Hydrogen on hybrid MoS2/graphene nanostructures

Transition metal dichalcogenides are rising candidates for the replacement of Pt catalysts in water splitting. In this theoretical study we focus on the hydrogen evolution reaction part of this process and on how hydrogen (H) interacts with MoS₂ nanostructures, free‐standing or positioned on a graphene substrate. Density functional theory calculations confirm the stability of such nanostructures and our results for H on several configurations, from 2D infinite monolayers to quasi‐1D MoS₂ ribbons and quasi‐0D MoS₂ flakes, are presented. We calculate the adsorption energy of H atoms on various sites of the MoS₂ nanostructures, notably at Mo and S active edges. Comparing free‐standing and MoS₂/graphene hybrid systems we find that the effect of the support on the adsorption of H on MoS₂ nanostructures is quite significant when the substrate induces strain. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Hydrogenated BN monolayers: A first principles study

In the present contribution we apply first principles calculations to investigate the electronic structures and stability of BN hydrogenated monolayers which include a substitutional carbon atom. For comparison, additional C hydrogenated structures are considered. The obtained results demonstrate that BN chair-like monolayers are more stable than boat-like configurations. It is found that the most stable structures present bond angles quite similar to the characteristic one observed for s p ³ hybridization. Moreover, a net magnetic moment arises from the introduction of a substitutional carbon impurity. In addition, the results indicate that carbon substitutionals can induce a remarkable reduction of the work function.     

Hydrogen incorporation in ultrananocrystalline diamond/amorphous carbon films

The incorporation of hydrogen within ultrananocrystalline diamond/amorphous carbon composite films has been investigated by nuclear reaction analysis (NRA) and Fourier transform infrared spectroscopy (FTIR). The film bulk contains ca. 7.5–8% H (for a deposition temperature of 600 °C), while the H concentration in the surface region is considerably higher. FTIR measurements show that the hydrogen‐rich surface is formed right at the beginning of the deposition process and grows outward as the film thickness increases. It can thus be concluded that surface hydrogen species play an active role in the formation of ultrananocrystalline diamond/amorphous carbon films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Theoretical study of defects of BN nanotubes: A molecular-mechanics study

We investigate the structure and the formation energy of the pentagon–heptagon pairs (5775) defects of BN nanotubes using a molecular-mechanics method. For (n, 0) BN nanotubes, the homoelemental bonds of the 5775 defect may be located nearly either parallel or perpendicularly in the direction of tube axis. The former is energetically favored and strongly affects the reduction of the strain with decreasing radius. The formation energy of the 5775 defect, which increases with increasing radius, is lower than that of the tetragon–octagon pairs (4884). The 5775 defect of BN nanotubes is structurally and energetically stable, as compared to the 4884 defect.     

Substrate-induced magnetism in BN layer: A first-principles study

We predict an accepted configuration of hexagonal boron nitride (BN) layer on Co(111) surface by first-principles calculations. The calculated adsorption energy of this configuration is around −0.51 eV with a corrugation close to 0.1 Å. Polarized spin states are induced in BN layer due to the hybridization of the BN layer with the substrate Co, which gives rise to a magnetic moment of 0.2 μB on each pair of BN. The finding of high spin polarization on the absorbed BN layer ensures a high degree of passage of the preferred spin and is important in the development of nanoscale devices for spintronics applications.     

Hydrogen incorporation in diamond: the vacancy-hydrogen complex

We report the identification of the vacancy-hydrogen complex in single crystal diamond synthesized by chemical vapor deposition. The S=1 defect is observed by electron paramagnetic resonance in the negative charge state. The hydrogen atom is bonded to one of the carbon atoms neighboring the vacancy. Unlike the analogous defect in silicon, no symmetry lowering reconstruction occurs between the three remaining carbon dangling orbitals. The very small measured hydrogen hyperfine interaction is explained by dipolar coupling between the hydrogen and the unpaired electron probability density delocalized on the three equivalent carbon neighbors.     

