• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
• /
• pp.132.2-132.2
• /
• 2013

Electrons in graphene make ballistic transport with very high mobility (${\sim}2{\times}105 $cm2V-1s-1), which holds promises for applications in fast electronic devices. However, such expectations have been hampered by the semi-metallicity or zero bandgap of graphene, which makes it impossible to completely turn off graphene transistor devices. Here, we report the observations of local bandgap modulations in Moir$\acute{e}$ patterned graphene on metal substrates using scanning tunneling microscopy and spectroscopy. The Moir$\acute{e}$ patterned graphene was made by combinations of self-assembly processes, and they showed additional electronic states that could be interpreted as sub-band states. Our experimental observations could be explained with orbital transitions of carbon atoms from sp2 to sp3, as supported by our density functional theory calculation results. Our findings will add new poweful components for device applications.

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

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
• /
• pp.172-173
• /
• 2012

Currently GaN based LED is known to show high internal or external efficiency at low current range. However, this LED operation occurs at high current range and in this range, a significant performance degradation known as 'efficiency droop' occurs. Auger process, carrier leakage process, field effect due to lattice mismatch and thermal effects have been discussed as the causes of loss of efficiency, and these phenomena are major hindrance in LED performance. In order to investigate the main effects of efficiency loss and overcome such effects, it is essential to obtain relative proportion of measurements of internal quantum efficiency (IQE) and various radiative and nonradiative recombination processes. Also, it is very important to obtain radiative and non-radiative recombination times in LEDs. In this research, we measured the IQE of InGaN/GaN multiple quantum wells (MQWs) LEDs with PSS and Planar substrate using modified ABC equation, and investigated the physical mechanism behind by analyzing the emission energy, full-width half maximum (FWHM) of the emission spectra, and carrier recombination dynamic by time-resolved electroluminescence (TREL) measurement using pulse current generator. The LED layer structures were grown on a c-plane sapphire substrate and the active region consists of five 30 ${\AA}$ thick In0.15Ga0.85N QWs. The dimension of the fabricated LED chip was $800um{\times}300um$. Fig. 1. is shown external quantum efficiency (EQE) of both samples. Peak efficiency of LED with PSS is 92% and peak efficiency of LED with planar substrate is 82%. We also confirm that droop of PSS sample is slightly larger than planar substrate sample. Fig. 2 is shown that analysis of relation between IQE and decay time with increasing current using TREL method.

• 한국진공학회:학술대회논문집
• /
• 한국진공학회 2009년도 제38회 동계학술대회 초록집
• /
• pp.121-121
• /
• 2010

ZnO is a promising material for the application of high efficiency light emitting diodes with short wavelength region for its large bandgap energy of 3.37 eV which is similar to GaN (3.39 eV) at room temperature. The large exciton binding energy of 60 meV in ZnO provide provides higher efficiency of emission for optoelectronic device applications. Several ZnO/ZnMgO multiple quantum well (MQW) structures have been grown on various substrates such as sapphire, GaN, Si, and so on. However, the achievement of high quality ZnO/ZnMgO MQW structures has been somehow limited by the use of lattice-mismatched substrates. Therefore, we propose the optical properties of ZnO/ZnMgO multiple quantum well (MQW) structures with different well widths grown on lattice-matched ZnO substrates by molecular beam epitaxy. Photoluminescence (PL) spectra show MQW emissions at 3.387 and 3.369 eV for the ZnO/ZnMgO MQW samples with well widths of 2 and 5 nm, respectively, due to the quantum confinement effect. Time-resolved PL results show an efficient photo-generated carrier transfer from the barrier to the MQWs, which leads to an increased intensity ratio of the well to barrier emissions for the ZnO/ZnMgO MQW sample with the wider width. From the power-dependent PL spectra, we observed no PL peak shift of MQW emission in both samples, indicating a negligible built-in electric field effect in the ZnO/$Zn_{0.9}Mg_{0.1}O$ MQWs grown on lattice-matched ZnO substrates.

• 한국섬유공학회:학술대회논문집
• /
• 한국섬유공학회 2007년도 학술발표회 논문집
• /
• pp.7-9
• /
• 2007

See Full Text

• 한국표면공학회:학술대회논문집
• /
• 한국표면공학회 2006년도 춘계학술발표회 초록집
• /
• pp.11-11
• /
• 2006

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2009년도 Korea Superconductivity Society Meeting 2009
• /
• pp.9-9
• /
• 2009

• Asian Pacific Journal of Cancer Prevention
• /
• 제14권4호
• /
• pp.2213-2216
• /
• 2013

Recently, use of natural products available from marine sources, and especially algae products, are receiving more attention. Scientific evidence for claimed nutraceutical and therapeutical effects of one such marine algae product, fucoxanthin, is discussed in this paper with a summary of the currently available literature regarding its antioxidant, anti-obesity and anticancer activities. It is safe for use in humans, but as it has poor solubility a nano-suspension mode of delivery may be adopted to improve efficacy of supplments. We conclude from ourliterature review that the marine algae product fucoxanthin has significant antioxidant, anti-obesity and anticancer activity with established mechanisms of action.

• Advances in nano research
• /
• 제1권4호
• /
• pp.211-218
• /
• 2013

A low-cost, green and reproducible citric acid assisted synthesis of nanocrystalline $Al_{0.5}Ag_{0.5}TiO_3$ (n-AAT) powder is reported. X-ray, FTIR, energy dispersive X-ray, transmission electron microscopy and scanning electron microscopy analyses are performed to ascertain the formation of n-AAT. X-ray diffraction data analysis indicated the formation of monoclinic structure. Spherical shaped particles having the sizes of 3-15 nm are found. The mechanism of nano-transformation for the soft-chemical synthesis of n-AAT has been explained using simple organic chemistry rules and nucleation and growth theory. Dielectric study revealed that AAT ceramic might be a suitable candidate for capacitor applications.

• Journal of Microbiology and Biotechnology
• /
• 제30권1호
• /
• pp.1-10
• /
• 2020

FK506, also known as tacrolimus, is a clinically important immunosuppressant drug and has promising therapeutic potentials owing to its antifungal, neuroprotective, and neuroregenerative activities. To generate various FK506 derivatives, the structure of FK506 has been modified by chemical methods or biosynthetic pathway engineering. Herein, we describe the mode of the antifungal action of FK506 and the structure-activity relationship of FK506 derivatives in the context of immunosuppressive and antifungal activities. In addition, we discuss the neurotrophic mechanism of FK506 known to date, along with the neurotrophic FK506 derivatives with significantly reduced immunosuppressive activity. This review suggests the possibility to generate novel FK506 derivatives as antifungal as well as neuroregenerative/neuroprotective agents.