Quick Phase Search Method on an Adsorbed System

유대황,김형국,류기홍,이호섭,백현종,황윤회 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.I

The desorption rate of adsorbed nitrogen on planar graphite was measured as the change in the adsorbed amount with increasing temperature. There exist regions in which the desorption rate changes with increasing temperature, and the regions coincide with the phase boundaries of nitrogen on graphite. These regions are caused by changes in the binding energy and the heat of adsorption under a phase transition in the adsorbed system, which affects the interaction between an adsorbed particle and either neighboring particles or the substrate. Those results show that this temperature scanning adsorption method is useful for a rough search of phases and phase boundaries in an adsorbed system without the help of other auxiliary measurements such as heat capacity measurements. This method is different from the traditional isothermal adsorption process in which much effort is needed to follow measurements repeated at different temperatures and in which other experimental methods are needed to obtain information for phases and phase changes related to the phase diagram for the adsorbed system. Through this experimental method, we can easily find the phases and the phase boundaries needed to complete the phase diagram of the adsorbed system, so the method saves much time for traditional isothermal adsorption experiments.

에너지수확 관점에서의 압전 및 변전 효과: 나노발전기

황윤회(Yoon-Hwae HWANG) 한국물리학회 2021 물리학과 첨단기술 Vol.30 No.9

Binding Energy of Oxigen and Methane Adsorbed on Bundles of Open-Ended Single-Wall Carbon Nanotubes

서주연,유대황,곽진성,황윤회,김형국 부산대학교 유전체물성연구소 2004 유전체 논문집 Vol.3 No.

The adsorption of oxygen and methane on the bundles of open-ended single wall carbon nanotube(SWNT) was studied using the volumetric adsorption qst was obtained from the adsorption isotherm measurements performed at different temperatures. The trend in the values of the methane isosteric heat of adsorption showed three regions, representative of the adsorption on the different types of adsorption sites. In case of oxygen, on the other hand, such distinguishable regions were not appeared in the N-qst graph. From the results of qst the binding energies of oxygen and methane adsorbed on open-ended SWITs were estimated.

In-Situ Size Measurement of Nano-Sized Colloidal Particles

서정아,황윤회,김형국,Hyun-Joung Kwon 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.5I

The size of nano-particles was measured by using photon correlation spectroscopy and dielectric loss spectroscopy. The size was estimated from the relaxation time by using the Stoke-Einstein relation. The results obtained from the two different methods were in good agreement and were further confirmed via conventional scanning probe microscopy. Therefore, photon correlation spectroscopy and dielectric loss spectroscopy are convenient techniques for measuring the nano-sized biomaterials and colloidal particles.

Relaxation behaviors of enantiomorphic S-ibuprofen as revealed by dielectric and photon correlation spectroscopies

신동명,황윤회,고재현,Seiji Kojima 한국물리학회 2015 Current Applied Physics Vol.15 No.9

Relaxation behaviors of enantiomorphic S-ibuprofen were investigated in its amorphous state by using dielectric and photon correlation spectroscopies. The dielectric relaxation processes of the S-ibuprofen were nearly identical to those of the racemic RS-ibuprofen. The relaxation parameters and the dielectric strengths of the a-process and the D-process for the S-ibuprofen were very similar to those for the RSibuprofen. These results indicate that the stereochemistry of ibuprofen molecules do not have any substantial effect on molecular motions in the amorphous state of ibuprofen. The relaxation times of the main relaxation process probed by using the photon correlation spectroscopy were consistent with those of the dielectric a-process. The fragility of the S-ibuprofen was 76, which was nearly the same to that determined based on the thermal relaxation times and smaller than that of the racemic compound.

