고성능 PVK계 광굴절 고분자 복합체

장차익,양회룡,정경복,최승평 한국물리학회 2004 새물리 Vol.49 No.4

A diraction eciency of nearly 100 % with a 100 m thick sample has been reported for acomposite of a hole-transporting polymer, poly (n-vinyl carbazole) (PVK), doped with DMNPAA, ECZ, and TNF. However, there are two drawbacks to this material. One is the short lifetime caused by crystallization. BisCzPro can be used as a plasticizer instead of ECZ to avoid the crystallization. The other issue is the slow response. The photorefractive time constant is typically on the order of 100 ms to seconds at a recording beam intensity of 1 W/cm2 under moderate external electric eld. In this research, by modifying the structure of DMNPAA, we developed new photorefractive polymer composites that have fast response time constants on the order of 10 ms and high diraction eciency . The idea is that if the structure of the NLO is modied to have exible side chains, the NLO becomes much more mobile in an electrical eld without reducing the of large anisotropy in the polarizability. Alkyl groups are substituted in DMNPAA to realize this idea. Rahn et al. reported that the substitution of alkyl can enhance the birerngence of chromophores. We synthesized several new NLOs and measured the response rate of the reorientation and the induced birefringence. We also discuss the inuence of the dispersivity and the glass transition temperature on the rapidity of the reorientation rate in the modied NLOs.

Hot Wall Epitaxy(HWE)에 의한 $ZnGa_2Se_4$단결정 박막 성장과 특성에 관한 연구

장차익,홍광준,정준우,백형원,정경아,방진주,박창선 한국결정학회 2001 韓國結晶學會誌 Vol.12 No.3

ZnGa₂Se₄단결정 박막은 수평 전기로에서 함성한 ZnGa₂Se₄다결정을 증발원으로하여, hot wall epitaxy(HWE) 방법으로 증발원과 기판(반절연성-GaAs(100))의 온도를 각각 610℃, 450℃로 고정하여 단결정 박막을 성장하였다. 10 K에서 측정한 광발광 exciton 스펙트럼과 이중결정 X-선 요동곡선(DCRC)의 반치폭(FWHM)을 분석하여 단결정 박막의 최적 성장 조건을 얻었다. Hall효과는 van der Pauw방법에 의해 측정되었으며, 온도에 의존하는 운반자 농도와 이동도는 293 K에서 각각 9.63×10/sup 17/㎤, 296 ㎠/V·s였다. 광전류 봉우리의 10 K에서 단파장대의 가전자대 갈라짐(splitting)에의해서 측정된 Δcr (crystal field splitting)은 183.2meV, △so (spin orbit splitting)는 251.9meV였다. 10K의 광발광 측정으로부터 고품질의 결정에서 볼 수 있는 free exciton 과 매우 강한 세기의 중성 받개 bound exciton등의 피크가 관찰되었다. 이때 중성 받개 bound exciton등의 피크가 관찰되었다. 이때 중성 반개 bound excition의 반치폭과 결합에너지는 각각 11meV와 24.4meV였다. 또한 Hanes rule에 의해 구한 불순물의 활성화 에너지는 122meV였다. A stoichiometric mixture of evaporating materials for ZnGa₂Se₄single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, ZnGa₂Se₄mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were 610℃ and 450℃, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of ZnGa₂Se₄single crystal thin films measured from Hall effect by von der Pauw method are 9.63×10/sup 17/㎤ and 296 ㎠/V·s at 293 K, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c-axis of the ZnGa₂Se₄single crystal thin film, we have found that the values of spin orbit splitting △so and the crystal field splitting Δcr were 251.9meV and 183.2 meV at 10 K, respectively. From the photoluminescence measurement on th ZnGa₂Se₄single crystal thin film, we observed free excition (Ex) existing only high quality crystal and neutral bound exiciton (A°, X) having very strong peak intensity. Then, the full-width-at-half-maximum (FWHM) and binding energy of neutral acceptor bound excition were 11 meV and 24.4 meV, respectivity. By Haynes rule, an activation energy of impurity was 122 meV.

CR-39 검출기에 의한 Radon기체 농도측정에 관한 연구

장차익,이상열,김동호,이관교,김현구,김영기 조선대학교 기초과학연구소 1988 自然科學硏究 Vol.11 No.1

A study on the measurement of radon gas concentration has been carried out using the CR-39 track detector. A special arrangement was made in order to expose a number of tube-detector systems simultaneously to the same radon source. In this respect, the effects of factors like radon source strength, exposure time, size of the tube and etching conditions have been studied. An observation worth noting is that in the beginning, the track density did not vary as a linear function of time and in the sources A and B, the most suitable exposure time was 13 and 30 hours respectively. It is interesting to note that in the beginning the track density increased with tube size but beyond a certain value, about 3Ocm, any further increase of the tube diameter did not result in an appreciable increase in the track density.

