Superior structural, physical and electronic properties make ferroelectric nanocrystals essential in enabling a range of next-generation devices. Ferroelectric responses are determined by crystal structure and domain morphology. The ability to reversibly displace, create and annihilate elastic domains is critical to device applications. Whereas electric-field control has been demonstrated for ferroelectric 180° surface domain walls and vortices, similar control of ferroelastic domains and domain boundaries This article is protected by copyright. All rights reserved. 2 within individual nanocrystals remains challenging. Using controlled external compressive and tensile axial stress, deterministic and reversible control of highly mobile ferroelastic domains and axial polarization in three dimensions is demonstrated. While many studies exist on ferroelastic domains in thin films and bulk, little is known about ferroelastic interactions at the single nanoparticle level, especially involving domain boundaries. Through combining Bragg coherent X-ray diffractive imaging and Landau theory, strain gradients in individual BaTiO 3 nanocrystals are shown to stabilize needlelike ferroelastic twin domains. These domains are highly labile under applied axial stress, producing a locally enhanced electric polarization mediated by a ferroelectric phase transition. The efficacy of Bragg coherent X-ray diffractive imaging in studying in operando domains in three-dimensions is demonstrated, while synergy with theory provides a paradigm for domain boundary engineering and potential for nanoscale functional devices.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

Simultaneously non-destructive, high resolution, and label-free imaging are of paramount importance for studies of complex biological systems, from viruses to cell cultures. Electron imaging techniques achieve extreme resolution but require slicing the sample to obtain volumetric information. On the other hand, X-rays’ high penetrative ability combined with cryogenic temperatures allows access to high resolution while preserving the sample’s structure. However, both X-ray and electron techniques do not currently allow label-free imaging with tissue specificity. Here, we combine a polarimetric approach with coherent diffractive imaging to reveal new ways to overcome this by mapping variations of anisotropy in the complex refractive index of cellular structures to differentiate between various tissues without chemical labeling. In this article, we demonstrate imaging of cancer-associated fibroblasts using birefringent coherent diffractive imaging with enhanced sensitivity to fibrous structures and their orientation as well as the possibility to differentiate the nucleus of the cell. We also propose a modeled soft X-ray experiment on the SARS-CoV-2 virus to address the possibility of leveraging the polarimetric birefringent contrast to spatially resolve the dynamical interaction of the virus with its host environment. We hope that our approach can open up avenues in the future to map and understand how SARS viruses bind with human epithelial cells.

Defects in strongly correlated materials such as V2O3 play influential roles on their electrical properties. Understanding the defects’ structure is of paramount importance. In this project, we investigate defect structures...

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