• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.189-189
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• 2012

Lead sulfide (PbS) nanocrystal quantum dots (NQDs) are promising materials for various optoelectronic devices, especially solar cells, because of their tunability of the optical band-gap controlled by adjusting the diameter of NQDs. PbS is a IV-VI semiconductor enabling infrared-absorption and it can be synthesized using solution process methods. A wide choice of the diameter of PbS NQDs is also a benefit to achieve the quantum confinement regime due to its large Bohr exciton radius (20 nm). To exploit these desirable properties, many research groups have intensively studied to apply for the photovoltaic devices. There are several essential requirements to fabricate the efficient NQDs-based solar cell. First of all, highly confined PbS QDs should be synthesized resulting in a narrow peak with a small full width-half maximum value at the first exciton transition observed in UV-Vis absorbance and photoluminescence spectra. In other words, the size-uniformity of NQDs ought to secure under 5%. Second, PbS NQDs should be assembled carefully in order to enhance the electronic coupling between adjacent NQDs by controlling the inter-QDs distance. Finally, appropriate structure for the photovoltaic device is the key issue to extract the photo-generated carriers from light-absorbing layer in solar cell. In this step, workfunction and Fermi energy difference could be precisely considered for Schottky and hetero junction device, respectively. In this presentation, we introduce the strategy to obtain high performance solar cell fabricated using PbS NQDs below the size of the Bohr radius. The PbS NQDs with various diameters were synthesized using methods established by Hines with a few modifications. PbS NQDs solids were assembled using layer-by-layer spin-coating method. Subsequent ligand-exchange was carried out using 1,2-ethanedithiol (EDT) to reduce inter-NQDs distance. Finally, Schottky junction solar cells were fabricated on ITO-coated glass and 150 nm-thick Al was deposited on the top of PbS NQDs solids as a top electrode using thermal evaporation technique. To evaluate the solar cell performance, current-voltage (I-V) measurement were performed under AM 1.5G solar spectrum at 1 sun intensity. As a result, we could achieve the power conversion efficiency of 3.33% at Schottky junction solar cell. This result indicates that high performance solar cell is successfully fabricated by optimizing the all steps as mentioned above in this work.

• Analytical Science and Technology
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• v.28 no.1
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• pp.33-39
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• 2015

CdS-QD particles are a nano-sized semiconducting crystal that emits light. Their optical properties show great potential in many areas of applications such as disease-diagnostic reagents, optical technologies, media industries and solar cells. The wavelength of emitting light depends on the particle size and thus the quality control of CdS-QD particle requires accurate determination of the size distribution. In this study, CdS-QD particles were synthesized by a simple ${\gamma}$-ray irradiation method. As a particle stabilizer polyvinyl pyrrolidone (PVP) were added. In order to determine the size and size distribution of the CdS-QD particles, sedimentation field-flow fractionation (SdFFF) was employed. Effects of carious parameters including the the flow rate, external field strength, and field programming conditions were investigated to optimize SdFFF for analysis of CdS-QD particles. The Transmission electron microscopy (TEM) analysis show the primary single particle size was ~4 nm, TEM images indicate that the primarty particles were aggregated to form secondary particles having the mean size of about 159 nm. As the concentration of the stabilizer increases, the particle size tends to decrease. Mean size determined by SdFFF, TEM, and dynamic light scattering (DLS) were 126, 159, and 152 nm, respectively. Results showed SdFFF may become a useful tool for determination of the size and its distribution of various types of inorganic particles.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
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• v.7 no.10
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• pp.895-903
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• 2017

Quantum Cellular Automata(QCA) is one of the proposed techniques as an alternative solution to the fundamental limitations of CMOS. QCA has recently been extensively studied along with experimental results, and is attracting attention as a nano-scale size and low power consumption. Although the XOR gates proposed in the previous paper can be designed using the minimum area and the number of cells, there is a disadvantage that the number of added cells is increased due to the stability and the accuracy of the result. In this paper, we propose a gate that supplement for the drawbacks of existing XOR gates. The XOR gate of this paper reduces the number of cells by arranging AND gate and OR gate with square structure and propose a half-adder by adding two cells that serve as simple inverters using the proposed XOR gate. Also This paper use QCADesginer for input and result accuracy. Therefore, the proposed half-adder is composed of fewer cells and total area compared to the conventional half-adder, which is effective when used in a large circuit or when a half - adder is needed in a small area.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.228.1-228.1
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• 2013

