Faculty Profiles - SAITO, Nagahiro

Papers - SAITO, Nagahiro

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Surface potential images of microstructured organosilane self-assembled monolayers acquired by Kelvin probe force microscopy

Sugimura, H; Hayashi, K; Saito, N; Takai, O; Nakagiri, N

JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS Vol. 40 ( 2B ) page： L174 - L176 2001.2

Catalytic effects of copper on dibenzo-p-dioxin and polychlorinated dibenzo-p-dioxin generations using ab initio molecular orbital method

Hirota M., Kato J., Saito N., Fuwa A.

Toxicological and Environmental Chemistry Vol. 81 ( 3-4 ) page： 133 - 146 2001

Language：English Publishing type：Research paper (scientific journal) Publisher：Toxicological and Environmental Chemistry

The roles played by copper in dibenzo-p-dioxin formation from the precursor phenol have been investigated using ab initio molecular orbital calculation, and the following catalytic roles of copper has been identified: (i) stabilization of the total energy owing to the absorption of phenol, (ii) reduction of oxygen-hydrogen bond strength in phenol, and (iii) reduction of steric effect of hydrogen atom in pre-dioxin. The catalytic effect of copper has been shown in terms of the smaller apparent activation energy. In the case of polychlorinated dibenzo-p-dioxins generation from precursor polychlorinated phenols, the catalytic roles (i), i.e., the stabilization of the total energy of precursor, would become even stronger. On the other hand, the catalytic roles (ii) and (iii) are unchangeable regardless of the existence of substituted chlorine atom.

DOI： 10.1080/02772240109359026

Scopus

Behavior of Cu-In-Te electrodeposition from acid solution

Ishizaki T., Saito N., Yata D., Fuwa A.

Proceedings of the Second International Conference on Processing Materials for Properties page： 281 - 284 2000.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Second International Conference on Processing Materials for Properties

Ternary compound-semiconductor, CuInTe2, film was deposited cathodically under potentiostatic conditions on titanium substrate from aqueous solution containing CuCl2, InCl3, TeO2 and HCl in this study. The deposition parameters such as electrolytic solution composition, potential and temperature were optimized for electrodeposition of CuInTe2. Structural characterization of the deposited film was also carried out using XRD and SEM. Electrodeposited films were prepared and analyzed for their chemical composition using ICP. The ICP analyses showed that the stoichiometry of the films could be controlled by (1) the deposition potential and/or by (2) the electrolytic bath composition.

Scopus

Preparation of YSZ thin films by RF plasma-enhanced metal organic chemical vapor depodition

Nishimura T., Ichikawa T., Saito N., Fuwa A.

Proceedings of the Second International Conference on Processing Materials for Properties page： 267 - 270 2000.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Second International Conference on Processing Materials for Properties

Yttria-stabilized zirconia (YSZ) has high potential to be used as solid-oxide fuel cell (SOFC) electrolyte. However, the high efficiency of SOFC has not been yet achieved due to the high internal resistance of bulk electrolyte. The resistance becomes lower with the decrease in the electrolyte thickness. Thus, the decrease in electrolyte thickness leads to lower internal resistance. The aim of this study is as follows: (a) to prepare the thin films of YSZ by inductively-coupled RF plasma-enhanced metal organic chemical vapor deposition (PEMOCVD) process using Zr(t-OC4H9)4, Y(DPM)3 and oxygen, and (b) to reveal the relationship between the structural characterizations and the process parameters.

Scopus

The roles of metallic compounds on dioxins generation-decomposition behavior from thermodynamics and quantum chemistry

Saito N., Hirota M., Ishizaki T., Fuwa A.

