(The) impact of the nairobi ministerial declaration in the WTO framework about agricultural export subsidies in the agriculture sector of some country members of WTO

Hoang, Vuong Yen TLBU Graduate School of Law 2018 국내석사

Hydrogen sensitivity enhancement of GaN high electron mobility transistor sensors using normally-on operation and gate recess process

Vuong, Tuan Anh Hongik University, Graduate School 2019 국내석사

We are now living in a new era, the era of the explosive development of science and technology. Along with that is the continuous increase of demand for energy and the dream of exploring places with harsh environmental conditions or reaching out to the distant space in the universe, urging people to quickly find new energy sources which are friendly to the environment and not harmful to health. Hydrogen is being considered as one of the most efficient and non-polluting energy sources. However, storage of hydrogen is an extremely important issue, because hydrogen is colorless, odorless, and explosive. Moreover, at high temperatures, hydrogen can cause the effect, named High Temperature Hydrogen Attack, which can crack the steel by forming methane with carbon (from 204 oC); and the auto-ignition temperature of hydrogen is 500 oC. For these reasons, development of hydrogen gas sensor with high operating temperature is necessary. Until now, there are many types of gas sensors based on Si materials that can detect the occurrence of hydrogen, but these sensors are inoperable in high-temperature conditions due to the limitation of Si material at a temperature of 350 oC. Instead, scientists have been focusing on studying the potential applications of semiconductors such as GaN and SiC because components based on these materials are highly endurable high temperatures and electric fields, as well as harsh radiative conditions. Because of that reason, gallium nitride (GaN) or silicon carbide (SiC) are being considered as the promising candidates for the next-generation electronic device technology. When GaN forms heterojunction with AlGaN, the appearance of 2DEG near the surface will be an indispensable element in detecting the occurrence of gas molecules if they do change the surface potential. The capability of high temperature operation of AlGaN/GaN heterostructure-based devices is very attractive to the field of gas sensing application. In these studies, we have fabricated and studied hydrogen gas sensors based on the AlGaN/GaN heterostructure with a platinum as the catalyst. The study started with hydrogen gas sensor based on Pt- gate Schottky HEMT structure with 3 terminals: source, drain, gate, respectively. At a standard temperature of 200 oC with the injection of 4 % hydrogen in Ar background gas, the sensors exhibited the sensitivity to the appearance of hydrogen. Sensing performance is measured following two different methods focusing primarily on 0 voltage biasing / non-biasing (or floating) on the Pt-gate electrode to utilize normally-on characteristics of AlGaN/GaN high electron mobility transistors (HEMTs). Experimental results have confirmed the enhancement of sensitivity when 0 V was assigned to the gate. To further enhance the sensitivity, we carried out gate-recess etching to thin the AlGaN barrier, thereby improving the controllability of the Pt-gate over 2DEG channel through transconductance optimizing. As expected, the sensitivity was increased as the thickness of the under-gate-AlGaN layer was made thinner by dry etching technique. Next, the sensors with the interconnection between gate and source were fabricated because zero gate bias can be applied by connecting the gate to the source electrode. The source-connected gate (SCG) sensors demonstrated the sensitivity higher than that of floating gate sensors. To more enhance the sensitivity, the AlGaN layer was deeper etched to reach the thicknesses even thinner than the previous fabrication process, 15 and 9 nm, respectively. The sensors with 9 nm-AlGaN barrier, which the thinnest among our samples, exhibited highest sensitivity of 87 % at 200 oC. In the next step, a 9 nm-AlGaN SCG sensor was tested in the presence of hydrogen gas at a thermal range from 150 to 500 oC. This sensor still showed good operation with high sensitivity and stability. Other independent experiments were also performed to confirm the correlation between sensitivity and transconductance. Therefore, the sensors with AlGaN/GaN heterojunction-based sensor can be a strong candidate for hydrogen gas sensing application at high temperatures.