Photoreflectance (PR) 분광법은 비접촉, 비파괴적인 변조분광법으로서 반도체 표면 및 계면의 광학적 특성 연구에 많이 이용되고 있다. PR 신호의 Franz-Keldysh oscillation (FKO)으로부터 Molecular Beam Epitaxy (MBE) 방법으로 성장한 InAs/GaAs 양자점 태양전지 접합계면의 전기장을 조사하였다. InAs 양자점의 크기는 각각 1.7, 2.0, 2.5, 3.0 monolayer이며, p+-n-n+ 태양전지 구조의 표면으로부터 1.8 ${\mu}m$, 활성영역으로부터 약 1.1 ${\mu}m$ 위치에 삽입되어 있다. 여기광 세기가 큰 영역(1~200 $mW/cm^2$)에서 접합계면의 전기장으로부터 관측한 photovoltage 효과는 로그 스케일에서 대체로 선형적인 분포를 보였으며, 이를 계산결과와 비교 분석하였다. 또한, 양자점 크기 및 온도에 따른 photovoltage 효과는 활성영역에서 여기된 운반자의 양 및 양자점에 의한 전하트랩의 영향과 관련하여 비교 분석하였다.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.318-321
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• 2007

CdSe nanoparticles were prepared by chemical solution methods using $CdCl_2{\cdot}4H_2O$ (or $Cd(NO_3)_ 2{\cdot}4H_2O$) and $Na_2SeSO_3$. The characteristics of CdSe nanoparticles were controlled by the react ion time, reaction temperature and reaction method as well as the surfactants. Cetyltrimethyl ammonium bromide(CTAB) was used as a capping agent to control the chemical reactions in aqueous solution. Polyvinylalcohol(PVA) was used as a templet in sono-chemical method. CdSe nanoparticles synthesized in aqueous solution showed homogeneous size distribution with relatively stable surface. CdSe nanoparticles synthesized in non-aqueous solution containing diethanolamine(DEA) showed the structure transformation from cubic to hexagonal as the reduction temperature increased from 80 to $160^{\circ}C$. Core shell CdSe was synthesized by sono-chemical method. Characteristics of CdSe nanoparticles were analyzed using transmission electron microscopy(TEM), x-ray photoelectron spectroscopy(XPS), x-ray diffraction(XRD), UV-Vis absorption spectra, fourier transform infrared spectroscopy(FT-IR) and photoluminescence spectra spectroscopy(PL). This paper presents simple routes to prepare CdSe nanoparticles for solar cell applications.

• Safety and Health at Work
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• v.12 no.3
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• pp.403-415
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• 2021

Background: This study aimed to assess the possibility of benzene exposure in workers of a Korean semiconductor manufacturing company by reviewing the issued patents. Methods: A systematic patent search was conducted with the Google "Advanced Patent Search" engine using the keywords "semiconductor" and "benzene" combined with all of the words accessed on January 24, 2016. Results: As a result of the search, we reviewed 75 patent documents filed by a Korean semiconductor manufacturing company from 1994 to 2010. From 22 patents, we found that benzene could have been used as one of the carbon sources in chemical vapor deposition for capacitor; as diamond-like carbon for solar cell, graphene formation, or etching for transition metal thin film; and as a solvent for dielectric film, silicon oxide layer, nanomaterials, photoresist, rise for immersion lithography, electrophotography, and quantum dot ink. Conclusion: Considering the date of patent filing, it is possible that workers in the chemical vapor deposition, immersion lithography, and graphene formation processes could be exposed to benzene from 1996 to 2010.

• International Journal of Advanced Culture Technology
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• v.8 no.3
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• pp.316-324
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• 2020

It has experienced how difficult People with foreign language learning, it is to pronounce a new language different from the native language. The goal of various foreigners who want to learn Korean is to speak Korean as well as their native language to communicate smoothly. However, each native language's vocal habits also appear in Korean pronunciation, which prevents accurate information transmission. In this paper, the pronunciation of Chinese learners was compared with that of Korean. For comparison, the fundamental frequency and its variation of the speech signal were examined and the spectrogram was analyzed. The Formant frequencies known as the resonant frequency of the vocal tract were calculated. Based on these characteristics parameters, the classifier of the Supporting Vector Machine was found to classify the pronunciation of Koreans and the pronunciation of Chinese learners. In particular, the linguistic proposition was scientifically proved by examining the Korean pronunciation of /ㄹ/ that the Chinese people were not good at pronouncing.

