• 한국재료학회지
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• 제31권8호
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• pp.465-470
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• 2021

Deuterium is a crucial clean energy source required for nuclear fusion and is a future resource needed in various industries and scientific fields. However, it is not easy to enrich deuterium because the proportion of deuterium in the hydrogen mixture is scarce, at approximately 0.016 %. Furthermore, the physical and chemical properties of the hydrogen mixture and deuterium are very similar. Therefore, the efficient separation of deuterium from hydrogen mixtures is often a significant challenge when using modern separation technologies. Recently, to effectively separate deuterium, studies utilizing the 'Kinetic Quantum Sieving Effect (KQS)' of porous materials are increasing. Therefore, in this review, two different strategies have been discussed for improving KQS efficiency for hydrogen isotope separation performance using nanoporous materials. One is the gating effect, which precisely controls the aperture locally by adjusting the temperature and pressure. The second is the breathing phenomenon, utilizing the volume change of the structure from closed system to open system. It has been reported that efficient hydrogen isotope separation is possible using these two methods, and each of these effects is described in detail in this review. In addition, a specific-isotope responsive system (e.g., 2nd breathing effect in MIL-53) has recently been discovered and is described here as well.

• 한국재료학회지
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• 제22권3호
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• pp.140-144
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• 2012

Compared with bulk material, quantum dots have received increasing attention due to their fascinating physical properties, including optical and electronic properties, which are due to the quantum confinement effect. Especially, Luminescent CdSe quantum dots have been highly investigated due to their tunable size-dependent photoluminescence across the visible spectrum. They are of great interest for technical applications such as light-emitting devices, lasers, and fluorescent labels. In particular, quantum dot-based light-emitting diodes emit high luminance. Quantum dots have very high luminescence properties because of their absorption coefficient and quantum efficiency, which are higher than those of typical dyes. CdSe quantum dots were synthesized as a function of the synthesis time and synthesis temperature. The photoluminescence properties were found strongly to depend on the reaction time and the temperature due to the core size changing. It was also observed that the photoluminescence intensity is decreased with the synthesis time due to the temperature dependence of the band gap. The wavelength of the synthesized quantum dots was about 550-700 nm and the intensity of the photoluminescence increased about 22~70%. After the CdSe quantum dots were synthesized, the particles were found to have grown until reaching a saturated concentration as time increased. Red shift occurred because of the particle growth. The microstructure and phase developments were measured by transmission electron microscopy (TEM) and X-ray diffractometry (XRD), respectively.

• EDISON SW 활용 경진대회 논문집
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• 제3회(2014년)
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• pp.516-520
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• 2014

Fractional quantum Hall Effect (FQSH) is one of most fundamental issues in condensed matter physics, and the Topological insulator becomes its prominent applications. This article reviews the general frameworks of these development and the physical properties. FQSH states and topological insulators are supposed to be topologically invariant under the minor change of geometrical shape or internal impurities. The phase transitions involved in this phenomena are known not to be explained in terms of symmetry breaking or Landau-Ginsburg theory. The new type of phase transitions related to topological invariants has acquired new name - topological phase transition. The intuitive concepts and the other area having same type of phase transitions are discussed.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.477-477
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• 2011

In this paper, we synthesize ZnO wire on Si substrate by catalyst-free thermal chemical vapor deposition (CVD). Each ZnO wire is grew up at different condition such as temperature and O2 flow rate. The Young's modulus of individual ZnO wires were estimated using quasi-static and dynamic measurements, as well as resonance frequency measurements. Using this system, current-voltage characteristics of each ZnO wire structure fabricated on a trench were measured. A new concept of electromechanical device structure combined with the piezoelectric effect of ZnO will be suggested in the end of this paper.

• Applied Science and Convergence Technology
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• 제25권6호
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• pp.158-161
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• 2016

Debye temperature is an important thermodynamical factor in quantum dots (QDs); it can be used to determine the degree of homogeneity of a QD structure as well as to study the interdiffusion mechanism during growth. Direct estimation of the Debye temperature can be obtained using the Varshni relation. The Varshni relation is an empirical formula that can interpret the change of emission energy with temperature as a result of phonon interaction. On the other hand, phonons energy can be calculated using the Fan Expression. The Fan expression and Varshni relation are considered equivalent at a temperature higher than Debye temperature for InAs quantum dot. We investigated InAs quantum dot optically, the photoluminescence spectra and peak position dependency on temperature has been discussed. We applied a mathematical treatment using Fan expression, and the Varshni relation to obtain the Debye temperature and the phonon energy for InAs quantum dots sample. Debye temperature increase about double compared to bulk crystal. We concluded that the In/Ga interdiffusion during growth played a major role in altering the quantum dot thermodynamical parameters.

