Full-field X-ray reflection microscopy of epitaxial thin-films

Ferroelectric materials have remained one of the foci of condensed matter physics and materials science for over 50 years. In the last 20 years, the development of voltage-modulated scanning probe microscopy techniques, exemplified by Piezoresponse force microscopy (PFM) and associated time-and voltage spectroscopies, opened a pathway to explore these materials on a single-digit nanometer level. Consequently, domain structures, walls and polarization dynamics can now be imaged in real space. More generally, PFM has allowed studying electromechanical coupling in a broad variety of materials ranging from ionics to biological systems. It can also be anticipated that the recent Nobel prize 1 in molecular electromechanical machines will result in rapid growth in interest in PFM as a method to probe their behavior on single device and device assembly levels. However, the broad introduction of PFM also resulted in a growing number of reports on nearly-ubiquitous presence of ferroelectric-like phenomena including remnant polar states and electromechanical hysteresis loops in materials which are non-ferroelectric in the bulk, or in cases where size effects are expected to suppress ferroelectricity. While in certain cases plausible physical mechanisms can be suggested, there is remarkable similarity in observed behaviors, irrespective of the materials system. In this review, we summarize the basic principles of PFM, briefly discuss the features of ferroelectric surfaces salient to PFM imaging and spectroscopy, and summarize existing reports on ferroelectric-like responses in non-classical ferroelectric materials. We further discuss possible mechanisms behind observed behaviors, and possible experimental strategies for their identification.3

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“…focused X-ray methods 400,401 ), and chemical sensitivity (e.g. Raman or secondary ion mass-spectrometry 299,402,403 ).…”

Section: Discussionmentioning

confidence: 99%

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

Vasudevan

Balke

Maksymovych

et al. 2017

Applied Physics Reviews

270

206

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“…Of particular interest are those X-ray imaging modalities that place no restriction on the sample size nor its geometry and are of applicability to materials in thin-film form; one of the most technologically important class of materials. These modalities consist of: (i) nano- and micro-diffraction probes, whereby a focused beam is rastered across the sample to spatially map the diffracted intensity across a sample [7–9]; (ii) Bragg ptychography, where a real space image is reconstructed out of overlapping nano-diffraction patterns using phase-retrieval algorithms [10, 11]; (iii) full-field dark field X-ray microscopes which employ a combination of hard X-ray optics to form a real space image of the sample with diffraction contrast [12, 13]. …”

Section: Introductionmentioning

confidence: 99%

Dynamic X-ray diffraction imaging of the ferroelectric response in bismuth ferrite

Laanait

Saenrang

Zhou

et al. 2017

Adv Struct Chem Imag

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X-ray diffraction imaging is rapidly emerging as a powerful technique by which one can capture the local structure of crystalline materials at the nano- and meso-scale. Here, we present investigations of the dynamic structure of epitaxial monodomain BiFeO3 thin-films using a novel full-field Bragg diffraction imaging modality. By taking advantage of the depth penetration of hard X-rays and their exquisite sensitivity to the atomic structure, we imaged in situ and in operando, the electric field-driven structural responses of buried BiFeO3 epitaxial thin-films in micro-capacitor devices, with sub-100 nm lateral resolution. These imaging investigations were carried out at acquisition frame rates that reached up to 20 Hz and data transfer rates of 40 MB/s, while accessing diffraction contrast that is sensitive to the entire three-dimensional unit cell configuration. We mined these large datasets for material responses by employing matrix decomposition techniques, such as independent component analysis. We found that this statistical approach allows the extraction of the salient physical properties of the ferroelectric response of the material, such as coercive fields and transient spatiotemporal modulations in their piezoelectric response, and also facilitates their decoupling from extrinsic sources that are instrument specific.Electronic supplementary materialThe online version of this article (doi:10.1186/s40679-017-0044-3) contains supplementary material, which is available to authorized users.

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“…These imaging modalities are crucial to fundamental investigations of modern materials, which often display a range of structural configurations and order parameter phases. In many cases, some structural phases are not directly discernible by the diffraction-based methods of X-rays and neutron scattering [8, 9] due to either their small volume fraction and/or their lack of long-range periodicity, and therefore require an imaging approach [10, 11] for identification.…”

Section: Introductionmentioning

confidence: 99%

Identifying local structural states in atomic imaging by computer vision

Laanait

Ziatdinov

et al. 2016

Adv Struct Chem Imag

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The availability of atomically resolved imaging modalities enables an unprecedented view into the local structural states of materials, which manifest themselves by deviations from the fundamental assumptions of periodicity and symmetry. Consequently, approaches that aim to extract these local structural states from atomic imaging data with minimal assumptions regarding the average crystallographic configuration of a material are indispensable to advances in structural and chemical investigations of materials. Here, we present an approach to identify and classify local structural states that is rooted in computer vision. This approach introduces a definition of a structural state that is composed of both local and nonlocal information extracted from atomically resolved images, and is wholly untethered from the familiar concepts of symmetry and periodicity. Instead, this approach relies on computer vision techniques such as feature detection, and concepts such as scale invariance. We present the fundamental aspects of local structural state extraction and classification by application to simulated scanning transmission electron microscopy images, and analyze the robustness of this approach in the presence of common instrumental factors such as noise, limited spatial resolution, and weak contrast. Finally, we apply this computer vision-based approach for the unsupervised detection and classification of local structural states in an experimental electron micrograph of a complex oxides interface, and a scanning tunneling micrograph of a defect-engineered multilayer graphene surface.Electronic supplementary materialThe online version of this article (doi:10.1186/s40679-016-0028-8) contains supplementary material, which is available to authorized users.

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Full-field X-ray reflection microscopy of epitaxial thin-films

Cited by 42 publications

References 46 publications

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

Ferroelectric or non-ferroelectric: Why so many materials exhibit “ferroelectricity” on the nanoscale

Dynamic X-ray diffraction imaging of the ferroelectric response in bismuth ferrite

Identifying local structural states in atomic imaging by computer vision

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