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Ferroelectric and Magnetoelectric Properties of BiFeO3 Thin Films Prepared on a Membrane Structure
Seiji Nakashima,Kwi-Young Yun,Masanori Okuyama,Yoshitaka Nakamura 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Multiferroic BiFeO3 (BFO) thin films have been deposited on Pt/TiO2/SiO2 membrane and Pt/TiO2/SiO2/Si plate structures by using pulsed laser deposition. The X-ray diffraction pattern of the BFO thin film on the membrane structure slightly shifted to lower angle compared to that of the film on the Pt/TiO2/SiO2/Si substrate. Ferroelectric hysteresis loops were also obtained successfully at a measurement temperature of 150 K. The BiFeO3 thin film on the membrane structure showed a remanent polarization (Pr) of 91 μC/cm2 for a maximum applied voltage of 20 V, which was larger than that of the film on the Pt/TiO2/SiO2/Si plate structure at the same measurement conditions (Pr: 54 μC/cm2). Under a magnetic field perpendicular to the film plane, the remanent polarization (Pr) of the BiFeO3 thin film on the membrane structure at 150 K increased from 91 μC/cm2 (0 T) to 97 μC/cm2 (1.1 T).
Seiji Nakashima,Hironori Fujisawa,Masaru Shimizu,Osami Sakata,Tomoaki Yamada,Hiroshi Funakubo,박정민,Takeshi Kanashima,Masanori Okuyama 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
An electric-field-induced strain at 80 K in a 350-nm-thick BiFeO_3 (BFO) thin film deposited by pulsed laser deposition has been investigated by a time-resolved x-ray diffraction under an electric field using a synchrotron radiation. A 300-nsec-width and 804.09-nsec-period voltage pulses were applied to the BFO thin film during the measurements. The time-resolved-x-ray diffraction profile around BFO (001) diffraction peak indicates that BFO (001) diffraction peak shifts to lower angle side during the voltage application. A strain estimated from the peak shift lineally increases with increasing the amplitude of the voltage pulses. A piezoelectric constant (d_(33)) of (001)-oriented domains in the polycrystalline BFO thin film at 80 K is 20.2 pm/V. The value is smaller than that measured at RT of 27.8 pm/V in our previous report.
Seiji Nakashima,Tomohisa Uchida,Kouta Takayama,Hironori Fujisawa,Masaru Shimizu 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.9
Recently, an anomalous photovoltaic effect in a BiFeO3 (BFO) thin film has attracted much attention. In this research, Pt/BFO/Pt coplanar capacitors have been prepared using striped- and single-domain structured BFO thin films, and the influence of the polarization direction of incident violet laser light (λ = 405 nm) on the photovoltage of these capacitors has been investigated. In a specific geometry, both coplanar capacitors, the one using a striped-domain and the other using a single-domain structured BFO thin film showed anomalous photovoltages above band gap of BFO, indicating that an anomalous photovoltage should be observed under randomly-polarized light illumination such as that by a halogen lamp.
Detecting a Human Body Direction Using a Feature Selection Method
Yuuki Nakashima,Joo Kooi Tan,Seiji Ishikawa,Takashi Morie 제어로봇시스템학회 2010 제어로봇시스템학회 국제학술대회 논문집 Vol.2010 No.10
This paper describes a novel technique for detecting a human body direction using SVM constructed by HOG feature selected by AdaBoost. HOG feature is well-known feature for the robust judgment of a human. We employ the feature for detecting a human body direction. We compared some feature selecting methods with the previous one. Experimental results show effectiveness of the proposed method.
Two-step Growth of ZnO Nanorods by Using MOCVD and Control of Their Diameters and Surface Densities
Hironori Fujisawa,Chiaki Kobayashi,Seiji Nakashima,Masaru Shimizu 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.8
We investigated the growth of ZnO nanorods on Al2O3(1120) substrates by using metalorganic chemical vapor deposition and demonstrated the ability to control their diameters and surface densities by using a two-step growth method. Following the first step, the ZnO nanorods were found to be densely packed due to random nucleation across the substrate surface, and their diameters and surface densities (numbers per unit area) were interdependent. During the second growth step,because nucleation sites were limited to the tips of existing nanorods, an upper limit was placed on the surface density of the second-layer nanorods. The surface density of the second-layer nanorods was also influenced by the reaction pressure during the second growth step. The diameter of the ZnO nanorods in the second layer was determined by the growth temperature during the second step and could be controlled independently of the surface density. Consequently, ZnO nanorods with small diameters (< 100 nm), low surface densities (< 10 µm−2) and large spacings (> 200 nm), which are difficult grow using a one-step growth method, were successfully produced. The deposition of 180-nm-thick Pb(Zr,Ti)O3 coatings onto sparsely-grown ZnO nanorods was also demonstrated.
