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나노구조 박막의 Morphology에 따른 초전도 특성 변화에 관한 연구
고태준(Taejoon Kouh) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.1
Transport and tunneling measurements of nanostructured superconducting thin films are presented. To understand the effects of film morphology on their superconducting properties, thermal annealing experiments have been performed. The transition temperature increases with thermal annealing temperature towards the bulk value. Also, thermal annealing results in a shift of transverse phonon mode. These can be understood with changes in film morphology and suggest its importance on the superconducting state properties.
Annealing에 의한 나노구조 박막의 전기적 특성 연구
고태준(Taejoon Kouh) 한국자기학회 2006 韓國磁氣學會誌 Vol.16 No.1
Electron transport properties of nanostructured Pb thin film, consisting of grains, have been studied. Nanostructured thin films were fabricated on a substrate held at low temperature and their thicknesses were less than 10 ㎚. While temperature of the film increased from 1.3 K to room temperature, the change in normal state sheet resistance has been measured. As the annealing temperature varies, the normal state sheet resistance shows a non-monotonic and irreversible change. Such behavior can be understood with the Pb grain growth due to annealing of the film.
Hyperthermia Properties of Fe₃O₄ Nanoparticle Synthesized by Hot-injection Polyol Process
Seong Noh Lee(이성노),Taejoon Kouh(고태준),In-Bo Shim(심인보) 한국자기학회 2014 韓國磁氣學會誌 Vol.24 No.2
The Fe₃O₄ nanoparticle was synthesized by the hot-injection method while varying the injection time of the precursor solution. The crystal structure was determined to be cubic inverse spinel with space group of Fd-3m based on X-ray diffraction (XRD) measurements and the morphology of the prepared Fe₃O₄ nanoparticle was studied with a high-resolution transmission electron microscope (HR-TEM). When the precursor solution was injected for 0.5 min, the size of the Fe₃O₄ nanoparticle was 7.63 nm, while the size of the obtained particle was 21.27 nm with the injection time of 60 min. The magnetic properties of the prepared Fe₃O₄ nanoparticle were investigated by both vibrating sample magnetometer (VSM) and <SUB>57</SUB>Co Mossbauer spectroscopy at various temperatures. From the hyperthermia measurement, we observed that the temperature of the Fe₃O₄ nanoparticle powder reached around 120 ℃ under 250 Oe at 50 kHz, when the injection time of the precursor solution was 60 min.
다공성 알루미나 마스크를 이용한 니켈 나노점 구조 제작
임수환(Suhwan Lim),김철성(Chul Sung Kim),고태준(Taejoon Kouh) 한국자기학회 2013 韓國磁氣學會誌 Vol.23 No.4
We have fabricated an ordered Ni nanodot structure using an alumina mask prepared via 2-step anodization technique under phosphoric acid. We have formed a porous structure with average pore size of 279 nm on 2 μm thick alumina film and the thermal deposition of thin Ni film though the mask led to the formation of ordered Ni nanodot structure with an average dot size of 293 nm, following the pore structure on the mask. We further investigated the magnetic properties of the nanodot structure by measuring the hysteresis curve at room temperature. When compared to the magnetic properties of a continuous Ni film, we observed the decrease in the squareness and the increase in coercivity along the magnetization easy axis, due to the isolated nanodot structure. Our study suggests that the ordered nanodot structure can be easiy fabricated with thin film deposition technique using anodized alumina mask as a mask.
얇은 다공 구조 박막에서의 두께에 따른 박막 저항 변화
송아리(Aree Song),김철성(Chul Sung Kim),고태준(Taejoon Kouh) 한국자기학회 2012 韓國磁氣學會誌 Vol.22 No.1
We have observed the change in the film resistance of thin nickel film up to 13 nm, which is deposited on a porous anodic alumina substrate, prepared by two-step anodization technique under phosphoric acid. The resulting film grows as a porous film, following the pore structure on the surface of the alumina substrate, and the value of the resistance lies above 150 kΩ within the range of thickness studied here, decreasing very slowly with the film thickness. The observed resistance value is much higher than the reported value of a uniform film at the same thickness. Since the observed value of the surface coverage with the pores is smaller than the critical value, expected from the percolation theory, the pore structure limits the formation of conduction channel across the film. In addition, by comparing to the typical model of thickness-dependent resistivity, we expect that the scattering at the pore edge further increases the film resistance.