수정된 화학전이 NMR 영상법에 의한 수분과 지질의 비율 측정에 관한 연구

신용진,장차익,홍광준,유상하,이관교,양경승,백창현,김남수,정준우 조선대학교 기초과학연구소 1996 自然科學硏究 Vol.19 No.1

다양한 화학종(化學種)의 선택적인 핵자기공명(nuclear magnetic resonance, NMR) 영상(imaging)을 얻기 위한 몇몇 기술들이 가장 일반적인 Dixon's, CHESS, SECSI 등 3가지 방법들과 함께 발전해 왔다. 모든 화학전이 영상법(chemical shift imaging method)에 있어서 가장 큰 문제점은 정자기장의 균일성과 RF(radiofrequency) 코일에 대전된 시료가 인가되었을 때 나타나는 자기장의 찌그러짐이다. 만약 자기장의 shimming이 없다면, 약 3.5ppm으로 분리된 수분(water)과 지질(fat)의 선택적 양성자 영상을 얻는데 위 세 가지 방법들은 이용될 수 없다. 2.5ppm에서 3.5ppm의 선폭(linewidth)을 가진 시료(phantom)를 이용한 실험으로 위의 세 가지 기술과 새로운 화학전이 영상기술을 정량적으로 분석할 수 있었다. 본 연구에서는 선택적인 포화(saturation)와 재집중(refocusing) pulse가 포함된 새로운 화학전이 영상기술(modified CHESS+SECSI technique)이 다양한 시료에서 수분과 지질의 정량적 비율을 측정하는데 이용될 수 있도록 개발되었다. There are several methods developed to achieve selective NMR image of differing chemical species with the three most popular being Dixon's, CHESS, and SECSI, A major problem common to all chemical shift imaging methods is the uniformity of the static magnetic field and distortions introduced when RF coils are loaded with a conducting specimen. Without magnetic field shimming, these methods cannot be used to selectively image protons in fat and water which are separated by approximately 3.5ppm. Experiments with a phantom, with linewidths of 2.5 to 3.5ppm, were quantitatively evaluated for the above three methods and a new chemical shift imaging method. In this study the new chemical shift imaging method (modified CHESS+SECSI technique) which included a selective saturation and refocusing pulse, was developed to determine the ratio of water and fat in different samples.

低周波 電磁場 속에서 불활성 기체 원자에 의한 電子의 산란단면적

정경복,장차익,최승평 조선대학교 기초과학연구소 1997 自然科學硏究 Vol.20 No.1

The scattering cross section is the physical quantity which is susceptible of a reasonably direct experimental measurement and which at the same time lends itself readily to calculation, and which establish contact between scattering theory and scattering experiment to assist each other. We have calculated one-photon free-free absorption cross sections without target distortion at the frequencies of the CO_2, Nd, and ruby lasers, for targets consisting of the ground states of He, Ne, Ar. The calculations yield total cross sections averaged over all orientations of the polarzation, which is taken to be linear. Electron energies are in the range up to about 13 eV. The atomic potential used to represent the interaction of the atom in our calculation is the same one that is replaced atom by the potential used by Robinsion and Geltman in the evaluation of photodetachment cross-sections. We used the Numerov method for numerical integration of our differential equations. This method appears to be most efficient numerical intergration scheme available for second-order differential equations with the first derivative absent.

1.88 A GeV ^56Fe 이온에 의한 원자핵 건판내에서의 발생각에 대한 연구

박복남,최승평,장차익,김동호 조선대학교 기초과학연구소 1990 自然科學硏究 Vol.13 No.1

LBL 667H 실험의 일환으로써 1.88A GeV ^56Fe이온이 원자핵 전판내에서 일으킨 핵반응을 비적스캔닝(along-the-track-scanning) 법으로 총 473개를 발견하였다. 그중 302개에 대한 방출각을 실험데이타로 삼아 ^56Fe 핵과 원자핵건판들과의 충돌에서 얻어진 다중도 분포의 여러파라미더와 이차파쇄핵의 각분포를 측정하여 6.2∼400 GeV 양성자-원자핵 상호작용과 비교검토 하였으며 알파입자에 대한 분포회귀함수는 β_T^-1??e^(r-nb)이고 β_T^-1=(e^(r_p-nb)) 임을 나타냈다. The results of multiple production produced by 1.88 A GeV ^56Fe ions in nuclear emulsion have been studied. Using by the along-the-track scanning method, We found 473 inelastic events and analysed 302 events. Angular distribution of secondary particles and several parameters of multiplicity distribution at the collisions of ^56Fe ions with emulsion nuclei are measured. And data are compared with those of 6.2-400 GeV protons with nuclei in nuclear emulsion. Regression function of alpha particles is well fitted by use of β_T^-1=exp(r-n_b).

