Visible Color Tunable Emission in Three-Dimensional Light Emitting Diodes by MgO Passivation of Pyramid Tip

Kim, Ji-Hyun,Ye, Byeong Uk,Park, Joonmo,Yoo, Chul Jong,Kim, Buem Joon,Jeong, Hu Young,Hur, Jin-Hoe,Kim, Jong Kyu,Lee, Jong-Lam,Baik, Jeong Min American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.50

<P>We demonstrated visible color tunable three-dimensional (3D) pyramidal light emitting diodes by depositing the MgO on and near the tip of the pyramid as an insulating layer. Here, we show that the degradation of the materials (i.e., <I>p</I>-GaN) crystallinity and the built-in electric field due to the nanoscale geometry of the tip region is responsible for the large leakage current observed in LEDs. Confocal scanning electroluminescence microscopy images clearly showed that the intensity of the light emitted out of the side facet of the pyramid is much higher than that of the light extracted out of the tip surface, indicating that the MgO layer prohibited the carrier injection to the MQWs layer, suppressing the leakage occurring at or near the tip region of the pyramids. The color range of the LEDs can be also tuned by using the MgO layer, a blue-shift by 10.3 nm in the wavelength. This technique is simple and scalable, providing a promising solution for developing 3D pyramidal LEDs with low leakage current and controllable light emission.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-50/acsami.5b08729/production/images/medium/am-2015-08729j_0001.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b08729'>ACS Electronic Supporting Info</A></P>

Simulation Based Investigation of Focusing Phased Array Ultrasound in Dissimilar Metal Welds

Kim, Hun-Hee,Kim, Hak-Joon,Song, Sung-Jin,Kim, Kyung-Cho,Kim, Yong-Buem Korean Nuclear Society 2016 Nuclear Engineering and Technology Vol.48 No.1

Flaws at dissimilar metal welds (DMWs), such as reactor coolant systems components, Control Rod Drive Mechanism (CRDM), Bottom Mounted Instrumentation (BMI) etc., in nuclear power plants have been found. Notably, primary water stress corrosion cracking (PWSCC) in the DMWs could cause significant reliability problems at nuclear power plants. Therefore, phased array ultrasound is widely used for inspecting surface break cracks and stress corrosion cracks in DMWs. However, inspection of DMWs using phased array ultrasound has a relatively low probability of detection of cracks, because the crystalline structure of welds causes distortion and splitting of the ultrasonic beams which propagates anisotropic medium. Therefore, advanced evaluation techniques of phased array ultrasound are needed for improvement in the probability of detection of flaws in DMWs. Thus, in this study, an investigation of focusing and steering phased array ultrasound in DMWs was carried out using a time reversal technique, and an adaptive focusing technique based on finite element method (FEM) simulation. Also, evaluation of focusing performance of three different focusing techniques was performed by comparing amplitude of phased array ultrasonic signals scattered from the targeted flaw with three different time delays.

Microstructure and mechanical properties of the as-cast and warm rolled Mg-9Li-x(Al-Si)-yTi alloys with x = 1, 3, 5 and y = 0.05 wt.%

Kim, JeongTae,Jeong, Hae Joon,Moon, Yeabin,Kim, Ki Buem,Son, Hyeon Taech,Jeon, Changwoo,Sim, Jae Won,Moon, Sudong,Park, Jin Man Elsevier 2017 Journal of alloys and compounds Vol.711 No.-

<P><B>Abstract</B></P> <P>The as-cast Mg-9Li alloys with difference Al-Si addition were fabricated using induction casting method under the argon atmosphere and then warm rolling process was performed at 473 K. The Al-Si addition to Mg-9Li alloy leads to the formation of Mg<SUB>2</SUB>Si intermetallic compounds and microstructural evolutions such as increased volume fraction of α-Mg phases and changed morphology of α-Mg primary phase on the as-cast specimens. Moreover, the addition of 0.05 wt.% Ti elements on Mg-9Li-3(Al-Si) alloy raised the further microstructural evolutions, e.g. volume fraction of α-Mg phases, which bring about change in the microstructure after warm rolling process. The effects of this micro alloying influences the formation of fine microstructure after warm rolling process, which is the main factor in determining the mechanical properties. With these microstructural evolutions, tensile strength was increased from 101.71 MPa to 247.41 MPa by the minor alloying and warm rolling process. Moreover, the remarkably enhanced strength of Mg-9Li-3(Al-Si) alloy was the results of the addition of 0.05 wt.% Ti from 247 MPa to 412 MPa. Furthermore, the warm press-forming tests were carried out at 523 K to evaluate the applicability of this novel alloy for commercial products.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The as-rolled microstructure is distinctly alternated by minor alloying of Al, Si, and Ti. </LI> <LI> The Al-Si added Mg-9Li-based alloy indeed shows a highly increased strength and elongation. </LI> <LI> The Ti containing alloy with 0.05 wt.% shows the highest tensile strength of 412 MPa. </LI> <LI> This novel Mg-9Li-based alloy is capable of near-net shaping via simple press forming process. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of Reflective P-Type Ohmic Contact on Thermal Reliability of Vertical InGaN/GaN LEDs

