Structural and Electrical Properties of SrRuO₃ thin Film Grown on SrTiO₃ (110) Substrate

O-Ung Kwon,Namic Kwon,B. W. Lee,C. U. Jung 한국자기학회 2013 Journal of Magnetics Vol.18 No.1

We studied the structural and electrical properties of SrRuO₃ thin films grown on SrTiO₃ (110) substrate. High resolution X-ray diffraction measurement of the grown film showed 1) very sharp peaks for SrRuO₃ film with a very narrow rocking curve with FWHM = 0.045° and 2) coherent growth behavior having the same in-plane lattice constants of the film as those of the substrate. The resisitivity data showed good metallic behavior; ρ = 63 (205) μΩㆍ㎝ at 5 (300) K with a residual resistivity ratio of ~3. The observed kink at ρ(T) showed that the ferromagnetic transition temperature was ~10 K higher than that of SrRuO₃ thin film grown on SrTiO₃ (001) substrate. The observed rather lower RRR value could be partially due to a very small amount of Ru vacancy generally observed in SrRuO₃ thin films grown by PLD method and is evident in the larger unit-cell volume compared to that of stoichiometric thin film.

아르곤 2p₄준위의 Hanle 신호 연구

권남익,김태한 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 1996 기초과학연구 Vol.4 No.-

794.8nm의 반도체 레이저를 이용하여 전극이 없는 rf 방전관에서 아르곤의 들뜬상태(1s₃→2p₄) 2p₄준위로부터의 Hanle 신호를 조사하였다. 자기장을 변화시키면서 레이저 빔의 편광 방향에 대한 각도가 0, π/4, π/2인 지점에서 Hanle 신호를 조사하였다. 각각의 위치에 따라 서로 다른 신호가 나왔으며, 자기장 세기의 변화에 따라 신호의 세기도 변화하였다. 이처럼 자기장 세기의 변화와 레이저 빔의 편광 방향에 대한 각도가 0, π/4, π/2 인 지점에서의 신호가 각기 다르게 나오는 이유를 설명하였으며, 측정된 신호의 FWHM(full width of half maximum) △B½와 Lande 인자 g를 통해 2p₄준위의 수명(lifetime) τ를 구하였다. The Hanle signals from the Ar 2p₄level, excited via ls₃→2p₄transition, have been investigated in electrodeless rf discharge using a semiconductor laser (794.8nm). As the magnetic field was slowly varied from 0 G to 30 G, the Hanle signals were observed at the points which were changed along the direction of polarization of the laser beam(∠ a= 0, π/4, π/2in Fig.1) The shape of the Hanle signals in each point was different and depended on the magnetic field. From these results, we see that Hanle signals depend on the experimental geometry and the magnetic field. The lifetime τof the Ar 2p₄level was measured from the Lande factor g and FWHM(full width of half maximum) △B½of the Hanle signals.

간섭계형 공초점 현미경 연구

권남익 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 1999 기초과학연구 Vol.9 No.-

마이켈슨 간섭계를 이용한 간섭계형 공초점 현미경을 구성하고 특성을 조사하였다. 본 간섭계형 공초점 현미경은 시료 표면의 반사 신호와 거울의 반사 신호가 합쳐져서 일어난 간섭신호를 이용해서 3차원 영상을 얻는다. He-Ne(λ=633nm)레이저를 사용한 간섭계는 반파장(312.5nm)의 경로차가 생길때마다 같은 무늬가 반복해서 나타난다. 본 간섭계형 공초점 현미경은 이러한 간섭 신호를 이용하기 때문에 white-light interfermeter 수준의 수직 해상도를 얻을 수 있었으며, 공초점 효과 때문에 일반 공초점 현미경의 수평해상도를 유지할수 있었다. We have constructed an interferometric confocal microscope using a Michelson interferometer and a He-Ne laser. Three dimensional image was obtained by the interference from the reflected light by a sample surface and from the reflected light by a mirror. The axial resolution obtained by interferometric confocal microscope was as good as that of the white-light interferometer, but the same fringe was repeated when optical path difference was half-wavelength. Due to the confocal effect, lateral resolution was as good as that of scanning confocal microscope.

