Quantum-dot light-emitting diodes (QLEDs) with high brightness have potential application in lighting and display. The high brightness is realized at high current density (J). However, at high J, the efficiency drops significantly, thereby limiting the achievable brightness. This notorious phenomenon has been known as efficiency roll-off, which is likely caused by the Auger- and/or thermal-induced emission quenching. In this work, we show that the Joule heat generated during device operation significantly affects the roll-off characteristics of QLEDs. To realize ultrabright and efficient QLEDs, the thermal stability of QDs is improved by replacing the conventional oleic acid ligands with 1-dodecanethiol. By further using a substrate with high thermal conductivity, the Joule heat generated at high J is effectively dissipated. Because of the effective thermal management, thermal-induced emission quenching is significantly suppressed, and consequently, the QLEDs exhibit a high external quantum efficiency (EQE) of 16.6%, which is virtually droop-free over a wide range of brightness (e.g., EQE = 16.1% @ 105 cd/m2 and 140 mA/cm2). Moreover, due to the reduced efficiency roll-off and enhanced heat dissipation, the demonstrated QLEDs can be operated at a very high J up to 3885 mA/cm2, thus enabling the devices to exhibit a record-high brightness of 1.6 × 106 cd/m2 and a lumen density of 500 lm/cm2. Our work demonstrates the significance of thermal management for the development of droop-free and ultrabright QLED devices for a wide variety of applications including lighting, transparent display, projection display, outdoor digital signage, and phototherapy.

Layered double hydroxide (LDH) materials, especially metal–organic framework (MOF)-derived LDHs, have attracted much attention in electrochemical capacitor applications. However, the construction of porous three-dimensional microsphere architectures with controlled morphology is highly demanded for high-performance supercapacitor electrodes. Thus, a simple and effective strategy is recommended to design and fabricate the well-defined layered structure of LDHs with high performance. In this study, we demonstrate the synthesis of nickel–cobalt-LDHs (NiCo-LDHs) by in-situ etching of the Ni-MOF template at different hydrolysis times. Based on the different characterization results of the sample, a formation mechanism has been proposed in terms of the proton production rate and etching process. As a result of the disparity in the layered structure and the surface area, the electrochemical behavior of the NiCo-LDHs has been altered. The sample NiCo-LDH/10 (prepared after the 10 h reaction) exhibited a high surface area and the large size of LDH sheets on microspheres, which promoted the rapid electrolyte ion transportation for supercapacitors and displayed a maximum specific capacity of 1272 C g–1 at 2 A g–1. In addition, the assembled asymmetric supercapacitor delivered a remarkable energy density of 36.1 Wh kg–1 with an outstanding cyclic stability (103.9% after 5000 cycles). This work establishes an effective strategy to synthesize a well-defined NiCo-LDH structure from the MOF template toward high-performance asymmetric supercapacitors, which could be extended to large-scale preparation of other transition metal-based LDHs from Ni-MOFs.

The presence of oxygen functional groups in GO enhances the charge storage behavior of Ce-MOF/GO composites for use as supercapacitor electrode materials.

The increasing population of the elderly and motion-impaired people brings a huge challenge to our social system. However, the walking stick as their essential tool has rarely been investigated into its potential capabilities beyond basic physical support, such as activity monitoring, tracing, and accident alert. Here, we report a walking stick powered by ultralow-frequency human motion and equipped with deep-learningenabled advanced sensing features to provide a healthcaremonitoring platform for motion-impaired users. A linear-torotary structure is designed to achieve highly efficient energy harvesting from the linear motion of a walking stick with ultralow frequency. Besides, two kinds of self-powered triboelectric sensors are proposed and integrated to extract the motion features of the walking stick. Augmented sensing functionalities with high accuracies have been enabled by deep-learningbased data analysis, including identity recognition, disability evaluation, and motion status distinguishing. Furthermore, a selfsustainable Internet of Things (IoT) system with global positioning system tracing and environmental temperature and humidity amenity sensing functions is obtained. Combined with the aforementioned functionalities, this walking stick is demonstrated in various usage scenarios as a caregiver for real-time well-being status and activity monitoring. The caregiving walking stick shows the potential of being an intelligent aid for motion-impaired users to help them live life with adequate autonomy and safety.

No abstract

Controllable degradation and excellent biocompatibility during/after a lifetime endow emerging transient electronics with special superiority in implantable biomedical applications. Currently, most of these devices need external power sources, limiting their real-world utilizations. Optimizing existing bioresorbable electronic devices requires natural-material-based construction and, more importantly, diverse or even all-in-one multifunctionalization. Herein, silk-based implantable, biodegradable, and multifunctional systems, self-powered with transient triboelectric nanogenerators (T ENGs), for real-time in vivo monitoring and therapeutic treatments of epileptic seizures, are reported. These T ENGs are of customizable in vitro/in vivo operating life and biomechanical sensitivity via the adjustments of silk molecular size, surface structuralization, and device configuration. Functions, such as drug delivery and structural-integrity optical readout (parallel to electronic signals), are enabled for localized anti-infection and noninvasive degradation indication, respectively. A proof-of-principle wireless system is built with mobile-device readout and "smart" treatment triggered by specific symptoms (i.e., epilepsy), exhibiting the practical potential of these silk T ENGs as self-powered, transient, and multifunctional implantable bioelectronic platforms.

We show that accurate sheet resistance measurements on small samples may be performed using microfour-point probes without applying correction factors. Using dual configuration measurements, the sheet resistance may be extracted with high accuracy when the microfour-point probes are in proximity of a mirror plane on small samples with dimensions of a few times the probe pitch. We calculate theoretically the size of the "sweet spot," where sufficiently accurate sheet resistances result and show that even for very small samples it is feasible to do correction free extraction of the sheet resistance with sufficient accuracy. As an example, the sheet resistance of a 40 m ͑50 m͒ square sample may be characterized with an accuracy of 0.3% ͑0.1%͒ using a 10 m pitch microfour-point probe and assuming a probe alignment accuracy of Ϯ2.5 m.

Abstract:We introduce a versatile, robust, and integrated technique to selectively fill fluid into a desired pattern of air holes in a photonic crystal fiber (PCF). Focused ion beam (FIB) is used to efficiently mill a microchannel on the end facet of a PCF before it is spliced to a single-mode fiber (SMF). Selected air holes are therefore exposed to the atmosphere through the microchannel for fluid filling. A low-loss in-line tunable optical hybrid fiber device is demonstrated by using such a technique. ©2011 Optical Society of America