Hydrogen incorporation in diamond: the nitrogen-vacancy-hydrogen complex

We report the identification of the nitrogen-vacancy-hydrogen complex in a freestanding nitrogen-doped isotopically engineered single crystal diamond synthesized by chemical vapor deposition. The hydrogen atom is located in the vacancy of a nearest-neighbor nitrogen-vacancy defect and appears to be bonded to the nitrogen atom maintaining the trigonal symmetry of the center. The defect is observed by electron paramagnetic resonance in the negative charge state in samples containing a suitable electron donor (e.g., substitutional nitrogen N(0)(S)).     

Self-assembly of adenine-dimer chains on Cu(1 1 0): Driving forces from first-principles calculations

The formation of self-assembled adenine-dimer chains on the Cu(1 1 0) surface is studied theoretically by means of ab initio calculations. The main driving forces for the appearance of the long-range order within the molecular overlayer are identified. The stable and metastable adenine overlayers are the result of the interplay between dimer bonding, intra- and interchain interactions and geometry effects imprinted by the metal surface. An adsorption pathway is proposed to explain the characteristic directionality of the dimer chains. Scanning tunneling microscopy images are computed for the optimized chain structures and compared with the available experimental data.     

In situ characterization of optoelectronic nanostructures and nanodevices

One-dimensional (1-D) semiconductor nanostructures can effectively transport electrons and photons, and are considered to be promising building blocks for future optoelectronic nanodevices. In this review, we present our recent efforts to integrate optical techniques and in situ electron microscopy for comprehensively characterizing individual 1-D optoelectronic nanostructures and nanodevices. The technical strategies and their applications in “green” emission and optical confinement in 1-D ZnO nanostructures will be introduced. We also show in situ assembly and characterization of nanostructures for optoelectronic device purposes. Using these examples, we demonstrate that the combination of optical techniques and in situ electron microscopy can be powerful for the studies of optoelectronic nanomaterials and nanodevices.     

Smallest fullerene-like clusters in two-probe device junctions: first principle study

First principle calculations based on density functional theory are realised to investigate the electron transport of the smallest fullerene-like clusters as two-probe junction devices. The junction devices are constructed by mechanically controlled break junction techniques to ensure the maximum stability of the Be₂₀, B₂₀ and N₂₀ cluster molecular junctions. We investigate the density of states, transmission spectrum, molecular orbitals, current and differential conductance characteristics at discrete bias voltages to gain insight about the various transport phenomena occurring in these nano-junctions. The results show that B₂₀ molecule when stringed to gold electrodes works as an ideal nano-device similar to the pure C₂₀ device and is more symmetric in its characteristic nature. However, in N₂₀ molecular device, the conduction is negligible due to the higher atomic interactions within N₂₀ molecule, despite the fact that it is constructed with penta-valent atoms.     

Experimental study of hydroxyl incorporation into olivine under pressure

Incorporation of water into synthetic olivine in the forsterite-water-graphite system at high pressures and temperatures has been investigated by micro-IR spectroscopy and micro-Raman spectroscopy. The results obtained are compared with the IR data on natural samples. The IR spectra of OH groups were found to be the narrowest in comparison with the existing data. A significant effect of graphite on the formation of OH centers has been revealed.     

A density functional theoretic study of novel silicon-carbon fullerene-like nanostructures: Si40C20, Si60C20, Si36C24, and Si60C24

Fullerene-like silicon nanostructures with twenty and twenty-four carbon atoms on the surface of the Si₆₀ cage by substitution, as well as inside the cage at various orientations have been studied within the generalized gradient approximation to density functional theory. Full geometry optimizations have been performed without any symmetry constraints using the Gaussian 03 suite of programs and the LANL2DZ basis set. Thus, for the silicon atom, the Hay-Wadt pseudopotential with the associated basis set is used for the core electrons and the valence electrons, respectively. For the carbon atom, the Dunning/Huzinaga double zeta basis set is employed. Electronic and geometric properties of these nanostructures are presented and discussed in detail. Optimized silicon-carbon fullerene like nanostructures are found to have increased stability compared to the bare Si₆₀ cage and the stability depends on the number and the orientation of carbon atoms, as well as on the nature of silicon-carbon and carbon-carbon bonding.     

