Atomic structure of the Se-passivated GaAs(001) surface revisited.

We present a combined experimental and theoretical study of the Se-treated GaAs(001)-([Formula: see text]) surface. The ([Formula: see text]) structure with the two-fold coordinated Se atom at the outermost layer and the three-fold coordinated Se atom at the third layer was found to be energetically stable and agrees well with the experimental data from scanning tunneling microscopy, low energy electron diffraction, and x-ray photoelectron spectroscopy. This atomic geometry accounts for the improved stability of the Se-treated surface against the oxidation.

Size Optimization of a N-Doped Graphene Nanocluster for the Oxygen Reduction Reaction.

N-Doped graphene nanoclusters (N-GNCs) are promising electrocatalysts for the oxygen reduction reaction (ORR) at the cathode of fuel cells. In this study, the dependence of the ORR activity on the size of N-GNCs was investigated using first-principles calculations based on density functional theory. The maximum electrode potential ( ) was estimated from the free energy of the reaction intermediates of the ORR.

Edge-State-Induced Stacking of Zigzag Graphene Nanoribbons.

We have investigated the structural stabilities and electronic properties for AA and the Bernal-stacked AB bilayer zigzag graphene nanoribbons (ZZGNRs) using first-principles calculations within density functional theory. The AB-stacked ZZGNR exhibits the spin-polarized state, while the AA-stacked ZZGNR has the nonmagnetic ground state, being more energetically stable than the AB-stacked one. For the AA-stacked ZZGNR, the interaction between the so-called edge states rather than the van der Waals (vdW) interaction plays an important role: the occupied up-spin and the unoccupied down-spin states at one end of ZZGNR interact with each other, and vice versa at the other end, forming the non-spin-polarized bonding and antibonding states at the zigzag edge.

Effect of Water on the Manifestation of the Reaction Selectivity of Nitrogen-Doped Graphene Nanoclusters toward Oxygen Reduction Reaction.

We investigated the selectivity of N-doped graphene nanoclusters (N-GNCs) toward the oxygen reduction reaction (ORR) using first-principles calculations within the density functional theory. The results show that the maximum electrode potentials ( ) for the four-electron (4e) pathway are higher than those for the two-electron (2e) pathway at almost all of the reaction sites. Thus, the N-GNCs exhibit high selectivity for the 4e pathway, that is, the 4e reduction proceeds preferentially over the 2e reduction.

Atomic structure and passivated nature of the Se-treated GaAs(111)B surface.

We have systematically studied the atomic structure and electronic properties of the Se-treated GaAs(111)B surface using scanning tunneling microscopy, reflection high-energy electron diffraction, x-ray photoelectron spectroscopy, and first-principles calculations. We have found that Se atoms substitute [Formula: see text] monolayer of As atoms at the outermost layer of the ideal (111)B surface. Charge transfer from Se to As eliminates all of unsaturated dangling bonds, so that the surface is electronically stabilized, leaving no surface states in the mid-gap region.

Formation of Water Layers on Graphene Surfaces.

Although graphitic materials were thought to be hydrophobic, recent experimental results based on contact angle measurements show that the hydrophobicity of graphitic surfaces stems from airborne contamination of hydrocarbons. This leads us to question whether a pristine graphitic surface is indeed hydrophobic. To investigate the water wettability of graphitic surfaces, we use molecular dynamics simulations of water molecules on the surface of a single graphene layer at room temperature.