As the brightness of GaN-based light-emitting diodes (LEDs) has increased, they have recently attracted considerable interest for use in full-color display panels, traffic signals, and solid-state lighting, because of their many advantages, such as long lifetime, small size, and low energy consumption. [1,2] In spite of these advantages, the overall external quantum efficiency, which depends on the internal quantum efficiency (IQE) and the light extraction efficiency (LEE), is still low in conventional In x Ga 1-x N/GaN quantum well (QW) structures. The IQE is strongly influenced by nonradiative recombination processes, by dislocations and other defects, and by separation of the electron and hole wave functions by spontaneous polarization and strain-induced piezoelectric polarization. The LEE is limited by the total internal reflection of generated light and successive re-absorption due to the high refractive index difference between LED structures and air. Recently, it has been suggested that surface plasmons (SPs), excited on a rough metallic surface by the interaction between light and metal, can significantly enhance light emission by improving the IQE. [3][4][5][6][7][8][9][10][11][12][13][14] Although it has been shown that SPs can significantly enhance the quantum efficiency of InGaN emitters, the realization of a GaN-based LED structure with QW-SP coupling has not yet been reported. Here, we demonstrate for the first time an SP-enhanced InGaN/GaN multiple quantum well (MQW) blue LED with a Ag nanoparticle layer inserted between the n-GaN layer and the MQW layer. SPs have attracted great interest because optical properties can be greatly enhanced by coupling between SPs and the QW in LEDs. The coupling of spontaneous emission from the QW into the SP mode can be observed due to the increased absorption at the SP frequency.[10] Time-resolved photoluminescence (TR-PL) measurements showed that the recombination rate in the QW was 90 times faster than spontaneous emission from the QW, when the emission was resonantly coupled to a SP. [11] Recently, Okamoto et al. [12] reported a 14-fold PL enhancement and a 6.8-fold IQE enhancement of InGaN QWs by QW-Ag coupling. Despite the significant enhancement of the IQE of InGaN emitters by SPs, the realization of a GaN-based LED structure with QW-SP coupling is yet to be reported. In previous optical studies [10][11][12] a metal layer was deposited on the surface of the InGaN QW structure together with a GaN spacer layer of thickness 10$12 nm for efficient QW-SP coupling, in order to observe the PL enhancement of the QW, because electron-hole pairs located within the near-field of the QW surface can couple to the SP mode. To realize SP-enhanced LEDs, the metal layer should be deposited on a p-type GaN/MQW structure and the thickness of that p-type GaN layer is critical for QW-SP coupling. The penetration depth of the SP fringing field into the semiconductor is given by Z ¼ l=2p½ð"where " 0 GaN and " 0 metal make up the real part of the dielectric constant of the semicond...

Monolayer (1L) transition metal dichalcogenides (TMDCs) are promising materials for nanoscale optoelectronic devices because of their direct band gap and wide absorption range (ultraviolet to infrared). However, 1L-TMDCs cannot be easily utilized for practical optoelectronic device applications (e.g., photodetectors, solar cells, and light-emitting diodes) because of their extremely low optical quantum yields (QYs). In this investigation, a high-gain 1L-MoS photodetector was successfully realized, based on the surface plasmon (SP) of the Ag nanowire (NW) network. Through systematic optical characterization of the hybrid structure consisting of a 1L-MoS and the Ag NW network, it was determined that a strong SP and strain relaxation effect influenced a greatly enhanced optical QY. The photoluminescence (PL) emission was drastically increased by a factor of 560, and the main peak was shifted to the neutral exciton of 1L-MoS. Consequently, the overall photocurrent of the hybrid 1L-MoS photodetector was observed to be 250 times better than that of the pristine 1L-MoS photodetector. In addition, the photoresponsivity and photodetectivity of the hybrid photodetector were effectively improved by a factor of ∼1000. This study provides a new approach for realizing highly efficient optoelectronic devices based on TMDCs.

