• 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.

• Korean Journal of Metals and Materials
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• v.48 no.4
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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.

• Carbon letters
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• v.15 no.2
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• pp.77-88
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• 2014

Double walled carbon nanotubes (DWCNTs) are considered an ideal model for studying the coupling interactions between different concentric shells in multi-walled CNTs. Due to their intrinsic coaxial structures they are mechanically, thermally, and structurally more stable than single walled CNTs. Geometrically, owing to the buffer-like function of the outer tubes in DWCNTs, the inner tubes exhibit exciting transport and optical properties that lend them promise in the fabrication of field-effect transistors, stable field emitters, and lithium ion batteries. In addition, by utilizing the outer tube chemistry, DWCNTs can be useful for anchoring semiconducting quantum dots and also as effective multifunctional fillers in producing tough, conductive transparent polymer films. The inner tubes meanwhile preserve their excitonic transitions. This article reviews the synthesis of DWCNTs, their electronic structure, transport, and mechanical properties, and their potential uses.

• Bulletin of the Korean Chemical Society
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• v.32 no.1
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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.

• Journal of Powder Materials
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• v.24 no.3
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• pp.216-222
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• 2017

Synthesized monocrystalline nanodiamond (nD) particles are heat-treated at various temperatures to produce highly structured diamond crystals. The heat-treated nDs show different weight loss ratios during thermogravimetric analysis. The crystallinities of the heat-treated nDs are analyzed using Raman spectroscopy. The average particle sizes of the heat-treated nDs are measured by a dynamic light scattering (DLS) system and direct imaging observation methods. Moreover, individual dispersion behaviors of the heat-treated nD particles are investigated based on ultrasonic dispersion methods. The average particle sizes of the dispersed nDs according to the two different measurement methods show very similar size distributions. Thus, it is possible to produce highly crystallized nD powder particles by a heat-treatment process, and the nD particles are relatively easy to disperse individually without any dispersant. The heat-treated nDs can lead to potential applications such as in nanocomposites, quantum dots, and biomedical materials.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.3
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• pp.351-359
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• 1996

We have investigated the effect of hydrogen plasma on the formation of InAs QDs (quantum dots) structure by using a CBE (chemical beam epitaxy)system equipped with ECR (electron cyclotron resonance) plasma source. It is confirmed that the formation of self-organized InAs-QDs on GaAs is started after the growth of InAs layer up to 2.6 ML (monolayer) with the irradiation of hydrogen plasma while it is started after 1.9 ML without hydrogen gas and hydrogen plasma through the observation of RHEED patterns. Density and size of the QDs formed at $T_{sub}=370^{\circ}C$ are $1.9{\times}10^{11}cm^{-2}$ and 17.7 nm without hydrogen plasma, and $1.3{\times}10^{11}cm^{-2}$ and 19.4 nm with hydrogen plasma, respectively. It is also observed from the PL(photoluminescence) measurement on InAs-QDs that red shift in PL peak energy and broadening in FWHM (full width at half maximum)of PL peak caused by the effects of hydrogen plasma on the increment of size and its distribution. These effects of hydrogen plasma are considered as a act of atomic hydrogen which enhances the layer-growth of InAs on GaAs resulted from the relief of misfit strain between GaAs substrate and InAs.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.194.2-194.2
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• 2015

본 논문에서는 InP 기판에 자발형성법 (Self-assembled Mode)으로 성장한 InAs/InAlGaAs 양자점(Quantum Dots)의 외부 열처리 온도에 따른 광학적 특성을 논의한다. 분자선증착기 (Molecular Beam Epitaxy, VH80MBE)로 5주기 적층구조를 갖는 InAs/InAlGaAs 양자점 시료 (기준시료)를 성장 후 온도 의존성 및 여기광세기 의존성 포토루미네슨스 (photoluminescence, PL) 분광법으로 기본특성을 평가하였다. 양자점 시료를 $500{\sim}800^{\circ}C$에서 열처리를 수행하고 광학적 특성을 열처리 전과 비교하여 분석하였다. $550^{\circ}C$에서 열처리한 InAs/InAlGaAs 양자점 시료의 저온 (11K) PL 파장은 1465 nm를 보였으며, 이는 열처리를 하지 않은 기준시료의 1452 nm 보다 13 nm 장파장으로 이동하였다. 열처리 온도가 $700^{\circ}C$ 이상인 경우, 양자점 PL 파장이 다시 단파장으로 이동하는 현상을 보였지만 여전히 열처리하지 않은 기준시료보다 장파장을 나타내었다. $700^{\circ}C$에서 열처리한 양자점 시료의 저온 PL 광세기는 기준시료보다 15.5배 더 크게 나타났으며, 주변 온도가 증가할수록 더디게 감소하는 것을 확인할 수 있었다. 온도의존성 PL로부터 구한 활성화에너지 (Activation Energy)는 $700^{\circ}C$ 열처리 온도의 경우 175.9 meV를 나타내었다. InAs/InAlGaAs 양자점 시료의 열처리 온도에 따른 광특성 변화를 InAs 양자점과 InAlGaAs 장벽층 계면에서 III족 원소인 In, Al 및 Ga의 상호확산과 결함이 완화되는 현상으로 해석할 수 있다.

• Journal of the Korean Vacuum Society
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• v.15 no.3
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• pp.280-286
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• 2006

A distributed Bragg reflector (DBR) for the application of $1.3{\mu}m$ vertical cavity surface emitting laser (VCSEL) has grown by digital-alloy AlGaAs layer using the molecular beam epitaxy (MBE) method. The measured reflection spectra of the digital-alloy AlGaAs/GaAs DBR have uniformity in 0.35% over the 1/4 of 3-inch wafer. Furthermore, the TEM image showed that the composition and the thickness of the digital-alloy AlGaAs layer in AlGaAs/GaAs DBR was not affected by the temperature distribution over the wafer whole surface. Therefore, the digital-alloy AlGaAs/GaAs DBR can be used to get higher yield of VCSEL with the active medium of InAs quantum dots whose gain is inhomogeneously broadened.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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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.

• Journal of Sensor Science and Technology
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• v.32 no.5
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• pp.285-289
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• 2023

Recently, the demand for lidar systems for autonomous driving is increasing, and research on Shortwave Infrared(SWIR) photodetectors for this purpose is being actively conducted. Most SWIR photodetectors currently being developed are based on InGaAs, and have the disadvantages of complex processes, high prices, and limitations in research due to monopoly. In addition, current SWIR photodetectors use lasers in the 905 nm wavelength band, which can pass through the pupil and cause damage to the retina. Therefore, it is required to develop a SWIR photodetector using a wavelength band of 1400 nm or more to be safe for human eyes, and to develop a material that can replace the proprietary InGaAs. PbS QDs are group 4-6 compound semiconductors whose absorption wavelength band can be adjusted from 1000 to 2700 nm, and have the advantage of being simple to process. Therefore, in this study, PbS QDs having an absorption wavelength peak of 1415 nm were synthesized, and a SWIR photodetector was fabricated using this. In addition, the photodetector's responsivity was improved by applying P3HT and ZnO NPs to improve electron hole mobility. As a result of the experiment, it was confirmed that the synthesized PbS QDs had excellent FWHM characteristics compared to commercial PbS QDs, and it was confirmed that the photodetector had a maximum current change of about 1.6 times.