Maskless photolithography based on ultraviolet micro-LEDs and direct writing method for improving pattern resolution.

Ultraviolet micro-LEDs show great potential as a light source for maskless photolithography. However, there are few reports on micro-LED based maskless photolithography systems, and the studies on the effects of system parameters on exposure patterns are still lacking. Hence, we developed a maskless photolithography system that employs micro-LEDs with peak wavelength 375 nm to produce micrometer-sized exposure patterns in photoresists. We also systematically explored the effects of exposure time and current density of micro-LED on static direct writing patterns, as well as the effects of stage velocity and current pulse width on dynamic direct writing patterns. Furthermore, reducing the size of micro-LED pixels enables obtaining high-resolution exposure patterns, but this approach will bring technical challenges and high costs. Therefore, this paper proposes an oblique direct writing method that, instead of reducing the micro-LED pixel size, improves the pattern resolution by changing the tilt angle of the sample. The experimental results show that the linewidths of the exposed lines decreased by 4.0% and 15.2%, respectively, as the sample tilt angle increased from 0° to 15° and 30°, which confirms the feasibility of the proposed method to improve the pattern resolution. This method is also expected to correct the exposure pattern error caused by optical distortion of the lens in the photolithography system. The system and method reported can be applied in various fields such as PCBs, photovoltaics, solar cells, and MEMS.

Temperature-dependent electroluminescence of red high-In-content MQWs of dual-wavelength micro-LED.

Temperature-dependent electroluminescence (TDEL) measurements have been employed to investigate the carrier transport and recombination processes of InGaN red micro-LED based on dual-wavelength InGaN/GaN MQWs structure. EL peak energy and carrier transport of the red micro-LED both show temperature dependence, due to temperature-induced changes in defect activation. In addition, the current density at which the blue peak of the low-In-content appears in the EL spectrum varies with temperature. As the temperature increases, the blue peak of the low In component tends to appear at higher current densities, which may be attributed to the increase in thermally activated defects hindering the injection of holes into the low-In-content MQWs further away from p-GaN. Furthermore, the IQEs of the high-In-content MQWs are estimated from the TDEL method and then reveal the temperature-dependent efficiency droop. The IQE decreases as temperature increases, particularly above 50 K, where it drops sharply due to temperature-dependent nonradiative recombination. And the two different variation trends in IQE of MQWs with high and low In content reveal a competitive mechanism in carrier distribution, implying that more escaping holes from high-In-content MQWs will further reduce red emission efficiency but enhance carrier injection and blue emission in low-In-content MQWs.

Ultrafast-Loaded Nickel Sulfide on Vertical Graphene Enabled by Joule Heating for Enhanced Lithium Metal Batteries.

The design and fabrication of a lithiophilic skeleton are highly important for constructing advanced Li metal anodes. In this work, a new lithiophilic skeleton is reported by planting metal sulfides (e.g., Ni3S2) on vertical graphene (VG) via a facile ultrafast Joule heating (UJH) method, which facilitates the homogeneous distribution of lithiophilic sites on carbon cloth (CC) supported VG substrate with firm bonding. Ni3S2 nanoparticles are homogeneously anchored on the optimized skeleton as CC/VG@Ni3S2, which ensures high conductivity and uniform deposition of Li metal with non-dendrites. By means of systematic electrochemical characterizations, the symmetric cells coupled with CC/VG@Ni3S2 deliver a steady long-term cycle within 14 mV overpotential for 1800 h (900 cycles) at 1 mA cm-2 and 1 mAh cm-2. Meanwhile, the designed CC/VG@Ni3S2-Li||LFP full cell shows notable electrochemical performance with a capacity retention of 92.44% at 0.5 C after 500 cycles and exceptional rate performance. This novel synthesis strategy for metal sulfides on hierarchical carbon-based materials sheds new light on the development of high-performance lithium metal batteries (LMBs).

Targeting ferroptosis by poly(acrylic) acid coated Mn3O4 nanoparticles alleviates acute liver injury.

