• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.451-451
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• 2012

Instead of a highly toxic CdSe and ZnScore-shell,InP/ZnSecore-shell quantum dots [1,2] were investigated as an active material for quantum dot light emitting diode (QD-LED). In this paper, aquantum dot light-emitting diode (QDLED), consisting of a InP/ZnS core-shell type materials, with the device structure of glass/indium-tin-oxide (ITO)/PEDOT:PSS/Poly-TPD/InP-ZnS core-shell quantum dot/Cesium carbonate(CsCO3)/Al was fabricated through a simple spin coating technique. The resulting InP/ZnS core-shell QDs, emitting near blue green wavelength, were more efficient than the above CdSe QDs, and their luminescent properties were comparable to those of CdSe QDs.Thebrightness ofInP/ZnS QDLED was maximumof 179cd/m2.

• Current Optics and Photonics
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• 제4권3호
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• pp.161-173
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• 2020

Colloidal quantum dots (QDs) have gained tremendous attention as a key material for highly advanced display technologies. The performance of QD light-emitting diodes (QLEDs) has improved significantly over the past two decades, owing to notable progress in both material development and device engineering. The brightness of QLEDs has improved by more than three orders of magnitude from that of early-stage devices, and has attained a value in the range of traditional inorganic LEDs. The emergence of high-luminance (HL) QLEDs has induced fresh demands to incorporate the unique features of QDs into a wide range of display applications, beyond indoor and mobile displays. Therefore it is necessary to assess the present status and prospects of HL-QLEDs, to expand the application domain of QD-based light sources. As part of this study, we review recent advances in HL-QLEDs. In particular, based on reports of brightness exceeding 10⁵ cd/㎡, we have summarized the major approaches toward achieving high brightness in QLEDs, in terms of material development and device engineering. Furthermore, we briefly introduce the recent progress achieved toward QD laser diodes, being the next step in the development of HL-QLEDs. This review provides general guidelines for achieving HL-QLEDs, and reveals the high potential of QDs as a universal material solution that can enable realization of a wide range of display applications.

• 대한금속재료학회지
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• 제56권12호
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• pp.900-909
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• 2018

A $ZnO/TiO_2$ photocatalyst decorated with PbS quantum dots (QDs) was synthesized to achieve high photocatalytic efficiency for the decomposition of dye in aqueous media. A $TiO_2$ porous layer, as a precursor photocatalyst, was fabricated using micro-arc oxidation, and exhibited irregular porous cells with anatase and rutile crystalline structures. Then, a ZnO-deposited $TiO_2$ catalyst was fabricated using a zinc acetate solution, and PbS QDs were uniformly deposited on the surface of the $ZnO/TiO_2$ photocatalyst using the successive ionic layer adsorption and reaction (SILAR) technique. For the PbS $QDs/ZnO/TiO_2$ photocatalyst, ZnO and PbS nanoparticles are uniformly precipitated on the $TiO_2$ surface. However, the diameters of the PbS particles were very fine, and their shape and distribution were relatively more homogeneous compared to the ZnO particles on the $TiO_2$ surface. The PbS QDs on the $TiO_2$ surface can induce changes in band gap energy due to the quantum confinement effect. The effective band gap of the PbS QDs was calculated to be 1.43 eV. To evaluate their photocatalytic properties, Aniline blue decomposition tests were performed. The presence of ZnO and PbS nanoparticles on the $TiO_2$ catalysts enhanced photoactivity by improving the absorption of visible light. The PbS $QDs/ZnO/TiO_2$ heterojunction photocatalyst showed a higher Aniline blue decomposition rate and photocatalytic activity, due to the quantum size effect of the PbS nanoparticles, and the more efficient transport of charge carriers.

• 한국분말재료학회지
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• 제27권2호
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• pp.154-163
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• 2020

Fluorescent nanoparticles are characterized by their unique properties such as luminescence, optical transparency, and sensitivity to various chemical environments. For example, semiconductor nanocrystals (quantum dots), which are nanophosphors doped with transition metal or rare earth ions, can be classified as fluorescent nanoparticles. Tuning their optical and physico-chemical properties can be carried out by considering and taking advantage of nanoscale effects. For instance, quantum confinement causes a much higher fluorescence with nanoparticles than with their bulk counterparts. Recently, various types of fluorescent nanoparticles have been synthesized to extend their applications to other fields. In this study, State-of-the-art fluorescent nanoparticles are reviewed with emphasis on their analytical and anti-counterfeiting applications and synthesis processes. Moreover, the fundamental principles behind the exceptional properties of fluorescent nanoparticles are discussed.

• 마이크로전자및패키징학회지
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• 제26권3호
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• pp.71-74
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• 2019

본 연구는 발광층으로의 전자 주입을 억제하기 위해 ZnO 나노입자보다 낮은 전자 이동도를 갖는 $TiO_2$ 나노입자를 무기 전자 수송층으로 사용하여 standard와 inverted 두 가지 구조의 양자점 전계발광 소자를 제작하고 그 특성을 비교하였다. Standard 구조의 소자에서는 전류 밀도가 낮은 것에 비해 inverted 구조의 소자에서는 전류 밀도가 매우 높은 것을 확인하였다. 휘도의 경우 inverted 구조의 소자가 standard 구조의 소자보다 더 높았지만 높은 전류 밀도로 인해 낮은 전류 효율을 나타냈다. 또한 전류 밀도가 높은 만큼 구동 전압이 높았으며, 방출 파장 스펙트럼에서 적색 편이를 확인하였다. Standard 구조의 소자에서 나타난 낮은 전류 밀도를 통해, $TiO_2$ 나노입자가 양자점 전계발광 소자에서 전자 주입을 억제할 수 있는 가능성을 확인하였다.