(A)New Auto Exposure and Auto White-Balance Algorithm for High Dynamic Range Conditions using CMOS Technology

Vuong, Quoc Kien Department of electrical engineering, Graduate sch 2009 국내석사

Lead-Free MA3Bi2I9 with Dopants Br and Cl Deposited via Engineering Chemical Vapor Deposition for Self-Powered Photodetectors

Vuong Hoang 忠南大學校 大學院 2021 국내석사

최근, Lead-free 유-무기 perovskite-inspired materials (PIMS)는 새로운 광 흡수 재료로써 광 전자 재료의 가장 유망한 후보군으로 많은 관심을 받아오고 있다. 이들은 조정 가능한 밴드 갭, 높은 흡수 계수 및 긴 캐리어 확산 길이를 지니는 주류 납 기반의 페로브스카이트와 비슷한 전기적 광학적 특성을 가졌으며, 또한 낮은 독성과 매우 우수한 대기 안정성을 보인다. 납을 대체하기 위한 많은 재료와 이들을 광학적 디바이스에 실질적으로 활용하기 위한 많은 연구가 진행되어 왔다. 그러나 PIMS 광 검출기는 현재까지 상용화 되기엔 효율성과 안정성의 문제에 직면해 있다. 예를 들어, Sn, Ge금속은 납-페로브스카이트를 대체하는데 많은 관심을 받고 있다. 비록 이 두 물질이 납-페로브스카이트와 비슷한 광학적 전기적 특성을 보이지만, 이들은 110 대기중에 쉽게 Sn2+, Ge2+에서 Sn4+, Ge4+로 산화되기 때문에 낮은 성능과 안정성을 보여준다. 따라서 그들은 잠재적인 활용과 재현성이 제한되어 있다. MA3Bi2I9에 Br과 Cl를 도핑한 새로운 Lead-free PIMS는 CVD 방식으로 접근을 통해 광반응 물질을 성장시킴으로써 이러한 단점을 극복했다. 용액 공정을 통한 박막은 품질이 좋지 않고 결정성이 제한되 있는 반면, 두개의 관 (Two-tube, 2T)을 지닌 CVD (2T-CVD)는 더 매끄러운 표면과 우수하고 컴팩트한 형태의 높은 결정성을 지닌 박막을 생산할 수 있다. 따라서 2T-CVD로 제작한 MA3Bi2I9 and MA3Bi2I6Br3, MA3Bi2I6Cl3의 광전자 잠재력은 고 성능의 자가 전력 광 검출기를 통해 입증된다. UV 조명하에 특정 탐지능력과 높은 반응성을 제공하며 봉지화처리를 하지 않은 2T-CVD 기기는 장시간 수분 안정성을 보인다. 저가, 낮은 독성과 쉬운 제조를 통해 납 기반의 페로브스카이트를 대체할 수 있으리라 기대된다. 이러한 결과는 2T-CVD는 고성능 PIMS를 개발을 위한 플랫폼으로 우수하다는 것을 나타낸다.

Modified Electronic Structure Of Zinc Oxides For Photocatalytic Hydrogen Evolution

