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Highlights: • Clarify the effect of vacancy on H 2 S dissociation and H atom diffusion on Fe(1 0 0) surfaces. • Demonstrate the effects of adjacent vacant atom on H atom diffusion. • Reveal the minimum energy-diffusion path of the H atom from the Fe(1 0 0) surfaces into the bulk Fe. Abstract Vacancy defects on an iron surface have a great influence on the occurrence of hydrogen embrittlement. The adsorption/dissociation mechanism of H 2 S and the diffusion behavior of H atoms were calculated by first-principles spin-polarization density functional theory (DFT) on defect-free and vacancy-defective Fe(1 0 0) surfaces. The results show that the maximum dissociation energy barriers of H 2 S on the Fe(1 0 0) surface of defect-free and first-layer vacancy-defective Fe are 0.35 and 0.17 eV, respectively, indicating that the reactivity of the vacancy-defective Fe(1 0 0) surface is moderately increased. The existence of vacancy defects changes the preferential H atom diffusion entrance to the subsurface and shortens the diffusion path. For H diffusion in bulk Fe(1 0 0), it is found that H atoms diffuse via a tortuous path from one tetrahedral-site to a neighboring tetrahedral-site rather than diffusing through a linear trajectory. Moreover, the previously suggested path via the octahedral site is excluded due to its higher barrier and the rank of the saddle point. Diffusion barriers computed for H atom penetration from the surface into the inner-layers are approximately 0.54 eV (except for second-layer vacancy defects), which are all greater than the activation energy for dissociation of H 2 S on the Fe(1 0 0) surfaces. This suggests that H diffusion is more probable than H 2 S dissociation as the rate-limiting step for hydrogen permeation into the bulk Fe(1 0 0). [ABSTRACT FROM AUTHOR]

Ab initio density functional theory (DFT) calculations of the interactions between selected semiconducting and metallic single-walled carbon nanotubes (SWCNTs) (as well between single and double graphene sheets) and single oxygen molecules are carried out in order to provide a rationale for the recent experimental observations of UV-light accelerated oxidation of carbon nanotubes and the accompanying changes in the thermoelectric power. The computational results obtained show that these experimental findings can be related to UV-light excitation of oxygen molecules from their ground spin-triplet state into a higher-energy spin-singlet state. Such excitation lowers the activation energy for molecular-oxygen chemisorption to a nanotube, increases the adsorption energy and promotes charge transfer from the nanotube to the oxygen molecule. Lattice defects such as 7-5-5-7 and Stone–Wales defects are found to play a critical role in enhancing oxygen molecule/nanotube bonding and in affecting the extent of charge transfer. Contrary to this, the effects of nanotube diameter and chirality and the number of walls appear to be less significant. [Copyright &y& Elsevier]

Ab initio density functional theory (DFT) calculations of the interactions between isolated infinitely-long semiconducting zig-zag (10, 0) or isolated infinitely-long metallic arm-chair (5, 5) single-walled carbon-nanotubes (SWCNTs) and single oxygen-molecules are carried out in order to determine the character of molecular-oxygen adsorption and its effect on electronic transport properties of these SWCNTs. A Green’s function method combined with a nearest-neighbor tight-binding Hamiltonian in a non-orthogonal basis is used to compute the electrical conductance of SWCNTs and its dependence on the presence of topological defects in SWCNTs and of molecular-oxygen adsorbates. The computational results obtained show that in both semiconducting and metallic SWCNTs, oxygen-molecules are physisorbed to the defect-free nanotube walls, but when such walls contain topological defects, oxygen-molecules become strongly chemisorbed. In semiconducting (10, 0) SWCNTs, physisorbed O2-molecules are found to significantly increase electrical conductance while the effect of 7-5-5-7 defects is practically annulled by chemisorbed O2-molecules. In metallic (5, 5) SWCNTs, both O2 adsorbates and 7-5-5-7 defects are found to have a relatively small effect on electrical conductance of these nanotubes. [Copyright &y& Elsevier]

