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.     

Large Hexagonal Bi‐ and Trilayer Graphene Single Crystals with Varied Interlayer Rotations

Bi‐ and trilayer graphene have attracted intensive interest due to their rich electronic and optical properties, which are dependent on interlayer rotations. However, the synthesis of high‐quality large‐size bi‐ and trilayer graphene single crystals still remains a challenge. Here, the synthesis of 100 μm pyramid‐like hexagonal bi‐ and trilayer graphene single‐crystal domains on Cu foils using chemical vapor deposition is reported. The as‐produced graphene domains show almost exclusively either 0° or 30° interlayer rotations. Raman spectroscopy, transmission electron microscopy, and Fourier‐transformed infrared spectroscopy were used to demonstrate that bilayer graphene domains with 0° interlayer stacking angles were Bernal stacked. Based on first‐principle calculations, it is proposed that rotations originate from the graphene nucleation at the Cu step, which explains the origin of the interlayer rotations and agrees well with the experimental observations.     

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.     

Adsorption of Hydrazoic Acid on Pristine Graphyne Sheet: A Computational StudySCI北大核心CSCD

Herein we have investigated the interaction between hydrazoic acid(HN3) and a pristine graphyne system based on density functional theory(DFT) method using generalized gradient approximation. The van der Waals dispersion correction is also considered for predicting the possibility of using the graphyne system for detection of hydrazoic acid. Pristine graphyne has a band gap of 0.453 eV, which decreases to 0.424 eV when HN3 is adsorbed on graphyne. The electrical conductivity of HN3-adsorbed graphyne is greater than that of its pristine counterpart. Charge transfer analysis reveals that the HN3-adsorbed graphyne system behaves as an n-type semiconductor; however, its pristine analogue acts as an intrinsic semiconductor. Pristine graphyne has zero dipole moment; however, its interaction with HN3 increases its dipole moment. The electronic properties of graphyne is significantly influenced by the presence of HN3, leading to the possibility of designing graphyne-based sensors for HN3 detection.     

A First-Principles Study of C3N Nanostructures: Control and Engineering of the Electronic and Magnetic Properties of Nanosheets,Tubes and Ribbons

Using first-principles calculations we systematically investigate the atomic, electronic and magnetic properties of novel two-dimensional materials (2DM) with a stoichiometry C₃N which has recently been synthesized. We investigate how the number of layers affect the electronic properties by considering monolayer, bilayer and trilayer structures, with different stacking of the layers. We find that a transition from semiconducting to metallic character occurs which could offer potential applications in future nanoelectronic devices. We also study the affect of width of C₃N nanoribbons, as well as the radius and length of C₃N nanotubes, on the atomic, electronic and magnetic properties. Our results show that these properties can be modified depending on these dimensions, and depend markedly on the nature of the edge states. Functionalization of the nanostructures by the adsorption of H adatoms is found induce metallic, half-metallic, semiconducting and ferromagnetic behavior, which offers an approach to tailor the properties, as can the application of strain. Our calculations give insight into this new family of C₃N nanostructures, which reveal unusual electronic and magnetic properties, and may have great potential in applications such as sensors, electronics and optoelectronic at the nanoscale.     

The permanent electric dipole moments and magnetic g factors of uranium monoxide

Permanent electric dipole moments and magnetic g factors for uranium monoxide (UO) have been determined from analyses of optical Stark and Zeeman spectra recorded at a spectral resolution that approaches the natural linewidth limit. Numerous branch features in the previously characterized [L. A. Kaledin et al., J. Mol. Spectrosc. 164, 27 (1994)] (0,0) [18403]5-X(1)4 and (0,0) [18404]5-X(1)4 electronic transitions were recorded in the presence of tunable static electric (Stark effect) or magnetic (Zeeman effect) fields. The lines exhibited unusually large Zeeman tuning effects. A ligand field model and an ab initio electronic structure calculation [R. Tyagi, Ph.D. thesis, The Ohio State University (2005)] were used to interpret the ground state properties. The results indicate that the low energy electronic states of UO are sufficiently ionic for the meaningful application of ligand field theory models. The dipole moments and g factors were distinctly different for the three electronic states examined, which implies that these properties may be used to deduce the underlying electronic state configurations.     