VUONG HOAI THANH 울산대학교 대학원 2022 국내석사

In this thesis, the concentration was put on the fabrication of ZnO-based heterojunction photocatalysts to improve photocatalytic activities of hydrogen generation from water. The studies have been divided into two parts, including p-n heterojunctions and type II heterojunctions. The mechanism of each type of catalyst under UV and visible light irradiation was clearly illustrated in the thesis. The first part describes the in-situ synthesis of multicomponent ZnO-based photocatalysts for hydrogen production. The fabricated ZnO coupled with Cu-Cu2O nanoparticles and modified reduced graphene oxide (mRGO) ameliorated hydrogen production. The simultaneous introduction of mRGO and Cu-Cu2O enhanced the generation rate of photocatalytic hydrogen to 3085.02 µmol g-1 h-1 due to significant alteration of the electronic structure. The bandgap energy of the prepared catalysts decreased from 3.2 eV for pristine ZnO to 2.64 eV for a composite containing 15% CuCu2O. The optimized designated heterostructure efficiently separates photo charge carriers and prevents charge carriers’ recombination by accelerating charge transfer with the help of mRGO and metallic Cu and as a result leading to efficient hydrogen yields. The second part obviously demonstrates the role of EDTA molecules to enhance the photocatalytic activity of CdS/ZnMn2O4. The composite strongly improved catalytic performance due to the low photo-resistance when bridging EDTA molecules between two materials. Besides that, the optimal composite showed superior hydrogen production at a rate of 26.34 mmol.g-1.h-1. Furthermore, the material possessed better photostability in both acid and basic environments for around 18 h under light irradiations. This research could be useful to validate the efficacy of organic-inorganic systems for photocatalysts because of the positive effect of organic factors in synthesizing heterojunction photocatalysts, promoting charge transfers, and reducing recombination of electron-hole pairs to increase photoactivity.

DETERMINANTS OF KOREAN DIRECT INVESTMENT IN VIETNAM IMPLICATIONS FOR POLICY

Vuong, Hieu Thi Minh KDI School of Public Policy and Management 2006 국내박사

This study addresses the main determinants, including pull and push factors, leading to the investment decision of Korean firms into Southeast Asian countries generally and Vietnam particularly. The author aims to describe the typical features of Korean investment in Vietnam and explain the reasons prompting Korean investors to engage in investment activities. Qualitative and quantitative techniques are applied in collecting the data. With analyzing methods including logical reasoning, comparative method and bivaritate analysis, the author finds that among the push factors prompting Korean to invest in Southeast Asia, low labor cost proves the key determinant. As for a particular case of Vietnam, pull factors include a competitive legal framework, low labor cost, an emerging market and cultural proximity to Korea. However, in a fierce competition context, the determinants implicit hinders for Vietnam in inducing and nurturing Korean direct investment. The country is facing with a series of challenges namely language barrier and information unavailability; bureau and red tape; inadequate infrastructure quality; and lack of supporting industries, which need tackling seriously in the coming time.

pH Sensor Based on Upconversion Nanoparticles inside Silica Nanotube

VUONG, VAN HAU 가천대학교 2015 국내석사

Silica nanotubes (SNTs) have been used more widely in the large number of different fields, especially for biomedical application due to their tubular structure and biocompatibility. Nanoparticle-embedded silica nanotube has been investigated to prevent nanoparticles aggregation and enhance the strongest effectiveness of nanoparticle properties. This work focused on introducing up-conversion nanoparticles (UCNPs) inside SNTs and applied it for pH sensing. Three kinds of inorganic up-conversion nanoparticles (with rear infrared, green, blue, ultra-violet emission) were introduced into successfully, forming functional SNTs with nanopeapod-UCNPs. UCNP size could be controlled differently by increasing or decrease the reaction time during synthesized process, however, only lower than 60 nm UCNPs were employed for inducing peapod-SNT structure effectively. An optical pH sensor based on intense ~660 nm wavelength of UCNP@SNT and bromothymol blue (BTB) was explored. A pH probe, bromothymol blue, was encapsulated inside UCNP@SNT by forming a polystyrene capping on the opened-end SNT through spin-coating method. Based on inner filter effect, the sensing system could operate on the pH measurement from 6 to 9 because the intensities of the red emission were linear with the changing of pH value.

(The) application of image acquisition and processing using LabVIEW-based FPGA implementation to wheeled mobile robots

Vuong, Duc-Phuc Mokpo National Maritime University 2014 국내석사

(The) transient torsional vibration and fatigue strength of 2-stroke low speed diesel engine propulsion shafting system during barred speed range passage

Vuong, Quang Dao Mokpo National Maritime University 2019 국내박사

Novel regulatory mechanisms of Sonic hedgehog signaling

Vuong, Tuan Anh Sungkyunkwan University 2017 국내박사