• Proceedings of the IEEK Conference
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• 2005.11a
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• pp.833-836
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• 2005

Nano-gap trench is fabricated by the novel electrochemical etching technique using forward biased PN junction formed at the backside of the wafer. PN junction is formed using boron nitride wafer and the concentration of the boron doping is the high value of $1{\times}10^{19}$ $cm^{-3}$. The electro-chemical etching is performed in the 5% HF solution under the forward bias voltage of $1{\sim}2V$. The relationship between the etch rate of the trench and the voltage of the forward bias is investigated and the dependence of the gap for the voltage also examined. The etch rate increase from 0.027 ${\mu}m/min$ to 0.031 ${\mu}m/min$ as the value of the applied voltage increase from 1V to 2V, but the the gap is kept constant value of 40 nm.

• Steel and Composite Structures
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• v.36 no.6
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• pp.671-687
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• 2020

The aim of this research is to analyze buckling and bending behavior of a sandwich Reddy beam with porous core and composite face sheets reinforced by boron nitride nanotubes (BNNTs) and shape memory alloy (SMA) wires resting on Vlasov's foundation. To this end, first, displacement field's equations are written based on the higher-order shear deformation theory (HSDT). And also, to model the SMA wire properties, constitutive equation of Brinson is used. Then, by utilizing the principle of minimum potential energy, the governing equations are derived and also, Navier's analytical solution is applied to solve the governing equations of the sandwich beam. The effect of some important parameters such as SMA temperature, the volume fraction of SMA, the coefficient of porosity, different patterns of BNNTs and porous distributions on the behavior of buckling and bending of the sandwich beam are investigated. The obtained results show that when SMA wires are in martensite phase, the maximum deflection of the sandwich beam decreases and the critical buckling load increases significantly. Furthermore, the porosity coefficient plays an important role in the maximum deflection and the critical buckling load. It is concluded that increasing porosity coefficient, regardless of porous distribution, leads to an increase in the critical buckling load and a decrease in the maximum deflection of the sandwich beam.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.240-240
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• 2016

반도체 양자점은 불연속적인 에너지준위의 특성 때문에 고전적인 빛과는 다른 단일광자를 방출하여 양자정보 처리과정에 기본 요소로써 사용 될 수 있다. III-Nitride (III-N) 반도체 물질은 III족 원소의 구성비를 조절하였을 때 밴드갭 에너지차이가 크므로 깊은 양자 우물을 만들 수 있으며 최근에는 기존에 연구되던 III-Arsenide 기반의 반도체 양자점과 다르게 상온 (300 K) 동작 가능한 단일광자 방출원이 개발되었다.[1] 또한 약한 split-off 에너지 때문에 양자점 모양에 작은 비대칭성만 존재해도 큰 선형편광도를 가질 수 있다. 하지만 III-N 반도체 양자점의 이러한 특성에도 불구하고 이종기판과의 격자상수 불일치에 따른 많은 threading dislocation, 압전효과에 의한 큰 내부전기장에 의해 발광 효율이 떨어지는 등의 문제가 있다. 이를 해결하기 위해 반도체 양자점을 3차원 구조체와 결합하여 threading dislocation 및 내부전기장을 줄이는 연구들이 진행되고 있다.[2] 본 연구에서는 선택적 영역 성장 방식을 통해 마이크로미터 크기를 가지는 피라미드 형태의 3차원 구조체를 이용, 피라미드의 꼭지점에 형성된 InGaN/GaN 양자점의 광학적 특성에 대해 분석하였다. 저온(9 K)에서 마이크로 photoluminescence 측정을 통해 양자점의 발광파장이 피라미드의 옆면의 파장과는 다름을 확인하였다. 여기광의 세기에 따른 양자점의 발광 세기 측정하여 여기광에 선형 비례함을 보이고, 양자점의 편광도를 측정하여 선형 편광임을 확인하였다. 마지막으로, 광량에 대해 시간에 따른 상관관계를 측정함으로써 양자점이 양자 발광체의 특성을 보이는 지 확인하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.100-100
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• 2016

Among various two-dimensional (2D) materials, 2D semiconductors and insulators have attracted a great deal of interest from nanoscience community beyond graphene, due to their attractive and unique properties. Such excellent characteristics have triggered highly active researches on 2D materials, such as hexagonal boron nitride (hBN), molybdenum disulfide (MoS2), and tungsten diselenide (WSe2). New physics observed in 2D semiconductors allow for development of new-concept devices. Especially, these emerging 2D materials are promising candidates for flexible and transparent electronics. Recently, van der Waals heterostructures (vdWH) have been achieved by putting these 2D materials onto another, in the similar way to build Lego blocks. This enables us to investigate intrinsic physical properties of atomically-sharp heterostructure interfaces and fabricate high performance optoelectronic devices for advanced applications. In this talk, fundamental properties of various 2D materials will be introduced, including growth technique and influence of defects on properties of 2D materials. We also fabricate high performance electronic/optoelectronic devices of vdWH, such as transistors, memories, and solar cells. The device platform based on van der Waals heterostructures show huge improvement of devices performance, high stability and transparency/flexibility due to unique properties of 2D materials and ultra-sharp heterointerfaces. Our work paves a new way toward future advanced electronics based on 2D materials.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.282.1-282.1
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• 2016

