• Bulletin of the Korean Chemical Society
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• 제30권12호
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• pp.2905-2908
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• 2009

Immuno-sensing for high accurate and selective sensing was performed by fluorescence spectroscopy and surface plasmon resonance (SPR), respectively. Engineered assembly of two fluorescent quantum dots (QDs) with bovine serum albumin (BSA) and anti-BSA was fabricated in PBS buffer for fluorescence analysis of fluorescence resonance energy transfer (FRET). Furthermore, the same bio-moieties were immobilized on Au plates for SPR analysis. Naturally-driven binding affinity of immuno-moieties induced FRET and plasmon resonance angle shift in the nanoscale sensing system. Interestingly, the sensing ranges were uniquely different in two systems: e.g., SPR spectroscopy was suitable for highly accurate analysis to measure in the range of 10$^{-15{\sim}-10$ng/mL while the QD fluorescent sensing system was relatively lower sensing ranges in 10$^{-10{\sim}-6$ng/mL. However, the QD sensing system was larger than the SPR sensing system in terms of sensing capacity per one specimen. It is, therefore, suggested that a mutual assistance of FRET and SPR combined sensing system would be a potentially promising candidate for high accuracy and reliable in situ sensing system of immune-related diseases.

• 대한금속재료학회지
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• 제48권4호
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• pp.363-368
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• 2010

N,N'-diphenyl-N,N'-bis(3-methylphenyl)1-1' biphenyl-4,4'-diamine (TPD) hole-transporting layers were deposited using a continuous slot-die coating method on ITO/PET flexible substrates. It is crucial that the substrates have a very smooth surface with a RMS roughness of less than 2 nm for the deposition of semiconductor nanocrystals or Quantum Dots. The parameters of the slot-die coating, including the solution concentration of the TPD, the gap between the slot-die and the substrates, and the coating speed were controlled in these experiments. To obtain full coverage of the TPD films on the ITO/PET substrates (40 mm wide and several meters long), the injection rates of the TPD solution were increased proportional to the coating speed of the flexible substrates. Additionally, the injection rates must be increased as the gap distance changes from 400 to 600 ${\mu}m$ at the same coating speed. A RMS surface roughness of less than 2 nm was obtained, in contrast to bare ITO/PET substrates, at 13 nm, as the coating speed and gap distance increased.

• Journal of the Korean Physical Society
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• 제73권11호
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• pp.1604-1611
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• 2018

Utilizing Sb-based bulk epilayers on large-scale low-cost substrates such as GaAs for fabricating infrared (IR) photodetectors is presently attracting significant attention worldwide. For this study, three sample series of $GaAs_xSb_{1-x}$, $In_{1-x}Ga_xSb$, and $InAs_xSb_{1-x}$ with different compositions were grown on semi-insulating GaAs substrates by using molecular beam epitaxy (MBE) and appropriate InAs quantum dots (QDs) as a defect-reduction buffer layer. Photoluminescence (PL) signals from these samples were observed over a wide IR wavelength range from $2{\mu}m$ to $12{\mu}m$ in agreement with the expected bandgap, including bowing effects. In particular, interband PL signals from $InAs_xSb_{1-x}$ and $In_{1-x}Ga_xSb$ samples even at room temperature show promising potential for IR photodetector applications.

• Bulletin of the Korean Chemical Society
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• 제32권1호
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• pp.263-272
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• 2011

Highly luminescent and monodisperse InP quantum dots (QDs) were prepared by a non-organometallic approach in a non-coordinating solvent. Fatty acids with well-defined chain lengths as the ligand, a non coordinating solvent, and a thorough degassing process are all important factors for the formation of high quality InP QDs. By varying the molar concentration of indium to ligand, QDs of different size were prepared and their absorption and emission behaviors studied. By spin-coating a colloidal solution of InP QD onto a silicon wafer, InP QD thin films were obtained. The thickness of the thin films cured at 60 and $200^{\circ}C$ were nearly identical (approximately 860 nm), whereas at $300^{\circ}C$, the thickness of the thin film was found to be 760 nm. Different contrast regions (A, B, C) were observed in the TEM images, which were found to be unreacted precursors, InP QDs, and indium-rich phases, respectively, through EDX analysis. The optical properties of the thin films were measured at three different curing temperatures (60, 200, $300^{\circ}C$), which showed a blue shift with an increase in temperature. It was proposed that this blue shift may be due to a decrease in the core diameter of the InP QD by oxidation, as confirmed by the XPS studies. Oxidation also passivates the QD surface by reducing the amount of P dangling bonds, thereby increasing luminescence intensity. The dielectric properties of the thin films were also investigated by capacitance-voltage (C-V) measurements in a metal-insulator-semiconductor (MIS) device. At 60 and $300^{\circ}C$, negative flat band shifts (${\Delta}V_{fb}$) were observed, which were explained by the presence of P dangling bonds on the InP QD surface. At $300^{\circ}C$, clockwise hysteresis was observed due to trapping and detrapping of positive charges on the thin film, which was explained by proposing the existence of deep energy levels due to the indium-rich phases.

