Chemical Bond Properties Research Articles

Effect of Annealing on the Optical and Chemical Bonding Properties of Hydrogenated Amorphous Carbon and Hydrogenated Amorphous Carbon Nitride Thin Films

Hydrogenated amorphous carbon (a-C:H) and hydrogenated amorphous carbon nitride (a-CNx:H) films were prepared in a custom-built radio-frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system with a parallel-plate configuration. Pure methane and a gas mixture of methane and nitrogen were used as gas sources to obtain these films. The films were characterized using Fourier transform infrared and optical transmission spectroscopy techniques. The incorporation of nitrogen and the effect of annealing (100–500 °C) on the film properties were studied. The films were determined to be thermally stable up to 300 °C. Upon annealing above 300 °C, the thickness and refractive index of both a-C:H and a-CNx:H films increase while the optical energy gap E04 decreases. These effects were more pronounced in a-CNx:H. From the IR spectra, these changes are considered to be due to the decreases in nitrogen and hydrogen concentrations in the films which result in their structural modification.

The irreducible bundle: Further structure in the kinetic energy distribution

Modern molecular sciences are often concerned with the properties and dynamics of chemical bonds. With the ability to experimentally measure charge density, there is a pressing need to find the relationships between charge density and the properties of chemical bonds. Here we show molecules can be partitioned into unique bond volumes characterized by well defined properties. Moreover, this partitioning recovers unrecognized structure in the kinetic energy distribution.

Ab initio calculation of magnetism in Fe, Co and Ni

A simple dimer cluster model combined with density functional B3LYP/6-311G(d,p) ab initio calculations is employed to describe the magnetic ordering in Fe, Co and Ni. The proposed adjacent spin-pair model reproduces the observed reduction of the Bohr magneton in the 3d metal series, and is in agreement with the Stoner theory and the multidisciplinary ideas of Pauling regarding electronic, magnetic and chemical bond properties in 3d transition metals.

Bonding Characteristics, Thermal Expansibility, and Compressibility of RXO4 (R = Rare Earths, X = P, As) within Monazite and Zircon Structures

Systematically theoretical research was performed on the monazite- and zircon-structure RXO(4) (R = Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; X = P, As) series by using the chemical bond theory of dielectric description. The chemical bond properties of R-O and X-O bonds were presented. In the zircon phase, the covalency fractions of X-O bonds increased in the order of V-O < As-O < P-O, which was in accordance with the ionic radii and electronegative trends, and the covalency fractions of R-O bonds varied slightly due to the lanthanide contraction. While in the monazite phase, both R-O and X-O bonds were divided into two groups by their covalency fractions. The contributions from the bond to the lattice energy, linear thermal expansion coefficient (LTEC), and bulk modulus were explored. The X-O bonds with short bond lengths and high chemical valence made greater contributions to the lattice energy and performed nearly rigidly during the deformation. A regular variation of lattice energy, LTEC, and bulk modulus with the ionic radii of the lanthanides was observed in both monazite and zircon phases.

ChemInform Abstract: Chemical Bonding Analysis and Properties of La7Os4C9 — A New Structure Type Containing C‐ and C2‐Units as Os‐Coordinating Ligands.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Quantum-chemical modeling of the electronic structure and chemical bond of Sn0.875M0.125O2 (M = Cr, Mn, Co)

The electronic structure of the Sn0.875M0.125O2 compounds (M = Cr, Mn, Co) with a rutile structure and magnetic moments of the transition metal atoms in them were calculated by the ab initio spin-polarized linear muffin-tin orbital method. The electron density and electron localization function maps for these compounds were constructed. Based on these data, the effect of the composition of these phases on the electronic spectrum, chemical bond, and magnetic and transport properties were analyzed.

Chemical bond characteristics, thermal expansion property and compressibility of AR 2O 4 (A = Ca, Sr, Ba; R = rare earths)

Theoretical researches were performed on the CaFe 2O 4-type binary rare earth oxides AR 2O 4 (A = Ca, Sr, Ba; R = rare earths) by using chemical bond theory of dielectric description. The chemical bond properties of these crystals were explored, and then the thermal expansion property and compressibility were studied. The theoretical values of linear thermal expansion coefficient (LTEC) and bulk modulus were presented. The calculations revealed that the LTECs and the bulk moduli do have linear relationship with the ionic radii of the rare earths. In the cases of Sc and Y, both the LTEC and bulk modulus values are larger than the lanthanide series. We attribute this to the difference in the electronic configuration between Sc (Y) and lanthanide series. For SrY 2O 4 and BaY 2O 4 crystals, the theoretical values of LTEC and bulk modulus agree well with experimental ones.