The remarkable physical properties of two-dimensional (2D) semiconducting materials such as molybdenum disulfide ($MoS_2$) and tungsten disulfide ($WS_2$) etc. have attracted considerable attentions for future high-performance electronic and optoelectronic devices. The ongoing studies of $MoS_2$ based nonvolatile memories have been demonstrated by worldwide researchers. The opening hysteresis in transfer characteristics have been revealed by different charge confining layer, for instance, few-layer graphene, $MoS_2$, metallic nanocrystal, hafnium oxide, and guanine. However, limited works built their nonvolatile memories using entirely of assembled 2D crystals. This is important in aspect view of large-scale manufacture and vertical integration for future memory device engineering. We report $WS_2$ based nonvolatile memories utilizing functional van der Waals heterostructure in which multi-layered graphene is encapsulated between $SiO_2$ and hexagonal boron nitride (hBN). We experimentally observed that, large memory window (20 V) allows to reveal high on-/off-state ratio (>$10^3$). Moreover, the devices manifest perfect retention of 13% charge loss after 10 years due to large graphene/hBN barrier height. Interestingly, the performance of our memories is drastically better than ever published work related to $MoS_2$ and black phosphorus flash memory technology.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.87.1-87.1
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• 2016

The unique properties of 2D materials significantly rely on the atomic structure and defects. Thus study at atomic scale is crucial for in-depth understanding of 2D materials and provides insights into its future applications. Using aberration-corrected transmission electron microscopes, atomic resolution imaging of individual atoms has been achieved even at a low kV. Ongoing optimization of aberration correction improves the spatial resolution better than angstrom and moreover boosts the contrast of light atoms. I present the recent progress of the study on the atomic structure and defects of monolayer and multilayer graphene, hBN and MoS2. Furthermore, the defect formation mechanisms of graphene, hexagonal boron nitride and MoS2 are discussed.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.59.1-59.1
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• 2015

In the Linford group at Brigham Young University we have recently developed three new sets of materials for three different areas of separations science: thin layer chromatography (TLC), high performance liquid chromatography (HPLC), and solid phase microextraction (SPME). First, via microfabrication we have grown patterned carbon nanotube (CNT) forests on planar substrates that we have infiltrated with inorganic materials such as silicon nitride. The coatings on the CNTs are conformal and typically deposited in a process like low pressure chemical vapor deposition. The resulting materials have high surface areas, are porous, and function as effective separation devices, where separations on our new TLC plates are typically significantly faster than on conventional devices. Second, we used the layer-by-layer (electrostatically driven) deposition of poly (allylamine) and nanodiamond onto carbonized poly (divinylbenzene) microspheres to create superficially porous particles for HPLC. Many interesting classes of molecules have been separated with these particles, including various cannabinoids, pesticides, tricyclic antidepressants, etc. Third, we have developed new materials for SPME by sputtering silicon onto cylindrical fiber substrates in a way that creates shadowing of the incoming flux so that materials with high porosity are obtained. These materials are currently outperforming their commercial counterparts. Throughout this work, the new materials we have made have been characterized by X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, scanning electron microscopy, transmission electron microscopy, etc.

• Journal of the Korea Society of Computer and Information
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• v.9 no.1
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• pp.9-15
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• 2004

New WSW(Wrap Side Wall) is proposed to decrease junction electric field in this paper. WSW process is fabricated after first gate etch, followed NM1 ion implantation and deposition & etch nitride layer. New WSW structure has buffer layer to decrease electric field. Also we compared the hot carrier characteristics of WSW and conventional. Also, we design a test pattern including pulse generator, level shifter and frequency divider, so that we can evaluate AC hot carrier degradation on-chip. It came to light that the universality of the hot carrier degradation between DC and AC stress condition exists, which indicates that the device degradation comes from the same physical mechanism for both AC and DC stress. From this universality, AC lifetime under circuit operation condition can be estimated from DC hot carrier degradation characteristics.

• Journal of Sensor Science and Technology
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• v.6 no.3
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• pp.221-227
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• 1997

The Pd/NiCr gate MISFET-type sensors were fabricated for detecting hydrogen dissolved in high-capacivity transformer oil. To improve stability and high concentration sensitivity of the sensor, Pd/NiCr double catalysis metal gate was used. To reduce the serious gate voltage drift of the sensor induced by hydrogen, the gate insulators of 2 FETs were constructed with double layer of silicon dioxide and silicon nitride. The hydrogen sensitivity of the Pd/NiCr gate MISFET is about a half of Pd/Pt gate MISFET's sensitivity but the Pd/NiCr gate MISFET has good stability and high concentration detectivity up to 1000 ppm.

• Journal of Welding and Joining
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• v.27 no.5
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• pp.55-61
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• 2009

Pure titanium and its alloys have good formability, excellent corrosion resistance and high strength to weight ratios. Therefore, it has been using to heat exchangers, offshore plants, sports equipments, and etc. As broad as its application fields, it also increases welding locations. Conventional GTAW and GMAW are very popular welding methods of titanium, but it has a high heat input and wide HAZ. It has a possibility of inducing Stress Corrosion Cracking. So, laser welding method has been using to get reliable welds by reducing heat input. Weld beads change its color to silver, gold, brown, blue, and gray by shied conditions. And the closer to gray, the more oxidize, nitride and embrittlement. The most effective atom to embrittlement was nitrogen. And shield gas flow was not so effective over the constant flow rates. In this study, weld properties of the pure titanium were investigated by pulsed & CW Nd:YAG lasers and evaluated by various shield conditions. And It is observed that nitrogen is more effective to oxidation and embrittlement of titanium compared with oxygen by oxygen and nitrogen quantitative analysis.