• 한국진공학회지
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• 제19권3호
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• pp.217-223
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• 2010

유기금속화학기상증착법으로 적층 InAs/$In_{0.1}Ga_{0.9}As$ DWELL (dot-in-a-well) 구조를 성장하여 n-i-n 구조의 적외선 수광소자를 제작하였으며, PL (photoluminescence) 발광 특성 및 암전류 특성을 분석하였다. 동일한 조건으로 양자점을 적층하였을 때 크기 및 밀도의 변화에 의한 이중 PL peak을 관찰하였으며, TMIn의 유량을 조절함으로써 단일 peak을 갖는 균일한 크기의 양자점 적층 구조를 성장할 수 있었다. 적외선 수광소자 구조를 성장함에 있어서, 상부의 n-형 GaAs의 성장 온도가 600도 이상인 경우 PL 발광 세기가 급격히 감소하였고 이에 따른 암전류의 증가를 관찰하였다. 0.5 V 인가 전압에서 암전류의 온도 의존성에 대한 활성화 에너지의 크기는 성장온도가 580도인 경우 106 meV이고, 650도의 경우는 48 meV로 급격이 낮아졌다. 이는 고온의 성장 온도에 의한 InAs 양자점과 $In_{0.1}Ga_{0.9}As$ 양자우물구조 계면에서의 열적 상호 확산에 의하여 비발광 천이가 증가되었기 때문이다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.422.1-422.1
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• 2016

Graphene quantum dots (GQDs), a new kind of carbon-based photo luminescent nanomaterial from chemically modified graphene oxide (CMGO) or chemically modified graphene (CMG), has attracted extensive research attention in the last few years due to its outstanding chemical, optical and electrical properties. To further extended its potential applications as optoelectronic devices, solar cells, bio and bio-sensors and so on, intensive research efforts have been devoted to the CMG. However, the CMG, a suspension of aqueous, have problematic since they are prone to agglomeration after drying a solvent. In this study, we synthesized the GQDs from graphite and deposited on silicon substrate by kinetic spray. The photo luminescent properties of deposited GQD films were analyzed and compared with initial GQDs suspension. In addition, its carbon properties were investigated with GQDs solution properties. The properties of deposited GQD films by kinetic spray were similar to that of the GQDs suspension in water. We could provide a pathway for silicon-based silicon based device applications. Finally, the well-adjusted GQD films with photo luminescence effects will show Energy-Down-Shift layer effects on silicon solar cells. The GQD layers deposited at nozzle scan speeds of 40, 30, 20, and 10 mm/s were evaluated after they were used to fabricate crystalline-silicon solar cells; the results indicate that GQDs play an important role in increasing the optical absorptivity of the cells. The short-circuit current density (Jsc) was enhanced by about 2.94 % (0.9 mA/cm2) at 30 mm/s. Compared to a reference device without a GQD energy-down-shift layer, the PCE of p-type silicon solar cells was improved by 2.7% (0.4 percentage points).

• 한국결정성장학회지
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• 제6권3호
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• pp.351-359
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• 1996

ECR (electron cyclotron resonance) 플라즈마원이 장착되어 있는 화학선에피탁시 (chemical beam epitaxy : CBE) 장치를 사용하여 InAs 양자점 구조형성에 미치는 수소플라즈마의 효과에 대하여 조사하였다. 자기조직화(self-organized)에 의해 GaAs 기판위에서 InAs 양자점의 형성을 RHEED(reflection high energy electron diffraction)로 관측한 결과 수소가스 및 수소플라즈마의 영향을 받지 않은 상태에서는 1.9 ML(monolayer)의 InAs 층성장(layer growth) 후에 형성되는데 비해 수소플아즈마를 조사한 상태에서는 약 2.6 ML의 InAs 층성장(layer growth) 후에 형성되는데 비해 수소플아즈마를 조사한 상태에서는 약 2.6 ML의 InAs층이 성장된 후 뒤늦게 이루어짐을 확인하였다. 기판의 온도 $370^{\circ}C$에서 동일한 조건으로 형성시킨 InAs 양자점의 밀도 및 크기는 수소플라즈마의 영향을 받지 않은 경우 $1.9{\times}10^{11}cm^{-2}$ 및 17.7 nm에서 수소플라즈마를 쪼인 경우 $1.3{\times}10^{11}cm^{-2}$ 및 19.4 nm로 양자점 형성 다소 완화되는 것으로 나타났다. 또한, 수소플아즈마에 의한 InAs 양자점의 PL(photoluminescence) 신호의 적색이동(red shift)과 반치폭 증가로부터 양자점 크기의 증가와 균일성이 다소 감소되는 모습을 알 수 있었다. 이와같은 수소플라즈마의 영향은 GaAs 기판과 InAs 사이의 부정합 변형환화 효과에의해 InAs의 충성장을 강화시키는 원자상 수소의 작용때문인 것으로 고려되었다.

