References of "Guennou, Mael 50034741"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailControlling electrical and optical properties of zinc oxide thin films grown by thermal atomic layer deposition with oxygen gas
Nguyen, Tai; Adjeroud, Noureddine; Guennou, Mael UL et al

in Results in Materials (2020), 6

The preparation of ZnO thin films with controlled electrical resistivity and optical properties is often challenged by the presence of defects, such as oxygen vacancies or interstitial zinc. Here, we ... [more ▼]

The preparation of ZnO thin films with controlled electrical resistivity and optical properties is often challenged by the presence of defects, such as oxygen vacancies or interstitial zinc. Here, we investigate the material properties of ZnO polycrystalline thin films prepared by thermal Atomic Layer Deposition (ALD) with the presence of molecular oxygen pulsing during the growth. By means of structural, electrical and optical characterizations, we identify key growth parameters of this unusual ALD process. Unexpectedly, the influence of oxygen molecules on the crystallography, microstructure and morphology of ZnO films is significant from hundred-nanometers to micrometer thick film. The electrical resistivity of the films grown with oxygen gas shows a dramatic increase from 3 to 4 orders of magnitude. Additionally, photoluminescence measurements reveal that deep-level emissions caused by defects located deep in the band gap can be reduced by applying an adequate pulsing of oxygen gas during the process. Finally, we conclude with a discussion about the degree of consistency between the chemical composition, the inner strain and the optical and electrical properties of the films obtained with the different thermodynamic parameters of growth. Several hypotheses are discussed in order to understand the dominance of (002) orientation in the presence of oxygen during the ALD growth process. [less ▲]

Detailed reference viewed: 36 (3 UL)
Full Text
Peer Reviewed
See detailArchetypal Soft-Mode-Driven Antipolar Transition in Francisite Cu3Bi(SeO3)(2)O2Cl
Milesi-Brault, Cosme; Toulouse, Constance UL; Constable, Evan et al

in PHYSICAL REVIEW LETTERS (2020), 124(9), 097603-6

Model materials are precious test cases for elementary theories and provide building blocks for the understanding of more complex cases. Here, we describe the lattice dynamics of the structural phase ... [more ▼]

Model materials are precious test cases for elementary theories and provide building blocks for the understanding of more complex cases. Here, we describe the lattice dynamics of the structural phase transition in francisite Cu3Bi(SeO3)(2)O2Cl at 115 K and show that it provides a rare archetype of a transition driven by a soft antipolar phonon mode. In the high-symmetry phase at high temperatures, the soft mode is found at (0,0,0.5) at the Brillouin zone boundary and is measured by inelastic x-ray scattering and thermal diffuse scattering. In the low-symmetry phase, this soft-mode is folded back onto the center of the Brillouin zone as a result of the doubling of the unit cell, and appears as a fully symmetric mode that can be tracked by Raman spectroscopy. On both sides of the transition, the mode energy squared follows a linear behavior over a large temperature range. First-principles calculations reveal that, surprisingly, the flat phonon band calculated for the high-symmetry phase seems incompatible with the displacive character found experimentally. We discuss this unusual behavior in the context of an ideal Kittel model of an antiferroelectric transition. [less ▲]

Detailed reference viewed: 34 (3 UL)
Full Text
Peer Reviewed
See detailDomain-wall engineering and topological defects in ferroelectric and ferroelastic materials
Nataf, G. F.; Guennou, Mael UL; Gregg, J. M. et al

in Nature Reviews. Physics (2020), 2(11), 634-648

Ferroelectric and ferroelastic domain walls are 2D topological defects with thicknesses approaching the unit cell level. When this spatial confinement is combined with observations of emergent functional ... [more ▼]

Ferroelectric and ferroelastic domain walls are 2D topological defects with thicknesses approaching the unit cell level. When this spatial confinement is combined with observations of emergent functional properties, such as polarity in non-polar systems or electrical conductivity in otherwise insulating materials, it becomes clear that domain walls represent new and exciting objects in matter. In this Review, we discuss the exotic polarization profiles that can arise at domain walls with multiple order parameters and the different mechanisms that lead to domain-wall polarity in non-polar ferroelastic materials. The emergence of energetically degenerate variants of the domain walls themselves suggests the existence of interesting quasi-1D topological defects within such walls. We also provide an overview of the general notions that have been postulated as fundamental mechanisms responsible for domain-wall conduction in ferroelectrics. We then discuss the prospect of combining domain walls with transition regions observed at phase boundaries, homo- and heterointerfaces, and other quasi-2D objects, enabling emergent properties beyond those available in today's topological systems. Ferroelectric and ferroelastic domain walls are 2D topological defects with thicknesses approaching the unit cell level and emergent functional properties. This Review discusses the exotic polarization profiles that arise at domain walls and the fundamental mechanisms responsible for domain-wall conduction. [less ▲]