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Flexible pulse sensors that can detect subtle skin surface deformation caused by arterial pulses are key components for developing non‐invasive continuous pulse waveform monitoring systems that provide vital health status parameters. Piezoelectric pulse sensors (PPSs) offer a promising solution for flexible pulse sensors due to their relatively high sensitivity and stability, and low power consumption, when compared with conventional active pulse sensors. However, the reported high‐performance PPSs contain toxic lead, which limits their practical applications. In this study, a highly sensitive and flexible PPS that detects surface deflections on the micrometer scale is fabricated with single‐crystalline group III‐nitride thin film. This biocompatible flexible PPS is sensitive enough to detect pulse waveform with detailed characteristic peaks from most arterial pulse sites when attached to the skin surface without applying external pressure. Useful physiological parameters such as the pulse rate, artery augmentation index, and pulse wave velocity can be drawn from the as‐acquired pulse waveforms. The flexible PPS can also be used to continuously monitor the arterial pulse waveform.

Accurate and continuous monitoring of eye movements using compact, low‐power‐consuming, and easily‐wearable sensors is necessary in personal and public health and safety, selected medical diagnosis techniques (point‐of‐care diagnostics), and personal entertainment systems. In this study, a highly sensitive, noninvasive, and skin‐attachable sensor made of a stable flexible piezoelectric thin film that is also free of hazardous elements to overcome the limitations of current computer‐vision‐based eye‐tracking systems and piezoelectric strain sensors is developed. The sensor fabricated from single‐crystalline III‐N thin film by a layer‐transfer technique is highly sensitive and can detect subtle movements of the eye. The flexible eye movement sensor converts the mechanical deformation (skin deflection by eye blinking and eyeball motion) with various frequencies and levels into electrical outputs. The sensor can detect abnormal eye flickering and conditions caused by fatigue and drowsiness, including overlong closure, hasty eye blinking, and half‐closed eyes. The abnormal eyeball motions, which may be the sign of several brain‐related diseases, can also be measured, as the sensor generates discernable output voltages from the direction of eyeball movements. This study provides a practical solution for continuous sensing of human eye blinking and eyeball motion as a critical part of personal healthcare, safety, and entertainment systems.

BackgroundGreater lymph node retrieval in gastric cancer improves staging accuracy and may improve survival from increased clearance of nodal micrometastasis. This retrospective cohort study investigated if more lymph nodes removed in gastric cancer increases survival and if such effect is stage-specific due to differential risks of nodal micrometastasis and systemic disease.MethodsThe prospectively collected database of curatively resected gastric cancer patients in National Cancer Center, South Korea between 2000 and 2009 was reviewed. Disease-free survival (DFS) and overall survival (OS) for all patients and for each stage according to number of lymph nodes examined (1–30, 31–45, > 45) were analyzed.ResultsOf 4049 patients, 96.6% and 98.4% underwent D2 (perigastric and extragastric) lymphadenectomy and had ≥ 15 lymph nodes examined. Mean number of nodes examined was 43. Five-year OS & DFS rates were 83.3% and 80.7%. Patients with > 45 nodes examined had significantly lower DFS (p = 0.002) and OS (p = 0.007) compared to those with 1–30 and 31–45 nodes. However, proportion of patients with > 45 nodes examined increased with stage (p = 0.0005). Per stage, there was no significant difference in DFS and OS according to number of nodes examined except for stage IIIA favoring more nodes (p = 0.018 and p = 0.044, respectively). Similar trend was seen in stage IIB. Number of examined nodes positively correlated with number of pathologic nodes for all patients (r = 0.144, p < .001) but not for stage IIB and IIIA. Number of nodes examined was a significant survival predictor in stage IIIA.ConclusionGreater lymph node harvest showed improved survival in intermediate-stage gastric cancer.Electronic supplementary materialThe online version of this article (10.1186/s12885-017-3872-6) contains supplementary material, which is available to authorized users.

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