The role of titanium nitride supports for single-atom platinum-based catalysts in fuel cell technology.

As a first step towards a microscopic understanding of single-Pt atom-dispersed catalysts on non-conventional TiN supports, we present density-functional theory (DFT) calculations to investigate the adsorption properties of Pt atoms on the pristine TiN(100) surface, as well as the dominant influence of surface defects on the thermodynamic stability of platinized TiN. Optimized atomic geometries, energetics, and analysis of the electronic structure of the Pt/TiN system are reported for various surface coverages of Pt. We find that atomic Pt does not bind preferably to the clean TiN surface, but under typical PEM fuel cell operating conditions, i.e. strongly oxidizing conditions, TiN surface vacancies play a crucial role in anchoring the Pt atom for its catalytic function. Whilst considering the energetic stability of the Pt/TiN structures under varying N conditions, embedding Pt at the surface N-vacancy site is found to be the most favorable under N-lean conditions. Thus, the system of embedding Pt at the surface N-vacancy sites on TiN(100) surfaces could be promising catalysts for PEM fuel cells.

A first-principles study of ultrathin nanofilms of MgO-supported TiN.

As a first step towards a microscopic understanding of supported ultrathin nanofilms of TiN, we present state-of-the-art density-functional theory (DFT) calculations to investigate the interfacial properties of the TiN/MgO system as a function of film thickness. Optimized atomic geometries, energetics, and analysis of the electronic structure of the TiN/MgO systems are reported. In particular, we find that the work function of 1 ML of TiN(100) on MgO(100) exhibits a significant decrease, rationalized by the large surface dipole moment formation due to the changes in charge densities at the interface of this system. This decrease in the work function of TiN/MgO systems (as compared to pristine MgO(100) surface) could well benefit their application in metal-oxide-semiconductor devices as an ideal gate-stack material.

Multi-field effect on the electronic properties of silicon nanowires.

The quantum confinement and electronic properties of silicon nanowires (SiNWs) under an external strain field ε and an electric field E-as well as both (ε plus E)-are systematically investigated using density functional theory. These two fields exist in working environments of integrated circuits. It is found that both ε and E lead to a drop of the band gap E(g)(ε,E) of the SiNWs. If both fields coexist, the interaction between ε and E causes that E(g)(ε,E) becomes orientation-dependent, which results from variations of both the conduction-band minimum and the valence-band maximum. The interaction is further illustrated by the density of states near the Fermi level and the eigenvalue of the highest occupied molecular orbital.