Detailed reference viewed: 75 (2 UL)
Full Text
Peer Reviewed
See detailHigh-contrast imaging of 180 degrees ferroelectric domains by optical microscopy using ferroelectric liquid crystals
Nataf, Guillaume F.; Guennou, Mael UL; Scalia, Giusy UL et al

in APPLIED PHYSICS LETTERS (2020), 116(21),

Ferroelectric liquid crystals (FLCs) couple the direction of their spontaneous electric polarization to the direction of tilt of their optic axis. Consequently, reversal of the electric polarization by an ... [more ▼]

Ferroelectric liquid crystals (FLCs) couple the direction of their spontaneous electric polarization to the direction of tilt of their optic axis. Consequently, reversal of the electric polarization by an electric field gives rise to an immediate and lasting optical response when an appropriately aligned FLC is observed between crossed polarizers, with one field direction yielding a dark image and the opposite direction yielding a bright image. Here, this peculiar electro-optic response is used to image, with high optical contrast, 180 degrees ferroelectric domains in a crystalline substrate of magnesium-doped lithium niobate. The lithium niobate substrate contains a few domains with upward electric polarization surrounded by regions with downward electric polarization. In contrast to a reference non-chiral liquid crystal that is unable to show ferroelectric behavior due to its high symmetry, the FLC, which is used as a thin film confined between the lithium niobate substrate and an inert aligning substrate, reveals ferroelectric domains as well as their boundaries, with strong black and white contrast. The results show that FLCs can be used for non-destructive readout of domains in underlying ferroelectrics, with potential applications in, e.g., photonic devices and non-volatile ferroelectric memories. [less ▲]

Detailed reference viewed: 34 (2 UL)
Full Text
Peer Reviewed
See detailMesoporous TiO2 anatase films for enhanced photocatalytic activity under UV and visible light
Ishchenko, Olga M.; Lamblin, Guillaume; Guillot, Jérôme et al

in RSC Adv. (2020), 10

Mesoporous TiO2 films with enhanced photocatalytic activity in both UV and visible wavelength ranges were developed through a non-conventional atomic layer deposition (ALD) process at room temperature ... [more ▼]

Mesoporous TiO2 films with enhanced photocatalytic activity in both UV and visible wavelength ranges were developed through a non-conventional atomic layer deposition (ALD) process at room temperature. Deposition at such a low temperature promotes the accumulation of by-products in the amorphous TiO2 films, caused by the incomplete hydrolysis of the TiCl4 precursor. The additional thermal annealing induces the fast recrystallisation of amorphous films, as well as an in situ acidic treatment of TiO2. The interplay between the deposition parameters, such as purge time, the amount of structural defects introduced and the enhancement of the photocatalytic properties from different mesoporous films clearly shows that our easily upscalable non-conventional ALD process is of great industrial interest for environmental remediation and other photocatalytic applications, such as hydrogen production. [less ▲]

Detailed reference viewed: 33 (0 UL)
Full Text
Peer Reviewed
See detailVibrational properties of LaNiO3 films in the ultrathin regime
Schober, Alexander; Fowlie, Jennifer; Guennou, Mael UL et al

in APL MATERIALS (2020), 8(6),

Collective rotations and tilts of oxygen polyhedra play a crucial role in the physical properties of complex oxides such as magnetism and conductivity. Such rotations can be tuned by preparing thin films ... [more ▼]

