ABSTRACT
InP/ZnSe/ZnS quantum dots (QDs) stand as promising candidates for advancing QD-organic light-emitting diodes (QLED), but low emission efficiency due to their susceptibility to oxidation impedes applications. Structural defects play important roles in the emission efficiency degradation of QDs, but the formation mechanism of defects in oxidized QDs has been less investigated. Here, we investigated the impact of diverse structural defects formation on individual QDs and propagation during UV-facilitated oxidation using high-resolution (scanning) transmission electron microscopy. UV-facilitated oxidation of the QDs alters shell morphology by the formation of surface oxides, leaving ZnSe surfaces poorly passivated. Further oxidation leads to the formation of structural defects, such as dislocations, and induces strain at the oxide-QD interfaces, facilitating In diffusion from the QD core. These changes in the QD structures result in emission quenching. This study provides insight into the formation of structural defects through photo-oxidation, and their effects on emission properties of QDs.
ABSTRACT
Elasto-inertial microfluidic separation offers many advantages including high throughput and separation resolution. Even though the separation efficiency highly depends on precise control of the flow conditions, no concrete guidelines have been reported yet in elasto-inertial microfluidics. Here, we propose a dimensionless analysis for precise estimation of the microsphere behaviors across the interface of Newtonian and viscoelastic fluids. Reynolds number, modified Weissenberg number, and modified elastic number are used to investigate the balance between inertial and elastic lift forces. Based on the findings, we introduce a new dimensionless number defined as the width of the Newtonian fluid stream divided by microsphere diameter. The proposed dimensionless analysis allows us to predict whether the microspheres migrate across the co-flow interface. The theoretical estimation is found to be in good agreement with the experimental results using 2.1- and 3.2-µm-diameter polystyrene microspheres in a co-flow of water and polyethylene oxide solution. Based on the theoretical estimation, we also realize submicron separation of the microspheres with 2.1 and 2.5 µm in diameter at high throughput, high purity (>95%), and high recovery rate (>97%). The applicability of the proposed method was validated by separation of platelets from similar-sized Escherichia coli (E.coli).
ABSTRACT
Indium gallium nitride (InGaN)-based micro-LEDs (µLEDs) are suitable for meeting ever-increasing demands for high-performance displays owing to their high efficiency, brightness and stability1-5. However, µLEDs have a large problem in that the external quantum efficiency (EQE) decreases with the size reduction6-9. Here we demonstrate a blue InGaN/GaN multiple quantum well (MQW) nanorod-LED (nLED) with high EQE. To overcome the size-dependent EQE reduction problem8,9, we studied the interaction between the GaN surface and the sidewall passivation layer through various analyses. Minimizing the point defects created during the passivation process is crucial to manufacturing high-performance nLEDs. Notably, the sol-gel method is advantageous for the passivation because SiO2 nanoparticles are adsorbed on the GaN surface, thereby minimizing its atomic interactions. The fabricated nLEDs showed an EQE of 20.2 ± 0.6%, the highest EQE value ever reported for the LED in the nanoscale. This work opens the way for manufacturing self-emissive nLED displays that can become an enabling technology for next-generation displays.
ABSTRACT
PURPOSE: The effects of creatine and exercise on chronic stress-induced depression are unclear. In the present study, we identified the effects of 4-week supplementation of creatine monohydrate and/or exercise on antidepressant behavior and raphe 5-HT expression in a chronic mild stress-induced depressed mouse model. METHODS: Seven-week-old male C57BL/6 mice (n=48) were divided randomly into 5 groups: (1) non-stress control (CON, n=10), (2) stress control (ST-CON, n=10), (3) stress and creatine intake (ST-Cr, n=10), (4) stress and exercise (ST-Ex, n=9), and (5) combined stress, exercise, and creatine intake (ST-Cr+Ex, n=9). After five weeks' treatment, we investigated using both anti-behavior tests (the Tail Suspension Test (TST) and the Forced Swimming Test (FST)), and 5-HT expression in the raphe nuclei (the dorsal raphe (DR) and median raphe (MnR)). RESULTS: Stress for 4 weeks significantly increased depressive behaviors in the mice. Treatment with creatine supplementation combined with exercise significantly decreased depressive behaviors as compared with the CON-ST group in both the TST and FST tests. With stress, 5-HT expression in the raphe nuclei decreased significantly. With combined creatine and exercise, 5-HT positive cells increased significantly and had a synergic effect on both DR and MnR. CONCLUSION: The present study found that even a single treatment of creatine or exercise has partial effects as an antidepressant in mice with chronic mild stress-induced depression. Furthermore, combined creatine and exercise has synergic effects and is a more effective prescription than a single treatment.
ABSTRACT
We studied the effects of high-intensity exercise (70-75% of VO2 max) combined with high-decibel music (100 dB) on cognitive function (measured by the Stroop test) and related blood flow changes to the prefrontal cortex (measured by Oxy-hemoglobin (Hb), Deoxy-Hb, tissue oxygen index (TOI), and normalized tissue hemoglobin index (nTHI)). The subjects of the study were 28 healthy female university students in their early 20s. Subjects were categorized into control group (CG), music group (MG), exercise group (Ex), and music and exercise group (MnEx). A crossover design was implemented so that all subjects participated in all test groups. We found no significant difference in reaction time between CG and MG for the neutral and incongruent tasks of Stroop test. However, there were significant improvements in the neutral and incongruent tasks for both the Ex (p < 0.01) and MnEx (p < 0.01) groups. Oxy-Hb measurements in the prefrontal cortex of the brain supported the Stroop test data. We found no difference between Ex and MnEx in the TOI; however, there was a significant decrease (p < 0.05) in MnEx compared to Ex. In addition, Ex resulted in a significant increase (p < 0.05) in nTHI as compared to CG. These results indicate that high decibel music could negatively affect prefrontal cortex activation of the brain during exercise.