손준호,Yang Hee Song,Buem Joon Kim,이종람 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.6

We report on the enhanced thermal reliability of vertical-LEDs (VLEDs) using novel reflective p-type ohmic contacts with good thermal stability. The reflective p-type ohmic contacts with Ni/Ag-Cu alloy multi-layer structure shows low contact resistivity, as low as 9.3 × 10−6 Ωcm2, and high reflectance of 86% after annealing at 450°C. The VLEDs with Ni/Ag-Cu alloy multi-layer structure show good thermal reliability with stress time at 300°C in air ambient. The improved thermal stability of the reflective ohmic contacts to p-type GaN is believed to play a critical role in the thermal reliability of V-LEDs.

Design Rule of Nanostructures in Light‐Emitting Diodes for Complete Elimination of Total Internal Reflection

Son, Jun Ho,Kim, Jong Uk,Song, Yang Hee,Kim, Buem Joon,Ryu, Chul Jong,Lee, Jong‐,Lam WILEY‐VCH Verlag 2012 Advanced Materials Vol.24 No.17

<P><B>Cone‐shaped nanostructures with controllable side‐wall angle</B> are success‐ fully fabricated with a SiO<SUB>2</SUB> nanosphere lithography (NSL) etching mask. Vertical LEDs with cone‐shaped nanostructures with a 24.1° side‐wall angle provide 6% more light output power compared to those using hexagonal pyramids formed by photochemical etching. This achievement is attributed to effective elimination of total internal reflection by angle‐controlled nanostructures.</P>

Enhancement of wall-plug efficiency in vertical InGaN/GaN LEDs by improved current spreading.

Son, Jun Ho,Kim, Buem Joon,Ryu, Chul Jong,Song, Yang Hee,Lee, Hwan Keon,Choi, Joo Won,Lee, Jong-Lam Optical Society of America 2012 Optics express Vol.20 No.2

<P>We present the enhancement of wall-plug efficiency in vertical InGaN/GaN light-emitting diodes (V-LEDs) by improved current spreading with a novel Al2O3 current blocking layer (CBL). The Al2O3 CBL deposited by electron-beam evaporation shows high transmittance and good corrosion resistance to acidic solutions. V-LEDs with an Al2O3 CBL show similar light output power but lower forward voltage as compared to those with a SiO2 CBL deposited by plasma-enhanced chemical vapor deposition. As a result, the wall-plug efficiency of V-LEDs with an Al2O3 CBL at 500 mA was improved by 5% as compared to those with a SiO2 CBL, and by 19% as compared to those without a CBL.</P>

Lipopolysaccharide/D-Galactosamine에 의해 유도된 급성 간 손상 생쥐모델에서 굴가수분해물의 간 보호 효과

류지현(Ji Hyeon Ryu),김은진(Eun-Jin Kim),Chengliang Xie,Marie Merci Nyiramana,Adrian S. Siregar,박시향(Si-Hyang Park),조수범(Soo Buem Cho),송대현(Dae Hyun Song),김남길(Nam-Gil Kim),최영준(Yeung Joon Choi),강상수(Sang Soo Kan 한국식품영양과학회 2017 한국식품영양과학회지 Vol.46 No.6

