• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.16 no.8
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• pp.700-704
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• 2003

This paper describes on characteristics of 2" 3C-SiC wafer bonding using PECVD (plasma enhanced chemical vapor deposition) oxide and HF (hydrofluoride acid) for SiCOI (SiC-on-Insulator) structures and MEMS (micro-electro-mechanical system) applications. In this work, insulator layers were formed on a heteroepitaxial 3C-SiC film grown on a Si (001) wafer by thermal wet oxidation and PECVD process, successively. The pre-bonding of two polished PECVD oxide layers made the surface activation in HF and bonded under applied pressure. The bonding characteristics were evaluated by the effect of HF concentration used in the surface treatment on the roughness of the oxide and pre-bonding strength. Hydrophilic character of the oxidized 3C-SiC film surface was investigated by ATR-FTIR (attenuated total reflection Fourier transformed infrared spectroscopy). The root-mean-square suface roughness of the oxidized SiC layers was measured by AFM (atomic force microscope). The strength of the bond was measured by tensile strength meter. The bonded interface was also analyzed by IR camera and SEM (scanning electron microscope), and there are no bubbles or cavities in the bonding interface. The bonding strength initially increases with increasing HF concentration and reaches the maximum value at 2.0 ％ and then decreases. These results indicate that the 3C-SiC wafer direct bonding technique will offers significant advantages in the harsh MEMS applications.ions.

• Bulletin of the Korean Chemical Society
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• v.22 no.11
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• pp.1231-1235
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• 2001

Pseudotetragonal ZrO0.75S whose space group is P212121 was synthesized and the cell dimensions were a=5.110(2) $\AA$, b=5.110(7) $\AA$, and c=5.198(8) $\AA.$ The space group P212121 seems to be resulted from lowering the symmetry of cubic ZrOS structure with P213 space group by lattice distortion due to the oxygen defects. In the distorted structure, bond shortening between metal-nonmetal by reduction of cell volume and alternation of Zr-Zr distance were observed. Dielectric constant and loss data of the bulk material in temperature range -170 to 20 $^{\circ}C$ and frequency range 50 Hz to 1 MHz showed that there was dielectric transition at around -70 $^{\circ}C$ originated from the relaxation of Zr-S segment. Comparing with ZrO2 exhibited the dielectirc constants, 9.0 at room temperature, ZrO0.75S showed high dielectric constant, k = 200.2 at 100 kHz. The activation energy of relaxation time due to dielectric relaxation of Zr-S was 0.47 eV (11.3 kcal/mole). According to the impedance spectra, ZrO0.75S showed more parallel circuit character between the resistance and capacitance components at the temperature (-70 $^{\circ}C)$ that the Zr-S dielectric relaxation was observed.

• Journal of the Korean Chemical Society
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• v.36 no.4
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• pp.517-522
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• 1992

The reaction of ${\beta}$-picoline with substituted benzoyl chlorides has been studied by means of conductometry under various pressures in acetonitrile. From the values of pseudo-first order and second order rate constants, the activation parameters (${\Delta}V{\neq}$, ${\Delta}{\beta}{\neq}$, ${\Delta}H{\neq}$, ${\Delta}S{\neq}$ and ${\Delta}G{\neq}$) and the pressure dependence of Hammett ${\rho}$ value were studied. The activation volume, the activation compressibility coefficient and the activation entropy were all negative. By increasing pressure the rate constant and Hammett ${\rho}$ value were increased, and the reaction mechanism was proceed in bond formation favored.

• Journal of the Korean Chemical Society
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• v.35 no.1
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• pp.64-69
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• 1991

Kinetics of the reaction of p-methylphenacyl arenesulfonates with pyridine in acetonitrile were investigated by an electric conductivity method at 1∼2000 bars and 35∼55$^{\circ}C$. The rates of these reactions were increased with raising pressures and temperatures. The activation enthalpy(${\Delta}H^{\neq}$), entropy(${\Delta}S^{\neq}$) and activation volume(${\Delta}V^{\neq}$) of the reaction were obtained with the rate constants. Activation volume and entropy were both negative valued, and activation enthalpy was positive. The acteivation parameters (${\Delta}V^{\neq}$ and ${\Delta}S^{\neq}$) were decreased with increasing pressure. From all of the above results, it was found that this reaction proceeds on the S$_N$2 in which C${\cdots}$O bond breaking is more advanced as pressure increases.

• Bulletin of the Korean Chemical Society
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• v.35 no.7
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• pp.2013-2018
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• 2014

The adsorption and decomposition of trimethylene oxide ($C_3H_6O$) molecule on the Al(111) surface were investigated by the generalized gradient approximation (GGA) of density functional theory (DFT). The calculations employed a supercell ($6{\times}6{\times}3$) slab model and three-dimensional periodic boundary conditions. The strong attractive forces between $C_3H_6O$ molecule and Al atoms induce the C-O bond breaking of the ring $C_3H_6O$ molecule. Subsequently, the dissociated radical fragments of $C_3H_6O$ molecule oxidize the Al surface. The largest adsorption energy is about -260.0 kJ/mol in V3, V4 and P2, resulting a ring break at the C-O bond. We also investigated the decomposition mechanism of $C_3H_6O$ molecules on the Al(111) surface. The activation energies ($E_a$) for the dissociations V3, V4 and P2 are 133.3, 166.8 and 174.0 kJ/mol, respectively. The hcp site is the most reactive position for $C_3H_6O$ decomposing.

