Photostrictive Actuators Based on Freestanding Ferroelectric Membranes.

Complex oxides offer a wide range of functional properties, and recent advances in the fabrication of freestanding membranes of these oxides are adding new mechanical degrees of freedom to this already rich functional ecosystem. Here, photoactuation is demonstrated in freestanding thin film resonators of ferroelectric Barium Titanate (BaTiO3) and paraelectric Strontium Titanate (SrTiO3). The free-standing films, transferred onto perforated supports, act as nano-drums, oscillating at their natural resonance frequency when illuminated by a frequency-modulated laser. The light-induced deflections in the ferroelectric BaTiO3 membranes are two orders of magnitude larger than in the paraelectric SrTiO3 ones. Time-resolved X-ray micro-diffraction under illumination and temperature-dependent holographic interferometry provide combined evidence for the photostrictive strain in BaTiO3 originating from a partial screening of ferroelectric polarization by photo-excited carriers, which decreases the tetragonality of the unit cell. These findings showcase the potential of photostrictive freestanding ferroelectric films as wireless actuators operated by light.

In situ compression of micropillars under coherent X-ray diffraction: a case study of experimental and data-analysis constraints.

Micropillar compression is a method of choice to understand mechanics at small scale. It is mainly studied with electron microscopy or white-beam micro-Laue X-ray diffraction. The aim of the present article is to show the possibilities of the use of diffraction with a coherent X-ray beam. InSb micropillars in epitaxy with their pedestals (i.e. their support) are studied in situ during compression. Firstly, an experiment using a collimated beam matching the pillar size allows determination of when the sample enters the plastic regime, independently of small defects induced by experimental artefacts. A second experiment deals with scanning X-ray diffraction maps with a nano-focused beam; despite the coherence of the beam, the contributions from the pedestal and from the micropillar in the diffraction patterns can be separated, making possible a spatially resolved study of the plastic strain fields. A quantitative measurement of the elastic strain field is nevertheless hampered by the fact that the pillar diffracts at the same angles as the pedestal. Finally, no image reconstructions were possible in these experiments, either in situ due to a blurring of the fringes during loading or post-mortem because the defect density after yielding was too high. However, it is shown how to determine the elastic bending of the pillar in the elastic regime. Bending angles of around 0.3° are found, and a method to estimate the sample's radius of curvature is suggested.

Author Correction: Continuous scanning for Bragg coherent X-ray imaging.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Continuous scanning for Bragg coherent X-ray imaging.

We explore the use of continuous scanning during data acquisition for Bragg coherent diffraction imaging, i.e., where the sample is in continuous motion. The fidelity of continuous scanning Bragg coherent diffraction imaging is demonstrated on a single Pt nanoparticle in a flow reactor at [Formula: see text] in an Ar-based gas flowed at 50 ml/min. We show a reduction of 30% in total scan time compared to conventional step-by-step scanning. The reconstructed Bragg electron density, phase, displacement and strain fields are in excellent agreement with the results obtained from conventional step-by-step scanning. Continuous scanning will allow to minimise sample instability under the beam and will become increasingly important at diffraction-limited storage ring light sources.

In situ three-dimensional imaging of strain in gold nanocrystals during catalytic oxidation.

The chemical properties of materials are dependent on dynamic changes in their three-dimensional (3D) structure as well as on the reactive environment. We report an in situ 3D imaging study of defect dynamics of a single gold nanocrystal. Our findings offer an insight into its dynamic nanostructure and unravel the formation of a nanotwin network under CO oxidation conditions. In situ/operando defect dynamics imaging paves the way to elucidate chemical processes at the single nano-object level towards defect-engineered nanomaterials.

A Carboniferous Mite on an Insect Reveals the Antiquity of an Inconspicuous Interaction.

Symbiosis [1], understood as prolonged interspecific association, is as ancient as the eukaryotic cell [2, 3]. A variety of such associations have been reported in the continental fossil record, albeit sporadically. As for mites, which as a group have been present since the Devonian (ca. 390 mya) [4, 5] and are involved in a tremendous variety of modern-day symbioses, reported associations are limited to a few amber-preserved cases [6-11], with the earliest instance in the Cretaceous (ca. 85 mya) [11]. As a consequence, the antiquity and origin of associations involving small-sized mites and larger animals are poorly understood. Here we report, recovered from the Carboniferous Xiaheyan locality (ca. 320 mya), an oribatid mite located on the thorax of an extinct relative of grasshoppers, crickets, and katydids [12]. The mite was investigated using several methods, including phase-contrast tomography. The detailed morphological data allowed the placement of the mite in a new family within Mixonomata, whose fossil record is thus extended by ca. 250 Ma. Specimen and abundance distribution data derived from the fossil insect sample indicate that specimens from the corresponding excavation site were buried rapidly and were sub-autochthonous, indicating a syn vivo association. Moreover, the mite is located in a sequestered position on the insect. The observed interaction best fits the definition for phoresy, in which the benefit is transport and protection for the mite. This discovery demonstrates that this association, a trait shared by representatives of the most speciose mite taxa, arose very early during mite evolution.

Coherent x-ray imaging of collagen fibril distributions within intact tendons.

The characterization of the structure of highly hierarchical biosamples such as collagen-based tissues at the scale of tens of nanometers is essential to correlate the tissue structure with its growth processes. Coherent x-ray Bragg ptychography is an innovative imaging technique that gives high resolution images of the ordered parts of such samples. Herein, we report how we used this method to image the collagen fibrillar ultrastructure of intact rat tail tendons. The images show ordered fibrils extending over 10-20 µm in length, with a quantifiable D-banding spacing variation of 0.2%. Occasional defects in the fibrils distribution have also been observed, likely indicating fibrillar fusion events.

Translation position determination in ptychographic coherent diffraction imaging.

Accurate knowledge of translation positions is essential in ptychography to achieve a good image quality and the diffraction limited resolution. We propose a method to retrieve and correct position errors during the image reconstruction iterations. Sub-pixel position accuracy after refinement is shown to be achievable within several tens of iterations. Simulation and experimental results for both optical and X-ray wavelengths are given. The method improves both the quality of the retrieved object image and relaxes the position accuracy requirement while acquiring the diffraction patterns.

Coherent X-ray diffraction investigation of twinned microcrystals.

Coherent X-ray diffraction has been used to study pseudo-merohedrally twinned manganite microcrystals. The analyzed compositions were Pr(5/8)Ca(3/8)MnO(3) and La(0.275)Pr(0.35)Ca(3/8)MnO(3). The prepared loose powder was thermally attached to glass (and quartz) capillary walls by gentle heating to ensure positional stability during data collection. Many diffraction data sets were recorded and some of them were split as expected from the main observed twin law: 180° rotation around [101]. The peak splitting was measured with very high precision owing to the high-resolution nature of the diffraction data, with a resolution (Δd/d) better than 2.0 × 10(-4). Furthermore, when these microcrystals are illuminated coherently, the different crystallographic phases of the structure factors induce interference in the form of a speckle pattern. The three-dimensional speckled Bragg peak intensity distribution has been measured providing information about the twin domains within the microcrystals. Research is ongoing to invert the measured patterns. Successful phase retrieval will allow mapping out the twin domains and twin boundaries which play a key role in the physical properties.