산화스트레스와 염증은 간 손상의 진행과정에 중요한 인자로 작용한다. 굴가수분해물의 항산화 및 항염증 활성은 지질대사, 혈압 및 혈당, 면역기능의 조절과 같은 다양한 기능에 관여한다. 그러나 급성 간 손상 모델에서 굴가수분해물의 효과를 확인한 연구 결과는 아직 확인된 바 없다. 본 연구는 LPS/D-GalN에 의해 유도된 급성 간 손상 생쥐 모델에서 굴가수분해물의 효과를 확인하기 위해 수행되었다. 실험군은 대조군(생리식염수), LPS/D-GalN 간 손상군, LPS/DGalN과 굴가수분해물(100 mg/kg, 200 mg/kg, 400 mg/kg)의 병합투여군 및 LPS/D-GalN과 silymarin(25 mg/kg) 병합투여군으로 나누었다. 급성 간 손상 모델은 1 μg/kg의 LPS와 400 mg/kg의 D-GalN으로 유도되었다. 먼저 시료의 항산화 및 항염증 활성을 분석한 결과 굴가수분해물은 농도 의존적으로 높은 DPPH 및 ABTS 라디칼 소거 활성을 보였으며, 인간 정상 간세포주(Chang)에서 과산화수소에 의한 세포 내 활성산소의 생성을 유의적으로 감소시켰다. 또한, 굴가수분해물은 농도 의존적으로 높은 COX-2 및 5-LOX 억제능을 보였으며, LPS에 의해 활성화된 생쥐 대식세포주 RAW264.7에서 발현되는 TNF-α, IL-6 및 IL-1α의 염증성 사이토카인의 mRNA 발현률을 감소시켰다. 굴가수분해물 투여는 LPS/D-GalN에 의한 혈청 ALT 및 AST증가를 유의적으로 감소시켰으며, 간 조직의 출혈 및 간세포의 자멸사를 감소시켰다. 또한, 간 균질의 TNF-α, IL-1β 및 IL-6 함량을 감소시켰으며, 감소한 catalase의 활성을 유의적으로 증가시켰다. 이상의 결과로부터 굴가수분해물은 간 보호 효과를 가지는 것으로 판단되며, 급성 간 손상의 예방 및 치료에 도움이 될 수 있는 시료로 활용될 수 있을 것으로 기대된다. Oxidative stress and inflammation are key factors responsible for progression of liver injury. A variety of functions of oyster hydrolysate (OH) are affected by their antioxidant and anti-inflammatory activities. However, little is known regarding the effects of OH on a liver injury model. This study was performed to evaluate the effects of OH on acute liver injury induced by lipopolysaccharide/D-galactosamine (LPS/D-GalN) in mice. Experimental groups were divided into six groups as follows (each group, n=10): control (saline), LPS/D-GalN, LPS/D-GalN+OH (100 mg/kg), LPS/D-GalN+OH (200 mg/kg), LPS/D-GalN+OH (400 mg/kg), and LPS/D-GalN+silymarin (25 mg/kg, positive control). The experimental acute liver injury model was induced with LPS (1 μg/kg) and D-GalN (400 mg/kg). We first analyzed antioxidant and anti-inflammatory activities in OH. OH showed high DPPH and ABTS radical scavenging activities and reduced ROS generation in Chang cells in a dose-dependent manner. In addition, OH showed anti-inflammatory activities, such as inhibition of cyclooxygenase-2 and 5-lipooxygenase. Treatment with OH down-regulated tumor necrosis factor (TNF)-α, interleukin (IL)-6, and IL-1α expression levels in LPS-stimulated RAW264.7 cells. OH significantly reduced LPS/D-GalN-induced increases in the concentrations of alanine transaminase and aspartate aminotransferase in serum. In the LPS/D-GalN group, liver tissues exhibited apoptosis of hepatocytes with hemorrhages. These pathological alterations were ameliorated by OH treatment. Consistently, hepatic catalase activity was low in the LPS/D-GalN group compared to the control group, and catalase activity was significantly restored by OH treatment (P<0.05). Furthermore, OH markedly reduced the LPS/D-GalN-induced increase in TNF-α, IL-1β, and IL-6 levels in liver tissue. Taken together, these results show that OH has hepatoprotective effects on LPS/D-GalN-induced acute liver injury via inhibition of oxidative stress and inflammation, suggesting that OH could be used as a health functional food and potential therapeutic agent for acute liver injury.

Design of Epitaxially Strained Ag Film for Durable Ag-Based Contact to p-Type GaN

Son, Jun Ho,Yu, Hak Ki,Song, Yang Hee,Kim, Buem Joon,Lee, Jong-Lam American Chemical Society 2011 Crystal Growth & Design Vol.11 No.11

<P>We demonstrated a novel contact structure of a silver (Ag) reflector that had an enhanced thermal stability at an elevated temperature. The Ag film was epitaxially grown on GaN by the insertion of an ultrathin Ni contact layer (∼10 Å). The Ag film in the Ni/Ag structure, which was tensilely strained due to the expansion of the lattice constant by oxidation of Ni (3.532 Å) to NiO (4.176 Å), could compensate for the thermal compressive stress of 0.83 GPa that developed at the interface of Ag with GaN at 500 °C. The tensile stress, as determined by high resolution X-ray diffraction, was 0.24 GPa for a single period of the Ni/Ag contact, but it increased to 0.65 GPa for triple periods of the Ni/Ag contact, resulting in further suppression of Ag agglomeration and improved long-term thermal stability.</P><P>The Ag film in the Ni/Ag structure, which was tensilely strained due to the expansion of the lattice constant by oxidation of Ni (3.532 Å) to NiO (4.176 Å), could compensate for the thermal compressive stress that developed at the interface of Ag with GaN, resulting in improved long-term thermal stability.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cgdefu/2011/cgdefu.2011.11.issue-11/cg200833y/production/images/medium/cg-2011-00833y_0006.gif'></P>