Proceedings of the Second International Conference on Processing Materials for Properties page： 727 - 732 2000.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the Second International Conference on Processing Materials for Properties

Owing to their extremely high toxicity in the environment, the dioxins have been attracting social, technical and scientific attention in recent years. The authors theoretically had predicted the thermodynamics properties of all the dioxins via quantum chemistry and statistical thermodynamics and elucidated the generation-decomposition behavior of dioxins in the equilibrium calculation of C-H-O-Cl system. In actual combustion processes, it is said that metallic compounds have much influence on the dioxins behavior. The aim of this study is to reveal the roles of metallic compounds the generation-decomposition behavior of dioxins is revealed from the viewpoints of quantum chemistry. Especially, the catalytic effect of copper has been investigated for the reaction, 2HCl(g)→H2(g)+Cl2(g) and for the etherification reaction from precursors, which is Phenol(g) here, to dioxins. The catalytic role of Cu is shown to have much influence on the generation -decomposition of dioxins.

Scopus

Kinetics of SiHCl<inf>3</inf> and SiCl<inf>4</inf> evolution in Si(s)-HCl(g) system simulated by ab-initio MO

Saito N., Ishizaki T., Fuwa A.

Materials Transactions, JIM Vol. 41 ( 3 ) page： 383 - 392 2000.3

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Transactions, JIM

A reaction model for a HCl(g)-Si(s) system is proposed in this study as follows: first, SiCl2(g) and H2(g) are produced by a heterogeneous surface reaction, and then SiHCl3(g) and SiH2Cl2(g) are produced by the homogeneous reaction between SiCl2(g) and HCl(g) and between SiCl2(g) and H2(g), respectively; finally, SiCl4(g) and SiHCl3(g) are produced by the homogeneous reaction between SiHCl3(g) and HCl(g) and between SiH2Cl2(g) and HCl(g), respectively. The mechanism in the first heterogeneous surface reaction step has been studied extensively in the past. However, the detail of the subsequent homogeneous reactions has not yet been understood. It is important to get information of the chemical kinetics of the reactions derived from the reaction intermediate of SiCl2(g) in the SiCl2(g)-HCl(g)-H2(g) system, so the most plausible elementary reactions of reversible unimolecular fission and chain reaction are proposed here. The structures of the molecules formed in these reactions are optimized using the minimization principle of energy calculated by ab-initio molecular orbital method and also their rate constants are calculated by conventional transition state theory. Using these rate constants, the ordinary differential equations are solved on mass balance, and the time dependent concentration profile of respective chemical species and the prior reaction paths are discussed in this study.

DOI： 10.2320/matertrans1989.41.383

Scopus

Prediction for thermodynamic function of dioxins for gas phase using semi-empirical molecular orbital method with PM3 Hamiltonian

Saito N., Fuwa A.

Chemosphere Vol. 40 ( 2 ) page： 131 - 145 2000.1

Language：English Publishing type：Research paper (scientific journal) Publisher：Chemosphere

DOI： 10.1016/S0045-6535(99)00215-5

Scopus

Gas phase equilibria for dibenzo-p-dioxin, dibenzo-p-furan and biphenyl in the C-H-O system

Saito N., Ishizaki T., Fuwa A.

Toxicological and Environmental Chemistry Vol. 74 ( 3-4 ) page： 165 - 177 2000

Language：English Publishing type：Research paper (scientific journal) Publisher：Toxicological and Environmental Chemistry

The gas phase equilibrium calculation for the C-H-O system at atmospheric pressure and temperature from 773 to 1773 K at intervals of 250 K was performed to understand the generation and decomposition behavior of dibenzo-p-dioxin (DD), dibenzo-p-furan (DF) and biphenyl (BP) in relation to the existing oxygen potential. It is possible to categorize these results into three regions from the viewpoint of this potential: region (A), region (B) and region (C) are that of the higher, modest and lower oxygen potential, respectively. In region (A), the equilibrium amounts of DD, DF and BP are nearly zero. In region (B), they increase once and then decrease with rise in temperature. In the most characteristic region (C), they increase uniformly with rise in temperature.