초기 산화 피막의 형성이 다공성 알루미나 막 제작에 미치는 영향
박영옥(Youngok Park),김철성(Chul Sung Kim),고태준(Taejoon Kouh) 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.2
We have investigated the effect of the formation of an initial oxide layer on the fabrication of the porous aluminium oxide. The porous aluminium oxide was fabricated by two-step anodization process with a electropolished aluminium foil. Before the first anodization step, the initial oxide layer with thickness of 10 nm was formed under the applied voltage of 1 V and later the anodization was continued under 40 V using oxalic acid solution. With the formation of the initial oxide layer, the anodization process was stable and the anodization current was constant throughout the process. In case of the absence of the initial oxide layer, the anodization was very unstable and the continuous increase in the anodization current was observed. This indicates the formation of the initial oxide layer on the aluminium surface prevents the burning of the surface due to the nonuniform distribution of the applied electric field, and allows the stable anodization process required for the porous aluminium oxide.
4분할 광 검출기 상의 광점 크기가 변위 측정감도에 미치는 영향
이은중(Eun Joong Lee),이진우(Jin Woo Lee),고태준(Taejoon Kouh) 한국자기학회 2008 韓國磁氣學會誌 Vol.18 No.2
In this paper, we have measured the effect of the optical spot size, incident upon the quadrant photodetector, on the optical displacement sensitivity of the optical beam deflection technique. We have built an optical displacement detection system based on the optical beam deflection method using 3 ㎽ He-Ne laser and measured the displacement sensitivity with changing the optical spot size on the quadrant photodetector. We have also calculated the changes in the optical displacement sensitivity as a function of the incident laser spot size by modeling a circular optical spot with constant laser intensity. Our experimental and theoretical studies show that the optical displacement sensitivity increases with the decrease in the optical spot size. This suggests that in the design of the optical motion detection systems with sub-nanometer sensitivity, the displacement sensitivity can be optimized by reducing the size of the incident optical spot on the detector.
초기 산화피막 제거와 양극산화 시간에 따른 다공성 알루미나 막의 성장
김대환(Dae Hwan Kim),류상희(Sang Hee Lue),이효진(Hyojin Lee),박영옥(Youngok Park),이은중(Eun Joong Lee),고태준(Taejoon Kouh) 한국자기학회 2010 韓國磁氣學會誌 Vol.20 No.5
We have investigated the effect of the removal of an initial oxide layer and the anodization time on the growth of the porous alumina layer. The porous alumina layer was fabricated by two-step anodization process with phosphoric acid. We have observed the changes in the uniformity of the pore structure by varying the removing time of the initial oxide layer after the first anodization with phosphoric acid and chromic acid, and noted that its uniformity improves with the removing time. We have also determined the thickness of the alumina layer after the final anodization process and found that the thickness increases linearly with the anodization time. Under 150 V of anodization voltage with phosphoric acid, the growth rate of the porous alumina layer is determined to be 22.5 ㎚/min.
자성나노입자의 표면 흡착에 의한 마이크로캔틸레버의 공진주파수 변화
박미령(Miryeong Park),최현경(Hyunkyung Choi),김삼진(Sam Jin Kim),김철성(Chul Sung Kim),고태준(Taejoon Kouh) 한국자기학회 2018 韓國磁氣學會誌 Vol.28 No.2
In this study, we have considered the physical adsorption of Fe₃O₄ magnetic nanoparticles - having a size of a few tens of nanometers - onto the surface of a microcantilever, and observed the following resonance frequency shift of the microcantilever. The change in the effective mass of the microcantilever depending on the level of the surface adsorption of nanoparticles on the microcantilever has been determined from the observed resonance frequency shift based on a simple mechanical model, leading to the estimation of the number of nanoparticles adsorbed on the microcantilever surface.