• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.444-444
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• 2011

Recently, patterned magnetic films and elements attract a wide interest due to their technological potentials in ultrahigh-density magnetic recording and spintronic devices. Among those patterned magnetic structures, magnetic anti-dot patterning induces a strong shape anisotropy in the film, which can control the magnetic properties such as coercivity, permeability, magnetization reversal process, and magneto-resistance. While majority of the previous works have been concentrated on anti-dot arrays with a single magnetic layer, there has been little work on multilayered anti-dot arrays. In this work, we report on study of the magnetic properties of bilayered anti-dot system consisting of upper perforated Co layer of 40 nm and lower continuous Ni layer of 5 nm thick, fabricated by photolithography and wet-etching processes. The magnetic hysteresis (M-H) loops were measured with a superconducting-quantum-interference-device (SQUID) magnetometer (Quantum Design: MPMS). For comparison, investigations on continuous Co thin film and single-layer Co anti-dot arrays were also performed. The magnetic-domain configuration has been measured by using a magnetic force microscope (PSIA: XE-100) equipped with magnetic tips (Nanosensors). An external electromagnet was employed while obtaining the MFM images. The MFM images revealed well-defined periodic domain networks which arise owing to the anisotropies such as magnetic uniaxial anisotropy, configurational anisotropy, etc. The inclusion of holes in a uniform magnetic film and the insertion of a uniform thin Ni layer, drastically affected the coercivity as compared with single Co anti-dot array, without severely affecting the saturation magnetization ($M_s$). The observed changes in the magnetic properties are closely related to the patterning that hinders the domain-wall motion as well as to the magneto-anisotropic bilayer structure.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.541-541
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• 2012

InP quantum dots capped by myristic acid (InP-MA QDs) were synthesized by a typical hot injection method using MA as stablizing agent. The current density across the InP-MA QDs thin film which was fabricated by spin-coating method is about $10^{-4}A/cm^2$ at the electric field of 0.1 MV/cm from I-V measurement on a metal-insulator-metal (MIM) device. The low conductivity of the InP-MA QDs thin film is interpreted as due to the long interdistances among the dots governed by the MA molecules. Therefore, replacing the MA with thioacetic acid (TAA) by biphasic ligand exchange was conducted in order to obtain TAA capped InP QDs (InP-TAA). InP-TAA QDs were designed due to: 1) the TAA is very short molecule; 2) the thiolate groups on the surface of the InP-TAA QDs are expected to undergo condensation reaction upon thermal annealing which connects the QDs within the QD thin film through a very short linker -S-; and 3) TAA provides better passivation to the QDs both in the solution and thin film states which minimizing the effect of surface trapping states.

• Applied Microscopy
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• 제36권spc1호
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• pp.35-40
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• 2006

Self-assembled InAs/GaAs quantum dots (QDs) were grown by the atomic layer epitaxy (ALE) and molecular beam epitaxy (MBE) techniques, The structure and the thermal stability of QDs have been studied by high resolution electron microscopy with in-situ heating experiment capability, The ALE and MBE QDs were found to form a hemispherical structure with side facets in the early stage of growth, Upon capping by GaAs layer, however, the apex of QDs changed to a flat one. The ALE QDs have larger size and more regular shape than those of MBE QDs. The QDs collapse due to elevated temperature was observed directly in atomic scale, In situ heating experiment within TEM revealed that the uncapped QDs remained stable up to $580^{\circ}C$, However, at temperature above $600^{\circ}C$, the QDs collapsed due to the diffusion and evaporation of In and As from the QDs, The density of the QDs decreased abruptly by this collapse and most of them disappeared at above $600^{\circ}C$.

• 한국재료학회지
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• 제16권3호
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• pp.183-187
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• 2006

We present the effects of rapid thermal annealing (RTA) temperature on the structural and optical properties of self-assembled InAs quantum dot (QD) structures grown on GaAs substrates by molecular beam epitaxy (MBE). The photoluminescence (PL) measurements are performed in a closed-cycle refrigerator as a function of temperature for the unannealed and annealed samples. RTA at higher temperature results in the increase in island size, the corresponding decrease in the density of islands, and the redshift in the PL emission from the islands. The temperature dependence of the PL peak energy for the InAs QDs is well expressed by the Varshni equation. The thermal quenching activation energies for the samples unannealed and annealed at $600^{\circ}C$ are found to be $25{\pm}5meV$ and $47{\pm}5$ meV, respectively.

• 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.