Collective rotations and tilts of oxygen polyhedra play a crucial role in the physical properties of complex oxides such as magnetism and conductivity. Such rotations can be tuned by preparing thin films in which dimensionality, strain, and interface effects come into play. However, little is known of the tilt and rotational distortions in films a few unit cells thick including the question of if coherent tilt patterns survive at all in this ultrathin limit. Here, a series of films of perovskite LaNiO3 is studied and it is shown that the phonon mode related to oxygen octahedral tilts can be followed by Raman spectroscopy down to a film thickness of three pseudocubic perovskite unit cells (similar to 1.2 nm). To push the limits of resolution to the ultrathin regime, a statistical analysis method is introduced to separate the Raman signals of the film and substrate. Most interestingly, these analyses reveal a pronounced hardening of the tilt vibrational mode in the thinnest films. A comparison between the experimental results, first principles simulations of the atomic structure, and the standing wave model, which accounts for size effects on the phononic properties, reveals that in the ultrathin regime, the Raman spectra are a hybrid entity of both the bulk and surface phononic behavior. These results showcase Raman spectroscopy as a powerful tool to probe the behavior of perovskite films down to the ultrathin limit. [less ▲]

Detailed reference viewed: 98 (16 UL)
Full Text
Peer Reviewed
See detailArchetypal Soft-Mode-Driven Antipolar Transition in Francisite Cu3BiðSeO3Þ2O2Cl
Milesi-Brault, Cosme; Toulouse, Constance UL; Constable, Evan et al

in Physical Review Letters (2020)

Detailed reference viewed: 25 (0 UL)
Full Text
Peer Reviewed
See detailRole of the ferroelastic strain in the optical absorption of BiVO4
Hill, Christina; Weber, Mads C.; Lehmann, Jannis et al

in APL MATERIALS (2020), 8(8),

Bismuth vanadate (BiVO4) has recently been under focus for its potential use in photocatalysis thanks to its well-suited absorption edge in the visible light range. Here, we characterize the optical ... [more ▼]

Bismuth vanadate (BiVO4) has recently been under focus for its potential use in photocatalysis thanks to its well-suited absorption edge in the visible light range. Here, we characterize the optical absorption of a BiVO4 single crystal as a function of temperature and polarization direction by reflectance and transmittance spectroscopy. The optical bandgap is found to be very sensitive to the temperature, and to the tetragonal-to-monoclinic ferroelastic transition at 523 K. The anisotropy, as measured by the difference in the absorption edge for the light polarized parallel and perpendicular to the principal axis, is reduced from 0.2 eV in the high-temperature tetragonal phase to 0.1 eV at ambient temperature. We show that this evolution is dominantly controlled by the ferroelastic shear strain. These findings provide a route for further optimization of bismuth vanadate-based light absorbers in photocatalytic devices. [less ▲]

Detailed reference viewed: 56 (4 UL)
Full Text
Peer Reviewed
See detailOptical studies of ferroelectric and ferroelastic domain walls
Nataf, G. F.; Guennou, Mael UL

in Journal of Physics: Condensed Matter (2020), 32(18), 183001

Recent studies carried out with atomic force microscopy or high-resolution transmission electron microscopy reveal that ferroic domain walls can exhibit different physical properties than the bulk of the ... [more ▼]

Recent studies carried out with atomic force microscopy or high-resolution transmission electron microscopy reveal that ferroic domain walls can exhibit different physical properties than the bulk of the domains, such as enhanced conductivity in insulators, or polar properties in non-polar materials. In this review we show that optical techniques, in spite of the diffraction limit, also provide key insights into the structure and physical properties of ferroelectric and ferroelastic domain walls. We give an overview of the uses, specificities and limits of these techniques, and emphasize the properties of the domain walls that they can probe. We then highlight some open questions of the physics of domain walls that could benefit from their use. [less ▲]

Detailed reference viewed: 87 (1 UL)
Full Text
Peer Reviewed
See detailLattice dynamics and Raman spectrum of BaZrO3 single crystals
Toulouse, Constance UL; Amoroso, Danila; Xin, Cong et al

in PHYSICAL REVIEW B (2019), 100

BaZrO3 is a perovskite that remains in the simple cubic phase at all temperatures, hence with no first-order Raman-active phonon mode allowed by symmetry. Yet, it exhibits an intense Raman spectrum with ... [more ▼]

BaZrO3 is a perovskite that remains in the simple cubic phase at all temperatures, hence with no first-order Raman-active phonon mode allowed by symmetry. Yet, it exhibits an intense Raman spectrum with sharp and well-defined features. Here, we report the evolution of the Raman spectrum of BaZrO3 single crystals in a broad temperature range (4-1200 K) and discuss its origin with the support of detailed first-principle calculations of the lattice dynamics. Phonon calculations are performed not only for the cubic phase of BaZrO3, but also for the low-symmetry phases with octahedra tilts that have been suspected to exist at the nanoscale. We show that the Raman spectrum shows no direct evidence for these nanodomains, but can instead be explained by classical second-order Raman scattering. We provide an assignment of the dominant features to phonon mode combinations. In particular, we show that the high frequency range of the spectrum is dominated by overtones and shows an image of the phonon density of states corresponding to the stretching modes of the oxygen octahedra. [less ▲]

