High-energy x-ray diffraction from surfaces and nanoparticles

Hejral, Uta; Müller, Patrick; Shipilin, Mikhail; Gustafson, Johan; Franz, Dirk; Shayduk, Roman; Rütt, U.; Zhang, C.; Merte, Lindsay R.; Lundgren, Edvin; Vonk, Vedran; Stierle, Andreas

doi:10.1103/physrevb.96.195433

Cited by 23 publications

(32 citation statements)

References 30 publications

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“…The results here are obtained with an incident angle of 0.06°. This is close to the critical angle for total external reflection of the planar samples, which is beneficial for the signal-to-noise ratio of the diffracted intensities 49 , 50 . A large area Perkin Elmer integrating detector, having square 200 µm pixels, is used for data collection.…”

Section: Methodsmentioning

confidence: 60%

Understanding electrochemical switchability of perovskite-type exsolution catalysts

et al. 2020

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Exsolution of metal nanoparticles from perovskite-type oxides is a very promising approach to obtain catalysts with superior properties. One particularly interesting property of exsolution catalysts is the possibility of electrochemical switching between different activity states. In this work, synchrotron-based in-situ X-ray diffraction experiments on electrochemically polarized La0.6Sr0.4FeO3-δ thin film electrodes are performed, in order to simultaneously obtain insights into the phase composition and the catalytic activity of the electrode surface. This shows that reversible electrochemical switching between a high and low activity state is accompanied by a phase change of exsolved particles between metallic α-Fe and Fe-oxides. Reintegration of iron into the perovskite lattice is thus not required for obtaining a switchable catalyst, making this process especially interesting for intermediate temperature applications. These measurements also reveal how metallic particles on La0.6Sr0.4FeO3-δ electrodes affect the H2 oxidation and H2O splitting mechanism and why the particle size plays a minor role.

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Section: Methodsmentioning

confidence: 60%

Understanding electrochemical switchability of perovskite-type exsolution catalysts

et al. 2020

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“…(c) Sum of images measured during a rotational scan on a metallic Ir(001) surface, the metallic Ir CTRs are visible as almost straight lines. Figure partly adapted from [31].…”

Section: Working Principle Of Conventional Sxrd and Hesxrdmentioning

confidence: 99%

High energy surface x-ray diffraction applied to model catalyst surfaces at work

Hejral

Shipilin

Gustafson

et al. 2020

J. Phys.: Condens. Matter

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Catalysts are materials that accelerate the rate of a desired chemical reaction. As such, they constitute an integral part in many applications ranging from the production of fine chemicals in chemical industry to exhaust gas treatment in vehicles. Accordingly, it is of utmost economic interest to improve catalyst efficiency and performance, which requires an understanding of the interplay between the catalyst structure, the gas phase and the catalytic activity under realistic reaction conditions at ambient pressures and elevated temperatures. In recent years efforts have been made to increasingly develop techniques that allow for investigating model catalyst samples under conditions closer to those of real technical catalysts. One of these techniques is high energy surface x-ray diffraction (HESXRD), which uses x-rays with photon energies typically in the range of 70-80 keV. HESXRD allows a fast data collection of three dimensional reciprocal space for the structure determination of model catalyst samples under operando conditions and has since been used for the investigation of an increasing number of different model catalysts. In this article we will review general considerations of HESXRD including its working principle for different model catalyst samples and the experimental equipment required. An overview over HESXRD investigations performed in recent years will be given, and the advantages of HESXRD with respect to its application to different model catalyst samples will be presented. Moreover, the combination of HESXRD with other operando techniques such as in situ mass spectrometry, planar laser-induced fluorescence and surface optical reflectance will be discussed. The article will close with an outlook on future perspectives and applications of HESXRD.

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“…The stepwise annealing of the specimens was carried out at beam line ID31 at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, and followed by in situ high-energy GIXRD and XRR measurements using a photon energy of 70 keV, while the data were collected using two separate 2D pixel detectors. The use of high photon energies provides fast access to large areas in reciprocal space, excluding the need of a time-consuming sample and detector movements [21,22].…”

Section: B Characterization Techniques and Experimental Setupsmentioning

confidence: 99%

Niobium near-surface composition during nitrogen infusion relevant for superconducting radio-frequency cavities

Semione

Pandey

Tober

et al. 2019

Phys. Rev. Accel. Beams

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A detailed study of the near-surface structure and composition of Nb, the material of choice for superconducting radio-frequency accelerator (SRF) cavities, is of great importance in order to understand the effects of different treatments applied during cavity production. By means of surface-sensitive techniques such as grazing incidence diffuse x-ray scattering, x-ray reflectivity, and x-ray photoelectron spectroscopy, single-crystalline Nb(100) samples were investigated in and ex situ during annealing in an ultrahigh vacuum as well as in nitrogen atmospheres with temperatures and pressures similar to the ones employed in real Nb cavity treatments. Annealing of Nb specimens up to 800°C in a vacuum promotes a partial reduction of the natural surface oxides (Nb 2 O 5 , NbO 2 , and NbO) into NbO. Upon cooling to 120°C, no evidence of nitrogen-rich layers was detected after nitrogen exposure times of up to 48 h. An oxygen enrichment below the Nb-oxide interface and posterior diffusion of oxygen species towards the Nb matrix, along with a partial reduction of the natural surface oxides, was observed upon a stepwise annealing up to 250°C. Nitrogen introduction to the system at 250°C promotes neither N diffusion into the Nb matrix nor the formation of new surface layers. Upon further heating to 500°C in a nitrogen atmosphere, the growth of a new subsurface Nb x N y layer was detected. These results shed light on the composition of the near-surface region of Nb after low-temperature nitrogen treatments, which are reported to lead to a performance enhancement of SRF cavities.

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High-energy x-ray diffraction from surfaces and nanoparticles

Cited by 23 publications

References 30 publications

Understanding electrochemical switchability of perovskite-type exsolution catalysts

Understanding electrochemical switchability of perovskite-type exsolution catalysts

High energy surface x-ray diffraction applied to model catalyst surfaces at work

Niobium near-surface composition during nitrogen infusion relevant for superconducting radio-frequency cavities

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