We report highly efficient quantum dot light-emitting diodes (QLEDs) with TiO2 nanoparticles (NPs) as an alternative electron transport layer (ETL) and poly (methyl methacrylate) (PMMA) as an insulating layer. TiO₂ NPs were applied as ETLs of inverted structured QLEDs and the effect of the addition of PMMA between ETL and emission layer (EML) on device characteristics was studied in detail. A thin PMMA layer supported to make the charge balance in the EML of QLEDs due to its insulating property, which limits electron injection effectively. Green QLEDs with a PMMA layer produced the maximum luminance of 112,488 cd/㎡ and a current efficiency of 25.92 cd/A. We expect the extended application of TiO₂ NPs as the electron transport layer in inverted structured QLEDs device in the near future.

With the advent of the IoT (internet of things) era, there has been discussion on how to efficiently use various information from daily life. In academic and industrial society, various smart devices such as smart watches, smart phones, and smart glasses have been developed and commercialized for narrowing the physical/psychological distance with user information. According to recent developments of smart devices, the contemporary people have desired to check their body information and treat disease by themselves. According to the needs of the time, biological researches by phototherapy/monitoring have been actively conducted. Among various light sources, microLEDs have been spotlighted due to their superior optoelectric properties and stability. In this paper, we would like to review the state-of-the research results on the next-generation biological therapy devices via microLEDs.

Micro-LEDs can be applied to various parts of a product. However, it has disadvantages compared to general LEDs in large displays such as low efficiency, intensity, and contrast ratio, among others, owing to their short history of study. The simulations were carried out using ray-tracing software to investigate the change in light intensity and light distribution according to pattern shapes on the sapphire substrate of the flip-chip micro-LED (FC μ-LED) array. Three patterns-concave square patterns, convex square patterns, and Ag coated convex patterns-which existed on the opposite side of FC μ-LEDs (115 ㎛ × 115 ㎛) array, were applied. The intensity of FC μ-LEDs on the center of the receivers depends on the pattern depth with shape. The concave square patterns having FC μ-LEDs arrays show that decreasing intensity as the patterns depth. On the contrary, the convex square patterns having FC μ-LEDs arrays shows that increasing intensity as the patterns depth. In addition, the highest intensity shows that FC μ-LEDs having Ag-coated convex patterns on the opposite side of sapphire lead to a reduction in light crosstalk owing to the Ag film.

It was proven that the light outputs of blue GaN-based light-emitting diodes (LEDs) was seriously influenced by the application of external stress. We have simulated the wave function overlap of an electron and hole, which are significantly reduced by the development of stress. Consequently, its internal quantum efficiency decreased from 67.0% to 37.5%. To experimentally investigate the effect of stress, we designed and prepared a special zig system. By applying external tensile stress to compensate for the compressive stress innately developed in Blue LEDs, it was found that the optical output was greatly enhanced from 83.1 mcd to 117.2 mcd at a current of 100 mA, an increase of approximately 41%. In contrast, when the compressive stress is developed more by external compressive stress, we observed that the light output power was reduced from 89.0 mcd to 80.7 mcd, a decrease of approximately 9.3%.

In this paper, we fabricated flexible CNT/PVDF piezoelectric composite device by introducing CNTs (carbon nanotubes) into PVDF (poly-vinylidene fluoride) solution using spray coating technique. Flexible PEDOT:PSS conducting polymer was used as electrodes. We tried to improve the piezoelectric performance from the CNT/PVDF composite film by increasing the portion of the β-phase PVDF in the film. We confirmed the structural conformation of the CNT/PVDF composite film as a function of CNT concentration by using FT-IR (fourier transform infra-red). As increasing CNT concentration, portion of the β-phase PVDF and resulting piezoelectric performance increased in the CNT/PVDF composite film. We found that CNTs introduced were played as seeds for formation of the β-phase PVDF in the CNT/PVDF composite film and resulting improvement of the piezoelectric performance.

It was firstly found in 1st group element. Recently, it has been reported on the improvement ofefficiency of the OLEDs by introducing thin layer of some carbonate materials of alkali metal. In order toimprove the efficiency of OLEDs which is one of the next generation displays, we have studied the electricalcharacteristics of the device depending on the thickness ratio of the hole-injection layer to theelectron-injection layer. Teflon-AF was used as the hole-injection material, and alkali-metal carbonates ofLi2CO3 were used as the electron-injection materials. To obtain a proper thickness ratio, we manufactured. Fourtypes of devices with the thickness ratio of HIL to EIL were made to be 1 : 4, 2 : 3, 3 : 2, and 4 : 1. Theresults of electrical and optical properties showed that the device with the thickness ratio of 4 : 1 is the mostexcellent result. In addition, to prepare a four-layer device by inserting the α-NPD is a hole transportingmaterial was compared with three-layer element. As a result, the maximum luminance, the maximum luminousefficiency, maximum external quantum efficiency of about 124 [%], 164 [%], 106 [%] improve was confirmed.

We investigated the variation of anion exchange membrane of hydrogen generator of alkaline electrolysis. We detected the variation of elements and change of anion exchange membrane using EDS and FE-SEM. We detected two different sites of membrane because of different structure of membrane. Sp2 shows that the distribution ratio of C, 0, Al is 98% very higher than Sp2 of 78%. Especially, the main elements of STS316 which is P. S. Fe, Ni were more detected at Sp2 than Sp,. We think that this result depends on the structure of membrane. This also affect the resistance, lifetime of membrane and decrease the efficiency of hydrogen production. We hope that this article is a foundation of developing of hydrogen production technology.

The effect of co-sputtering condition on the structural properties of Mg_xZn_1-xO thin films grown by RF magnetron co-sputtering system was investigated for manufacturing UV LED. Mg_xZn_1-xO thin films were grown with ZnO and MgO target varying RF power. Structural properties were investigated by X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The Mg_xZn_1-xO thin films have sufficient crystallinity on the high ZnO power. The EDS analyzed showed that the Mg content in the Mg_xZn_1-xO films decreased from 3.99 to 24.27 at.% as the RF power of ZnO target increased. The Mg content in the Mg_xZn_1-xO films could be controlled by co-sputtering power.

The effect of co-sputtering condition on the structural properties of MgxZn1-xO thin films grown by RF magnetron co-sputtering system was investigated for manufacturing ZnO/MgZnO structure LED. MgxZn1-xO thin films were grown with ZnO and MgO target varying RF power. Structural properties were investigated by X-ray diffraction (XRD) and Energy dispersive spectroscopy (EDS). The ZnO thin films have sufficient crystallinity on the high RF power. As RF power of ZnO target increased, the contents of MgO in the MgxZn1-xO film decreased. LED was manufactured using ZnO/MgZnO multi-layer on p-GaN/Al2O3 substrate. Threshold voltage of multi-layer LED was appeared at 8 V, and it was luminesced at wave length of 550 nm.

In this study, a method to measure the thickness of thin film by EDS (energy dispersive spectroscopy) is suggested. We have developed a model which calculates the thickness of thin film from the characteristic x-ray intensity ratio of the elements in thin film and substrate by considering incident electron beam energy, x-ray generation curve, backscattering and absorption of x-ray, take-off angle of x-ray and tilt angle of the sample. We obtained the relation curve between the film thickness measured experimentally and the x-ray intensity ratio of elements. The film thicknesses calculated from the model agrees quite well with those measured experimentally. Therefore, the thin film thickness can be measured rapidly and accurately by using the model developed in this study and the x-ray intensity ratio obtained in EDS analysis.