First-principle’s quantum-mechanical density functional theory (DFT) calculations are carried out to analyze the effect of single water-vapor molecules, three- and five-molecule water-vapor clusters and several other single-molecules with high dipole moments absorbed at the tip of capped (5,5) metallic armchair nanotubes on the ionization potential which is a measure of the ease at which electrons are extracted from carbon nanotubes during field emission. The results obtained show that in the absence of an externally applied electric field, the adsorption energies of both single- and multi-molecule clusters are quite low (typically less than 0.7 kcal/mol or 0.03 eV/molecule) suggesting that these adsorbates are not stable and would most likely desorb before a typical field-emission temperature of ∼900 K is reached. In sharp contrast, under a typical field-emission electric field of 1 eV/A˚, the adsorption energy is substantially higher (typically around 20 kcal/mol or 0.867 eV/molecule) making the adsorbates stable. The increased stability of the adsorbates is found to be the result of electrostatic interactions between dipole moments of the adsorbates and the applied electric field. These interactions increase the energy of the highest occupied molecular orbital in the nanotube and, in turn facilitate field emission. These findings are generally consistent with the available experimental results. [Copyright &y& Elsevier]

[Display omitted] • Understanding the physicochemical interactions at the nano-bio interface. • Binding interplay between the electrochemically roughened Ag electrode and CBR-5884. • Selective contribution of the charge-transfer mechanism in the SERS spectra. • Effect of potential and excitation wavelength on the molecule–metal interaction. This article presents the first physical insights into the binding interaction between the electrochemically roughened silver electrode and CBR-5884, an anticancer drug. The work gives a comprehensive account of the influence of applied electrode potential and excitation wavelength on the molecular adsorption on the metal surface. This type of research, based on the unique surface phenomena, may lead to a far-reaching improvement in biosensing and bioimaging applications, which may result in significant improvement in combined cancer chemo-immunotherapy. The main concern of the paper was to explore the possibility of surface-enhanced Raman spectroscopy (SERS) to understand physicochemical interactions at the nano-bio interface. Simultaneously, the molecular geometry in the equilibrium state and Raman frequencies were calculated based on the density functional theory (DFT) at the B3LYP 6-311G(d,p) level of theory. The highest SERS signal amplification is observed at the potential of –0.3 V for lower excitation wavelength, while at more negative electrode potential the molecule slowly desorbs or decomposes from the metal surface. At higher wavelengths, the enhancement of the SERS of individual bands is observed, which confirms the selective contribution of the charge-transfer mechanism in the SERS spectra along with the detection of different metal complexes adsorbed on the surface. [ABSTRACT FROM AUTHOR]

[Display omitted] • Au/Si(111)5 × 2-Au surface is a quasi-1D metallic system built of Au atomic rows. • Adsorbed Bi atoms substitute Au atoms in the edge rows of four-atom-wide Au ridges. • Adsorbed Bi atoms donate electrons increasing the Fermi energy of the system. • This provides an opportunity to tune system metallic properties by controlled Bi dosing. Changes in the structural and electronic properties of the quasi-one-dimensional metal-chain Au/Si(111)5 × 2 reconstruction induced by Bi adsorption were investigated using scanning tunneling microscopy observations, angle-resolved photoelectron spectroscopy measurements and density-functional theory calculations. It was found that Bi atoms substitute the Au atoms in the edge rows of the four-atomic-row Au ridge of the Au/Si(111)5 × 2 reconstruction. The Au/Si(111)5 × 2 surface, which is originally highly heterogenous in its electronic properties, becomes still more heterogeneous upon Bi substitutional adsorption. The overall effect of Bi adsorption resides in the increase of the system Fermi energy due to the electron donation from the Bi atoms to the reconstructed surface. This provides a possibility to tune the metallic properties of the system via controlled Bi dosing. [ABSTRACT FROM AUTHOR]