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PZT 세라믹스에서 Pb 대신 치환된 이온이 유전 및 압전특성과 압전열화에 미치는 영향
문학범,정윤해 한국결정학회 1996 韓國結晶學會誌 Vol.7 No.2
본 연구는 Pb(Zr0.52Ti0.48)O3을 기본 조성으로하여 Pb-site에 Pb2+보다 이온 반경이 큰 Ba2+, 비슷한 크기의 Sr2+ 그리고 이온 반경이 작은 Ca2+를 치환하여 유전 및 압전 특성을 조사하고, 압전 열화에 대한 영향을 고찰하고자 하였다. 치환하지 않은 기본 조성에 비해 치환된 조성의 비유전율과 전기기계결합게수는 Ba2+ 치환시 가장 높았고, Sr2+ 치환시 기본조성과 비슷하였으며 Ca2+ 치환시 감소하였다. 기계적 품질계수는 지본 조성에 비해 Ba2+ 치환시에는 감소하였으며, Sr2+, Ca2+ 치환으로 갈수록 증가하는 경향을 나타내었다. 그리고 압전 열화시 주파수 변화 특성에서는 각 이온 치환에 따른 변화는 보이지 않았으나 상온 방치시와 고온 방치(100℃)후의 열화속도가 상온방치후보다 빨랐다. The effects of Ba2+, Sr2+, and Ca2+-substitutions for Pb2+ at Pb(Zr0.52Ti0.48)O3 composition were studied for thier dielictric, piezoelectric, and aging properties. For relative dielectric constants and electromechanical coupling factors, the Ba2+-substituted composition was the highest and the Ca2+-substityed composition was the lowest. In the case of mechanical quality factors, the opposite behavior occurred. Time dependence of frequency for various ion-substituted compositions is similar to that of non-substituted composition. The piezoelectric properties after aging at high temperature was the worse than that after aging at room temperature.
CVD방법으로 Pt/TiO2/SiO2/Si 기판에 성장시킨 CrO2 박막
손종역,조진형,김경현,문학범,박정우,방석현,송경숙,장영훈 한국물리학회 2004 새물리 Vol.48 No.6
We report dierences in the growth mechanisms of half-metallic CrO2 thin lms deposited on preferentially oriented (111) and (200) Pt/TiO2/SiO2/Si substrates by using chemical vapor deposition method. The CrO2 thin films grown on (111) Pt/TiO2/SiO2/Si substrates were (200) oriented and had crystalline rectangular grains. On the other hand, for (200) Pt/TiO2/SiO2/Si substrates, the CrO2 thin lms were (110) oriented and had wedge-shaped grains. The ferromagnetic domains of the CrO2 thin lms were observed with a magnetic force microscope at room temperature and the orientational dependence of the magnetization was observed using a SQUID magnetometer. While the ferromagnetic domains of both lms showed an in-plane ferromagnetic easy-axis, resulting from shape anisotropy, and orientation of the easy-axis along the in-plane lm direction at the domain boundaries, the magnetic domains showed marked contrast difference at domain boundaries resulting from the dierent surface topographies. Ellipsometery measurements were performed on the CrO2 thin films, and the optical conductivity was obtained from the ellipsometry data. The dependence of the optical conductivity on the photon energy was compared with the band structure calculated using the local spin density approximation.
Photoinduced Effects of PbZr1-xTixO3 Thin Films asObtained by Using Piezoresponse Force Microscopy
장윤형,김철환,황호준,문학범,방석현,조진형 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.5
Piezoresponse force microscopy (PFM) has been used to investigate the photoinduced effect of ferroelectric domains in PbZr1-xTixO3 (PZT) thin films. In order to perform nondestructive visualization of the high-resolution domain structure, we optimized the imaging condition, such as applying a lower voltage than 1.0 Vpp (peak-to-peak voltage). In this study, domain changes were measured before and after illumination on the surface of PZT films by using an UV light emitting diode (LED) source (?? = 310 nm) with a focusing lens to investigate the influence of the photoinduced carriers on the ferroelectric polarization. In addition, to investigate the photoinduced effects on the domain distribution, we performed histogram of positive and negative domains before and after UV-light illumination. The illumination with UV light resulted in an increase of the positive domain of the out-of-plane mode. Also, a change in the out-of-plane domain distribution was observed before and after UV illumination. The relaxation of photoinduced changes was monitored by repeated scans within a time range of 20 ¡ 60 minutes.