Ferroptosis, a newly characterized form of regulated cell death, is induced by excessive accumulation of lipid peroxidation catalyzed by intracellular bioactive iron. Increasing evidence has suggested that ferroptosis is involved in the pathogenesis of several human diseases, including acute liver injury. Targeted inhibition of ferroptosis holds great promise for the clinical treatment of these diseases. Herein, we report a simple and one-pot synthesis of ultrasmall poly(acrylic) acid coated Mn3O4 nanoparticles (PAA@Mn3O4-NPs, PMO), which perform multiple antioxidant enzyme-mimicking activities and can scavenge broad-spectrum reactive oxygen species. PMO could potently suppress ferroptosis. Mechanistically, after being absorbed mainly through macropinocytosis, PMO are largely enriched in lysosomes, where PMO detoxify ROS, inhibit ferritinophagy-mediated iron mobilization and preserve mTOR activation, which collectively confer the prominent inhibition of ferroptosis. Additionally, PMO injection potently counteracts lipid peroxidation and alleviates acetaminophen- and ischaemia/reperfusion-induced acute liver injury in mice. Collectively, our results reveal that biocompatible PMO act as potent ferroptosis inhibitors through multifaceted mechanisms, which ensures that PMO have great translational potential for the clinical treatment of ferroptosis-related acute liver injury.

Size-dependent sidewall defect effect of GaN blue micro-LEDs by photoluminescence and fluorescence lifetime imaging.

Sidewall defects play a key role in determining the efficiency of GaN-based micro-light emitting diodes (LEDs) for next generation display applications, but there still lacks direct observation of defects-related recombination at the affected area. In this Letter, we proposed a direct technique to investigate the recombination mechanism and size effect of sidewall defects for GaN blue micro-LEDs. The results show that mesa etching will produce stress release near the sidewall, which can reduce the quantum confinement Stark effect (QCSE) to improve the radiative recombination. Meanwhile, the defect-related non-radiative recombination generated by the sidewall defects plays a leading role under low-power injection. In addition, the effective area of the mesas affected by the sidewall defects can be directly observed according to the fluorescence lifetime imaging microscope (FLIM) characterization. For example, the effective area of the mesa with 80 µm is affected by 23% while the entire area of the mesa with 10 µm is almost all affected. This study provides guidance for the analysis and repair of sidewall defects to improve the quantum efficiency of micro-LEDs display at low current density.

InGaN micro-LED array with integrated emission and detection functions for color detection application.

InGaN-based micro-LEDs can detect and emit optical signals simultaneously, owing to their overlapping emission and absorption spectra, enabling color detection. In this paper, we fabricated a green InGaN-based micro-LED array with integrated emission and detection functions. On the back side of the integrated device, when the 80 µm micro-LED emitted light, the 200 µm LED could receive reflected light to accomplish color detection. The spacing between the 80 µm and the 200 µm micro-LEDs was optimized to be 1 mm to reduce the effect of the direct light transmitted through the n-GaN layer without reflection. The integrated device shows good detection performance for different colors and skin colors, even in a dark environment. In addition, light can be emitted from the top side of the device. Utilization of light from both sides of the integrated device provides the possibility of its application in display, communication, and detection on the different sides.

Improvements of the modulation bandwidth and data rate of green-emitting CsPbBr3 perovskite quantum dots for Gbps visible light communication.

CsPbBr3 perovskite quantum dots (PQDs) as promising color conversion materials have been widely used in display and visible light communication (VLC), but most CsPbBr3 PQDs for VLC are randomly selected without optimization. Thereby the exploration of fundamental experimental parameters of QDs is essential to better employ their performance advantages. Herein, we investigated the concentration and solvent effects on photoluminescence (PL) properties and communication performance of CsPbBr3 PQDs. The PL, time-resolved PL characterization and communication measurements of CsPbBr3 PQDs all exhibit concentration dependence, suggesting that there exists an optimum concentration to take advantages of performance merits. CsPbBr3 PQDs with a concentration of 0.5 mg/ml show the shortest carrier lifetime and achieve the highest -3 dB bandwidth (168.03 MHz) as well as the highest data rate (660 Mbps) comparing to other concentrations. And in terms of the optimal concentration, we further explored the approach to improve the communication performance, investigating the effect of polarity solvent on the communication performance of CsPbBr3 PQDs. Original 0.5 mg/ml CsPbBr3 PQDs (1 ml) with 55 µL ethanol added in obtain a higher -3 dB bandwidth of 363.68 MHz improved by ∼116.4% and a record data rate of 1.25 Gbps improved by ∼89.4% but weaker PL emission due to energy transfer. The energy transfer assisted improvement may open up a promising avenue to improve the communication performance of QDs, but more feasible energy transfer path needs to be explored to ensure the stability of QDs.

