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X-ray Photoelectron and UV Photoyield Spectroscopic on Sr$_x$Bi$_y$Ta$_2$O$_9$ Films
M. Takahashi,H. Funakubo,K. Kodama,M. Noda,M. Okuyama,T. Watanabe 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
Photoemissions from ferroelectric SrxBiyTa2O9 (SBT) thin lms deposited by metalorganic chemical vapor deposition (MOCVD), pulsed lased deposition (PLD) and metalorganic decomposition (MOD) have been analyzed by X-ray photoelectron spectroscopy (XPS) and UV-photoyield spectroscopy (UV-PYS) in order to study their valence bands, Bi 4f core levels and Fermi levels. The XPS has shown band tails above the valence bands in all of the SBT lms, which are considered to induce UV-PYS signal from the Fermi levels. The XPS have also indicated that there exist less stable (Bi2O2)2+ layers in the inside of the PLD-SBT than in the MOCVD- and the MOD-SBT lms. P-E hystereses have been measured at various voltage sweeping rates, and have suggested that leakage currents through the capacitors are increased as the band tails in the valence bands are enlarged.
M. Sohgawa,M. Yoshida,M. Okuyama,T. Kanashima 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
SrBi2Ta2O9 (SBT)/SiO2/Si structures have been characterized by photore ectance spectroscopy (PRS) without electrode formation. SBT lm was deposited on SiO2/n-Si by the metal-organic decomposition (MOD) method and annealed in O2 atmosphere at 600 C. The voltage was applied by attaching ITO transparent electrodes during PRS measurement. The PRS spectral intensity of SBT/SiO2/Si structure has hysteresis characteristics as well as a C-V curve. Additionally, the spectral intensity gradually decreases with time, in a similar way to reduction of the capacitance. These results mean that the spectral intensity indicates the ferroelectricity of SBT flm in SBT/SiO2/Si structure, so that it is considered that characterization of MFIS structure without electrode can be measured by PRS.
D. Ricinschi,L. Mitoseriu,M. Iwata,M. Okuyama,M. Noda,Y. Ishibashi 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
In this paper we studied the switching kinetics using a discrete Landau-type three-dimensional polarization thermodynamic potential, with the elastic constraints of a lm attached to a substrate. We have shown that 180 domain reversal and polarization vector rotations are possible switching mechanisms, depending on eld strength and elastic stresses. The nature of nucleation seeds is also of crucial importance for the switching process. By drawing polarization vector representations of the ferroelectric lattice, the role of in-plane polarization components to switching has been investigated and shown to support experimental ndings.
Kaoru Yamashita,M Okuyama,N Shimizu 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.2I
Piezoelectric-type ultrasonic array sensors have been fabricated on micromachined diaphragm structures. A vibrating piezoelectric diaphragm has an inhomogeneity in induced charge distribution; charges in the central region and in the surroundings have opposite signs. These two charge signals can be summed up effectively by putting two kinds of electrodes for the regions and connecting the capacitors complementarily. Moreover, statically deflected diaphragms cause a larger lateral strain in piezoelectric layer than flat ones do. Combining these two effects, new sensors have been designed to have optimum electrodes for a complementary configuration on statically deflected diaphragms. The new sensor has shown sensitivity over five times higher than that of a conventional sensor.
T. Kanashima,M. Okuyama,H. Kanda,K. Ikeda,M. Sohgawa 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV
High-k thin lms of ZrO2, PrOx of 10 nm thickness have been prepared by pulsed laser deposition, and characterized in microscopic structure and electrical properties. Crystallization is promoted in ZrO2 lms deposited above 400 C, but a signicant XRD peak was not observed in the ZrO2 lm grown below 400 C. The leakage current is decreased by increasing growth temperature, but an equivalent-oxide thickness (EOT) obtained from accumulation capacitance of C .. V characteristics becomes large. The lms deposited at 400 C were annealed at 400 C in O2 gas to reduce the leakage. The leakage current change to be small, but the EOTs become large. Oxygen radical annealing is carried out to reduced the leakage, and is eective for ZrO2 thin lm. On the other hand, only small improvement is observed in the PrOx lms.
Coagulation of bipolarly charged ultrafine aerosol particles
Park, S.H.,Lee, K.W.,Shimada, M.,Okuyama, K. Elsevier 2005 Journal of aerosol science Vol.36 No.7
<P><B>Abstract</B></P><P>Particle charging during coagulational growth is widely used in material synthesis processes as well as with industrial particle removal equipment. Coagulation behavior of charged particles is significantly different from that of neutral particles. To calculate the change in size/charge distribution of particles undergoing bipolar coagulation, a two-dimensional sectional model has been usually used. This method, however, needs considerable computation time although it gives very accurate prediction. In this study, the moment model, to solve the bipolar coagulation problem in the free-molecule regime, was developed to provide a time-efficient tool. Simultaneous particle charging by bipolar ions was also considered in this study. The developed model is based on the assumption that particles cannot have more than one unit charge and the particle size distribution remains log normal. The developed model was compared to the two-dimensional sectional model, with good agreement being shown. Some characteristics of bipolar coagulation were investigated using the developed model. The bipolar coagulation with simultaneous bipolar diffusion charging was shown to significantly increase the coagulation rate compared to the neutral Brownian coagulation. It was also shown from the simulation results that if one needs a higher coagulation rate in the initial stage, bipolar coagulation without ions is recommended, while bipolar coagulation with simultaneous charging by bipolar ions should be used if one wants a high coagulation rate for a long time.</P>
Park, J.Y.,Kim, C.S.,Okuyama, K.,Lee, H.M.,Jang, H.D.,Lee, S.E.,Kim, T.O. Elsevier Sequoia 2016 Journal of Power Sources Vol.306 No.-
The influence of Cu doping on the function of dye-sensitized solar cells (DSSCs) dependent on Cu/N-doped TiO<SUB>2</SUB> photoelectrodes was examined. Cu/N-doped TiO<SUB>2</SUB> photoelectrodes with diverse Cu concentration were synthesized using the sol-gel process. Upon adequate addition of Cu, the nanoparticles exhibited small particle sizes, high surface area, and a significant red alteration of their absorption to the visible region in relation to Degussa P25 nanomaterials. Furthermore, the traces of Cu/N-doped TiO<SUB>2</SUB> nanoparticles enhanced the charge transfer and reduced the charge recombination. The addition of sufficient Cu and N increased the surface area, elevating the dye adsorption degree, and decreasing the level of electron recombination. A DSSC fabricated with a 1 mM Cu/N-doped TiO<SUB>2</SUB> nanoparticles accomplished 11.35% of the highest power conversion efficiency, with a short-circuit current of 22.5 mA/cm<SUP>2</SUP>. The energy conversion efficiency of this photoelectrode was approximately 37% greater than that of the control, Degussa P25. The increased energy efficiency can be resulted from the extension in surface area, which enabled larger dye charging amount, and the deduction in charge recombination, which accelerated the charge transfer.