Electronic properties of capped, finite-length armchair carbon nanotubes in an electric field

This study investigates the electronic properties of finite-length armchair carbon nanotubes in an electric field (E) using a single-pi-band tight-binding model. Three different tip configurations are considered, namely, open ends with hydrogen terminations (H-terminations), one end capped with half of C60 fullerene and the other end open with H-terminations, and both ends capped with half of C60 fullerene. In general, the electronic states and energy gaps of low-energy electronic structures are highly sensitive to changes in the direction and magnitude of the applied electric field and to the tip configuration. The present results show that the electric field induces a strong modulation of the state energies and energy gaps of the current nanotubes, changes their energy spacings, and prompts the occurrence of semiconductor-metal transitions (SMTs). It is found that the SMTs occur more frequently as the direction of the electric field approaches the symmetry axis or when its magnitude becomes sufficiently large. The present results also indicate that the Fermi levels and energy gaps of the three nanotubes considered in this study are strongly influenced by the cap configuration. Finally, the convergent decay behavior of the energy gap which is observed as the length of the nanotube is increased is also strongly dependent on the tip configuration.     

Investigation on probing explosive nitroaromatic compound vapors using graphyne nanosheet: a first-principle study

Structural Chemistry - We studied the geometric stability of pristine graphyne nanosheet (Gpn-NS) and electronic properties for the possible use of graphyne sheet for the chemical sensor. The...     

石墨炔的化学修饰及功能化

石墨炔特殊的电子结构和孔洞结构使其在信息技术、电子、能源、催化以及光电等领域具有潜在、重要的应用前景。近几年石墨炔的基础和应用研究已取得了重要成果,并迅速成为了碳材料研究中的新领域。石墨炔中炔键单元的高活性为其化学修饰与掺杂提供了良好的平台。在这篇综述中,我们将重点介绍石墨炔的非金属杂原子掺杂、金属原子修饰以及表面改性,并深入探讨掺杂与衍生化对石墨炔材料的电子性质的影响及其对光电化学催化性能的协同增强。     

6影响稀土复合氧化物电性的因素

合成了多种类型的稀土复合氧化物, 研究它们的结构、电学性质。通过大量实验数据, 总结了电子构型、自旋状态、电子输运通道与原子簇对稀土化合物电性影响的规律。中心离子的最外层电子轨道中若有未成对电子, 并未呈半充满状态时,导电性好; 化合物结构中必须具有原子间距小于0.31nm的-M-X-M-X-或-M-M-M-连续输运通道, 且中心离子的电子构型符合上述导电性好的条件, 化合物导电性好。孤立的原子簇不能成为导电通道, 因此它的存在将减少导电性能。     

Ab initio investigations of the electric field dependence of the geometric and electronic structures of molecular wires

Theoretical investigations on the typical molecular wire, polyacetylene, which bridges two chemically inert electrodes, have been carried out at the Hartree-Fock level by incorporating the external electric field into the calculations. The results demonstrate that both the geometric and the electronic structures of the conjugated molecular wires are sensitive to the electric field. When the electric field increases, the carbon-carbon single bonds become shorter and the double bonds become longer, leading to a higher conjugation. The electric field reduces the HOMO-LUMO gap and increases the dipole moment. The spatial distributions of the molecular orbitals are used to analyze the electrical properties of the molecular wire. All of these features are more pronounced with increasing conjugation chain length. Quantitative correlations between most of these features and the electric field have been discussed as well.     

On the origin of the unique properties of supported Au nanoparticles

The unique catalytic activity of supported Au nanoparticles has been ascribed to various effects including thickness/shape, the metal oxidation state, and support effects. Previously, we reported the synthesis of ordered Au monolayers and bilayers on TiO(x), with the latter being significantly more active for CO oxidation than the former. In the present study, the electronic and chemical properties of ordered monolayer and bilayer Au films have been characterized by infrared reflection adsorption spectroscopy using CO as a probe and ultraviolet photoemission spectroscopy. The Au overlayers are found to be electron-rich and to have significantly different electronic properties compared with bulk Au. The common structural features of ordered Au bilayers and Au bilayer nanoparticles on TiO2(110) are described, and the exceptionally high catalytic activity of the Au bilayer structure related to its unique electronic properties.     