Detailed reference viewed: 160 (8 UL)
Full Text
Peer Reviewed
See detailCrossover in the pressure evolution of elementary distortions in RFeO3 perovskites and its impact on their phase transition
Vilarinho, Rui; Bouvier, Pierre; Guennou, Mael UL et al

in Physical Review. B (2019), 99

This work reports on the pressure dependence of the octahedral tilts and mean Fe-O bond lengths in RFeO3 (R = Nd, Sm, Eu, Gd, Tb, and Dy), determined through synchrotron x-ray diffraction and Raman ... [more ▼]

This work reports on the pressure dependence of the octahedral tilts and mean Fe-O bond lengths in RFeO3 (R = Nd, Sm, Eu, Gd, Tb, and Dy), determined through synchrotron x-ray diffraction and Raman scattering, and their role on the pressure-induced phase transition displayed by all of these compounds. For larger rare-earth cations (Nd-Sm), both anti- and in-phase octahedral tilting decrease as pressure increases, whereas the reverse behavior is observed for smaller ones (Gd-Dy). EuFeO3 stands at the borderline, with nearly pressure-independent tilt angles. For the compounds where the tilts increase with pressure, the FeO6 octahedra are compressed at lower rates than for those ones exhibiting opposite pressure tilt dependence. The crossover between the two opposite pressure behaviors is discussed in relation to the general rules proposed from different theoretical approaches. The similarity of the pressure-induced isostructural insulator-to-metal phase transition, observed in the whole series, points out that the tilts play a minor role in its driving mechanisms. A clear relationship between octahedral compressibility and critical pressure is ascertained. [less ▲]

Detailed reference viewed: 122 (1 UL)
Full Text
Peer Reviewed
See detailSingle crystal growth of BaZrO3 from the melt at 2700 degrees C using optical floating zone technique and growth prospects from BaB2O4 flux at 1350 degrees C
Xin, Cong; Veber, Philippe; Guennou, Mael UL et al

in CRYSTENGCOMM (2019), 21(3), 502-512

We report the growth of BaZrO3 single crystals by the optical floating zone technique and the investigation on its flux growth using BaB2O4 as a solvent. 6 mm long colorless and transparent single ... [more ▼]

We report the growth of BaZrO3 single crystals by the optical floating zone technique and the investigation on its flux growth using BaB2O4 as a solvent. 6 mm long colorless and transparent single crystals were obtained with a mirror furnace without the need for post-treatment annealing. Its properties are determined and compared with those of two commercial crystals grown by the tri-arc Czochralski method. The chemical composition was investigated using glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS), which indicate minor impurities of Sr, Hf, Ca and Ti, with maximal concentrations for Sr and Hf in the range of 0.3-0.5 at. The optical band gap determined by UV-visible spectroscopy is found to be similar to 4.8 eV and indicates the high quality of the BaZrO3 crystals grown by the optical floating zone technique. Raman spectroscopy at ambient conditions and at low temperatures down to 4.2 K reveals a relatively sharp second-order spectrum and does not reveal any structural phase transition. Prospective high-temperature solution growth using BaB2O4 self-flux was investigated and led to 150-200 mu m BaZrO3 crystals. This solvent opens the way to grow BaZrO3 at half its melting point by the flux method. [less ▲]

Detailed reference viewed: 67 (7 UL)
Full Text
Peer Reviewed
See detailSuppression of the cooperative Jahn-Teller distortion and its effect on the Raman octahedra-rotation modes of TbMn1-xFexO3
Vilarinho, R.; Passos, D. J.; Queiros, E. C. et al

in PHYSICAL REVIEW B (2018), 97(14),

This work reports the changes in structure and lattice dynamics induced by substituting the Jahn-Teller-active Mn3+ ion by the Jahn-Teller-inactive Fe3+ in TbMn1-xFexO3 over the full composition range ... [more ▼]

