Optical and electronic functionality arising from controlled defect formation in nanoscale complex oxide lateral epitaxy.

Epitaxial crystallization of complex oxides provides the means to create materials with precisely selected composition, strain, and orientation, thereby controlling their functionalities. Extending this control to nanoscale three-dimensional geometries can be accomplished via a three-dimensional analog of oxide solid-phase epitaxy, lateral epitaxial crystallization. The orientation of crystals within laterally crystallized SrTiO systematically changes from the orientation of the SrTiO substrate.

Cl alloying improves thermal stability and increases luminescence in iodine-rich inorganic perovskites.

The inorganic perovskite CsPbI shows promising photophysical properties for a range of potential optoelectronic applications but is metastable at room temperature. To address this, Br can be alloyed into the X-site to create compositions such as CsPbIBr that are stable at room temperature but have bandgaps >1.9 eV - severely limiting solar applications.

In-Operando Spatiotemporal Imaging of Coupled Film-Substrate Elastodynamics During an Insulator-to-Metal Transition.

The drive toward non-von Neumann device architectures has led to an intense focus on insulator-to-metal (IMT) and the converse metal-to-insulator (MIT) transitions. Studies of electric field-driven IMT in the prototypical VO thin-film channel devices are largely focused on the electrical and elastic responses of the films, but the response of the corresponding TiO substrate is often overlooked, since it is nominally expected to be electrically passive and elastically rigid. Here, in-operando spatiotemporal imaging of the coupled elastodynamics using X-ray diffraction microscopy of a VO film channel device on TiO substrate reveals two new surprises.

A soil-inspired dynamically responsive chemical system for microbial modulation.

Interactions between the microbiota and their colonized environments mediate critical pathways from biogeochemical cycles to homeostasis in human health. Here we report a soil-inspired chemical system that consists of nanostructured minerals, starch granules and liquid metals. Fabricated via a bottom-up synthesis, the soil-inspired chemical system can enable chemical redistribution and modulation of microbial communities.

High-resolution ptychographic imaging enabled by high-speed multi-pass scanning.

As a coherent diffraction imaging technique, ptychography provides high-spatial resolution beyond Rayleigh's criterion of the focusing optics, but it is also sensitively affected by the decoherence coming from the spatial and temporal variations in the experiment. Here we show that high-speed ptychographic data acquisition with short exposure can effectively reduce the impact from experimental variations. To reach a cumulative dose required for a given resolution, we further demonstrate that a continuous multi-pass scan via high-speed ptychography can achieve high-resolution imaging.

X-ray nanodiffraction imaging reveals distinct nanoscopic dynamics of an ultrafast phase transition.

SignificancePhase transitions, the changes between states of matter with distinct electronic, magnetic, or structural properties, are at the center of condensed matter physics and underlie valuable technologies. First-order phase transitions are intrinsically heterogeneous. When driven by ultrashort excitation, nanoscale phase regions evolve rapidly, which has posed a significant experimental challenge to characterize.

Rational design of mechanically robust Ni-rich cathode materials via concentration gradient strategy.

Mechanical integrity issues such as particle cracking are considered one of the leading causes of structural deterioration and limited long-term cycle stability for Ni-rich cathode materials of Li-ion batteries. Indeed, the detrimental effects generated from the crack formation are not yet entirely addressed. Here, applying physicochemical and electrochemical ex situ and in situ characterizations, the effect of Co and Mn on the mechanical properties of the Ni-rich material are thoroughly investigated.

Optical transient grating pumped X-ray diffraction microscopy for studying mesoscale structural dynamics.

A fundamental understanding of materials' structural dynamics, with fine spatial and temporal control, underpins future developments in electronic and quantum materials. Here, we introduce an optical transient grating pump and focused X-ray diffraction probe technique (TGXD) to examine the structural evolution of materials excited by modulated light with a precisely controlled spatial profile. This method adds spatial resolution and direct structural sensitivity to the established utility of a sinusoidal transient-grating excitation.

Wireless Optogenetic Modulation of Cortical Neurons Enabled by Radioluminescent Nanoparticles.

