A 1300 mm2 Ultrahigh‐Performance Digital Imaging Assembly using High‐Quality Perovskite Single Crystals

By fine‐tuning the crystal nucleation and growth process, a low‐temperature‐gradient crystallization method is developed to fabricate high‐quality perovskite CH₃NH₃PbBr₃ single crystals with high carrier mobility of 81 ± 5 cm² V^?1 s^?1 (>3 times larger than their thin film counterpart), long carrier lifetime of 899 ± 127 ns (>5 times larger than their thin film counterpart), and ultralow trap state density of 6.2 ± 2.7 × 10⁹ cm^?3 (even four orders of magnitude lower than that of single‐crystalline silicon wafers). In fact, they are better than perovskite single crystals reported in prior work: their application in photosensors gives superior detectivity as high as 6 × 10¹³ Jones, ≈10–100 times better than commercial sensors made of silicon and InGaAs. Meanwhile, the response speed is as fast as 40 µs, ≈3 orders of magnitude faster than their thin film devices. A large‐area (≈1300 mm²) imaging assembly composed of a 729‐pixel sensor array is further designed and constructed, showing excellent imaging capability thanks to its superior quality and uniformity. This opens a new possibility to use the high‐quality perovskite single‐crystal‐based devices for more advanced imaging sensors.     

Real‐Time Tracking of Superparamagnetic Nanoparticle Self‐Assembly

The spontaneous self‐assembly process of superparamagnetic nanoparticles in a fast‐drying colloidal drop is observed in real time. The grazing‐incidence small‐angle X‐ray scattering (GISAXS) technique is employed for an in situ tracking of the reciprocal space, with a 3 ms delay time between subsequent frames delivered by a new generation of X‐ray cameras. A focused synchrotron beam and sophisticated sample oscillations make it possible to relate the dynamic reciprocal to direct space features and to localize the self‐assembly. In particular, no nanoparticle ordering is found inside the evaporating drop and near‐surface region down to a drop thickness of 90 µm. Scanning through the shrinking drop‐contact line indicates the start of self‐assembly near the drop three‐phase interface, in accord with theoretical predictions. The results obtained have direct implications for establishing the self‐assembly process as a routine technological step in the preparation of new nanostructures.     

Ptychographic X‐Ray Imaging of Colloidal Crystals

Ptychographic coherent X‐ray imaging is applied to obtain a projection of the electron density of colloidal crystals, which are promising nanoscale materials for optoelectronic applications and important model systems. Using the incident X‐ray wavefield reconstructed by mixed states approach, a high resolution and high contrast image of the colloidal crystal structure is obtained by ptychography. The reconstructed colloidal crystal reveals domain structure with an average domain size of about 2 µm. Comparison of the domains formed by the basic close‐packed structures, allows us to conclude on the absence of pure hexagonal close‐packed domains and confirms the presence of random hexagonal close‐packed layers with predominantly face‐centered cubic structure within the analyzed part of the colloidal crystal film. The ptychography reconstruction shows that the final structure is complicated and may contain partial dislocations leading to a variation of the stacking sequence in the lateral direction. As such in this work, X‐ray ptychography is extended to high resolution imaging of crystalline samples.     

Polymer‐Stabilized Micropixelated Liquid Crystals with Tunable Optical Properties Fabricated by Double Templating

Self‐organized nano‐ and microstructures of soft materials are attracting considerable attention because most of them are stimuli‐responsive due to their soft nature. In this regard, topological defects in liquid crystals (LCs) are promising not only for self‐assembling colloids and molecules but also for electro‐optical applications such as optical vortex generation. However, there are currently few bottom‐up methods for patterning a large number of defects periodically over a large area. It would be highly desirable to develop more effective techniques for high‐throughput and low‐cost fabrication. Here, a micropixelated LC structure consisting of a square array of topological defects is stabilized by photopolymerization. A polymer network is formed on the structure of a self‐organized template of a nematic liquid crystal (NLC), and this in turn imprints other nonpolymerizable NLC molecules, which maintains their responses to electric field and temperature. Photocuring of specific local regions is used to create a designable template for the reproducible self‐organization of defects. Moreover, a highly diluted polymer network (≈0.1 wt% monomer) exhibits instant on–off switching of the patterns. Beyond the mere stabilization of patterns, these results demonstrate that the incorporation of self‐organized NLC patterns offers some unique and unconventional applications for anisotropic polymer networks.     

Hierarchical nanostructures by sequential self-assembly of styrene-dimethylsiloxane block copolymers of different periods

Poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) block copolymers with a period as low as 13 nm have been self-assembled on a template formed from PS-b-PDMS of a 34–40 nm period, which is itself templated by micron-scale substrate features prepared using conventional lithography. This hierarchical process provides a simple method for directing the self-assembly of sub-10 nm features and registering them on the substrate.