Interface water dynamics and porating electric fields for phospholipid bilayers

Lipid bilayers, normally a barrier to charged species and large molecules, are permeabilized by electric fields, a phenomenon exploited by cell biologists and geneticists for porating and transfecting cells and tissues. Recent molecular simulation studies have advanced our understanding of electroporation, but the relative contributions of atomically local details (interface water and headgroup dipole and counterion configurations) and medium- and long-range electrostatic gradients and changes in membrane structural shifts to the initiating conditions and mechanisms of pore formation remain unclear. Molecular dynamics simulations of electroporation in several lipid systems presented here reveal the effects of lipid hydrocarbon tail length and composition on the magnitude of the field required for poration and on the location of the initial sites of field-driven water intrusion into the bilayer. Minimum porating external fields of 260 mV nm(-1), 280 mV nm(-1), 320 mV nm(-1), and 380 mV nm(-1) were found for 1,2-dilauroyl-sn-glycero-3-phosphatidylcholine (DLPC), 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC), 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC), and 1,2-dioleoyl- sn-glycero-3-phosphatidylcholine (DOPC) bilayers, respectively, and correlated most strongly with the bilayer thickness. These phospholipid systems share several common features including a wide, dynamic distribution of the headgroup dipole angle with the bilayer normal ranging from 0 to 155 degrees that is only slightly shifted in a porating electric field, and similar electric field-induced shifts in water dipole orientation, although the mean water dipole moment profile at the aqueous-membrane interface is more sensitive to the electric field for DOPC than for the other phospholipids. The location of pore initiation, at the anode- or cathode-facing leaflet, varies with the composition of the bilayer and correlates with a change in the polarity of the localized electric field at the interface.     

Potential-driven structural changes in Langmuir-Blodgett DMPC bilayers determined by in situ spectroelectrochemical PM IRRAS

Combined Langmuir-Blodgett vertical withdrawing and Langmuir-Schaefer horizontal touch (LB-LS) methods were employed to transfer DMPC bilayers onto a Au(111) electrode surface. Charge density measurements and photon polarization modulation infrared reflection absorption spectroscopy were employed to investigate electric field induced changes in the structure of the bilayer. The results show that the physical state and the molecular arrangement found in the monolayer at the air-water interface is to a large extent preserved in the bilayer formed by the LB-LS method. This approach provides an opportunity to produce supported bilayers with a well-designed architecture. The properties of the bilayer formed by the LB-LS method were compared to the properties of the bilayer produced by spontaneous fusion of unilamellar vesicles investigated in an earlier study (Bin, X.; Zawisza, I.; Lipkowski, J. Langmuir 2005, 21, 330-347). The tilt angles of the acyl chains are much smaller in the bilayer formed by the LB-LS method and are closer to the angles observed for vesicles and stacked hydrated bilayers. The tilt angles of the phosphate and choline groups are also smaller and are characteristic of an orientation in which the area per DMPC molecule is small. The electric field induced changes of these angles are also less pronounced in the bilayer formed by the LB-LS method. We have shown that these differences are a result of the higher packing density of the phospholipid molecules in the bilayer formed by the LB-LS method.     

First-principles study of the triwing graphene nanoribbons: junction-dependent electronic structures and electric field modulations

Using first-principles calculations, we investigate the structural, electronic and magnetic properties of triwing zigzag graphene nanoribbons (TW-ZGNRs), as well as the electric field effects on their electronic structures. The TW-ZGNRs have comparable energetic stabilities to the normal ZGNRs and exhibit fascinating junction-dependent electronic properties. With the sp(2) hybridized junctions, the TW-ZGNRs undergo a Peierls distortion and behave as ferromagnetic metals. While the TW-ZGNRs with sp(3) hybridized junctions become semiconductors, which have a ferrimagnetic ground state. An external electric field can further modulate the band structures of semiconducting TW-ZGNRs. The parallel electric field directly moves the flat bands around the Fermi level, while the perpendicular field controls the edge states at the ribbon wings. By these electric field modulations, the band gaps are effectively tuned and half-metallicity can be induced into TW-ZGNRs. Our studies demonstrate that the junctions play an important role in the electronic structures of TW-ZGNRs, which have well-tunable electronic and magnetic properties for potential applications in nanoelectronics and spintronics.     