Adhesion characteristics of Cu/Ni–Cr/polyimide flexible copper clad laminates according to Ni:Cr ratio and Cu electroplating layer thickness

The adhesion strength of Cu/Ni–Cr/polyimide flexible copper clad laminate (FCCL) was evaluated according to the composition ratio of the Ni–Cr layer and the thickness of the Cu electroplating layer, by using a 90° peel test. The changes in the morphology, chemical bond and adhesion property were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The peel strength of the FCCL increased with increasing Cr content and increasing Cu electroplating layer thickness. This increasing FCCL peel strength was attributed to a lower C–N bond and higher C–O and carbonyl (C=O) bonds in the polyimide surface compared to the FCCL with a lower adhesion strength. The adhesion property of the FCCLs was significantly affected by the Ni:Cr ratio.

Investigation of Thermal Expansion and Compressibility of Rare-Earth Orthovanadates Using a Dielectric Chemical Bond Method

The chemical bond properties, lattice energies, linear expansion coefficients, and mechanical properties of ReVO 4 (Re = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y) are investigated systematically by the dielectric chemical bond theory. The calculated results show that the covalencies of Re-O bonds are increasing slightly from La to Lu and that the covalencies of V-O bonds in crystals are decreasing slightly from La to Lu. The linear expansion coefficients decrease progressively from LaVO 4 to LuVO 4; on the contrary, the bulk moduli increase progressively. Our calculated results are in good agreement with some experimental values for linear expansion coefficients and bulk moduli.

Thorium compounds with non-metals: Electronic structure, chemical bond, and physicochemical properties

The current state of research on the nature of the chemical bond and the physicochemical properties of binary Th-X (X = H, B, C, N, O, P, S, As, Se, Sb) and ternary (carbonitrides, thorates, and silicates) thorium compounds by modern ab initio methods of the band structure theory is reviewed. The possibilities of the ab initio band structure methods in describing the structural states, phase stability, elasticity characteristics, X-ray emission, absorption, and photoelectron spectra of thorium-containing systems are discussed.

Chemical Bonding and Physical Properties of Yb5Bi3.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Structural relaxation of amorphous silicon carbide thin films in thermal annealing

Amorphous Si 0.4C 0.6 thin films were deposited by radio frequency magnetron sputtering onto non-heated single crystal Si substrates, followed by annealing at 800 °C or 1100 °C in the vacuum chamber. The chemical bond properties and atomic local ordering as a function of the annealing temperature were characterized by Auger electron spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, Infrared absorption spectroscopy, X-ray diffraction, and Raman spectroscopy measurements. We have examined the evolution of microstructure in annealing-induced relaxation process, and investigated the initial stages of thermal crystallization of amorphous Si 0.4C 0.6. Meanwhile, the structure of excess C in the films also has been studied.

Barrelane‐Like Germanium Clusters in Eu3Ge5: Crystal Structure, Chemical Bonding and Physical Properties.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Calculation of the thermal expansion coefficient for Bi 2Sr 2CaCu 2O 8

An estimation method of thermal expansion coefficient in term of lattice energy which was developed earlier for simple materials is extended to a complex material of Bi 2Sr 2CaCu 2O 8 (Bi-2212). The calculation of the chemical bond property and thermal expansion coefficient of Bi-2212 has been carried out and the theoretical values were in good agreement with the corresponding experimental results. The dependence of the thermal expansion coefficient on the different structures and on the flexible oxidation states of Bi and Cu are investigated. The results indicate that the thermal expansion coefficients of Bi-2212 are insensitive to the low lattice distortion of the average structure and the changes of formal valences of Bi and Cu ions.

Crystal Structures of Alkali‐Metal Indium(III) Phosphates of [M3In(PO4)2]n (M = K, n = 10; M = Rb, n = 2) Compounds, and Band Structures and Chemical Bond Properties of [Rb3In(PO4)2]2 Crystal.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Chemical Bonding, Permittivity and Elastic Properties in Locally Modified Organosilicate Glass

AbstractChanging local electronic polarizability and chemical bonding in OSG in such a way that the effective permittivity - and consequently the electrical performance of the Cu/low-k structure - deteriorates only slightly and that adhesion and stiffness are improved significantly is an extremely challenging task [1], [2]. As the interconnect line spacings continue to shrink, optimization of the electrical and mechanical properties of the ILD material becomes increasingly important for Cu/low-k integration since the effect of thin regions that have been modified by special treatments on the effective material properties, e. g. keff, increases. Composition and chemical bonding, changed by plasma or beam treatments, effect the materials properties significantly. Plasma processes for resist stripping, trench etching and post-etch cleaning remove C and H containing molecular groups from the near-surface layer of OSG. Electron-beam interaction with OSG changes the chemical bonding in the low-k material. In this paper, the effect of chemical bonding on permittivity and elastic modulus is studied. Compositional analysis and chemical bonding characterization of structured ILD films with nanometer resolution is done with electron energy loss spectroscopy (EELS). The fine structure near the C-K electron energy loss edge, allows to differentiate between C-H, C-C, and C-O bonds, and consequently, between individual low-k materials and their modifications. Dielectric permittivity changes are studied based on VEELS (valence EELS) measurements and subsequent Kramers-Kronig analysis. The elastic modulus is determined with atomic force microscopy (AFM) in force modulation (FM) mode. Nanoindentation was applied as a complementary technique to obtain reference data.