• 한국전기전자재료학회논문지
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• 제20권10호
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• pp.864-868
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• 2007

Effect of high-temperature annealing on morphology of fully coherent self-assembled InAs quantum dots' grown on Si (100) substrates at $450^{\circ}C$ by atmospheric pressure metalorganic chemical vapor deposition(APMOCVD) was investigated by atomic force microscopy(AFM). When the dots were annealed at 500 - 600$^{\circ}C$ for 15 sec - 60 min, there was no appreciable change in the dot density but the heights of the dots increased along with the reduction in the diameters. In segregation from the InAs quantum dots and/or from the 2-dimensional InAs wetting layer which was not transformed into quantum dots looked responsible for this change in the dot size. However the change rates remained almost same regardless of annealing time and temperature, which may indicate that the morphological change due to thermal annealing is done instantly when the dots are exposed to high temperature annealing.

• Applied Science and Convergence Technology
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• 제25권6호
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• pp.154-157
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• 2016

The energy dispersion and magnetization of a modified magnetic dot are investigated numerically. The effects of additional electrostatic potential, magnetic field non-uniformity, and Zeeman spin splitting are studied. The modified magnetic quantum dot is a magnetically formed quantum structure that has different magnetic fields inside and outside of the dot. The additional electrostatic potential prohibits the ground-state angular momentum transition in the energy dispersion as a function of the magnetic field inside the dot, and provides oscillation of the magnetization as a function of the chemical potential energy. The magnetic field non-uniformity broadens the shape of the magnetization. The Zeeman spin splitting produces additional peaks on the magnetization.

• Electronic Materials Letters
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• 제14권6호
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• pp.774-783
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• 2018

Full maximum-entropy mobility-spectrum analysis (FMEMSA) is the best algorithm among mobility spectrum analyses by which we can obtain a set of partial-conductivities associated with mobility values (mobility spectrum) by analyzing magnetic-field-dependent conductivity-tensors. However, it is restricted to a direct band-gap semiconductor and should be modified for materials with other band structures. We developed the modified version of FMEMSA which is appropriate for a material with a single anisotropic valley, or an indirect-band-gap semiconductor quantum-well with a single non-degenerate conduction-band valley e.g., (110)-oriented AlAs quantum wells with a single anisotropic valley. To demonstrate the reliability of the modified version, we applied it to several sets of synthetic measurement datasets. The results demonstrated that, unlike existing FMEMSA, the modified version could produce accurate mobility spectra of materials with a single anisotropic valley.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2008년도 Asian Magnetics Conference
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• pp.42.2-42.2
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• 2008

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.184-184
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• 2012

Recently, InGaN/GaN multi-quantum well grown on GaN pyramid structures have attracted much attention due to their hybrid characteristics of quantum well, quantum wire, and quantum dot. This gives us broad band emission which will be useful for phosphor-free white light emitting diode. On the other hand, by using quantum dot emission on top of the pyramid, site selective single photon source could be realized. However, these structures still have several limitations for the single photon source. For instance, the quantum efficiency of quantum dot emission should be improved further. As detection systems have limited numerical aperture, collection efficiency is also important issue. It has been known that micro-cavities can be utilized to modify the radiative decay rate and to control the radiation pattern of quantum dot. Researchers have also been interested in nano-cavities using localized surface plasmon. Although the plasmonic cavities have small quality factor due to high loss of metal, it could have small mode volume because plasmonic wavelength is much smaller than the wavelength in the dielectric cavities. In this work, we used localized surface plasmon to improve efficiency of InGaN qunatum dot as a single photon emitter. We could easily get the localized surface plasmon mode after deposit the metal thin film because lnGaN/GaN multi quantum well has the pyramidal geometry. With numerical simulation (i.e., Finite Difference Time Domain method), we observed highly enhanced decay rate and modified radiation pattern. To confirm these localized surface plasmon effect experimentally, we deposited metal thin films on InGaN/GaN pyramid structures using e-beam deposition. Then, photoluminescence and time-resolved photoluminescence were carried out to measure the improvement of radiative decay rate (Purcell factor). By carrying out cathodoluminescence (CL) experiments, spatial-resolved CL images could also be obtained. As we mentioned before, collection efficiency is also important issue to make an efficient single photon emitter. To confirm the radiation pattern of quantum dot, Fourier optics system was used to capture the angular property of emission. We believe that highly focused localized surface plasmon around site-selective InGaN quantum dot could be a feasible single photon emitter.