ATM orchestrates ferritinophagy and ferroptosis by phosphorylating NCOA4.

Ferroptosis is a newly characterized form of programmed cell death, which is driven by the lethal accumulation of lipid peroxides catalyzed by the intracellular bioactive iron. Targeted induction of ferroptotic cell death holds great promise for therapeutic design against other therapy-resistant cancers. To date, multiple post-translational modifications have been elucidated to impinge on the ferroptotic sensitivity. Here we report that the Ser/Thr protein kinase ATM, the major sensor of DNA double-strand break damage, is indispensable for ferroptosis execution. Pharmacological inhibition or genetic ablation of ATM significantly antagonizes ferroptosis. Besides, ATM ablation-induced ferroptotic resistance is largely independent of its downstream target TRP53, as cells defective in both Trp53 and Atm are still more insensitive to ferroptotic inducers than the trp53 single knockout cells. Mechanistically, ATM dominates the intracellular labile free iron by phosphorylating NCOA4, facilitating NCOA4-ferritin interaction and therefore sustaining ferritinophagy, a selective type of macroautophagy/autophagy specifically degrading ferritin for iron recycling. Our results thus uncover a novel regulatory circuit of ferroptosis comprising ATM-NCOA4 in orchestrating ferritinophagy and iron bioavailability.Abbreviations: AMPK: AMP-activated protein kinase; ATM: ataxia telangiectasia mutated; BSO: buthionine sulphoximine; CDKN1A: cyclin-dependent kinase inhibitor 1A (P21); CQ: chloroquine; DFO: deferoxamine; DFP: deferiprone; Fer: ferrostatin-1; FTH1: ferritin heavy polypeptide 1; GPX4: glutathione peroxidase 4; GSH: glutathione; MEF: mouse embryonic fibroblast; NCOA4: nuclear receptor coactivator 4; PFTα: pifithrin-α; PTGS2: prostaglandin-endoperoxide synthase 2; Slc7a11: solute carrier family 7 member 11; Sul: sulfasalazine; TFRC: transferrin receptor; TRP53: transformation related protein 53.

Vertical stack integration of blue and yellow InGaN micro-LED arrays for display and wavelength division multiplexing visible light communication applications.

In this work, we demonstrated a convenient and reliable method to realize the vertical stack integration of the blue and yellow InGaN micro-LED arrays. The standard white and color-tunable micro-light sources can be achieved by adjusting the current densities injection of the micro-LEDs. The spectra cover violet, standard white, cyan, etc., showing an excellent color-tunable property. And the mixed standard white light can be separated into red-green-blue three primary colors through the color filters to realize full-color micro-LED display with a color gamut of 75% NTSC. Besides, the communication capability of the integrated micro-LED arrays as visible light communication (VLC) transmitters is demonstrated with a maximum total data rate of 2.35 Gbps in the wavelength division multiplexing (WDM) experimental set-up using orthogonal frequency division multiplexing modulation. In addition, a data rate of 250 Mbps is also realized with the standard white light using on-off keying (OOK) modulation. This integrated device shows great potential in full-color micro-LED display, color-tunable micro-light sources, and high-speed WDM VLC multifunctional applications.

Red, green and blue InGaN micro-LEDs for display application: temperature and current density effects.