• Toxicological Research
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• v.29 no.1
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• pp.35-42
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• 2013

Quantum dots (QDs) have received considerable attention due to their potential role in photosensitization during photodynamic therapy. Although QDS are attractive nanomaterials due to their novel and unique physicochemical properties, concerns about their toxicity remain. We suggest a combination strategy, CdSe/ZnS QDs together with curcumin, a natural yellow pigment from turmeric, to reduce QD-induced cytotoxicity. The aim of this study was to explore a potentially effective cancer treatment: co-exposure of HL-60 cells and human normal lymphocytes to CdSe/ZnS QDs and curcumin. Cell viability, apoptosis, reactive oxygen species (ROS) generation, and DNA damage induced by QDs and/or curcumin with or without ultraviolet A (UVA) irradiation were evaluated in both HL-60 cells and normal lymphocytes. In HL-60 cells, cell death, apoptosis, ROS generation, and single/double DNA strand breaks induced by QDs were enhanced by treatment with curcumin and UVA irradiation. The protective effects of curcumin on cell viability, apoptosis, and ROS generation were observed in normal lymphocytes, but not leukemia cells. These results demonstrated that treatment with QD combined with curcumin increased cell death in HL-60 cells, which was mediated by ROS generation. However, curcumin acted as an antioxidant in cultured human normal lymphocytes.

• ETRI Journal
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• v.34 no.6
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• pp.950-953
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• 2012

Schottky barrier single electron transistors (SB-SETs) and Schottky barrier single hole transistors (SB-SHTs) are fabricated on a 20-nm thin silicon-on-insulator substrate incorporating e-beam lithography and a conventional CMOS process technique. Erbium- and platinum-silicide are used as the source and drain material for the SB-SET and SB-SHT, respectively. The manufactured SB-SET and SB-SHT show typical transistor behavior at room temperature with a high drive current of $550{\mu}A/{\mu}m$ and $-376{\mu}A/{\mu}m$, respectively. At 7 K, these devices show SET and SHT characteristics. For the SB-SHT case, the oscillation period is 0.22 V, and the estimated quantum dot size is 16.8 nm. The transconductance is $0.05{\mu}S$ and $1.2{\mu}S$ for the SB-SET and SB-SHT, respectively. In the SB-SET and SB-SHT, a high transconductance can be easily achieved as the silicided electrode eliminates a parasitic resistance. Moreover, the SB-SET and SB-SHT can be operated as a conventional field-effect transistor (FET) and SET/SHT depending on the bias conditions, which is very promising for SET/FET hybrid applications. This work is the first report on the successful operations of SET/SHT in Schottky barrier devices.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.1
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• pp.107-116
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• 2009

Quantum-dot Cellular Automata (QCA) is one of the most promising next generation nanoelectronic devices which will inherit the throne of CMOS which is the domineering implementation technology for large scale low power digital systems. In late 1990s, the basic operations of the QCA cell were already demonstrated on a hardware implementation. Also, design tools and simulators were developed. Nevertheless, its design technology is not quite ready for ultra large scale designs. This paper proposes a new approach which enables the QCA designs to inherit the verification methodologies and tools of CMOS designs, as well. First, a set of disciplinary rules strictly restrict the cell arrangement not to deviate from the predefined structures but to guarantee the deterministic digital behaviors is proposed. After the gate and interconnect structures of. the QCA design are identified, the signal integrity requirements including the input path balancing of majority gates, and the prevention of the noise amplification are checked. And then the digital logic is extracted and stored in the OpenAccess common engineering database which provides a connection to a large pool of CMOS design verification tools. Towards validating the proposed approach, we designed a 2-bit adder, a bit-serial adder, and an ALU bit-slice. For each design, the digital logic is extracted, translated into the Verilog net list, and then simulated using a commercial software.