Electronic structures and bonding of graphyne sheet and its BN analog

Using density functional theory and generalized gradient approximation for exchange and correlation, we present theoretical analysis of the electronic structure of recently synthesized graphyne and its boron nitride analog (labeled as BN-yne). The former is composed of hexagonal carbon rings joined by C-chains, while the latter is composed of hexagonal BN rings joined by C-chains. We have explored the nature of bonding and energy band structure of these unique systems characterized by sp and sp(2) bonding. Both graphyne and BN-yne are found to be direct bandgap semiconductors. The bandgap can be modulated by changing the size of hexagonal ring and the length of carbon chain, providing more flexibilities of energy band engineering for device applications. The present study sheds theoretical insight on better understanding of the properties of the novel carbon-based 2D structures beyond the graphene sheet.     

Statistical mechanically averaged molecular properties of liquid water calculated using the combined coupled cluster/molecular dynamics method

Liquid water is investigated theoretically using combined molecular dynamics (MD) simulations and accurate electronic structure methods. The statistical mechanically averaged molecular properties of liquid water are calculated using the combined coupled cluster/molecular mechanics (CC/MM) method for a large number of configurations generated from MD simulations. The method includes electron correlation effects at the coupled cluster singles and doubles level and the use of a large correlation consistent basis set. A polarizable force field has been used for the molecular dynamics part in both the CC/MM method and in the MD simulation. We describe how the methodology can be optimized with respect to computational costs while maintaining the quality of the results. Using the optimized method we study the energetic properties including the heat of vaporization and electronic excitation energies as well as electric dipole and quadrupole moments, the frequency dependent electric (dipole) polarizability, and electric-field-induced second harmonic generation first and second hyperpolarizabilities. Comparisons with experiments are performed where reliable data are available. Furthermore, we discuss the important issue on how to compare the calculated microscopic nonlocal properties to the experimental macroscopic measurements.     

The effect of electric field and Al doping on the sensitivity of hexa‐peri‐hexabenzocoronene nanographene to chloropicrin

It has been previously reported that the recently synthesized hexa‐peri‐hexabenzocoronene (HBC) nanographene cannot detect toxic chloropicrin (CP) gas. To overcome this problem, we examined the effect of Al doping and applying an electric field on the sensitivity of HBC towards CP gas by means of density functional theory calculations. We found that the Al‐doping process significantly increases the adsorption energy of CP gas from ?7.1 to ?39.9 kcal mol^?1 but decreases the sensitivity of HBC. By applying an electric field, the HBC is polarized with two different electrostatic potentials on its different surfaces, which increases the adsorption energy. By increasing the electric field strength, the adsorption energy and electronic sensitivity of HBC are increased. We predicted that in the presence of an electric field of about ?0.025 au, HBC can act as an electronic senor or a work function‐type sensor with a short recovery time. At this field, the electrical conductivity of HBC is significantly increased on CP adsorption which generates an electrical signal. Increasing the electric field to higher intensities is not favourable because of increasing recovery times, and decreasing it to lower intensities reduces the sensitivity of HBC.     

Excitation of Electronic States of N<Subscript>2</Subscript> in Radio-Frequency Electric Field by Electron Impact

Excitation of electronic states of the N₂ molecule by electron impact is recognized as an essential process in nitrogen plasmas that strongly impacts their chemical reactivity and other properties. Many surface and coating technologies are based on radio-frequency plasma discharges in nitrogen. In this paper the electron impact excitation rate coefficients for singlet and triplet electronic states of the N₂ molecule have been calculated in non-equilibrium conditions in the presence of a radio-frequency electric field. A Monte Carlo simulation has been performed in order to determine non-equilibrium electron energy distribution functions within one period of the electric field. By using these distribution functions, the excitation rate coefficients have been obtained in the frequency range from 13.56 up to 500 MHz, at reduced electric field values from 200 to 700 Td.