반도체 레이저를 이용한 아르곤의 분광학적 연구

권남익 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 1996 기초과학연구 Vol.4 No.-

반도체 레이저를 이용하여 전극이 없는 rf 방전관 안에서 아르곤의 들뜬 상태에 대해 optogalvanic 신호를 조사하였다. 직류 방전관이나 hollow cathode 방전관에서 관찰되어 보고되어온 opogalvanic 신호들과 달리, 전극이 없는 방전관에서는 항상 일정한 규칙성을 가지고 있었다. 총 각운동량이 1 이어서 바닥상태로의 쌍극자 전이가 허용된 복사상태(1s₂, 1s₄)를 광펌핑 했을 때는 항상 양의 optogalvanic 신호가 나왔고, 쌍극자 전이가 금지된 준안정화 상태에서 광펌핑 했을 때는 음의 신호가 나왔다. 펌핑광과 probing 광을 함께 사용하여 복사상태를 펌핑할때 준안정화상태의 밀도변화를 조사하여 optogalvanic 신호가 양의 신호가 나오는 이유를 설명하였다. Optogalvanic effect from the first excited states of argon was studied in electrodeless rf discharge using cw diode lasers. Unlike previously reported optogalvanic signals studied in do discharge or hollow cathode discharge, the optogalvaic signals which was obtained in a electrodeless discharge has shown a consistent property. The equilibrium optogalvanic signals from the metastable states were always negative, and the signals from the radiative states were always positive, By using a probing beam and a chopped pumping laser beam, variation of the density of the metastable atoms were measured. From that result, the cause of the positive optogalvanic signal from radiative state has been explained.

소형 거울 회전기의 제작과 특성 조사

이병현,권남익 한국외국어대학교 기초과학연구소 2001 기초과학연구 Vol.11 No.-

소형의 기기에 유용하게 이용될 수 있는 작은 거울 회전기를 제작하였으며 그 성능을 시험해 보았다. 영구자석과 코일을 이용하여 galvanometric 방법으로 제작하였으며 전체 크기는 6mm×6mm×4mm 이다. 거울 회전기의 공진 주파수는 105 Hz 이며 현미경에 이용하여 일그러짐이 없는 영상을 구할 수 있었다. Construction of a Miniature Mirror Rotator and Study of Its Characteristics We have constructed a miniature mirror rotator to use in small optical devices and tested characteristics of the rotator. The mirror rotator was made of permanent magnets and coils for galvanometric operation, and the dimension was 6 mm x 6 mm x 4 mm. Resonance frequency of the rotator was 105 Hz, and confocal image without any distortion were obtained with this mirror rotator.

반도체 레이저를 이용한 극소형 scanning Confocal Microscope의 제작

이진서,권남익 한국외국어대학교 외국학종합연구센터 부설 기초과학연구소 1996 기초과학연구 Vol.5 No.-

반도체 레이저를 이용하여 작고 간단한 scanning confocal microscope를 구성하였다. 반도체 레이저는 단일 모드이고 파장이 780 nm인 Sharp LT022MC를 사용하였다. 그리고 반도체 레이저를 사용하게 되면 시료표면에서 반사되는 신호를 직접 검출할 수 있어서 편리하다. Scanning confocal microscope는 3차원 영상을 얻을 수 있으므로 기존의 금속 현미경으로는 관찰할 수 없었던 시료표면의 깊이와 거칠기를 관찰할 수 있다. 따라서 표면 측정용으로 널리 사용할 수 있을 뿐만 아니라 반도체 분야, 생물학 분야 등 여러 분야에서 폭넓게 사용될 수 있다. 시료로는 TIP-32C power transistor, compact disk 그리고 반도체 mask를 사용하였다. Compact disk의 정보를 담고 있는 pit는 표준 시료를 대신할 수 있는 것으로 우리가 구성한 scanning confocal microscope의 분해능을 간접적으로 보여준다. 시료를 3차원 scan 하기 위해 X, Y축은 magnet galvanometer를 사용하였고 Z축은 linear stage를 이용하였다. 이때 사용된 magnet galvanometer는 linear tracking 방식의 CD-player에서 사용되는 actuator를 사용하였다. 또한 magnet galvanometer를 제어하기 위해 data acquisition 보도 DT31-EZ의 DAC를 사용하였으며, 영상 신호 입력에는 ADC 단자를 이용하였다. Data acquisition 보드의 DAC와 ADC를 제어하기 이한 소프트웨어 프로그램은 비쥬얼 베이직으로 구성하였다. A compact scanning confocal microscope has been constructed using a semiconductor laser. A single mode Sharp LT022MC with 780nm was used as a semiconductor laser. Semiconductor laser is convenient to use as a illuminating source because it also detects the signal reflected from the surface of a specimen. Scanning confocal microscope can observe depth and roughness of specimen because it displayed three-dimensional images. Therefore it is widely used for the fields of the semiconductor or biology. Specimens were a TIP-32C power transistor, a semiconductor mask and a compact disk. The resolution of our device was obtained by using compact disk pit as a test sample. The magnet galvanometer which was taken from a CD player was used to scan the surface of the specimen along the X, Y axes and to adjust a linear stage along the Z axis. The DAC channel of a data acquisition board DT31-EZ was used to control the magnet galvanometer and the ADC channel was used to obtain image signal. Visual basic was used as software program to control DAC and ADC of a data acquisition board.