This work reports the changes in structure and lattice dynamics induced by substituting the Jahn-Teller-active Mn3+ ion by the Jahn-Teller-inactive Fe3+ in TbMn1-xFexO3 over the full composition range. The structural analysis reveals that the amplitude of the 0 (pure 0.5, where it is completely suppressed. We then correlate this evolution with the behavior of the Raman modes across the solid solution. In particular, we show that the Raman modes associated with the rotation of octahedra, whose wave number is commonly considered to scale linearly with the tilt angles in orthorhombic Pnma perovskites are also sensitive to the amplitude of the Jahn-Teller distortion. [less ▲]

Detailed reference viewed: 244 (1 UL)
Full Text
Peer Reviewed
See detailRaman signatures of ferroic domain walls captured by principal component analysis
Nataf, G. F.; Barrett, N.; Kreisel, Jens UL et al

in JOURNAL OF PHYSICS-CONDENSED MATTER (2018), 30(3),

Ferroic domain walls are currently investigated by several state-of-the art techniques in order to get a better understanding of their distinct functional properties. Here, principal component analysis ... [more ▼]

Ferroic domain walls are currently investigated by several state-of-the art techniques in order to get a better understanding of their distinct functional properties. Here, principal component analysis (PCA) of Raman maps is used to study ferroelectric domain walls (DWs) in LiNbO3 and ferroelastic DWs in NdGaO3. It is shown that PCA allows us to quickly and reliably identify small Raman peak variations at ferroelectric DWs and that the value of a peak shift can be deduced-accurately and without a priori-from a first order Taylor expansion of the spectra. The ability of PCA to separate the contribution of ferroelastic domains and DWs to Raman spectra is emphasized. More generally, our results provide a novel route for the statistical analysis of any property mapped across a DW. [less ▲]

Detailed reference viewed: 81 (2 UL)
Full Text
Peer Reviewed
See detailRules and mechanisms governing octahedral tilts in perovskites under pressure
Xiang, H. J.; Guennou, Mael UL; Iniguez, Jorge et al

in PHYSICAL REVIEW B (2017), 96(5),

The rotation of octahedra (octahedral tilting) is common in ABO(3) perovskites and relevant to many physical phenomena, ranging from electronic and magnetic properties, metal-insulator transitions to ... [more ▼]

The rotation of octahedra (octahedral tilting) is common in ABO(3) perovskites and relevant to many physical phenomena, ranging from electronic and magnetic properties, metal-insulator transitions to improper ferroelectricity. Hydrostatic pressure is an efficient way to tune and control octahedral tiltings. However, the pressure behavior of such tiltings can dramatically differ from one material to another, with the origins of such differences remaining controversial. In this paper we discover several new mechanisms and formulate a set of simple rules that allow us to understand how pressure affects oxygen octahedral tiltings via the use and analysis of first-principles results for a variety of compounds. Besides the known A-O interactions, we reveal that the interactions between specific B ions and oxygen ions contribute to the tilting instability. We explain the previously reported trend that the derivative of the oxygen octahedral tilting with respect to pressure (dR/dP) usually decreases with both the tolerance factor and the ionization state of the A ion by illustrating the key role of A-O interactions and their change under pressure. Furthermore, three new mechanisms/rules are discovered, namely that (i) the octahedral rotations in ABO(3) perovskites with empty low-lying d states on the B site are greatly enhanced by pressure, in order to lower the electronic kinetic energy; (ii) dR/dP is enhanced when the system possesses weak tilt instabilities, and (iii) for the most common phase exhibited by perovskites-the orthorhombic Pbnm state-the in-phase and antiphase octahedral rotations are not automatically both suppressed or both enhanced by the application of pressure because of a trilinear coupling between these two rotation types and an antipolar mode involving the A ions. We further predict that the polarization associated with the so-called hybrid improper ferroelectricity could be manipulated by hydrostatic pressure by indirectly controlling the amplitude of octahedral rotations. [less ▲]

Detailed reference viewed: 91 (2 UL)
Full Text
Peer Reviewed
See detailControl of surface potential at polar domain walls in a nonpolar oxide
Nataf, G. F.; Guennou, Mael UL; Kreisel, Jens UL et al

in PHYSICAL REVIEW MATERIALS (2017), 1(7),

Ferroic domain walls could play an important role in microelectronics given their nanometric size and often distinct functional properties. Until now, devices and device concepts were mostly based on ... [more ▼]

