AFM study of forces between silica, silicon nitride and polyurethane pads

Interaction of silica and silicon nitride with polyurethane surfaces is rather poorly studied despite being of great interest for modern semiconductor industry, e.g., for chemical-mechanical planarization (CMP) processes. Here we show the results from the application of the atomic force microscopy (AFM) technique to study the forces between silica or silicon nitride (AFM tips) and polyurethane surfaces in aqueous solutions of different acidity. The polyurethane surface potentials are derived from the measured AFM data. The obtained potentials are in rather good agreement with measurements of zeta-potentials using the streaming-potentials method. Another important parameter, adhesion, is also measured. While the surface potentials of silica are well known, there are ambiguous results on the potentials of silicon nitride that is naturally oxidized. Deriving the surface potential of the naturally oxidized silicon nitride from our measurements, we show that it is not oxidized to silica despite some earlier published expectations.     

Biological responses to silicon and nitrogen-rich PVD silicon nitride coatings

Most structural bioceramics are comprised of metallic oxides such as alumina and zirconia. They are generally considered to be completely bioinert, but a non-oxide ceramic, silicon nitride, achieves equivalent levels of mechanical reliability while being bioactive. Silicon nitride can not only stimulate cellular proliferation but it is also antipathogenic with demonstrated efficacy against Gram-positive and Gram-negative bacteria, fungi, and viruses. In this work, three physical vapor deposition coatings with different Si:N ratios (silicon-rich, stoichiometric, and nitrogen-rich) were deposited on mirror-polished silica glass substrates. The coatings were characterized by spectroscopic and microscopic techniques and tested in vitro against E. coli and KUSA-A1 mesenchymal cells. Results showed that nitrogen-enriched Si_xN_y has a strong antibacterial effect against E. coli and contributes to cellular proliferation while silicon-enriched Si_xN_y stimulates the production of bone tissue, with higher indexes for mineralization and quality. These results suggest that Si_xN_y's biological properties can be optimized for specific applications by carefully tuning its surface chemistry.     

Ab initio study of chemical bond interactions between covalently functionalized carbon nanotubes via amide,ester and anhydride linkages

In this paper, we have investigated the chemical bond interactions between covalently functionalized zigzag (5,0) and (8,0) SWCNT–SWCNT via various covalent linkages. Side-to-side junctions connected via amide, ester and anhydride linkages were particularly studied. The geometries and energy of the forming reaction were investigated using first-principles density functional theory. Furthermore, the band structures and the total density of states (DOS) of the junctions have also been analyzed. Our results show that several promising structures could be obtained by using chemical connection strategy and particularly the junctions formed by coupling amino functionalized SWCNT and carboxylic acid functionalized SWCNT was more favorable.     

Modelling of interactions between volatile anaesthetics (halothane,enflurane) and aromatic compounds,ab initio study

For many years halothane and enflurane have been used clinically as volatile anaesthetics, however, their mechanism of action is still not fully understood. Recently, it has been suggested that they can act by a direct bonding to neuroreceptors containing the aromatic groups. In this work, the halothane?benzene and enflurane?benzene complexes were studied by the ab initio MP2 and CCSD(T) methods. All possible structures of the complexes were calculated by means of the counterpoise CP-corrected gradient optimization technique. It has been found that among these species, the C–H?π hydrogen bonded complexes are the most stable. The CCSD(T)/CBS calculated stabilization energies for halothane and enflurane complexes are: −10.56 and −9.72 kcal mol⁻¹, respectively. The interaction energy is mainly dominated by the dispersion attraction. In the case of enflurane, the C–H bond shows a very small contraction (by −0.0008 Å) upon complexation. This change is accompanied by the blue-shift (20 cm⁻¹) of the C–H stretching frequency and an increase of the infrared intensity of the corresponding mode by 7 km mol⁻¹. Similar results were obtained for the halothane complex: a small contraction of the C–H bond; an increase of the C–H stretching frequency by 11 cm⁻¹ (blue-shift); and an increase of the infrared intensity by 37 km mol⁻¹. In order to explain the nature of these effects, the halothane and enflurane molecules were studied in the electric field generated by benzene atoms, and Natural Bond Orbital (NBO) analyses were performed. The molecular dipole moments of these molecules were calculated with respect to the C–H bond changes. The positive dipole moment derivative obtained for halothane is in agreement with the literature data, while, in the case of enflurane, an unusual effect is observed, the blue-shift of the C–H stretching frequency is accompanied by the positive dipole moment derivative for one C–H bond and the negative for the other C–H bond. The mechanisms responsible for contraction and strengthening of the C–H bonds are discussed.     