• Advances in nano research
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• 제5권1호
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• pp.13-25
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• 2017

We examine the total optical dielectric function (TODF) of impurity doped GaAs quantum dot (QD) from the viewpoint of anisotropy, position-dependent effective mass (PDEM) and position dependent dielectric screening function (PDDSF), both in presence and absence of noise. The dopant impurity potential is Gaussian in nature and noise employed is Gaussian white noise that has been applied to the doped system via two different modes; additive and multiplicative. A change from fixed effective mass and fixed dielectric constant to those which depend on the dopant coordinate manifestly affects TODF. Presence of noise and also its mode of application bring about more rich subtlety in the observed TODF profiles. The findings indicate promising scope of harnessing the TODF of doped QD systems through expedient control of site of dopant incorporation and application of noise in desired mode.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.221-221
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• 2013

Striving to replace the well known silicon nanocrystals embedded in oxides with solution-processable charge-trapping materials has been debated because of large scale and cost effective demands. Herein, a silicon quantum dot-polystyrene nanocomposite (SiQD-PS NC) was synthesized by postfunctionalization of hydrogen-terminated silicon quantum dots (H-SiQDs) with styrene using a thermally induced surface-initiated polymerization approach. The NC contains two miscible components: PS and SiQD@PS, which respectively are polystyrene and polystyrene chains-capped SiQDs. Spin-coated films of the nanocomposite on various substrate were thermally annealed at different temperatures and subsequently used to construct metal-insulator-semiconductor (MIS) devices and thin film field effect transistors (TFTs) having a structure p-$S^{++}$/$SiO_2$/NC/pentacene/Au source-drain. C-V curves obtained from the MIS devices exhibit a well-defined counterclockwise hysteresis with negative fat band shifts, which was stable over a wide range of curing temperature ($50{\sim}250^{\circ}C$. The positive charge trapping capability of the NC originates from the spherical potential well structure of the SiQD@PS component while the strong chemical bonding between SiQDs and polystyrene chains accounts for the thermal stability of the charge trapping property. The transfer curve of the transistor was controllably shifted to the negative direction by chaining applied gate voltage. Thereby, this newly synthesized and solution processable SiQD-PS nanocomposite is applicable as charge trapping materials for TFT based memory devices.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.400.1-400.1
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• 2016

Interfacial engineering approaches as an efficient strategy for improving the power conversion efficiencies (PCEs) of inverted polymer solar cells (iPSCs) has attracted considerable attention. Recently, polymer surface modifiers, such as poly(ethyleneimine) (PEI) and polyethylenimine ethoxylated (PEIE), were introduced to produce low WF electrodes and were reported to have good electron selectivity for inverted polymer solar cells (iPSCs) without an n-type metal oxide layer. To obtain more efficient solar cells, quantum dots (QDs) are used as effective sensitizers across a broad spectral range from visible to near IR. Additionally, they have the ability to efficiently generate multiple excitons from a single photon via a process called carrier multiplication (CM) or multiple exciton generation (MEG). However, in general, it is very difficult to prepare a bilayer structure with an organic layer and a QD interlayer through a solution process, because most solvents can dissolve and destroy the organic layer and QD interlayer. To present a more effective strategy for surpassing the limitations of traditional methods, we studied and fabricated the highly efficient iPSCs with mono-layered QDs as an effective multi-functional layer, to enhance the quantum yield caused by various effects of QDs monolayer. The mono-layered QDs play the multi-functional role as surface modifier, sub-photosensitizer and electron transport layer. Using this effective approach, we achieve the highest conversion efficiency of ~10.3% resulting from improved interfacial properties and efficient charge transfer, which is verified by various analysis tools.

• 한국전기전자재료학회논문지
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• 제29권12호
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• pp.737-749
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• 2016

Recently perovskite materials with much cheaper cost and marvellous optoelectronic properties have been studied for next generation LED display devices overseas. Technology development trends of inorganic $CsPbX_3$(X=halogen) based LEDs (PeLEDs) with assumed high stability were investigated on literature worldwide. It was found that syntheses methods of these nanocrystals (NCs, mainly quantum dots, QDs) made great progress. A new room temperature synthesis method showed outstanding PL (photoluminescence) properties such as high quantum yield (QY), narrow emission width, storage stability comparable with, or often exceeding those of conventional hot injection method and CdSe@ZnS type inorganic colloidal QDs. PeLEDs with shell layers might be more promising, indicating urgent real research start of this solution processing technology for small businesses in Korea.

• Journal of Electrical Engineering and Technology
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• 제6권4호
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• pp.535-538
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• 2011

The electromodulation methods of photoreflectanceand the related technique of contactless electroreflectance(CER) are valuable tools in the evaluation of important device parameters for structures such as heterojunction bipolar transistors, pseudomorphic high electron mobility transistors, and quantum dots(QDs). CER is a very general principle of experimental physics. Instead of measuring the optical reflectance of the material, the derivative with respect to a modulating electric field is evaluated. This procedure generates sharp, differential-like spectra in the region of interband (intersubband) transitions. We conduct electric-optical studies of both GaAs layers and InAs selfassembled QDs grown by molecular beam epitaxy. Strong GaAsbandgap energy is measured in both structures. In the case of lnAs monolayers in GaAs matrices, the strong GaAsbandgap energy is caused by the lateral quantum confinement.