Micro-LED has attracted tremendous attention as next-generation display, but InGaN red-green-blue (RGB) based high-efficiency micro-LEDs, especially red InGaN micro-LED, face significant challenges and the optoelectronic performance is inevitably affected by environmental factors such as varying temperature and operating current density. Here, we demonstrated the RGB InGaN micro-LEDs, and investigated the effects of temperature and current density for the InGaN RGB micro-LED display. We found that temperature increase can lead to the changes of electrical characteristics, the shifts in electroluminescence spectra, the increase of full width at half maximum and the decreases of light output power, external quantum efficiency, power efficiency, and ambient contrast ratios, while current density increase can also give rise to different changing trends of the varieties of parameters mentioned just above for the RGB micro-LED display, creating great challenges for its application in practical scenarios. Despite of the varying electrical and optical charateristics, relatively high and stable colour gamut of the RGB display can be maintained under changing temperature and current density. Based on the results above, mechanisms on the temperature and current density effects were analyzed in detail, which would be helpful to predict the parameters change of micro-LED display caused by temperature and current density, and provided guidance for improving the performance of InGaN micro-LED display in the future.

Full-color micro-LED display based on a single chip with two types of InGaN/GaN MQWs.

In this Letter, we have successfully realized the full-color micro-LED display on a single-chip utilizing multi-wavelength multi-quantum wells (MQWs). The epitaxial wafer used for micro-LED array chips is designed with two types of MQWs including In0.1Ga0.9N/GaN and In0.55Ga0.45N/GaN grown by metal-organic chemical vapor deposition (MOCVD). A single-chip broad-spectrum multi-wavelength emission from 620 to 450 nm can be realized by changing the injection current to realize the regulation of carrier injection in the MQWs with different emission wavelengths. And the full-color micro-LED display with uniform brightness can be achieved by adopting the pulse width modulation (PWM) to adjust the duty cycle of micro-LED pixels at different pulse voltages. We expect this study will provide a promising research direction for full-color micro-LED displays, thus effectively avoiding the problems caused during the massive transfer and color conversion.

4.0 Gbps visible light communication in a foggy environment based on a blue laser diode.

Fog has a strong attenuation effect on the optical channel, which will greatly degrade the performance of visible light communication (VLC). Studying the effect of the fog on communication performance is crucial to realize outdoor VLC for next generation networks, but there is little research on this topic. In this work, the transmission characteristics of visible light band in the foggy channel were measured and a high-speed VLC system based on a 450 nm blue laser diode (LD) and 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing (16-QAM-OFDM) in the artificial fog environment was demonstrated experimentally. Through a foggy channel of 60 cm, a maximum data rate of up to 4 Gbps was achieved at the pass loss of 13.06 dB with a bit error rate (BER) of 3.5 × 10-3 below the forward error correction (FEC) limit (3.8 × 10-3), which was the highest data rate ever reported for VLC in the foggy channel. Even at a higher pass loss of 17.32 dB, the proposed system still could achieve a data rate of 2.84 Gbps with a BER of 2.8 × 10-3. Further extending the distance to 16.9 m for a more practical application, a data rate of 2.0 Gbps was also demonstrated successfully.

2 Gbps free-space ultraviolet-C communication based on a high-bandwidth micro-LED achieved with pre-equalization.

In this Letter, we experimentally achieve high-speed ultraviolet-C (UVC) communication based on a 276.8 nm UVC micro-LED. A record ${-}{{3}}\;{\rm{dB}}$ optical bandwidth of 452.53 MHz and light output power of 0.854 mW at a current density of ${{400}}\;{\rm{A/c}}{{\rm{m}}^2}$ are obtained with a chip size of 100 µm. A UVC link over 0.5 m with a data rate of 2 Gbps is achieved using 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing and pre-equalization, and an extended distance over 3 m with a data rate of 0.82 Gbps is also presented. The demonstrated high-speed performance shows that micro-LEDs have great potential in the field of UVC communication.

Robotic-assisted versus laparoscopic cholecystectomy for benign gallbladder diseases: a systematic review and meta-analysis.

