• Bulletin of the Korean Chemical Society
• /
• v.24 no.3
• /
• pp.325-333
• /
• 2003

An analysis of the electronic structure and bonding in the ternary silicide YNiSi₃is made, using extended Huckel tight-binding calculations. The YNiSi₃structure consists of Ni-capped Si₂dimer layers and Si zigzag chains. Significant bonding interactions are present between the silicon atoms in the structure. The oxidation state formalism of $(Y^{3+})(Ni^0)(Si^3)^{3-}$ for YNiSi₃constitutes a good starting point to describe its electronic structure. Si atoms receive electrons from the most electropositive Y in YNiSi₃, and Ni 3d and Si 3p states dominate below the Fermi level. There is an interesting electron balance between the two Si and Ni sublattices. Since the ${\pi}^*$ orbitals in the Si chain and the Ni d and s block levels are almost completely occupied, the charge balance for YNiSi₃can be rewritten as $(Y^{3+})(Ni^{2-})(Si^{2-})(Si-Si)^+$, making the Si₂layers oxidized. These results suggest that the Si zigzag chain contains single bonds and the Si₂double layer possesses single bonds within a dimer with a partial double bond character. Strong Si-Si and Ni-Si bonding interactions are important for giving stability to the structure, while essentially no metal-metal bonding exists at all. The 2D metallic behavior of this compound is due to the Si-Si interaction leading to dispersion of the several Si₂π bands crossing the Fermi level in the plane perpendicular to the crystallographic b axis.

• Bulletin of the Korean Chemical Society
• /
• v.34 no.4
• /
• pp.1055-1060
• /
• 2013

The adsorption structures of threonine on the Ge(100) surface were investigated using core-level photoemission spectroscopy (CLPES) in conjunction with density functional theory (DFT) calculations. CLPES measurements were performed to identify the experimentally preferred adsorption structure. The preferred structure indicated the relative reactivities of the carboxyl and hydroxymethyl groups as electron donors to the Ge(100) surface during adsorption. The core-level C 1s, N 1s, and O 1s CLPES spectra indicated that the carboxyl oxygen competed more strongly with the hydroxymethyl oxygen during the adsorption reaction. Three among six possible adsorption structures were identified as energetically favorable using DFT calculation methods that considered the inter- and intra-bonding configurations upon adsorption onto the Ge(100) surface. These structures were O-H dissociated N dative inter bonding, O-H dissociated N dative intra bonding, O-H dissociation bonding. One of the adsorption structures: O-H dissociated N dative inter bonding was predicted to be stable in light of the transition state energies. We thus confirmed that the most favorable adsorption structure is the O-H dissociated N dative-inter bonding structure using CLPES and DFT calculation.

• Bulletin of the Korean Chemical Society
• /
• v.14 no.3
• /
• pp.344-347
• /
• 1993

• Bulletin of the Korean Chemical Society
• /
• v.34 no.7
• /
• pp.2171-2175
• /
• 2013

The electronic structure and elastic properties of the 4d transition metal carbides MC (M = Y, Zr, Nb, Rh) were studied by means of extended H$\ddot{u}$ckel tight-binding band electronic structure calculations. As the valence electron population of M increases, the bulk modulus of the MC compounds in the rocksalt structure does not increase monotonically. The dominant covalent bonding in these compounds is found to be M-C bonding, which mainly arises from the interaction between M 4d and C 2p orbitals. The bonding characteristics between M and C atoms affecting the variation of the bulk modulus can be understood on the basis of their electronic structure. The increasing bulk modulus from YC to NbC is associated with stronger interactions between M 4d and C 2p orbitals and the successive filling of M 4d-C 2p bonding states. The decreased bulk modulus for RhC is related to the partial occupation of Rh-C antibonding states.

• Bulletin of the Korean Chemical Society
• /
• v.24 no.8
• /
• pp.1215-1218
• /
• 2003

An analysis of the bonding situation in CaM₂P₂ (M=Fe, Ni) with ThCr₂Si₂ structure is made in terms of DOS and COOP plots. The main contributions to covalent bonding are due to M-P and P-P interactions in both compounds. Particularly, the interlayer P-P bonding by variation in the transition metal is examined in more detail. It turns out that the shorter P-P bonds in CaNi₂P₂ form as a result of the decreasing electron delocalization into ${{\sigma}_p}^*$ of P₂ due to the weaker bonding interaction between the metal d and ${{\sigma}_p}^*$ as the metal d band is falling from Fe to Ni.