자가 형성된 보머-웨버(Volmer-Weber)형 산화아연 나노 결정체의 시분해 광발광 특성 연구

박세정,황윤회,김형국,박소현,주태하,이익재,김진우,이재호,김양도 한국물리학회 2009 새물리 Vol.58 No.4

Self-assembled Volmer-Weber-type ZnO nanocrystals were fabricated on Pt(111)/TiO2/SiO2/Si(100) substrates by using a RF sputtering method. The structure was analyzed by using a synchrotron X-ray method (at beamline 5C2, Pohang Acceleration Laboratory). The temperature-dependent photoluminescence of the Volmer-Weber ZnO nanocrystals was measured from 6 K to 300 K, and the time-resolved photoluminescence was measured at 12 K. We found from the X-ray experiment that the Volmer-Weber-type ZnO nanocrystals had a c-axis orientation. In the temperature-dependent photoluminescence experiment, two intensive UV emissions, 3.368 eV and 3.312 eV, were observed between 6 K and 20 K. As the temperature was increased, the two peaks combined into one at 3.299 eV. In the time-resolved photoluminescence experiment at 12 K, the dynamics of the peaks at 3.368 eV had one relaxation time of approximately 180 ps and that of the peak at 3.312 eV had three relaxation times of 79 ps, 870 ps and 2.2 ns. 라디오 주파수 마그네트론 스퍼터링 방법을 이용하여 제작한 자가 형성된 보머-웨버 (Volmer-Weber)형 산화아연 나노 결정체의 광학적 특성을 연구하였다. 먼저, 방사광 엑스선 회절 실험 (포항가속기 연구소 5C2 빔라인)을 이용하여 산화아연 나노 결정체의 구조를 분석하였고, 헬륨-카드뮴 레이저 (325 nm)를 이용하여 6 K~ 300 K 범위에서 온도 의존성 광발광 (temperature dependent photoluminescence) 특성과 펨토초 레이저를 이용한 저온 시분해 발광 (low-temperature time-resolved photoluminescence) 특성을 연구하였다. 엑스선 회절 실험에서는 보머-웨버형 산화아연 나노 결정체들이 c축 우선 방향성을 보였다. 온도 의존 광발광 실험에서는 보머-웨버형 산화아연 나노 결정체가 낮은 온도 영역 (6 K~20 K)에서 3.368 eV와 3.312 eV의 두 개의 강한 자외선 발광 특성을 보이나 온도가 증가하면서 두 봉우리가 상온에서 3.299 eV의 에너지를 가지는 하나의 봉우리로 합쳐졌다. 12 K에서 수행된 시분해 광발광 실험에서 측정한 감쇄 함수는 3.368 eV 발광 봉우리의 경우 하나의 완화시간으로 분석할 수 있었으나, 3.312 eV 발광 봉우리는 세 개의 완화시간으로 분석이 가능하였다.

Investigation of Ultraviolet Carrier Recombination of Volmer-Weber Type ZnO Nanocrystals and Nanorods through Varshni’s Formula and Arrhenius Plots

박세정,황윤회,김형국 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.3

The carrier recombination in Volmer-Weber-type ZnO nanocrystals (VW ZnO NCs) and Volmer-Weber-type ZnO nanorods (VW ZnO NRs) synthesized by using a physical sputtering method and a hydrothermal method, respectively, was investigated by using temperature-dependent photoluminescence. The main mechanism of UV emission observed in both materials was attributed to the neutral donor bound to the exciton (D0X) and a two-electron satellite (TES). Using the energies of D0X and its TES, we found that the donor binding energy was higher than that of a ZnO crystal. The change in the main carrier recombination and the activation energy were estimated using Varshni’s formula and an Arrhenius plot, respectively. For the VW ZnO NCs, the change from D0X to free exciton (FX) was examined at 150 K, and an activation energy of 6.8 meV was obtained. For the VW ZnO NRs, no switch of the main carrier recombination was obvious at 150 K, but some deviations with different origins appeared at temperatures above 150 K on Varshni’s curve and the Arrhenius plot. The activation energy was double that of the VW ZnO NCs due to the existence of a number of donor impurities. The carrier recombination in Volmer-Weber-type ZnO nanocrystals (VW ZnO NCs) and Volmer-Weber-type ZnO nanorods (VW ZnO NRs) synthesized by using a physical sputtering method and a hydrothermal method, respectively, was investigated by using temperature-dependent photoluminescence. The main mechanism of UV emission observed in both materials was attributed to the neutral donor bound to the exciton (D0X) and a two-electron satellite (TES). Using the energies of D0X and its TES, we found that the donor binding energy was higher than that of a ZnO crystal. The change in the main carrier recombination and the activation energy were estimated using Varshni’s formula and an Arrhenius plot, respectively. For the VW ZnO NCs, the change from D0X to free exciton (FX) was examined at 150 K, and an activation energy of 6.8 meV was obtained. For the VW ZnO NRs, no switch of the main carrier recombination was obvious at 150 K, but some deviations with different origins appeared at temperatures above 150 K on Varshni’s curve and the Arrhenius plot. The activation energy was double that of the VW ZnO NCs due to the existence of a number of donor impurities.

