First principle study of adsorption of boron-halogenated system on pristine graphyne

To ensure the possibility of using graphyne as a gas sensor, we have studied the adsorption of boron-halogenated system on pristine graphyne with the help of density functional theory using generalized gradient approximation. Depending on binding energy the most stable orientation, adsorption strength and optimal distance between the above mention molecules and graphyne surface have been determined. The band gap of graphyne slightly increases with the adsorption of the boron-halogenated system. The graphyne system behaves as n-type semiconductor when it interacts with BI₃ and BCl₃ molecules, and it behaves as p-type semiconductor when interaction with BF₃ molecule takes place. Our result reveals that the electronic properties of pristine graphyne are highly influenced by the adsorption of boron-halogenated molecule. We have observed that pristine graphyne has zero electric dipole moment, but with the interaction of boron-halogenated molecule, a significant change in the electric dipole moment takes place. Hence, by measuring the electric dipole moment change, graphyne-based gas sensor can be design for the detection of above-mentioned molecules.     

Electronic properties of bilayer and trilayer graphyne in the presence of electric field

The influence of electric field on the electronic properties of bilayer and trilayer graphyne has been studied using the density functional theory. We have investigated alpha graphyne due to its analogous to graphene. The bilayer and trilayer graphyne with different stacking style configurations have been considered. Our results indicate that the electronic properties of alpha graphyne are insensitive to the number of graphyne layer and configuration. The bilayer and trilayer graphyne are semimetal similar to the monolayer graphyne. It is found that applying a uniform electric field perpendicular to the graphyne sheet changes the electronic properties of AB-stacked bilayer and ABC-stacked trilayer graphyne so that they become semiconductor. The band gaps of the bilayer and trilayer graphyne with these configurations are enhanced by increasing strength of the electric field. Therefore, possibility of controlling the electronic properties of graphyne by applying electric field makes graphyne as a good candidate for next generation nanoelectronic devices.     

Epitaxial growth of InN films by molecular-beam epitaxy using hydrazoic acid (HN3) as an efficient nitrogen source

Epitaxial InN films have been successfully grown on c-plane GaN template by gas-source molecular-beam epitaxy with hydrazoic acid (HN3) as an efficient nitrogen source. Results in residual-gas analyzer show that the HN3 is highly dissociated to produce nitrogen radicals and can be controlled in the amounts of active nitrogen species by tuning HN3 pressure. A flat and high-purity InN epifilm has been realized at the temperature near 550 degrees C, and a growth rate of 200 nm/hr is also achieved. Moreover, the epitaxial relationship of the InN(002) on the GaN(002) is reflected in the X-ray diffraction, and the full-width at half-maximum of the InN(002) peak as narrow as 0.05 degrees is related to a high-quality crystallinity. An infrared photoluminescence (PL) emission peak at 0.705 eV and the integrated intensity increasing linearly with excitation power suggest that the observed PL can be attributed to a free-to-bound recombination.     

Adsorption of polycyclic aromatic hydrocarbons onto graphyne: Comparisons with graphene

Density functional theory calculations were implemented to expand the knowledge about graphyne and its interaction with polycyclic aromatic hydrocarbons (PAHs). Due to the porous character of graphyne, the adsorption strength of PAHs onto graphyne surfaces is expected to be lower with respect to graphene (a perfect π‐extended system). However, there are not quantitative evidences for this assumption. This work shows that the adsorption strength of adsorbed PAHs onto γ‐graphyne nanosheets (GY) is weakened in 12 ? 23% with respect to the adsorption onto graphene, with a decrease of 10 ? 20% in the dispersive interactions. The adsorption energies (in eV) of the GY–PAH systems can be straightforward obtained as E _ads/eV≈0.033N _H + 0.031N _C, where N _H and N _C is the number of H and C atoms in the aromatic molecule, respectively. This equation predicts the binding energy of graphene–graphyne bilayers with a value of ～31 meV/atom. Analysis of the electronic properties shows that PAHs behaves as n‐dopants for GY, introducing electrons in GY and also reducing its bandgap in up to ～0.5 eV. Strong acceptor or donor substituted PAHs decrease the bandgap of γ‐graphyne in up to ～0.8 eV, with changes in its valence or conduction band, depending on the chemical nature of the adsorbate. Finally, these data will serve for future studies related to the bandgap engineering of graphyne surfaces by nonaggressive molecular doping, and for the development of graphyne‐based materials with potential applications in the removal of persistent aromatic pollutants.     

The infrared fundamental intensities and polar tensor of CH3NC

The molecular force field and polar tensor of methyl isocyanide have been determined from its gas phase vibrational frequencies and infrared intensities. Quantum chemical results from MP2(FC), B3LYP and quadratic configuration interaction calculation including single and double substitutions procedures using a 6-311 + +G(3d,3p) basis set have been used to determine the signs of the dipole moment derivatives with respect to the normal coordinates as well as estimate individual fundamental intensities of the overlapped v1-v5 and v3-v6 band systems. Principal component graphical representations of the A1 and E symmetry polar tensor elements were useful in determining preferred sets of tensor elements. The mean dipole moment derivative (GAPT charge) of the methyl carbon in CH3NC, 0.347 e, is between the corresponding values in CH3CN, 0.110 e, and CH3F, 0.541 e. The mean dipole moment derivatives obtained here indicate the correct 1s methyl carbon ionization energy as 293.35 eV which is 0.98 eV higher than the corresponding ionization energy of the terminal atom.     