• 한국세라믹학회지
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• 제55권2호
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• pp.174-177
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• 2018

ZnO/Ag/ZnO multilayers were fabricated and their optical properties were investigated in terms of the micro-cavity effect in electroluminescent devices based on colloidal quantum dots. The top and bottom ZnO layers were formed by a sol-gel method while the middle Ag layer was deposited by thermal evaporation. After the fabrication of the ZnO/Ag/ZnO structure, the transmittance increased to 74%. When the oxide/metal/oxide multilayers were applied to quantum dot light-emitting diodes, the color purity was enhanced due to the narrower full width at half maximum.

• The Plant Pathology Journal
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• 제34권2호
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• pp.85-92
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• 2018

Enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR), widely used for the detection of plant viruses, are not easily performed, resulting in a demand for an innovative and more efficient diagnostic method. This paper summarizes the characteristics and research trends of biosensors focusing on the physicochemical properties of both interface elements and bioconjugates. In particular, the topological and photophysical properties of quantum dots (QDs) are discussed, along with QD-based biosensors and their practical applications. The QD-based Fluorescence Resonance Energy Transfer (FRET) genosensor, most widely used in the biomolecule detection fields, and QD-based nanosensor for Rev-RRE interaction assay are presented as examples. In recent years, QD-based biosensors have emerged as a new class of sensor and are expected to open opportunities in plant virus detection, but as yet there have been very few practical applications (Table 3). In this article, the details of those cases and their significance for the future of plant virus detection will be discussed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.428-428
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• 2013

Red color light emitting diodes were fabricated using CdSe/CdS/ZnS quantum dots (QDs). Patterned indium-tin-oxide (ITO) was used as a transparent anode, and oxygen plasma treatment on a surface of ITO was performed. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) was spin coated on the ITO surface as a hole injection layer. Then CdSe/CdS/ZnS QDs was spin coated and thermal treatment was performed for the cross-linking of QDs. TiO2 was coated on the QDs as an electron transport layer, and 150 nm of aluminum cathode was formed using thermal evaporator and shadow mask. The device shows a pure red color emission at 606 nm wavelength. Device characteristics will be presented in detail.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 2000년도 Proceedings of 2000 International Nano Crystals/Ceramics Forum and International Symposium on Intermaterials
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• pp.87-125
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• 2000

A new paradigm of crystal growth was suggested in a charged cluster model, where charged clusters of nanometer size are suspended in the gas phase in most thin film processes and are a major flux for thin film growth. The existence of these hypothetical clusters was experimentally confirmed in the diamond and silicon CVD processes as well as in gold and tungsten evaporation. These results imply new insights as to the low pressure diamond synthesis without hydrogen, epitaxial growth, selective deposition and fabrication of quantum dots, nanometer-sized powders and nanowires or nanotubes. Based on this concept, we produced such quantum dot structures of carbon, silicon, gold and tungsten. Charged clusters land preferably on conducting substrates over on insulating substrates, resulting in selective deposition. if the behavior of selective deposition is properly controlled, charged clusters can make highly anisotropic growth, leading to nanowires or nanotubes.

• 한국진공학회지
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• 제16권1호
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• pp.27-32
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• 2007

양자우물의 두께가 다른 4종류의 $In_xGa_{1-x}N(x=0.15)/GaN$ 다중 양자우물 구조의 PL 스펙트럼을 분석하여 InGaN에서의 결정상 분리 현상을 조사하였다. 우물폭이 1.5 nm에서 6.0 nm로 증가함에 따라, PL스펙트럼은 비대칭성이 점점 강해지는 이중 피크의 특성을 나타내었다. 곡선맞춤을 수행하여 분리한 2개의 피크를 분석하여, InGaN 우물에서의 부준위 천이에 해당하는 고에너지 피크의 세기는 줄어드는 반면, 상분리에 의하여 생성된 저에너지 피크의 강도는 점점 강해짐을 볼 수 있었다. 이것은 InGaN 우물에는 In 조성이 다소 다른 2개의 결정상이 존재하여, 우물폭 증가와 함께 InN 상분리가 강해지면서 In 조성이 큰(In-rich) InGaN 결정상이 상대적으로 증대됨을 보여 주는 결과로 해석된다. 우물 두께가 6.0 nm인 시료에서는 저에너지 영역(${\sim}2.0eV$)에서 또 하나의 피크이 관측되었는데, 이것은 GaN에서 잘 알려져 있는 결함에 기인한 황색준위(YB)와 그 근원이 같은 것으로, InN의 상분리가 임계값 이상으로 발달하여 생성된 결함과 관련된 준위인 것으로 해석된다.