He 원자 구조에 관한 수치 해석적 연구

양희룡,최승평,장차익 조선대학교 기초과학연구소 1997 自然科學硏究 Vol.20 No.1

The one-electron theory of atoms, molecules, and crystals has enjoyed a wide success in many branches of physics. This theory provides a physically appealing description of the eletronic structure of many-electron systems. In addition, this theory provides a convenient basis for performing the detailed calculations on specific many-electron systems. In such calculations, it is usually necessary to introduce many simplifying assumptions in order to make a progress. Since the principal computational difficulty posed by the Hartree-Fock equations is the treatment of the exchange terms, it would be very desirable to simplify the treatment of these terms by using Slater's the average of the exchange potential. The first order correction of the energy in the ground state of He atom is calculated by using the unperturbed wave function obtained with the Hartree-Fock-Slater approximation and compared with the result obtained by the simple analytical metod. The numerical result agrees with an experimental result for the ground state of the He atom with tolerance 0.65%.

불활성 원자에 의한 전자의 산란

최숙경,양희룡,장차익 朝鮮大學校 自然科學硏究所 1995 自然科學硏究 Vol.18 No.1

The Scattering cross section is the physical quantity which is susceptible of a reasonably direct experimental measurement and which at the same time lends itself readily to calculation, and this which establish contact between scattering theory and scattering experiment to assist each other. We have calculated scattering cross sections for targets consisting of He, Ne, Ar in ground state and He in metastable state, that is, ^(3)S_(1)i. In our study we have calculated elastic scattering cross sections for low energy electrions (E < 10 eV). The atomic potential used to represent the interaction of the atom in our calculations is the same one that is replaced atom by the potential used by Robinson and Geltman in the evaluation of photodetachment cross sections. We have shown that the total scattering cross sections of He, Ne and Ar decrease with the increase of the electron energy. We used the Numerov method for numerical integration of our differential equations. This method appears to be most efficient numerical integration scheme available for second-order differential equations with the first derivative absent.

모델원자들에 의한 전자 산란 단면적 계산

정진,양회룡,최승평,장차익 조선대학교 기초과학연구소 1998 自然科學硏究 Vol.21 No.1

The scattering cross section in model atom is the physical quantity which is susceptible of a reasonably direct experimental measurement and which at the same time lends itself readily to calculation, and which establish contact between scattering theory and scattering experiment to assist each other. We have calculated the differential cross section and total cross sections of electrons by targets which are Cu, S, He, Ne, Ar on the ground state without the targets distortion with the Born approximation and the Eikonal approximation. the electron energies are in the range up to about 1.3 ev∼10 kev. The potential used to represent the interaction between atom and electron in our calculation is the same as that is used by Lens-Jensen in the evaluation of the cross-sections. We used the Gauss Legndre quadrature for our numerical integration in our differential equations.

FT NMR의 고 분해능에 관한 연구

박소희,양경승,김영섭,신용진,장차익 조선대학교 기초과학연구소 2001 自然科學硏究 Vol.24 No.-

FT NMR Spectroscopy is the method of obtaining the spectrum by Fourier transform(FT) of a time varying signal called the free induction decay(FID) signal Usually, Resolution of spectrum are decided by Fourier transform. It's hard to distinguish those nuclei with close frequency at low external magnetic field. So we are going to use simulation which is corresponding to a lot of the variable parameters In this study frequencies were provided to the four nuclei with high natural abundance and the high NMR frequency, and the intensities corresponding to the frequencies were applies. We verified that the unidentical intensity was provided and the signal has been amassed for two nuclei. Also We scrutinized that the nuclei of the analogous frequencies have constituted resolution of two peaks as shown in Fourier transform. Resolution with FT is determined by FID data points when the range of measurement in NMR is given and then we made a vigorous examination method for high resolution through simulation for two real nuclei of close. From this research, we can understand NMR and apply experimental method. Therefore, these high resolution method was willing to applied many experimental NMR.