NHCH=CHR自由基结构和稳定性ab initio研究

用ＵＨＦ／４－３１Ｇ基组，全构型优化，研究了ＮＨＣＨ＝ＣＨＲ（Ｒ＝Ｈ，ＢＨ２，ＣＮ，Ｆ，ＯＨ，ＮＨ２）６个氮自由基的构型和稳定化能△Ｅ，以ＮＨＣＨ＝ＣＨ２自由基为参考，它们的△Ｅ分别为０．００，－３４．９２，－８．３５，－０．９３，３３．０５，５０．８５ｋＪ．ｍｏｌ＾－１，说明供电子基团ＯＨ和ＮＨ２对氮自由基起稳定化作用，吸电子基团ＣＮ和ＢＨ２起去稳定化作用，而Ｆ对氮自由基的稳定性影响不大。     

Electron interactions in the closo-carboranes 1,2- and 1,7-C2B10H12

Ultra-soft X-ray fluorescence spectra of ortho- and meta-carborane C₂B₁₀H₁₂ were obtained. Ab initio self-consistent field (SCF) quantum-chemical calculations of these molecules were performed to interpret BK and CK spectra. Distinctions between electronic structure of closo-carboranes 1,2- and 1,7-C₂B₁₀H₁₂ are caused by different efficiency in the interaction of carbon and boron atoms. Location of boron atom between carbon atoms leads to stronger delocalization of electron density in meta-carborane molecule. The correlation between molecular orbitals (MOs) of the anion B₁₂H₁₂²⁻ and the closo-carboranes was carried out.     

OCH＝CHR（R＝H，BH_2，CN，F，OH，NH_2）自由基结构和稳定性的ab initio研究

用ＵＨＦ／４－３１Ｇ基组，全构型优化ＯＣＨＣＨＲ（Ｒ＝Ｎ，ＢＨ_２，ＣＮ，Ｆ，ＯＨ，ＮＨ_２）６个氧自由基的构型并研究其稳定化能△Ｅ。以ＯＣＨＨ_２自由基为参考标准，它们的△Ｅ分别为０．００、－７５．９７、１．１１、０．７６、２２．０６和４０．６５ｋＪ／ｍｏｌ，说明供电子基团ＯＨ和ＮＨ_２对氧自由基起稳定化作用，ＢＨ_２对氧自由基起去稳定化作用，而ＣＮ和Ｆ对氧自由基的稳定性影响不大。     

η5-Phospholylgallium: The First Monomeric Polyhapto Compound between a Phospholyl Ligand and a Main Group Metal

Monomeric polyhapto-bound phospholyl compounds were hitherto unknown for the main group elements. Use of a solution of metastable GaBr has allowed the synthesis of monomeric η⁵-phospholylgallium, which has been characterized by X-ray structure analysis as the Cr(CO)₅ complex 1 .     

Addition reactions of nitrones on the reconstructed C(1 0 0)-2 × 1 surfaces

In this paper, the reactions of nitrone, N-methyl nitrone, N-phenyl nitrone and their hydroxylamine tautomers (vinyl-hydroxylamine, N-methyl-vinyl-hydroxylamine and N-phenyl-vinyl-hydroxylamine) on the reconstructed C(1 0 0)-2 × 1 surface have been investigated using hybrid density functional theory (B3LYP), Møller–Plesset second-order perturbation (MP2) and multi-configuration complete-active-space self-consistent-field (CASSCF) methods. The calculations showed that all the nitrones can react with the surface “dimer” via facile 1,3-dipolar cycloaddition with small activation barriers (less than 12.0 kJ/mol at B3LYP/6-31g(d) level). The [2+2] cycloaddition of hydroxylamine tautomers on the C(1 0 0) surface follows a diradical mechanism. Hydroxylamine tautomers first form diradical intermediates with the reconstructed C(1 0 0)-2 × 1 surface by overcoming a large activation barrier of 50–60 kJ/mol (B3LYP), then generate [2+2] cycloaddition products via diradical transition states with negligible activation barriers. The surface reactions result in hydroxyl or amino-terminated diamond surfaces, which offers new opportunity for further modifications.     

The interaction between morin and CTAB aggregates

Electronic absorption spectra, fluorescence emission spectra, ATR-FTIR spectra, cyclic voltammetric measurements, and ab initio quantum calculation are used to study the properties of morin in CTAB micelles with different microstructures and microenvironments and to gain information about the binding of morin with CTAB micelles. Morin can be located in the CTAB micelle with its phenyl group (deviating with 38.98 degrees from the planarity) only in the form of the monomer, which leads to increase of the planarity and extension of the pi conjugation of the whole molecule. The embedding of two hydroxyl groups on the phenyl into a more hydrophobic microenvironment makes the oxidation peak of morin move to a higher potential with a decreased peak current. The binding of morin with CTAB micelles is a spontaneous (DeltaG<0) and endothermic process (DeltaH>0), and the hydrophobic and electrostatic force is the main driving force for its solubilization.     