Ferroic domain walls could play an important role in microelectronics given their nanometric size and often distinct functional properties. Until now, devices and device concepts were mostly based on mobile domain walls in ferromagnetic and ferroelectric materials. A less explored path is to make use of polar domain walls in nonpolar ferroelastic materials. Indeed, while the polar character of ferroelastic domain walls has been demonstrated, polarization control has been elusive. Here, we report evidence for the electrostatic signature of the domain-wall polarization in nonpolar calcium titanate (CaTiO3). Macroscopic mechanical resonances excited by an ac electric field are observed as a signature of a piezoelectric response caused by polar walls. On the microscopic scale, the polarization in domain walls modifies the local surface potential of the sample. Through imaging of surface potential variations, we show that the potential at the domain wall can be controlled by electron injection. This could enable devices based on nondestructive information readout of surface potential. [less ▲]

Detailed reference viewed: 87 (0 UL)
Full Text
Peer Reviewed
See detailConductivity and Local Structure of LaNiO3 Thin Films
Fowlie, Jennifer; Gibert, Marta; Tieri, Giulio et al

in ADVANCED MATERIALS (2017), 29(18),

A marked conductivity enhancement is reported in 6-11 unit cell LaNiO3 thin films. A maximal conductivity is also observed in ab initio calculations for films of the same thickness. In agreement with ... [more ▼]

A marked conductivity enhancement is reported in 6-11 unit cell LaNiO3 thin films. A maximal conductivity is also observed in ab initio calculations for films of the same thickness. In agreement with results from state of the art scanning transmission electron microscopy, the calculations also reveal a differentiated film structure comprising characteristic surface, interior, and heterointerface structures. Based on this observation, a three-element parallel conductor model is considered and leads to the conclusion that the conductivity enhancement for films of 6-11 unit cells, stems from the onset of intercompetition between the three local structures in the film depth. [less ▲]

Detailed reference viewed: 80 (0 UL)
Full Text
Peer Reviewed
See detailRaman spectroscopy of rare-earth orthoferrites RFeO3 (R=La, Sm, Eu, Gd Tb, Dy)
Weber, Mads Christof; Guennou, Mael UL; Zhao, Hong Jian et al

in PHYSICAL REVIEW B (2016), 94(21),

We report a Raman scattering study of six rare-earth orthoferrites La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of SmFeO3 and first-principles calculations enable the assignment ... [more ▼]

We report a Raman scattering study of six rare-earth orthoferrites La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of SmFeO3 and first-principles calculations enable the assignment of the observed phonon modes to vibrational symmetries and atomic displacements. The assignment of the spectra and their comparison throughout the whole series allow correlating the phonon modes with the orthorhombic structural distortions of RFeO3 perovskites. In particular the positions of two specific A(g) modes scale linearly with the two FeO6 octahedra tilt angles, allowing the distortion to be tracked throughout the series. At variance with literature, we find that the two octahedra tilt angles scale differently with the vibration frequencies of their respective A(g) modes. This behavior, as well as the general relations between the tilt angles, the frequencies of the associated modes, and the ionic radii are rationalized in a simple Landau model. The reported Raman spectra and associated phonon-mode assignment provide reference data for structural investigations of the whole series of orthoferrites. [less ▲]

Detailed reference viewed: 98 (2 UL)
Full Text
Peer Reviewed
See detailLow energy electron imaging of domains and domain walls in magnesium-doped lithium niobate
Nataf, G. F.; Grysan, P.; Guennou, Mael UL et al

in SCIENTIFIC REPORTS (2016), 6

The understanding of domain structures, specifically domain walls currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in ... [more ▼]

The understanding of domain structures, specifically domain walls currently attracts a significant attention in the field of (multi)-ferroic materials. In this article, we analyze contrast formation in full field electron microscopy applied to domains and domain walls in the uniaxial ferroelectric lithium niobate, which presents a large 3.8 eV band gap and for which conductive domain walls have been reported. We show that the transition from Mirror Electron Microscopy (MEM - electrons reflected) to Low Energy Electron Microscopy (LEEM - electrons backscattered) gives rise to a robust contrast between domains with upwards (P-up) and downwards (P-down) polarization, and provides a measure of the difference in surface potential between the domains. We demonstrate that out-of-focus conditions of imaging produce contrast inversion, due to image distortion induced by charged surfaces and also carry information on the polarization direction in the domains. Finally, we show that the intensity profile at domain walls provides experimental evidence for a local stray, lateral electric field. [less ▲]

Detailed reference viewed: 54 (0 UL)