BACKGROUND: Robotic surgery, an emerging technology, has some potential advantages in many complicated endoscopic procedures compared with laparoscopic surgery. But robot-assisted cholecystectomy (RAC) is still a controversial issue on its comparative merit compared with conventional laparoscopic cholecystectomy (LC). The aim of this study was to evaluate the safety and efficacy of RAC compared with LC for benign gallbladder disease. METHODS: A systematic literature search was conducted using the PubMed, EMBASE, and Cochrane Library databases (from their inception to December 2017) to obtain comparative studies assessing the safety and efficacy between RAC and LC. The quality of the literature was assessed, and the data analyzed using R software, random effects models were applied. RESULTS: Twenty-six studies, including 5 RCTs and 21 NRCSs (3 prospective plus 18 retrospective), were included. A total of 4004 patients were included, of which 1833 patients (46%) underwent RAC and 2171 patients (54%) underwent LC. No significant differences were found in intraoperative complications, postoperative complications, readmission rate, hospital stay, estimated blood loss, and conversion rate between RAC and LC groups. However, RAC was related to longer operative time compared with LC (MD = 12.04 min, 95% CI 7.26-16.82) in RCT group, which was consistent with NRCS group; RAC also had a higher rate of incisional hernia in NRCS group (RR = 3.06, 95% CI 1.42-6.57), and one RCT reported that RAC was similar to LC (RR = 7.00, 95% CI 0.38-129.84). CONCLUSIONS: The RAC was not found to be more effective or safer than LC for benign gallbladder diseases, which indicated that RAC is a developing procedure instead of replacing LC at once. Given the higher costs, the current evidence is in favor of LC in cholecystectomy.

Synthesis of polymer-functionalized nanoscale graphene oxide with different surface charge and its cellular uptake, biosafety and immune responses in Raw264.7 macrophages.

Polymer-functionalized graphene oxide (GO) has superior properties such as large surface area, extraordinary mechanical strength, high carrier mobility, good stability in physiological media and low cytotoxicity, making it an attractive material for drug and gene delivery. Herein, we successfully synthesized GO with an average size of 168.3 nm by a modified Hummers' method. Branched polyethylenimine (PEI) and 6-armed polyethylene glycol (PEG) functionalized GO complexes (GO-PEI and GO-PEG) with different zeta potentials of 47.2 mV and -43.0 mV, respectively, were successfully synthesized through amide linkages between the COOH groups of GO and the NH2 groups of PEI and PEG. Then, the interactions between GO-PEI and GO-PEG complexes and Raw264.7 mouse monocyte-macrophage cells were investigated. The GO-PEI and GO-PEG complexes could both be internalized by Raw264.7 cells. However, compared with the GO-PEG complex, the GO-PEI complex showed higher intracellular delivery efficiency in Raw264.7 cells. Moreover, it was found that the GO-PEI complex not only gathered in endosomes but also in the cytoplasm, whereas GO-PEG gathered in endosomes only. The MTT tests showed that both GO-PEI and GO-PEG complexes exhibited very low cytotoxicity towards Raw264.7 cells when at a low concentration. The cellular immune response test demonstrated the GO-PEG complex enhanced the secretion of IL-6, illustrating it was more stimulus towards macrophage cells. The above results indicated that the GO-PEI complex, with a positive surface charge, demonstrated better potential to be used in effective drug and gene delivery.

Interactions between rGO/TNT nanocomposites and cells: Regulation of cell morphology, uptake, cytotoxicity, adhesion and migration.

Reduced graphene oxide/titanium dioxide nanotube (rGO/TNT) composites have superior properties, such as a large surface area, extraordinary mechanical strength, high carrier mobility, etc. However, the biosafety and biocompatibility of these composites, such as their influences on cell viability and cell functions, which are of paramount importance, are still not fully addressed. In this study, rGO/TNT nanocomposites were successfully synthesized through a modified hydrothermal treatment method. Then, the interactions between the rGO/TNT nanocomposites and Raw264.7 mouse monocyte-macrophage cells were further investigated. The results show that the rGO/TNT nanocomposites could be internalized by Raw264.7 cells and mainly gathered inside the cytoplasm. No rGO/TNT nanocomposites were observed in the nucleus. Moreover, the rGO/TNT nanocomposites exhibited low cytotoxicity toward Raw264.7 cells at a lower dose, though they may exhibit cytotoxicity to some extent at very high concentrations. In addition, the uptake of the nanocomposites influenced the cell cytoskeleton organization, while the cell adhesion and migration abilities were also impaired.