Importance of Interfacial Structures in the Catalytic Effect of Transition Metals on Diamond Growth.

Here, using ab initio calculations, we investigated the interaction between transition metals (M) and diamond C(111) surfaces. As a physical parameter describing the catalytic effect of a transition metal on diamond growth, we considered interfacial energy difference, ΔE int, between 1 × 1 and 2 × 1 models of M/C(111). The results showed that the transition-metal elements in the middle of the periodic table (groups 4-10) favor a 1 × 1 M/C(111) structure with diamond bulk-like interfaces, while the elements at the sides of the periodic table (groups 3, 11, and 12) favor a 2 × 1 M/C(111) structure with the 2 × 1 Pandey chain structure of C(111) underneath M. In addition, calculations of MC carbide formation for early transition metals (groups 3-6) showed that they have a tendency to form MC rather than M/C(111), which explains their low efficiency as catalysts for diamond growth. Further analysis suggests that ΔE int could serve as another parameter (catalytic descriptor) for describing catalytic diamond growth in addition to the conventional parameter of the melting temperature of M.

Significant THz absorption in CH3NH2 molecular defect-incorporated organic-inorganic hybrid perovskite thin film.

The valid strong THz absorption at 1.58 THz was probed in the organic-inorganic hybrid perovskite thin film, CH3NH3PbI3, fabricated by sequential vacuum evaporation method. In usual solution-based methods such as 2-step solution and antisolvent, we observed the relatively weak two main absorption peaks at 0.95 and 1.87 THz. The measured absorption spectrum is analyzed by density-functional theory calculations. The modes at 0.95 and 1.87 THz are assigned to the Pb-I vibrations of the inorganic components in the tetragonal phase. By contrast, the origin of the 1.58 THz absorption is due to the structural deformation of Pb-I bonding at the grain boundary incorporated with a CH3NH2 molecular defect.

Surface Instability of Sn-Based Hybrid Perovskite Thin Film, CH3NH3SnI3: The Origin of Its Material Instability.

To understand the instability of Sn-based perovskite, CH3NH3SnI3, photoelectron spectroscopy with synchrotron radiation and theoretical calculations, such as density functional theory and ab initio molecular dynamics, were performed. Findings from this experimental and theoretical study highlight the crucial changes of surface-chemical states, the broken chemical bondings in Sn-I, and the depletion of a CH3-NH3+ cation on the surface region. The material instability origin of Sn-based perovskite can be explained by the chemical state instability in the surface.

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.