Crystal structures of alkali-metal indium (III) phosphates of [ M3In(PO 4) 2] n ( M=K, [formula omitted]; M=Rb, [formula omitted]) compounds, and band structures and chemical bond properties of [Rb 3In(PO 4) 2] 2 crystal

Ternary indium (III) phosphates with three-dimensional frameworks, [ M 3In(PO 4) 2] n ( M=K, n = 10 ; M=Rb, n = 2 ), are found and firstly reported in this paper. These compounds have been obtained by high temperature solid-state reactions and their crystal structures have been determined by single crystal X-ray diffraction analysis. The title compounds, which crystallize in monoclinic system, possess the same [In(PO 4) 2] n 3 n − anionic frameworks built up from interconnected InO 6 octahedra and PO 4 tetrahedra and have an interesting tunnel structure where M + cations are located. Optical and bonding properties of [Rb 3In(PO 4) 2] 2 are investigated in terms of measured absorption and emission spectra, and calculated band structures and density of states. The crystal band structures obtained by the DFT method show that the solid compound of [Rb 3In(PO 4) 2] 2 is an insulator with direct band gap, and the P–O covalent bond characters are larger than the In–O ones in this compound.

Electronic structures and chemical bonds of cobaltite and Ni-doped

The relation among electronic structure, chemical bond and thermoelectric property of Ca3 Co2 O6 and Ni-doped was studied by density function theory and discrete variation method (DFT-DVM). The results indicate that the highest valence band (HVB) and the lowest conduction, band(LCB) are mainly attributed to Co3d, Ni3d and O2p atomic orbitals. The property of a semiconductor is shown from the gap between HVB and LCB. The gap of Ni-doped one is less than that of Ca3 Co2 O6. The non-metal bond or ceramic characteristic of Ni-doped one is weaker than that of Ca3 Co2 O6, but the metal characteristics of Ni-doped one are stronger than those of Ca3 Co2 O6. The thermoelectric property should be improved by adding Ni element into the system of Ca3 Co2 O6.

A Solid State13C NMR, Crystallographic, and Quantum Chemical Investigation of Chemical Shifts and Hydrogen Bonding in Histidine Dipeptides

We report the first solid-state NMR, crystallographic, and quantum chemical investigation of the origins of the 13C NMR chemical shifts of the imidazole group in histidine-containing dipeptides. The chemical shift ranges for Cgamma and Cdelta2 seen in eight crystalline dipeptides were very large (12.7-13.8 ppm); the shifts were highly correlated (R2= 0.90) and were dominated by ring tautomer effects and intermolecular interactions. A similar correlation was found in proteins, but only for buried residues. The imidazole 13C NMR chemical shifts were predicted with an overall rms error of 1.6-1.9 ppm over a 26 ppm range, by using quantum chemical methods. Incorporation of hydrogen bond partner molecules was found to be essential in order to reproduce the chemical shifts seen experimentally. Using AIM (atoms in molecules) theory we found that essentially all interactions were of a closed shell nature and the hydrogen bond critical point properties were highly correlated with the N...H...O (average R2= 0.93) and Nepsilon2...H...N (average R2= 0.98) hydrogen bond lengths. For Cepsilon1, the 13C chemical shifts were also highly correlated with each of these properties (at the Nepsilon2 site), indicating the dominance of intermolecular interactions for Cepsilon1. These results open up the way to analyzing 13C NMR chemical shifts, tautomer states (from Cdelta2, Cepsilon1 shifts), and hydrogen bond properties (from Cepsilon1 shifts) of histidine residue in proteins and should be applicable to imidazole-containing drug molecules bound to proteins, as well.

Uranium nitride chloride UNCl: 30 K-class ferromagnet with layered structure

Uranium nitride chloride (UNCl) has an unique tetragonal crystal structure, in which the U/N/U trilayer is sandwiched by the chlorine (Cl) double layers. This structure is homologous to Hf(Zr)NCl, for which high- T C superconductivity ( T C = 25.5 K ) has been recently discovered to result from the lithium (Li) intercalation. Recent specific heat measurements on this compound have revealed the existence of a lambda-type phase transition around 32 K. In the present study, this anomaly was confirmed to be correspondent for a ferromagnetic transition in the uranium ions having a localized 4f 2(U 4+) character: Its saturation moment ( μ B(sat)) attains a value of ∼1.56 μ B at 2 K. Among varieties of actinide (An) compounds, UNCl and related systems, AnNX (X=halogens (Cl, Br, I)) may represent a novel class of layer mixed compounds with intriguing magnetic, electronic and chemical-bonding properties.