DOI： 10.1080/02772240009358879

Scopus

Thermodynamic investigation of the effect of oxygen and hydrogen chloride potential upon generation and decomposition behavior of dioxins

Nagahiro Saito, Takahiro Ishizaki, Akio Fuwa

Toxicological and Environmental Chemistry Vol. 75 ( 3-4 ) page： 161 - 179 2000

Language：English Publishing type：Research paper (scientific journal)

The thermodynamic equilibrium of the C-H-O-Cl system has been calculated to elucidate the generation and decomposition behavior of dioxins, and is discussed from the viewpoint of the oxygen and hydrogen chloride potential. The dioxins behavior is greatly dependent on the oxygen potential, i.e. higher temperature and oxygen potential lead to the complete decomposition of dioxins, while low hydrogen chloride potential under insufficient oxygen condition leads to an increase of multi-chlorine displacement of dioxins.

DOI： 10.1080/02772240009358902

Scopus

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Thermodynamic function derivation of dioxin substances using semi-empirical molecular orbital theory

Saito N., Fuwa A.

Proceedings of the TMS Fall Extraction and Processing Conference Vol. 3 page： 2009 - 2018 1999.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of the TMS Fall Extraction and Processing Conference

In this investigation, respective thermodynamic parameters of heats of formation, standard entropy and specific heat capacity at constant pressure for PCDDs, PCDFs, Co-PCB and PCBs as well as polychlorinated-benzens and polychlorinated-phenols have been evaluated by quantum chemical calculation using a semi-empirical molecular orbital method with the PM3 Hamiltonian and statistical thermodynamic correlation. The values of heats of formation for the dioxin substances and their precursors are calculated in the range of ±200 kJ/mol. The tolerance analysis indicates that the maximum discrepancy with experimental values would be reasonably estimated to be ±28 kJ/mol. The values of standard entropy for these compounds would be in the range of + 270 to + 500 J/mol K, and the estimated discrepancy between the calculated experimental heats of formation would be in the range of + 1 to + 9 J/mol K.

Scopus

Prediction of Elementary Reaction Mechanism for the CVD Process in Si<inf>2</inf>Cl<inf>6</inf>-H<inf>2</inf> System using Semi-Empirical Molecular Orbital Method

Saito N., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 3 ) page： 319 - 325 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

From our previous experimental study of the Si chemical vapor deposition in Si2Cl6-H2 system, the following elementary reaction mechanism was proposed: decomposition of Si2Cl6 to produce SiCl2, which becomes the adsorbent; Si2Cl6(g) → 2SiCl3(g) → SiCl4(g) + SiCl2(g) (→ SiCl2(a)), and hydrogen reduction reaction of the absorbed SiCl2 to produce Si(s). The preliminary quantum chemistry study for this reaction mechanism has shown that the reaction is so infeasible that the above-mentioned elementary reaction mechanism is unreasonable. The most feasible and appropriate reaction mechanism has been shown as follows: (Step 1) Si2Cl6(g) → SiCl4,(g) + SiCl2(g) (Step 2) SiCl2(g) +a → SiCl2(a) (Step 3) SiCl2(a) + H2(g) → SiCl(a) + 2HCl(g) (Step 3-1) SiCl2(a) + H2(g) → Si-2HCl(a) (Step 3-2) Si-2HCl(a) → Si(a) + 2HCl(g) where, a is the active site on silicon surface. On the assumption that step 3 is the rate-determining step, this elementary reaction mechanism can explain the experimental observation in the rate expression on the concentration dependence with respect to Si2Cl6 and H2.

DOI： 10.2320/jinstmet1952.63.3_319

Scopus

Prediction of pressure dependent rate constant for the reaction, SiH<inf>4</inf>(g)→SiH<inf>3</inf>(g)+H(g), using RRKM theory aided by ab-initio MO

Saito N., Hirota M., Ishizaki T., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 4 ) page： 520 - 526 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

The pressure dependent rate constant for the reaction, SiH4(g)→SiH3(g)+H was predicted using the Rice-Ramspger-Kassel-Marcus theory aided by Ab-initio molecular orbital (MO). It was calculated under conditions in which the temperatures were from 600 to 1500 K intervals of 100 K. The Arrhenius type rate expression was shown.

