Remote epitaxial crystalline perovskites for ultrahigh-resolution micro-LED displays
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Analyzing long-period structural evolution of biaxially stretched ultra-high molecular weight polyethylene films
Ultra-high molecular weight polyethylene (UHMWPE) films are widely used in high-performance applications due to their excellent mechanical properties. However, understanding the structural evolution, particularly the long-period structure under tensile fields, remains a challenge in both practical use and processing. Here, we investigate the long-period structural evolution of biaxially stretched UHMWPE films under tensile fields using time-resolved small-angle X-ray scattering. Our results reveal distinct changes in the long-period structure during the stretching process. Initially, the isotropic crystalline regions of UHMWPE align along the stretching direction, transitioning from a diffuse scattering pattern to an ellipsoidal one. As stretching progresses, fibrillar crystals form, dominating the scattering pattern with sharp, oriented features. In the later stages, fragmentation of the fibrillar structure leads to smaller crystalline regions and a butterfly-shaped scattering pattern due to rearranged lamellar structures. Based on these findings, we propose a new model that suggests a reverse transformation from fibrillar crystals to lamellar crystals, contrasting with the traditional “shish-kebab” model. The reduced crystallinity, as shown by differential scanning calorimetry data, further supports this structural transformation.
Fluorine-modified passivator for efficient vacuum-deposited pure-red perovskite light-emitting diodes
Vacuum-deposited perovskite light-emitting diodes (PeLEDs) have demonstrated significant potential for high-color-gamut active-matrix displays. Despite the rapid advance of green PeLEDs, red ones remain a considerable challenge because of the inferior photophysical properties of vacuum-deposited red-light-emitting materials. Here, a rationally designed fluorine-modified phosphine oxide additive was introduced to in-situ passivate vacuum-deposited perovskites. The highly polar 2-F-TPPO incorporated perovskite films demonstrated enhanced photoluminescence quantum yield (PLQY), suppressed defects, and improved crystallinity. When implemented as active layers in PeLEDs, an external quantum efficiency (EQE) of 12.6% with an emission wavelength of 640 nm is achieved, which was 6 times higher compared to the previously reported most efficient vacuum-deposited red PeLEDs (EQE below 2%). Our findings lay the foundations for the further exploration of high-performance vacuum-deposited PeLEDs toward full-color perovskite displays.
Accelerated symptom improvement in Parkinson’s disease via remote internet-based optimization of deep brain stimulation therapy: a randomized controlled multicenter trial
Deep brain stimulation (DBS) has emerged as an important therapeutic intervention for neurological and neuropsychiatric disorders. After initial programming, clinicians are tasked with fine-tuning DBS parameters through repeated in-person clinic visits. We aimed to evaluate whether DBS patients achieve clinical benefit more rapidly by incorporating remote internet-based adjustment (RIBA) of stimulation parameters into the continuum of care.
Surfactant-induced hole concentration enhancement for highly efficient perovskite light-emitting diodes
It is widely acknowledged that constructing small injection barriers for balanced electron and hole injections is essential for light-emitting diodes (LEDs). However, in highly efficient LEDs based on metal halide perovskites, a seemingly large hole injection barrier is usually observed. Here we rationalize this high efficiency through a surfactant-induced effect where the hole concentration at the perovskite surface is enhanced to enable sufficient bimolecular recombination pathways with injected electrons. This effect originates from the additive engineering and is verified by a series of optical and electrical measurements. In addition, surfactant additives that induce an increased hole concentration also significantly improve the luminescence yield, an important parameter for the efficient operation of perovskite LEDs. Our results not only provide rational design rules to fabricate high-efficiency perovskite LEDs but also present new insights to benefit the design of other perovskite optoelectronic devices.
Imaging molecular structures and interactions by enhanced confinement effect in electron microscopy
Atomic imaging of molecules and intermolecular interactions are of great significance for a deeper understanding of the basic physics and chemistry in various applications, but it is still challenging in electron microscopy due to their thermal mobility and beam sensitivity. Confinement effect and low-dose imaging method may efficiently help us achieve stable high-resolution resolving of molecules and their interactions. Here, we propose a general strategy to image the confined molecules and evaluate the strengths of host-guest interactions in three material systems by low-dose electron microscopy. Then, we change the guest molecules to analyze how each kind of interaction strength influences the imaging quality of these molecules by using a same parameter, the aspect ratios of imaged molecular projections. In the material systems of perovskites (ionic) and zeolites with adsorbed molecules (van der Waals), we can obtain a clear image of molecular configurations by enhancing host-guest interactions. Even in metal organic framework (coordination) system, the atomic structures and bonds of aromatics can be achieved. These results provide a general description on the relation between molecular images and interactions, making it possible to study more molecular behaviors in wide applications by real-space imaging.
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