현미경 영상 분석 장치를 이용한 oil-in-water 에멀션의 고체화 현상에 대한 연구

류순란,황윤회,김형국 한국물리학회 2007 새물리 Vol.54 No.3

The de-mixing phenomenon in a polydispersive oil-in-water emulsion system was studied by using a microscope image analysis technique. Previously, R. P. Sear theoretically studied solidification and said that the depletion attraction due to small spheres with a higher number density de-mix the relatively larger spheres to form a cluster and that the cluster rises into the upper layer by buoyancy and forms a dense cream layer. This cream layer has a lattice-type structure, so the de-mixing phenomenon shows a phase transition behavior from a liquid phase to a solid phase. In this study, we found that the lattice structure was observed in the solid phase and that the phenomenologial constant c, which is related to the structure of the lattice, ranged from 0.06 to 0.1. This result shows that in their solid phase, the distance between the spheres in the solid phase is about 1/10 of their mean diameter. 본 연구에서는 현미경 영상 분석 방법을 사용하여 다 분산된 (polydispersed) 에멀션 (emulsion)에서 나타나는 고갈인력 (depletion attraction)에 의한 현상으로 에멀션이 액체상태에서 고체상태로 상전이 할 경우, R. P. Sears의 이론에서 제시된 고체상태에서 에멀션들이 얼마나 가깝게 분포하는지에 관련된 상수 c 값을 실험적으로 구하였다. 측정된 c 값은 약 0.06 $\sim$ 0.1 이었으며 이로부터 고체상태의 에멀션들 사이 떨어진 간격은 대략적으로 그 평균지름 ($\bar{\sigma}$)의 0.1 정도임을 알 수 있었다.

압전 나노발전기: 에너지 수확 기술

신동명,황윤회,Shin, Dong-Myeong,Hwang, Yoon-Hwae 한국진공학회 2016 진공 이야기 Vol.3 No.2

Piezoelectric nanogenerators are energy harvesting device to convert a mechanical energy into an electric energy using nanostructured piezoelectric materials. This review summarizes works to date on piezoelectric nanogenerators, starting with a basic theory of piezoelectricity and working mechanism, and moving through the reports of numerous nanogenerators using nanorod arrays, flexible substrates and alternative materials. A sufficient power generated from nanogenerators suggests feasible applications for either power supplies or strain sensors of highly integratedl nano devices. Further development of nanogenerators holds promise for the development of self-powered implantable and wearable electronics.

트레할로즈 분자내의 글리코시드 결합 변화에 대한 연구

서정아,김형국,황윤회 한국물리학회 2007 새물리 Vol.54 No.3

We studied the glycosidic bond in trehalose glass to understand the bioprotect mechanism. We measured the glycosidic bond vibration mode around 1140 cm$^{-1}$ with increasing temperature from 50 $^\circ$C to 210 $^\circ$C by using Raman spectroscopy, and we found that the slope of the Raman shift changed at 162 $^\circ$C. From this result, we can speculate that the glycosidic bond in trehalose glass changed around 162 $^\circ$C and that the change might originate from the change in the bond length of the bond angle between the glucose rings in trehalose glass. 본 연구에서는 온도증가에 따른 트레할로즈 유리의 글리코시드 결합의변화를 Raman specroscopy를 이용하여 측정하였다. 글루코즈 분자간진동에 의해 1140 cm$^{-1}$ 근처에서 나타나는 글리코시드 결합에 대한Raman 픽을 분석한 결과 온도증가에 따른 Raman 픽 변화의 기울기가 162 $^\circ$C 에서 변하였다. 이 결과로부터 트레할로즈 분자내의 글루코즈분자간의 결합이 162 $^\circ$C에서 변하기 시작한다는 것을 확인 할 수있었다.