장윤형,김철환,황호준,문학범,방석현,조진형 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.31
Piezoresponse force microscopy (PFM) has been used to investigate the photoinduced effect of ferroelectric domains in PbZr_(1-x)Ti_xO_3 (PZT) thin films. In order to perform nondestructive visualization of the high-resolution domain structure, we optimized the imaging condition, such as applying a lower voltage than 1.0 Vpp (peak-to-peak voltage). In this study, domain changes were measured before and after illumination on the surface of PZT films by using an UV light emitting diode (LED) source (λ = 310 nm) with a focusing lens to investigate the influence of the photoinduced carriers on the ferroelectric polarization. In addition, to investigate the photoinduced effects on the domain distribution, we performed histogram of positive and negative domains before and after UV-light illumination. The illumination with UV light resulted in an increase of the positive domain of the out-of-plane mode. Also, a change in the out-of-plane domain distribution was observed before and after UV illumination. The relaxation of photoinduced changes was monitored by repeated scans within a time range of 20 ~ 60 minutes.
황호준,김철환,장윤형,방석현,문학범,조진형 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.31
We report the growth mechanism and the magnetic properties of Ni nanowires on an anodized aluminum oxide (AAO) template. The porous AAO was fabricated using a two-step anodization process. The Ni nanowires were grown by using DC pulsed and AC electrodeposition methods, and the Ni nanowires were more uniformly grown by using the AC electrodeposition method than by using the DC pulsed electrodeposition method. We also studied the magnetic properties of the Ni nanowires and the post-annealed Ni nanowires (at 600 ℃ in air). The annealed Ni nanowires showed smaller ferromagnetic saturation than the unannealed Ni nanowires. This result indicates that NiO existed in the Ni nanowires after the post-annealing process. In addition, the magnetic properties of the Ni nanowires at 5 K showed that the easy magnetization axis in the annealed Ni nanowires had rotated from the parallel to the nanowire surface to the perpendicular to that surface. Since the shape anisotropy of continuous Ni thin films favors the direction of the easy magnetization axis being parallel to direction of their surfaces, these results show that at low temperatures, the magnetic properties of Ni nanowires behave as those of continuous Ni thin films.
고주파 마그네트론 스퍼터링 방법으로 제조한 Al이 도핑된 ZnO 박막의 구조적, 전기적, 광학적 특성
장영훈,송경숙,조진형,김철환,문학범,방석현,손종역 한국물리학회 2004 새물리 Vol.48 No.6
Al-doped ZnO thin films were prepared by using RF-magnetron sputtering method with a ZnO target doped with 2 mol\% Al$_2$O$_3$. The structural, the electrical and the optical properties were investigated for the AZO films grown at substrate temperature of 100, 200, 300, 350, 400 $^\circ$C. The X-ray diffraction patterns and AFM data showed the AZO thin films to have a single phase with preferentially oriented structures. The electrical properties were analyzed by using the van der Pauw method and Hall-effect measurements. The resistivity of the AZO films deposited at a substrate temperature of 400 $^\circ$C was 6.86 $\times$ 10$^{-4}$ $\Omega$-cm due to an increase in the carrier concentration. Optical measurements showed that all AZO films had an average transmittance of 90 \% in the visible range and an optical bandgap between 3.5 and 3.68 eV, which resulted from variations in the carrier concentrations. The decrease in the transmittance at near infrared was attributed to impurity scattering and the refractive indices of the AZO films shows 2.07 $\sim$ 2.11.