While offering high-precision control of neural circuits, optogenetics is hampered by the necessity to implant fiber-optic waveguides in order to deliver photons to genetically engineered light-gated neurons in the brain. Unlike laser light, X-rays freely pass biological barriers. Here we show that radioluminescent Gd(WO):Eu nanoparticles, which absorb external X-rays energy and then downconvert it into optical photons with wavelengths of ∼610 nm, can be used for the transcranial stimulation of cortical neurons expressing red-shifted, ∼590-630 nm, channelrhodopsin ReaChR, thereby promoting optogenetic neural control to the practical implementation of minimally invasive wireless deep brain stimulation.

Broadband X-ray ptychography using multi-wavelength algorithm.

Ptychography is a rapidly developing scanning microscopy which is able to view the internal structures of samples at a high resolution beyond the illumination size. The achieved spatial resolution is theoretically dose-limited. A broadband source can provide much higher flux compared with a monochromatic source; however, it conflicts with the necessary coherence requirements of this coherent diffraction imaging technique.

Understanding nanoscale structural distortions in Pb(ZrTi)O by utilizing X-ray nanodiffraction and clustering algorithm analysis.

Hard X-ray nanodiffraction provides a unique nondestructive technique to quantify local strain and structural inhomogeneities at nanometer length scales. However, sample mosaicity and phase separation can result in a complex diffraction pattern that can make it challenging to quantify nanoscale structural distortions. In this work, a k-means clustering algorithm was utilized to identify local maxima of intensity by partitioning diffraction data in a three-dimensional feature space of detector coordinates and intensity.

Multi-beam X-ray ptychography for high-throughput coherent diffraction imaging.

X-ray ptychography is a rapidly developing coherent diffraction imaging technique that provides nanoscale resolution on extended field-of-view. However, the requirement of coherence and the scanning mechanism limit the throughput of ptychographic imaging. In this paper, we propose X-ray ptychography using multiple illuminations instead of single illumination in conventional ptychography.

Bandgap tuning of two-dimensional materials by sphere diameter engineering.

Developing a precise and reproducible bandgap tuning method that enables tailored design of materials is of crucial importance for optoelectronic devices. Towards this end, we report a sphere diameter engineering (SDE) technique to manipulate the bandgap of two-dimensional (2D) materials. A one-to-one correspondence with an ideal linear working curve is established between the bandgap of MoS and the sphere diameter in a continuous range as large as 360 meV.

The Velociprobe: An ultrafast hard X-ray nanoprobe for high-resolution ptychographic imaging.

Motivated by the advanced photon source upgrade, a new hard X-ray microscope called "Velociprobe" has been recently designed and built for fast ptychographic imaging with high spatial resolution. We are addressing the challenges of high-resolution and fast scanning with novel hardware designs, advanced motion controls, and new data acquisition strategies, including the use of high-bandwidth interferometric measurements. The use of granite, air-bearing-supported stages provides the necessary long travel ranges for coarse motion to accommodate real samples and variable energy operation while remaining highly stable during fine scanning.

Homogenized halides and alkali cation segregation in alloyed organic-inorganic perovskites.

The role of the alkali metal cations in halide perovskite solar cells is not well understood. Using synchrotron-based nano-x-ray fluorescence and complementary measurements, we found that the halide distribution becomes homogenized upon addition of cesium iodide, either alone or with rubidium iodide, for substoichiometric, stoichiometric, and overstoichiometric preparations, where the lead halide is varied with respect to organic halide precursors. Halide homogenization coincides with long-lived charge carrier decays, spatially homogeneous carrier dynamics (as visualized by ultrafast microscopy), and improved photovoltaic device performance.

Evolution of a Novel Ribbon Phase in Optimally Doped BiSrCaCuO at High Pressure and Its Implication to High- T Superconductivity.

One challenge in studying high-temperature superconductivity (HTSC) stems from a lack of direct experimental evidence linking lattice inhomogeneity and superconductivity. Here, we apply synchrotron hard X-ray nanoimaging and small-angle scattering to reveal a novel micron-scaled ribbon phase in optimally doped BiSrCaCuO (Bi-2212, with δ = 0.1).

