Phase transitions in halide perovskites critically influence their optoelectronic performance and stability, yet the nanoscale pathways by which structural transformations proceed remain elusive because of their soft ionic lattice and electron-beam sensitivity. Here, we combine in situ heating with four-dimensional scanning transmission electron microscopy (4D-STEM) to investigate the phase-transition dynamics in single CsPbBrxI3-x nanowires, from the non-perovskite to the perovskite phase, with nanometer spatial and millisecond temporal resolution. We directly visualize and track the real-time propagation of the perovskite phase front along a nanowire, while mapping local crystallographic order and diffuse scattering during the transition. The emergence of amorphous diffraction rings indicates a breakdown of long-range crystalline order, and with molecular dynamics simulations, we can conclude that local atomic coordination is preserved. More broadly, this work establishes a general framework for resolving phase transition pathways in beam-sensitive materials beyond halide perovskites, with implications for stabilizing functional phases for future applications.

Efficient and stable one-dimensional semiconductor nanowires are critical for the development of next-generation on-chip optoelectronics. Here, we report a synthetic approach to produce high-quality nanowires based on chalcogenide perovskite via a vapor phase reaction inside a sealed ampule. An epitaxial vapor-phase growth mechanism is proposed. The nanowires are shown to be single crystalline and highly structurally stable, with a preferential growth along the [010] direction. Red and green photoluminescence (PL) is observed from BaZrS3 and SrHfS3 nanowires, respectively, and the emission is shown to be tunable with varying compositions. PL lifetime is measured by fitting the decay curve with a biexponential model. The longer radiative recombination lifetime component is on the time scale of nanoseconds, indicating good nanowire sample quality with a promising potential for optoelectronic applications.

Transmission electron microscopy (TEM) is essential for determining atomic scale structures in structural biology and materials science. In structural biology, three-dimensional structures of proteins are routinely determined from thousands of identical particles using phase-contrast TEM. In materials science, three-dimensional atomic structures of complex nanomaterials have been determined using atomic electron tomography (AET). However, neither of these methods can determine the three-dimensional atomic structure of heterogeneous nanomaterials containing light elements. Here, we perform ptychographic electron tomography from 34.5 million diffraction patterns to reconstruct an atomic resolution tilt series of a double wall-carbon nanotube (DW-CNT) encapsulating a complex ZrTe sandwich structure. Class averaging the resulting tilt series images and subpixel localization of the atomic peaks reveals a Zr 11 Te 50 structure containing a previously unobserved ZrTe 2 phase in the core. The experimental realization of atomic resolution ptychographic electron tomography will allow for the structural determination of a wide range of beam-sensitive nanomaterials containing light elements.

Halide perovskite is a unique dynamical system, whose structural and chemical processes happening across different timescales have significant impact on its physical properties and device-level performance. However, due to its intrinsic instability, real-time investigation of the structure dynamics of halide perovskite is challenging, which hinders the systematic understanding of the chemical processes in the synthesis, phase transition, and degradation of halide perovskite. Here, we show that atomically thin carbon materials can stabilize ultrathin halide perovskite nanostructures against otherwise detrimental conditions. Moreover, the protective carbon shells enable atomic-level visualization of the vibrational, rotational, and translational movement of halide perovskite unit cells. Albeit atomically thin, protected halide perovskite nanostructures can maintain their structural integrity up to an electron dose rate of 10,000 e-/Å2·s while exhibiting unusual dynamical behaviors pertaining to the lattice anharmonicity and nanoscale confinement. Our work demonstrates an effective method to protect beam-sensitive materials during in situ observation, unlocking new solutions to study new modes of structure dynamics of nanomaterials.

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Journal Article Engineering Chiral Structures Through Strain Release: Electron Tomography Study of Twisted Nanowires Get access Xiaohui Song, Xiaohui Song The Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Alex Bruefach, Alex Bruefach Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Philipp M Pelz, Philipp M Pelz Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Hannah Devyldere, Hannah Devyldere Current affiliation: Thermo Fischer Scientific, Guilford, Connecticut, USA Search for other works by this author on: Oxford Academic Google Scholar Mary Scott Mary Scott The Molecular Foundry, Lawrence Berkeley National Lab, Berkeley, CA, USADepartment of Materials Science and Engineering, University of California, Berkeley, Berkeley, CA, USA Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 25, Issue S2, 1 August 2019, Pages 1804–1805, https://doi.org/10.1017/S1431927619009759 Published: 01 August 2019

Electron beams carrying orbital angular momentum (OAM), or electron vortex beams (EVBs), can be produced in a Transmission Electron Microscope (TEM) with forked diffraction gratings. l'2 Just as optical vortex beams can be used to trap and rotate particles, EVBs have been reported to transfer their OAM to a nanoparticle on a dry substrate and cause it to spin.3,4 However the results have not been reproduced, perhaps due to contact friction. It has been suggested that a more dramatic effect could be observed by imaging particles levitated in an optical trap or in a liquid environment.3,5,6 To reproduce these results and demonstrate a more pronounced response, we are performing experiments to transfer OAM from an EVB to a nanoparticle suspended in a fluid. TEM liquid cells consist of a liquid sample sealed against the vacuum of the standard TEM column between two electron-transparent windows. These cells have enabled the study of liquid samples at nanometer to atomic resolution and have applications in the study of microfluidics, electrochemical processes, and biological samples. Electron vortex beams could provide a useful new tool to manipulate nanoparticles and liquids themselves inside such cells. Here we describe an experimental investigation of EVB-induced rotation in a liquid and show that initial results are inconclusive. A theoretical consideration using the fluctuation-dissipation theorem suggests that, unlike in an optical trap, viscous forces and rotational Brownian motion may overwhelm the subtle torqueing effect the EVB has on the particle.

Liquid cells have made it possible to study samples in liquid at atomic resolution in the Transmission Electron Microscope (TEM). These cells consist of a liquid sample sealed against the vacuum of the standard TEM column between two electron transparent windows. Thus far, trapping and positioning particles has been demonstrated [1,2,3]. By changing the structure of the imaging probe, these capabilities can be expanded.