guides for the viewer. [(b),(c)] Principal component analysis of the depth profiles on a nonimplanted region of the film: we can see the component signal (b) and the associated depth profiles (c) for the first two components associated to the substrate and the film, respectively.
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Figure 3
[(a),(b)] STEM images (HAADF) of ${BiFeO}_{3} / {SrRuO}_{3} / / {SrTiO}_{3}$ samples implanted with doses $5 \times 10^{15}$ (a) and $1 \times 10^{16}$ (b) He ${cm}^{- 2}$ . [(c)–(f)] GPA (geometrical phase analysis) of the strain in the epitaxial plane [(c),(e)] and out of plane [(d),(f)], using the ${SrTiO}_{3}$ substrate as a reference, of the samples with dose $5 \times 10^{15}$ [(c),(d)] and $1 \times 10^{16}$ [(e),(f)] He ${cm}^{- 2}$ . (g) EDX chemical analysis of the interface in the sample implanted with $5 \times 10^{15}$ He ${cm}^{- 2}$ .
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Figure 4
X-ray diffraction results of nonimplanted and implanted (with a $5 \times 10^{15}$ He ${cm}^{- 2}$ dose) regions of a ${BiFeO}_{3} / / {SrTiO}_{3}$ thin film. (a) Specular reflectivity. (b) ( $h, k$ ) reciprocal space maps integrated in the $- 0.05 < l < 0.05$ range. (c) ( $h, l$ ) reciprocal space maps measured at $k$ = 0.96 and (d) the corresponding one-dimensional plot by integrating the intensity of the map contained in the $0.98 < h < 1.02$ range. (e) $θ (2 θ)$ scans of regions implanted with various helium doses. (f) Extracted out-of-plane (blue triangles) and in-plane (green circles) lattice parameters (from 001, 101, and 011 Bragg peaks) as a function of the helium dose. The out-of-plane lattice parameters estimated from STEM observations are added as red diamonds. Similar experiments for a ${BiFeO}_{3} / / {DyScO}_{3}$ sample with (g) $θ (2 θ)$ scans of regions implanted with various helium doses and (h) the extracted out-of-plane (blue triangles) and in-plane (green circles) lattice parameters (from 001, 101, and 011 Bragg peaks) as a function of the helium dose.
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Physical Review Materials

Patterning enhanced tetragonality in BiFeO3 thin films with effective negative pressure by helium implantation

C. Toulouse, J. Fischer, S. Farokhipoor, L. Yedra, F. Carlà, A. Jarnac, E. Elkaim, P. Fertey, J.-N. Audinot, T. Wirtz, B. Noheda, V. Garcia, S. Fusil, I. Peral Alonso, M. Guennou, and J. Kreisel

Phys. Rev. Materials 5, 024404 – Published 9 February 2021

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Patterning enhanced tetragonality in $Bi Fe O_{3}$ thin films with effective negative pressure by helium implantation