• 공업화학
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• 제28권6호
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• pp.705-713
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• 2017

독창적 물질인 $Bi_2WO_6-GO-TiO_2$ 나노복합체를 쉬운 수열법에 의해 성공적으로 합성하였다. 수열반응을 하는 동안, 그래핀 시트 위에 $Bi_2WO_6$와 $TiO_2$를 도포하였다. 합성한 $Bi_2WO_6-GO-TiO_2$ 복합체형 광촉매는 X-선 회절법(XRD), 주사전자현미경(SEM), 에너지 분산 X-선(EDX) 분석, 투과전자현미경(TEM), 라만분광법, UV-Vis 확산반사 분광법(UV-vis-DRS), 및 X-선 광전자분광기(XPS)에 의하여 특성화하였다. $Bi_2WO_6$ 나노입자는 불규칙한 dark-square block 나노 플페이트 형상을 보였으며, 이산화티탄 나노입자는 퀜텀 도트 사이즈로 그래핀 시트 위 표면을 덮고 있었다. 로다민 비의 분해는 농도감소의 측정과 함께 UV 분광법에 의하여 관찰하였다. 합성된 물질의 광촉매 반응은 Langmuir-Hinshelwood 모델과 띠 이론으로 설명하였다.

• 대한화학회지
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• 제60권2호
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• pp.131-136
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• 2016

CdSe 기반 나노결정의 구리이온에 의한 형광 소광 특성 및 아연이온에 의한 형광 회복 특성을 관찰하였다. 구리이온이 첨가되었을 경우, CdSe 양자점에서는 매우 빠르고 급격한 형광 소광 특성을 보이는 반면에 CdSe 나노라드의 경우에서는 형광이 서서히 소광되는 특성을 보인다. 구리이온으로 형광을 소광시킨 CdSe/CdS(핵/껍질) 양자점에 아연이온이 첨가되면 소광된 양자점의 형광이 회복된다. 용액 내 1 μM의 아연농도에서 양자점의 형광이 50% 증가됨을 확인하였으며, 아연 농도가 증가함에 따라 양자점의 형광세기가 증가되며 이는 Langmuir binding isotherm 모델로 해석할 수 있다. 이러한 연구를 바탕으로 CdSe 기반의 나노결정을 이용한 형광 화학 센서를 구현할 수 있을 것으로 기대한다.

• Bulletin of the Korean Chemical Society
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• 제35권5호
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• pp.1455-1459
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• 2014

We report a sensitive and reliable FRET-based nanotechnology assay for efficient detection and quantification of bisulfite-unmodified or modified DNA. Bisulfite-untreated DNA or bisulfite-treated DNA is subjected to PCR amplification with biotin-conjugated primers so that the amounts of bisulfite-untreated and treated DNA can be differentiated. Streptavidin-coated quantum dots (QDs) are used to capture biotinylated PCR products intercalated with SYBR Green, enabling FRET measurement. Key features of our method include its low intrinsic background noise, high resolution, and high sensitivity, enabling detection of as little as 1.75 ng of bisulfite-untreated DNA in the presence of an approximately 1,000-fold excess of bisulfite-untreated DNA compared to bisulfate-treated DNA, with the use of PCR reduced (as low as 15 cycles). SYBR Green as an intercalating dye as well as a FRET acceptor allows for a single-step preparation without the need for primers or probes to be chemically conjugated to an organic fluorophore. Multiple acceptors per FRET donor significantly enhance the signal-to-noise ratio as well. In consideration of the high relevance of bisulfite treatment to DNA methylation quantitation, our system for FRET measurement between QDs and intercalating dyes can be generally utilized to analyze DNA methylation and to potentially benefit the scientific and clinical community.