박정민,Masayuki Sohgawa,Takeshi Kanashima,Masanori Okuyama,Seiji Nakashima 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.7
Epitaxial BiFeO<sub>3</sub> (BFO) thin films have been prepared on La-doped (001) SrTiO<sub>3</sub> substrates (La-STO) by using magnetic-field-assisted pulsed laser deposition. X-ray diffraction patterns of the epitaxial BFO thin films prepared under magnetic fields of 0, 0.1, and 0.4 T show only (00l) diffraction peaks without secondary phases. From the results of reciprocal space mapping for all epitaxial BFO thin films, (003) reflections show splitting spots, and asymmetric spots of (−103) and (103) reflections exhibit a rhombohedral structure. The microstructure of the epitaxial thin films was modified by the strength of magnetic field, and a columnar structure was shown in the film prepared under a high deposition rate for a magnetic field of 0.4 T. The polarization versus electric field hysteresis loops were obtained at room temperature (RT) in all the epitaxial films; in particular, the remanent polarization for the epitaxial film prepared under a magnetic field of 0.1 T was 46 μC/cm<sup>2</sup> at RT while the current density was reduced in comparison with those of other epitaxial films.
박정민,Fumiya Gotoda,Takeshi Kanashima,Masanori Okuyama,Seiji Nakashima 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
Polycrystalline BiFeO_3 thin film has been prepared on indium tin oxide (ITO)-coated glass substrate at 520^oC by pulsed laser deposition (PLD). The XRD pattern shows a polycrystalline perovskite phase and (010) preferred orientation. Higher deposition temperature for BFO thin film on ITO substrate was required for crystallization, compared to that of BFO thin film grown on Pt substrate. Grain size becomes smaller than that of the BFO thin film on Pt substrate and leakage current density is decreased. Optical transmittance is about 80 % around 780 nm and the direct band gap (E_g) is 2.72 ± 0.03 eV. P-E hysteresis loop of the BFO thin film on ITO substrate was obtained at RT and polarization difference at zero electric field (2P_(ro)), corresponding to the double remanent polarization was 140 μ/cm^2. The M-H hysteresis loop was obtained at RT and antiferromagnetic behavior is little affected by difference of the substrate.
박정민,Takeshi Kanashima,Masanori Okuyama,Seiji Nakashima,김경만,이재열,이희영 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.31
Epitaxial 0.7BiFeO_3-0.3.BaTiO_3 solid solution thin films were grown on La doped SrTiO_3 (001) substrates by using pulsed laser deposition (PLD). The XRD pattern and the pole figure showed peaks corresponding to (001) planes. The capacitance-voltage (C-V) measurement showed dielectric constant and loss values of 70 and 0.07, respectively. The polarization hysteresis (P-E) was obtained at room temperature with remnant polarization (2P_r) and coercive field (2E_c) values of 23 μC/cm^2 and 508 kV/cm, respectively. The magnetization hysteresis (M-H) loop showed a linear behavior of a typical paramagnetic nature.
Ryo Kishimoto,Masafumi Kobune,Hiroshi Nishioka,Takeyuki Kikuchi,Hajime Kishi,Hironori Fujisawa,Seiji Nakashima,Masaru Shimizu,Satoshi Kimura 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.7
<EM>a-</EM> and <I>b</I>-axis-oriented Bi<SUB>3.25</SUB>Nd<SUB>0.75</SUB>Ti<SUB>3</SUB>O<SUB>12</SUB> (BNT) nanoplates, 3.0 mm thick, were fabricated on conductive Nb:TiO<SUB>2</SUB>(101) substrates with 0.79 mass% Nb at 650C by high-temperature sputtering. Successively, the fabrication of inorganic-organic composites was carried out by introducing an epoxy resin to the spaces between BNT nanoplates. The fourier transform infrared spectroscopy (FT-IR) and energy dispersive X-ray (EDX) elemental mapping results confirmed that the fabricated composite was an inorganic-organic hybridized material which introduced the cured epoxy resin into the spaces between BNT nanoplates. Based on polarization reversal measurements of the fabricated BNT-epoxy resin composites by piezoresponse force microscopy (PFM), it is shown that the composites have potential as ferroelectric microelement materials.