Anisotropic Conductive Film Bonding by Making Use of a High-Power Diode Laser

Kwang Hyun Ryu,Namic Kwon,Myung Hee Seo,Myung Hoon Lee,Gi Jung Nam,No Heung Kwak IEEE 2006 IEEE TRANSACTIONS ON ADVANCED PACKAGING Vol.29 No.4

<P>Anisotropic conductive film (ACF) bonding between liquid crystal displays (LCDs) and driver integrated circuits (ICs) is one of the key technologies for developing high-resolution LCDs. The bonding pitch between LCD and tape carrier package (TCP), which influences the total reliability of LCD modules, depends on the characteristics and bonding conditions of ACF used. So, the bonding process between TCP and a glass panel with ACF using a high-power diode laser as a heat source for curing is preliminarily tested in this experiment. Also, laser transient thermal simulation was performed to analyze the thermal response of the assembly process for a package using ACF. The temperature on the ACF layer goes up to 180 degC (ACF curing temperature) within 1 s after exposure to laser light. This paper reports an effective bonding method using a diode laser, which accomplishes a fine-pitch ACF bonding and determines the optimum ACF bonding condition effectively</P>

Thickness effect on the stability of unipolar resistance switching in tin ferrite thin films

Guodong Gong,Changjin Wu,Pengfei Hu,Ying Li,Namic Kwon,Chunli Liu 한국물리학회 2016 Current Applied Physics Vol.16 No.9

We report the reproducible unipolar resistance switching behavior in Pt/SnFe2O4/Pt structures. The amorphous SnFe2O4 thin film was spin-coated on the Pt/TiO2/SiO2/Si substrate by a sol-gel method. The current-voltage characterization showed that as the spin coating cycles increased, the resistive switching (RS) characteristics became stable, and an excellent RS performance showing uniform set voltage distribution, stable resistance of both low resistance and high resistance states, and narrow reset current distribution can be obtained in SFO films with a thickness about 220 nm. Based on the conducting filament model, the variation of the RS behavior was ascribed to the increase of the electroforming voltage in the thicker films, which consequently induced more oxygen vacancies to participate in the RS process. Our results indicated that the electroforming voltage performs a significant role in the RS properties of the amorphous SnFe2O4 and the optimized RS behavior through the regulation of preparation process can be used for the resistance random access memory applications.

Thickness effect on the stability of unipolar resistance switching in tin ferrite thin films

Gong, Guodong,Wu, Changjin,Hu, Pengfei,Li, Ying,Kwon, Namic,Liu, Chunli Elsevier 2016 CURRENT APPLIED PHYSICS Vol.16 No.9

<P>We report the reproducible unipolar resistance switching behavior in Pt/SnFe2O4/Pt structures. The amorphous SnFe2O4 thin film was spin-coated on the Pt/TiO2/SiO2/Si substrate by a sol-gel method. The current-voltage characterization showed that as the spin coating cycles increased, the resistive switching (RS) characteristics became stable, and an excellent RS performance showing uniform set voltage distribution, stable resistance of both low resistance and high resistance states, and narrow reset current distribution can be obtained in SFO films with a thickness about 220 nm. Based on the conducting filament model, the variation of the RS behavior was ascribed to the increase of the electroforming voltage in the thicker films, which consequently induced more oxygen vacancies to participate in the RS process. Our results indicated that the electroforming voltage performs a significant role in the RS properties of the amorphous SnFe2O4 and the optimized RS behavior through the regulation of preparation process can be used for the resistance random access memory applications. (C) 2016 Elsevier B.V. All rights reserved.</P>

초소형 공초점 현미경의 제작과 금속의 구조 측정

서명희(Myeong Hee Seo),김종배(Jong Bae Kim),권남익(Namic Kwon) Korean Society for Precision Engineering 2008 한국정밀공학회지 Vol.25 No.11