Principle and Reconstruction Algorithm for Atomic-Resolution Holography

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To clarify atom‐resolved structural characterizations of materials, X‐ray fluorescence holography (XFH) technique is employed for drawing three‐dimensional (3D) atomic images around a specific element emitting fluorescent X‐rays. By taking the angle dependences of the fluorescent X‐ray intensity (hologram), 3D images of the surrounding atoms can be, in principle, obtained via simple Fourier transform‐like approaches with no special atomic models. In reality, however, an infinite number of the holograms with different incident X‐ray energies are necessary to reproduce the artifact‐less atomic images at the correct positions. Instead, here an inverse problem is applied using a sparse modeling approach of a L1‐regularized linear regression to solve such statistical problem of a small data size. The excellent results of this approach are presented on complex crystals of some functional materials, such as Mn doped Bi2Te3 topological insulator, Fe65Ni35 Invar alloy, and Fe chalcogenide high‐temperature superconductor.

g true({bold-italicr}_{i} true) = 0.

The excellent improvements of the atomic images using the L 1 ‐regularized linear regression are clearly given in Matsushita et al…”

Section: Spea‐l1 Analysismentioning

confidence: 95%

Section: Advantages Of Spea‐l1 Analysismentioning

confidence: 99%

Applications of a L₁‐Regularized Linear Regression to X‐Ray Fluorescence Holography Data of Functional Materials

Hosokawa

Stellhorn

Hayashi

et al. 2018

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“…To reconstruct the atomic images from the holograms, the scattering pattern extraction algorithm with L1 regularization (SPEA‐L1) with the steepest descent method, developed by one of the authors of this work, was used . SPEA‐L1 is a fitting based algorithm that uses L 1 regularized linear regression that begins with a reconstructed image obtained from Barton's method .…”

Section: Methodsmentioning

confidence: 99%

“…SPEA‐L1 is a fitting based algorithm that uses L 1 regularized linear regression that begins with a reconstructed image obtained from Barton's method . The SPEA‐L1 algorithm has been used to obtain good atomic reconstructions from single energy holograms and multiple energy holograms …”

Section: Methodsmentioning

confidence: 99%

Direct Imaging of Valence‐Sensitive X‐Ray Fluorescence Holograms of Fe₃O₄

Ang

Matsushita

Hashimoto

et al. 2018

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X‐ray fluorescence holography (XFH) is typically performed using zero‐dimensional detectors. This makes data acquisition in synchrotron facilities time consuming. Here, we report the first direct imaging of the X‐ray fluorescence hologram of a Fe3O4 sample using a 2D hybrid detector. The apparatus, data acquisition and data processing are described here. The recorded Fe Kα hologram agreed well with simulations, and the atomic images reconstructed using the SPEA‐L1 algorithm showed agreement with the expected Fe and O positions. Furthermore, by tuning the incident X‐ray energy, fluorescence from the Fe3+ cations can be suppressed, allowing the imaging of Fe Kα holograms from Fe2.5+ cations. The valence‐sensitivity of the holograms was confirmed by the appearance of different sets of Kossel lines in the hologram, and in the atomic reconstructions. Reconstructions from the holograms from Fe2.5+ cations show that these emitters are located on octahedral sites, and the reconstruction from the Fe3+ holograms shows emitters on the tetrahedral sites. These results demonstrate that the new 2D hybrid detector‐based apparatus is a good XFH alternative that can be used to clarify structures of multi‐valence materials. Further applications to radiation‐damage sensitive samples, and even time‐resolved XFH experiments can also be achieved using this new XFH apparatus.

“…Photoelectron and X‐ray fluorescence ARH have already been practicalised and have provided rich information on the anomalies of atomic structures in various exotic materials, such as dilute magnetic semiconductors, relaxor ferroelectric materials, topological insulators and so on, which can never be obtained by other probes . The technical details and principles of X‐ray fluorescence ARH can be found in review papers …”

Section: Introductionmentioning

confidence: 99%

White Neutron Holography in Pulsed Neutron Facilities

Ohoyama

Hayashi

2018

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Slight changes in atomic structures by doping foreign elements in materials play an important role in functionality. This article presents a review of the newly developed technique, white neutron holography, which is an effective probe for investigations of effects of doping on atomic structures, particularly for light elements. The principle and advantages of white neutron holography are explained. Observations of local structures around the dopant in B‐doped Si, Eu‐doped CaF2 and other materials have already been succeeded, meaning that white neutron holography can be applied to various fields in materials science.