HcnS^—与HSC^—n簇离子的量子化学从头计算

应用量子化学从头计算能量解析梯度法，以ＨＦ６／３１Ｇ为基组优化了ＨＣｎＳ＾－与ＨＳＣ＾－ｎ（ｎ＝１～９）同分异构团簇离子的几何结构，计算了它们的电子总能量，结果显示ＨＣｎＳ＾－比相应的ＨＳＣ＾－ｎ稳定，从相邻簇离子的能量差及簇离子的平均原子结构能可知ｎ为偶数的ＨＣｎＳ＾－与ＨＳＣｎ＾－较ｎ为奇数的簇离子稳定，能量的差异随着ｎ的增加而逐渐减小，计算和实验结果完全相符，还分别计算了ＨＣｎＳ＾－失去Ｈ，     

A theoretical study of the interactions between N,N-dimethylformamide and xylenes

The ab initio and density functional (DFT) methods were performed on binary systems of N,N-dimethylformamide (DMF) with xylenes (o-, or m-, or p-xylene), and seven stable configurations were obtained with no imaginary frequencies. To obtain the interaction energies of these complexes, single-point energy calculations with basis set superposition error (BSSE) correction were carried out at B3LYP/6-31G* and MP2/6-31G* levels. The structures, Chelpg (charges from electrostatic potentials using a grid-based method) charge distribution and bond characteristics of the mentioned complexes were calculated. The results indicated the presence of double C–H···O hydrogen bonds between DMF and xylenes in these complexes and the interaction energies of hydrogen bonding between DMF and xylene systems decreased in the following sequence: DMF–o-xylene: a1 > DMF–m-xylene: b1 > DMF–p-xylene: c1.     

Adsorption of Acetone onto MgO: Experimental and Theoretical Evidence for the Presence of a Surface Enolate

A new band at 1640 cm ⁻¹ is revealed by diffuse reflectance FT‐IR spectroscopy of acetone adsorbed on a MgO surface (shown schematically). On the grounds of ab initio quantum‐mechanical calculations, this band is assigned to an adsorbed enolate species. This evidence proves the catalytic role of the metal oxide surface in the condensation reaction mechanism.     

Binding Matter with Antimatter: The Covalent Positron Bond

We report sufficient theoretical evidence of the energy stability of the e⁺?H₂^2? molecule, formed by two H^? anions and one positron. Analysis of the electronic and positronic densities of the latter compound undoubtedly points out the formation of a positronic covalent bond between the otherwise repelling hydride anions. The lower limit for the bonding energy of the e⁺?H₂^2? molecule is 74 kJ mol^?1 (0.77 eV), accounting for the zero‐point vibrational correction. The formation of a non electronic covalent bond is fundamentally distinct from positron attachment to stable molecules, as the latter process is characterized by a positron affinity, analogous to the electron affinity.     

Dynamic Simulation on Surface Hydration and Dehydration of Monoclinic Zirconia

The commonly used oxide-supported metal catalysts are usually prepared in aqueous phase, which then often need to undergo calcination before usage. Therefore, the surface hydration and dehydration of oxide supports are critical for the realistic modeling of supported metal catalysts. In this work, by ab initio molecular dynamics (AIMD) simulations, the initial anhydrous monoclinic ZrO\begin{document}$_2$\end{document}(111) surfaces are evaluated within explicit solvents in aqueous phase at mild temperatures. During the simulations, all the two-fold-coordinated O sites will soon be protonated to form the acidic hydroxyls (HO\begin{document}$_{\rm{L}}$\end{document}), remaining the basic hydroxyls (HO^*) on Zr. The basic hydroxyls (HO^*) can easily diffuse on surfaces via the active proton exchange with the undissociated adsorption water (H\begin{document}$_2$\end{document}O^*). Within the temperatures ranging from 273 K to 373 K, in aqueous phase a certain representative equilibrium hydrated m-ZrO\begin{document}$_2$\end{document}(111) surface is obtained with the coverage (\begin{document}$\theta$\end{document}) of 0.75 on surface Zr atoms. Later, free energies on the stepwise surface water desorption are calculated by density functional theory to mimic the surface dehydration under the mild calcination temperatures lower than 800 K. By obtaining the phase diagrams of surface dehydration, the representative partially hydrated m-ZrO\begin{document}$_2$\end{document}(111) surfaces (0.25\begin{document}$\leq$\end{document}\begin{document}$\theta$\end{document} < 0.75) at various calcination temperatures are illustrated. These hydrated m-ZrO\begin{document}$_2$\end{document}(111) surfaces can be crucial and readily applied for more realistic modeling of ZrO\begin{document}$_2$\end{document} catalysts and ZrO\begin{document}$_2$\end{document}-supported metal catalysts.     