• Journal of the Korean Ceramic Society
• /
• v.30 no.5
• /
• pp.357-364
• /
• 1993

Chemical reaction occurred in the interface of Mn-Zn ferrite and glass after bonding. Effects of the formation of reaction layer on the magnetic properties were investigated. The composition of glass was 23PbO-61SiO2-6ZnO-8Na2O-2K2O and the ferrite was chosen to have a high permeability. Toroid samples of ferrites bonded with glasses, were heat-treated at $700^{\circ}C$, 80$0^{\circ}C$ and 90$0^{\circ}C$ for 1h. The reaction was observed to increase with bonding temperature, resulting in the development of reaction layer. Subsequently the initial permeability was found to be decreased. The permeabilities decreased by 25% with increasing bonding temperature from $700^{\circ}C$ to 80$0^{\circ}C$. At the bonding temperature of 90$0^{\circ}C$, the permeability was decreased by 45%, compared to that of 80$0^{\circ}C$.

• Carbon letters
• /
• v.15 no.4
• /
• pp.282-289
• /
• 2014

Blends of poly(vinyl alcohol) (PVA), polyethyleneimine (PEI), and graphene oxide (GO) were prepared by solution casting method. Calorimetric thermal properties of the blends were investigated. The $T_gs$ of PVA/PEI blends were higher than the $T_gs$ of either of the component polymers at low concentrations of PEI. These abnormal increases of $T_gs$ may be due to the negative entropy of mixing which is associated with strong hydrogen bonding between PVA and PEI. The degree of depression of $T^0_ms$ was not reduced by the negative entropy of mixing, since strong hydrogen bonding also causes an increase in the magnitude of negative ${\chi}$ between PVA and PEI. The $T_g$ of PVA was increased significantly by adding 0.7 wt.% GO into PVA. The magnitude of negative ${\chi}$ was increased by adding GO into the blends of PVA and PEI.

• Bulletin of the Korean Chemical Society
• /
• v.13 no.2
• /
• pp.122-127
• /
• 1992

Some perovskites $A($Cu_{1}3}Nb_{2}3}$)O_3(A=$Sr^{2+}$$, $Ba^{2+}$ and $Pb^{2+}$) and their series of mixed perovskites have been prepared by solid state reaction. Single perovskite phase was obtained in Sr or Ba rich samples, but pyrochlore phase was found in Pb rich samples. The stability of perovskite phase is dependent on the ionicity of bonding as well as the tolerance factor. All the obtained perovskites have tetragonal symmetry distorted by Jahn-Teller effect of $Cu^{2+}$. In the case of $Sr(Cu_{1}3}Nb_{2}3})O_3$, some superlattice lines caused by threefold enlarging of fundamental unit cell were observed. And, the symmetry of B site octahedron and the bonding character of B-O bond have been studied by IR, ESR and diffuse reflection spectroscopy. It appeared that the symmetry and the bonding character are influenced by such factors as the size and the basicity of A cation.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.3 s.96
• /
• pp.78-83
• /
• 1999

The bonding interface is dependent on the properties of surfaces prior to SDB(silicon wafer direct bonding). In this paper, we prepared silicon surfaces in several chemical solutions, and annealed bonding wafers which were combined with thermally oxidized wafers and bare silicon wafers in the temperature range of $600{\times}1000^{\circ}C$. After bonding, the bonding interface is investigated by an infrared(IR) topography system which uses the penetrability of infrared through silicon wafer. Using this procedure, we observed intrinsic bubbles at elevated temperatures. So, we verified that these bubbles are related to cleaning and drying conditions, and the interface oxides on silicon wafer reduce the formation of intrinsic bubbles.

• Macromolecular Research
• /
• v.16 no.5
• /
• pp.399-403
• /
• 2008

Monodisperse, micron-sized, hybrid particles having a core-shell structure were prepared by coating the surface of poly(methyl methacrylate)(PMMA) microspheres with silica and by copolymerizing acrylamide (AAm) to supply the hydrogen bonding effect by means of the amide groups. Tetraethoxysilane (TEOS) was then slowly dropped onto the medium under certain conditions. Because of the hydrogen bonding between the amide of the PMMA particles and the hydroxyl group of the hydrolyzed silanol, a silica shell was generated on the PMMA core particles. The morphology of the hybrid particles was investigated with transmission (TEM) and scanning (SEM) electron microscopy as a function of the medium conditions and the amount of TEOS. Improved thermal properties were observed by TGA analysis.