Defect-engineered epitaxial VO in strain engineering of heterogeneous soft crystals.

The success of strain engineering has made a step further for the enhancement of material properties and the introduction of new physics, especially with the discovery of the critical roles of strain in the heterogeneous interface between two dissimilar materials (for example, FeSe/SrTiO). On the other hand, the strain manipulation has been limited to chemical epitaxy and nanocomposites that, to a large extent, limit the possible material systems that can be explored. By defect engineering, we obtained, for the first time, dense three-dimensional strongly correlated VO epitaxial nanoforest arrays that can be used as a novel "substrate" for dynamic strain engineering, due to its metal-insulator transition.

Quantitative Observation of Threshold Defect Behavior in Memristive Devices with Operando X-ray Microscopy.

Memristive devices are an emerging technology that enables both rich interdisciplinary science and novel device functionalities, such as nonvolatile memories and nanoionics-based synaptic electronics. Recent work has shown that the reproducibility and variability of the devices depend sensitively on the defect structures created during electroforming as well as their continued evolution under dynamic electric fields. However, a fundamental principle guiding the material design of defect structures is still lacking due to the difficulty in understanding dynamic defect behavior under different resistance states.

Correlated High-Pressure Phase Sequence of VO under Strong Compression.

Understanding how the structures of a crystal behave under compression is a fundamental issue both for condensed matter physics and for geoscience. Traditional description of a crystal as the stacking of a unit cell with special symmetry has gained much success on the analysis of physical properties. Unfortunately, it is hard to reveal the relationship between the compressed phases.

Diamond anvil cell behavior up to 4 Mbar.

The diamond anvil cell (DAC) is considered one of the dominant devices to generate ultrahigh static pressure. The development of the DAC technique has enabled researchers to explore rich high-pressure science in the multimegabar pressure range. Here, we investigated the behavior of the DAC up to 400 GPa, which is the accepted pressure limit of a conventional DAC.

Thermal Fluctuations of Ferroelectric Nanodomains in a Ferroelectric-Dielectric PbTiO_{3}/SrTiO_{3} Superlattice.

Ferroelectric-dielectric superlattices consisting of alternating layers of ferroelectric PbTiO_{3} and dielectric SrTiO_{3} exhibit a disordered striped nanodomain pattern, with characteristic length scales of 6 nm for the domain periodicity and 30 nm for the in-plane coherence of the domain pattern. Spatial disorder in the domain pattern gives rise to coherent hard x-ray scattering patterns exhibiting intensity speckles. We show here using variable-temperature Bragg-geometry x-ray photon correlation spectroscopy that x-ray scattering patterns from the disordered domains exhibit a continuous temporal decorrelation due to spontaneous domain fluctuations.

Photon Transport in One-Dimensional Incommensurately Epitaxial CsPbX Arrays.

One-dimensional nanoscale epitaxial arrays serve as a great model in studying fundamental physics and for emerging applications. With an increasing focus laid on the Cs-based inorganic halide perovskite out of its outstanding material stability, we have applied vapor phase epitaxy to grow well aligned horizontal CsPbX (X: Cl, Br, or I or their mixed) nanowire arrays in large scale on mica substrate. The as-grown nanowire features a triangular prism morphology with typical length ranging from a few tens of micrometers to a few millimeters.

Enamel ribbons, surface nodules, and octacalcium phosphate in C57BL/6 mice and lyonization.

Background: Amelogenin is required for normal enamel formation and is the most abundant protein in developing enamel.

Methods: , , and molars and incisors from C57BL/6 mice were characterized using RT-PCR, Western blotting, dissecting and light microscopy, immunohistochemistry (IHC), transmission electron microscopy (TEM), scanning electron microscopy (SEM), backscattered SEM (bSEM), nanohardness testing, and X-ray diffraction.

Results: No amelogenin protein was detected by Western blot analyses of enamel extracts from mice.