甲醛与甲酰胺相互作用的从头算研究

The optimizations geometries and vibrational frequencies of H2CO,HCONH2 and acquired 3 complexes between H2CO?HCONH2 have been calculated by using the ab initio method at the MP2/6-31G（ d）and MP2 （FC）/6-311++G（d,p）level. The non-minimum structures with negative vibrational frequencies are excluded. The lowest energy conformer of these complexes is a cyclic structure with N - H?O and C - H?O hydrogen bonds in a common plane. No significant changes are observed in the geometries of the monomers in their complexed state. The most characteristic geometrical properties of the complex are the lengthening of the contacting N-H bonds by 0.4-1.1 pm,and the general shortening of the contacting C-H bonds by 0.3-0.4 pm with respect to the monomers. The interaction energies of complexes have been corrected by the basis set superposition error （BSSE）using the full Boys-Bernardi counterpoise correction scheme. The corrected complex interaction energies of 3 structures at MP2/6-311++G（2df,3p）/ / MP2（FC）/6-311++G（d,p）level are -29.94, -16.10 and -18.45 kJ/mol,respectively. The interaction energies indicate that C - H?O is a weak hydrogen bond. The results of natural bond orbital population analysis reveals that there is only a small charge-transfer in the process of forming the complexes. The results of natural bond orbital analysis and atom in the molecule scheme appear quite significant in view of their importance for understanding the mechanisms of intermolecular interaction leading to hydrogen bonding. The results of molecular interaction energy decomposition analysis show that the electrostatic interaction plays an essential role in stabilizing the H2CO?HCONH2 complexes.     

从头计算方法比较TiSi_2的C54相和C49相

采用平面波超软赝势描述多电子体系,利用密度泛函理论和广义梯度近似,计算出C54相和C49相TiSi2的晶格常数、体弹性模量、形成能、电子态密度(DOS)和Mulliken电荷布居等性质.通过比较这两种物质的性质,发现尽管两者形成能很相近,但C49相结构对称性差、体弹性模量小、熔点低,Ti原子d轨道的反键强、离子性弱.这些性质上的差异和C49相TiSi2在固相反应中优先形成有关.     

从头计算方法比较TiSi2的C54相和C49相

采用平面波超软赝势描述多电子体系,利用密度泛函理论和广义梯度近似,计算出C54相和C49相TiSi2的晶格常数、体弹性模量、形成能、电子态密度(DOS)和Mulliken电荷布居等性质.通过比较这两种物质的性质,发现尽管两者形成能很相近,但C49相结构对称性差、体弹性模量小、熔点低, Ti原子d轨道的反键强、离子性弱.这些性质上的差异和C49相TiSi2在固相反应中优先形成有关.     

Ab Initio Calculations on Halogen Bond Between N——Br and Electron-donating Groups

Ab initio calculations of complexes formed between N-bromosuccinimide and a series of electron-donating groups were performed at the level of MP2/Lanl2DZ to gain a deeper insight into the nature of the N—Br halogen bonding. For the small complexes, H3C—Br…NH3 and H2N—Br…NH3, the primary calculation has demonstrated that the N—Br in H2N—Br…NH3 can form a much stronger halogen-bonding complex than the C—Br. A comparison of neutral hydrogen bond complex series reveals that the electron-donating capacities of the atoms decrease in the order, N>O>S; O(sp3)>O(sp2), which is adequate for the C—Br halogen bonding. Interaction energies, in conjunction with the geometrical parameters show that the affinitive capacity of trihalide anions X-3 with N-bromosuccinimide are markedly lower than that of the corresponding X- with N-bromosuccinimide, even lower than those of neutral molecules with N-bromosuccinimide. AIM analyses further confirmed the above results.     

The evaluation of bond dissociation energies for simple sulphur containing molecules using ab initio and density functional methods

The S–H and C–S bond dissociation energies for simple alkylthiols and dialkylsulphides, along with the S–S bond dissociation energy for dimethyl disulphide, compounds which have been used in the metal–organic chemical vapour deposition (MOCVD) growth of wide band gap II–VI (12–16) Zn- and Cd-based compound semiconductors, have been computed using the ab initio (ROHF and MP2) and density functional theory (DFT) methods (BHandH, BHandHLYP, B3LYP, B3P86, B3PW91, BLYP and BP86) with the 6-311+G(2d,p) basis set along with high accuracy complete basis set, CBS-4 and CBS-Q energy computations. The computed energies are compared with experimental results and the suitability of the DFT methods, for the computational study of these systems, is discussed.