Sensing properties of BN nanotube toward carcinogenic 4-chloroaniline: A computational study

The viability of using a BN nanotube for detection of para-chloroaniline molecule was studied by means of density functional theory calculations. The results indicate that the molecule prefers to be adsorbed on the intrinsic BN nanotube from its N atom, releasing energy of 0.65 eV without significant effect on the electrical conductivity of the tube. Thus, para-chloroaniline cannot be detected using this intrinsic nanotube. To overcome this problem, a nitrogen atom of the tube wall was replaced by a Si atom. It was shown that the Si-doped tube not only can adsorb the molecule strongly, but also may detect its presence because of the drastic increase of the electrical conductivity of the tube.     

Structural and electronic properties of perfect and defective BN nanoribbons: A DFT study

This paper deals with structural and electronic properties of a BN nanoribbon with the lateral profile having a zig-zag geometry, either perfect or with different kinds of defects. Calculations were implemented under standard DFT calculation procedures aiming to determine equilibrium structural positions and electronic properties. The considered defects include single and multiple vacancies, anti-sites and substitutional defects with carbon. Besides a discussion about the specific characteristics, structural and electronic, found for each case, the results are compared with previous calculations and experimental results available in the literature for the infinite layer, including possible magnetization resulting from unpaired electronic spins. Formation energies associated with defects of the nanoribbon are also calculated and compared with similar results for the infinite BN monolayer.     

Amantadine antiparkinsonian drug adsorption on the AlN and BN nanoclusters: A computational study

To find a sensor for Amantadine (AM) antiparkinsonian drug, we studied its interaction with Al₁₂N₁₂ and B₁₂N₁₂ nanoclusters by density functional theory calculations. The AM molecule attaches via its –NH₂ group to the Al or B atoms of Al₁₂N₁₂ or B₁₂N₁₂ with Gibbs free energy change about −31.5 or −26.1 kcal/mol. Increasing the AM concentration, the interaction becomes weaker due to steric effects. The AM adsorbs on the Al₁₂N₁₂ and B₁₂N₁₂ with two different mechanisms, including electrostatic and charge transfer, respectively. The AM significantly reduces the Al₁₂N₁₂ work function from 4.50 to 3.66 eV, increasing the electron field emission. Thus, the AlN cluster may be a work function type sensor. Upon the AM adsorption on the BN cage, the HOMO level is largely destabilized, reducing the E_g from 6.84 to 5.01 eV which largely increases the electrical conductivity. This indicates that the BN cluster may be a potential electronic sensor.     

第一性原理计算Co/h-BN界面上的微弱Dzyaloshinsky-Moriya相互作用

用密度泛函理论的第一性原理计算程序VASP在广义布洛赫条件下计算了Co/h-BN反方向的自旋螺旋能量与波矢的色散关系E(q)与E(-q).E(q)与E(-q)能量之差反映了Co/h-BN界面上下层之间空间反演对称性破缺引起的Dzyaloshinsky-Moriya相互作用(DMI)的大小.通过海森伯作用(HBI)模型与DMI模型拟合计算值,得到Co原子间各近邻的HBI参数J_1—J_4及DMI参数d_1,d_2.在Co/h-BN中,J_1为负值起完全主导作用,J_3比J_1小一个量级,其他参数接近于0.因此,Co/h-BN的基态是三角反铁磁,而DMI很微弱.根据这种性质,h-BN可以作为其他DMI界面的覆盖层.     

Impurity doping into Mg2Sn: A first-principles study

We studied the formation energy and atomic structure of impurities in Mg₂Sn using first-principles plane-wave total energy calculations. Twenty elements, namely H, Li, Na, K, Rb, Sc, Y, La, Cu, Ag, Au, B, Al, Ga, In, N, P, As, Sb, and Bi, were selected as the impurity species. We considered structural relaxation of the atoms within the second nearest neighbors of the impurity atom in the 48-atom supercell. The results of the formation energy calculations suggested that Sc, Y, La, P, As, Sb, and Bi are good n-type dopants whereas Li and Na are good p-type dopants. The electrical properties of Li-, Na-, and Ga-doped Mg₂Sn and La-doped Mg₂(Si, Sn) composites reported previously can be explained by the low formation energies of Li, Na, Ga, and La in Mg₂Sn.