• Journal of the Korean Chemical Society
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• v.18 no.4
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• pp.223-238
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• 1974

CNDO/2 MO theoretical studies and kinetic studies of halide exchange reactions for alkylchloroformates have been carried out in order to investigate structure-reactivity relationship of alkylchloroformates. From the result of energetics, it was concluded that the most stable configuration of alkylchloroformate is that in which alkyl group and chlorine are trans to each other, and that the hindered rotation about the bond between the carbonyl carbon and alkoxy-oxygen bond is attributed to the ${\pi}-$electron delocalization. It has been found that the large charge separation is due to -M effect of carbonyl and alkoxy oxygens and-I effect of chlorine. The order of rates in solvents studied was $(CH_3)_2 > CO > CH_3CN{\gg}MeOH.$$I^->Br^->Cl^-$ in protic solvent, and of Cl^->Br^- >I^-$ in dipolar aprotic solvents. Alkyl group contribution has the decreasing order of $CH_3-> C_2H-{\gg}i-C_3H_7-.$ The solvent effect has been interpreted on the basis of initial and final state contribution. A transition state model has been suggested, and it has been proposed that the most favorable mechanism is the addition-elimination. From the results of activation parameters and electronic properties, an energy profile has been proposed. Structural factors determining reactivities of alkylchloroformates have been shown to be charge, energy level of ${\alpha}^*LUMO$ to C-Cl bond and ${\alpha}^{\ast} $antibonding strength with respect to C-Cl bond in this MO. Charge and polarizability of nucleophile, and the interaction of these effects with solvent structures are also found to be important.

• Bulletin of the Korean Chemical Society
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• v.6 no.6
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• pp.354-358
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• 1985

Carbon-13 nuclear spin-lattice relaxation times have been measured over the range of temperature from 213K to 353K for carbons in n-heptane in neat liquid. The experimental data have been analyzed to obtain informations of segmental motions in the chain polymers by employing a model which describes jumps between several discrete states with different lifetimes. The overall reorientation of the molecule is assumed to be isotropic rotational diffusion. From the above analysis the activation energies of each C-C bond reorientation as well as the overall reorientation have been obtained through the Arrhenius-type temperature dependence.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.830-833
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• 2003

This paper describes the fabrication and characteristics of 3C-SiCOI sotctures by SDB and etch-back technology for high-temperature MEMS applications. In this work, insulator layers were formed on a heteroepitaxial 3C-SiC film grown on a Si(001) wafer by thermal wet oxidation and PECVD process, successively. The pre-bonding of two polished PECVD oxide layers made the surface activation in HF and bonded under applied pressure. The wafer bonding characteristics were evaluated by the effect of HF concentration used in the surface treatment on the roughness of the oxide and pre-bonding strength. Hydrophilic character of the oxidized 3C-SiC film surface was investigated by ATR-FTIR. The strength of the bond was measured by tensile strengthmeter. The bonded interface was also analyzed by SEM. The properties of fabricated 3C-SiCOI structures using etch-back technology in TMAH solution were analyzed by XRD and SEM. These results indicate that the 3C-SiCOI structure will offers significant advantages in the high-temperature MEMS applications.

• Journal of the Korean Chemical Society
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• v.19 no.3
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• pp.149-155
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• 1975

Pivalic acid, which has a globular shape and is a plastic crystal, has been examined by means of temperature-dependent with-line proton magnetic resonance spectroscopy. Results of temperature-dependent line width, second moment, and spin-lattice relaxation time studies of pivalic acid were interpreted in terms of dynamic behavior and hydrogen bonding. The dynamic behavior consists of superimposed reorientation of the methyl groups about their three-fold axes$(C_3) and of the molecule about the central C-C bond(C_3'),$ general molecular reorientation about the center of gravity, and molecular self-diffusion. Activation energies for the motional processes have been obtained from line width measurements using the modified Bloembergen, Purcell, and Pound theory and from spin-lattice relaxation time measurements. The results were compared with the Pople-Karasz theory of fusion and the agreement was found to be poor. The discrepancy was interpreted in terms of hydrogen bonding in this molecule.

• Bulletin of the Korean Chemical Society
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• v.13 no.3
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• pp.296-306
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• 1992

$^{13}C$ spin-lattice relaxation times were measured for n-alkanes of moderate chain length, ranging from n-octane to n-dodecane, under the condition of proton broad-band decoupling within the temperature range of 248-318 K in order to gain some insight into basic features of segmental motions occurring in long chain ploymeric molecules. The NOE data showed that except for methyl carbon-13 dipole-dipole interactions between $^{13}C$ and directly bonded $^1H$ provide the major relaxation pathway, and we have analyzed the observed $T_1data$ on the basis of the internal rotational diffusion theory by Wallach and the conformational jump theory by London and Avitabile. The results show that the internal rotational diffusion constants about C-C bonds in the alkane backbone are all within the range of $10^9\;-10^10\;sec^{-1}$ in magnitude while the mean lifetimes for rotational isomers are all of the order of $10^{-11}\;-10^{-10}$ sec. Analysis by the L-A theory predicts that activation energies for conformational interconversion between gauche and trans form gradually increase as we move from the chain end toward the central C-C bond and they are within the range of 2-4 kcal/mol for all the compounds investigated.