DOI： 10.2320/jinstmet1952.63.4_520

Scopus

Effect of citric acid and EDTA addition on Cu-In alloy electrochemical deposition

Ishizaki T., Saito N., Fuwa A.

Materials Transactions, JIM Vol. 40 ( 9 ) page： 867 - 870 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Transactions, JIM

The standard electrode potential for Cu is 0.34 V and that of In is -0.34 V, which means that their deposition potentials are far apart, making the co-deposition difficult from a simple solution containing Cu and In ions. In order to bring these deposition potentials closer, a complex forming reagent of citric or EDTA is added to the CuSO4-In2(SO4)3 solution. The effect of these reagents was examined by linear sweep voltammetric measurement. An electrochemical deposition experiment of Cu-In alloy was conducted where effect citric acid or EDTA addition, current density and Cu concentration were examined.

DOI： 10.2320/matertrans1989.40.867

Scopus

Theoretical analysis for thermal chemical vapor deposition from Tetraethoxysilane using a semi-empirical molecular orbital method

Hirota M., Saito N., Ishizaki T., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 63 ( 7 ) page： 931 - 937 1999

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

In order to elucidate the reaction mechanism for the Tetraethoxysilane (TEOS) thermal decomposition at atmospheric pressure, its pertinent elemental reactions involving the SiO(OC2H5)2 reaction intermediate were first proposed. For respective species formed in these elemental reactions, the total energy and the electronic state were calculated using a semi-empirical molecular method. The adsorption process which involves adsorbent species formation and surface reaction mechanism were then analyzed from the standpoint of molecular orbital formation and charge transfer mechanism, and the results are summarized as follows: (1) A reaction intermediate, SiO(OC2H5)2(1A1), is probably formed through the following β-elimination reaction route: Si(OC2H5)4(1A1)→SiO(OC2H5) 2(1A1)+C2H4(1A1)+C2H5OH (1A1). (2) The adsorption of SiO(OC2H5)2(1A1) on SiO2 occurs with charge transfer from the dangling bond of silicon atom at an active site of the SiO2 surface to the π*-LUMO unoccupied orbital of SiO(OC2H5)2(1A1). (3) The sequence of surface reactions is considered as follows: (1) First, a dissociation reaction of C2H5(2A′) takes place, whereby producing a double bond between silicon atom and oxygen atom of the intermediate, since they possess unpaired electrons. (2) Si-O bond is successively formed following the mechanism similar to the one operating in the adsorption of SiO(OC2H5)2(1A1) on SiO2. (3) Electronic state of the reactant finally formed is in the 1A1 state, which has a σ-orbital to be fully occupied with electrons.

DOI： 10.2320/jinstmet1952.63.7_931

Scopus

Texture of thin silicon films deposited from Si<inf>2</inf>Cl<inf>6</inf>

Kato Y., Saito N., Fuwa A.

Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals Vol. 60 ( 8 ) page： 744 - 750 1996.8

Language：English Publishing type：Research paper (scientific journal) Publisher：Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals

Thin Silicon films were deposited on non-crystal quartz glass substrates by hydrogen reduction of Si2Cl6 at temperatures from 650 to 900 °C in a horizontal hot wall reactor. The microstructures of the thin silicon films deposited under various experimental conditions were analyzed. The thin silicon films deposited from 750 to 850 °C have the highest degree of preferred (220) plane orientation with the 〈111〉 direction along the plane, and the cross-sectional morphology exhibits a columnar structure. The experimental values of the lattice spacing approach a value cited in JCPDS for the films deposited in a higher temperature range. In the lower temperature range the morphology of surface is flat and smooth, and in the higher temperature range the surface becomes uneven remarkably.

DOI： 10.2320/jinstmet1952.60.8_744

Scopus

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Papers - SAITO, Nagahiro