Density-functional calculations of HCN adsorption on the pristine and Si-doped graphynes

Graphyne, a lattice of benzene rings connected by acetylene bonds, is one-atom-thick planar sheet of sp- and sp²-bonded carbons differing from the hybridization of graphene (considered as pure sp²). Here, HCN adsorption on the pristine and Si-doped graphynes was studied using density-functional calculations in terms of geometric, energetic, and electronic properties. It was found that HCN molecule is weakly adsorbed on the pristine graphyne and slightly affects its electronic properties. While, Si-doped graphyne shows high reactivity toward HCN, and, in the most favorable state, the calculated adsorption energy is about ?10.1 kcal/mol. The graphyne, in which sp-carbon was substituted by Si atom, is more favorable for HCN adsorption in comparison with sp²-carbon. It was shown that the electronic properties of Si-doped graphyne are strongly sensitive to the presence of HCN molecule and therefore it may be used in sensor devices.     

氢取代石墨单炔的机械化学合成及其电催化特性

氢取代石墨单炔是一种仅由苯环上的sp²杂化碳和氢与乙炔基上的sp杂化碳组成具有与石墨炔相似平面网状结构的二维富碳材料。本文以碳化钙和三溴苯为原料,通过机械化学方法合成了氢取代石墨单炔,并通过X射线电子能谱、拉曼光谱、固体核磁共振成像¹H谱和透射电子显微镜加以证实。紫外可见漫反射吸收光谱和电化学测试表明样品为p型半导体,带隙为2.30 eV,在硫酸钠溶液(pH = 7)中的析氧起始过电位为0.04 V,在催化产氧和光催化方面具有应用潜力。     

Rapid analysis of triterpenic acids by liquid chromatography using porous graphitic carbon and evaporative light scattering detection

An original system which uses Porous Graphitic Carbon as support and a mixture of organic solvents as mobile phase is proposed for the analysis of triterpenic acids by liquid chromatography. The separation of betulinic acid, ursolic acid, oleanolic acid, and 18alpha- and 18beta-glycyrrhetinic acids was carried out within a short time and monitored by evaporative light scattering detection as universal detection method. Molecular modelling studies show that the main contribution to the selectivity comes from the electrostatic interaction characterised by the dipole moment of the products.     

Reactions of hydrazoic acid and trimethylindium on TiO2 rutile (110) surface: a computational study on the formation of the first monolayer InN

This article reports the result of a computational study on the reaction of hydrazoic acid and trimethylindium (TMIn), coadsorbed on TiO2 rutile (110) surface. The adsorption geometries and energies of possible adsorbates including HN3-In(CH3)3(a) and its derivatives, HN3-In(CH3)2(a), N3-In(CH3)2(a), N3-In(CH3)(a), and N-In(a), have been predicted by first-principles calculations based on the density functional theory (DFT) and the pseudopotential method. The mechanisms of these surface reactions have also been explicitly elucidated with the computed potential energy surfaces. Starting from the interaction of three stable HN3 adsorbates, HN3-Ob(a), H(N2)N-Ob(a), and Ti-NN(H)N-Ob(a), where Ob is the bridged O site on the surface, with two stable intermediates from the adsorption and dissociative adsorption of TMIn, (H3C)3In-Ob(a) and (H3C)2In-Ob(a)+H3C-Ob(a), InN products can be formed exothermically via four reaction paths following the initial barrierless In-atom association with the N atom directly bonded to H, by CH4 elimination (with approximately 40 kcal/mol barriers), the InN-N bond breaking and the final CH3 elimination or migration (with <20 kcal/mol barriers). These Langmuir-Hinshelwood processes producing the two most stable InN(a) side-on adsorptions confirm that HN3 and TMIn are indeed very efficient precursors for the deposition of InN films on TiO2 nanoparticles. The result of similar calculations for the reactions occurring by the Rideal-Eley mechanism involving HN3(a)+TMIn(g) and HN3(g)+TMIn(a) indicates that they are energetically less favored and produce the less stable InN(a) with end-on configurations.     

Energy of charged states in the RDX crystal: trapping of charge-transfer pairs as a possible mechanism for initiating detonation

Calculations for the crystalline energetic material RDX (1,3,5-trinitro-1,3,5-triazacyclohexane) yield the effective polarizability (17.2 angstroms3), local electric field tensor, effective dipole moment (9.40 D), and dipole-dipole energy (-27.2 kJ/mol). Fourier-transform techniques give the polarization energy P for a single charge in the perfect crystal as -1.14 eV; the charge-dipole energy W(D) is zero if the crystal carries no bulk dipole moment. Polarization energies for charge-transfer (CT) pairs combine with the Coulomb energy E(C) to give the screened Coulomb energy E(scr); screening is nearly isotropic with E(scr) approximately = E(C)2.6. For CT pairs W(D) reduces to a term deltaW(D) arising from the interaction of the charge on each ion with the change in dipole moment on the other ion relative to the neutral molecule. The dipole moments are calculated as 7.40 D for the neutral molecule and 6.84 D and 7.44 D for the anion and cation, giving the lowest two CT pairs at -1.34 eV and -0.94 eV. The changes in P and W(D) near a molecular vacancy yield traps with depths that reach 400 meV for single charges and 185 meV for the nearest-neighbor CT pair. Divacancies yield traps with depths nearly equal to the sum of those produced by the separate vacancies. These results are consistent with a mechanism in which detonation of RDX is initiated by mechanical generation of CT pairs that localize at vacancies, recombine, and release energy sufficient to break bonds; crystals of molecules with lower dipole moments should be less sensitive.