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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.
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.
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.
Hideto Tada,Masafumi Kobune,Koji Fukushima,Hisashi Oshima,Daisuke Horit,Akihiro Tamura,Yusuke Daiko,Atsushi Mineshige,Tetsuo Yazawa,Hironori Fujisawa,Masaru Shimizu,Hideshi Yamaguchi,Koichiro Honda 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2
The structural characteristics, the mechanism of crystal growth, and the ferroelectric properties of partially Sm-substituted perovskite bismuth-samarium-nickel-titanate [(Bi1−xSmx)(Ni0.5Ti0.5)- O3; BSNT, x = 0− 0.9] thin films deposited on Pt(100)/MgO(100) substrates by rf sputtering have been investigated using X-ray diffraction, transmission electron microscope, and polarization - electric field hysteresis loop measurements. The fabricated BSNT samples with x≥0.6 were confirmed to have a single-phase perovskite structure. Of the four samples (x = 0.6 0.7, 0.8, and 0.9) with a single-phase perovskite structure, the c-axis-oriented epitaxial BSNT film with x = 0.9 exhibited the best hysteresis loop, with a remanent polarization of 2 μC/cm2 and a coercive field of 100 kV/cm. The structural characteristics, the mechanism of crystal growth, and the ferroelectric properties of partially Sm-substituted perovskite bismuth-samarium-nickel-titanate [(Bi1−xSmx)(Ni0.5Ti0.5)- O3; BSNT, x = 0− 0.9] thin films deposited on Pt(100)/MgO(100) substrates by rf sputtering have been investigated using X-ray diffraction, transmission electron microscope, and polarization - electric field hysteresis loop measurements. The fabricated BSNT samples with x≥0.6 were confirmed to have a single-phase perovskite structure. Of the four samples (x = 0.6 0.7, 0.8, and 0.9) with a single-phase perovskite structure, the c-axis-oriented epitaxial BSNT film with x = 0.9 exhibited the best hysteresis loop, with a remanent polarization of 2 μC/cm2 and a coercive field of 100 kV/cm.
Akihiro Tamura,Masafumi Kobune,Kazuki Imagawa,Hisashi Oshima,Yusuke Daiko,Atsushi Mineshige,Tetsuo Yazawa,Hiroshi Nishioka,Hironori Fujisawa,Masaru Shimizu,Hideshi Yamaguchi,Koichiro Honda 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.31
3.0-mm-thick a- and b-axis-oriented (Bi_(3.25)Nd_(0.75))Ti_3O_(12) (BNT-0.75) films were fabricated on conductive Nb:TiO_2(101) (Nb = 0, 0.048, 0.46, 0.79 mass%) single crystal substrates by high-temperature sputtering. A BNT films grown on undoped TiO_2 substrates have no orientation, whereas BNT films deposited on Nb:TiO_2 substrates with 0.46-0.79 mass% Nb show strong (h00/0k0) diffractions and grow with a heteroepitaxial relationship to the underlying Nb:TiO_2 substrates. The BNT-0.75 film deposited on Nb:TiO_2(101) substrate with 0.79 mass% Nb was indicated the peculiar shape of approximately 100-150-nm-thick nanoplates. We speculate that the driving force for producing a plate-like structure for BNT films is attributed to the large anisotropy of linear expansion coefficients for Bi_4Ti_3O12, and the comparatively small lattice matching between Nb:TiO_2 substrate and BNT film.