Theoretical study of metal/silica interfaces: Ti, Fe, Cr and Ni on β-cristobalite.

The understanding of interfacial effects and adhesion at oxide-metal contacts is of key importance in modern technology. Metal-silica interfaces specifically are relevant in electronics, catalysis and nanotechnology. However, adhesion at these interfaces is hindered by a formation of siloxane rings on the silica surface which saturate the dangling bonds at stoichiometric terminations.

Effects of surface hydroxylation on adhesion at zinc/silica interfaces.

The weak interaction between zinc and silica is responsible for the poor performance of anti-corrosive galvanic zinc coatings on modern advanced high-strength steels, which are fundamental in the automotive industry, and important for rail transport, shipbuilding, and aerospace. With the goal of identifying possible methods for its improvement, we report an ab initio study of the effect of surface hydroxylation on the adhesion characteristics of model zinc/β-cristobalite interfaces, representative of various surface hydroxylation/hydrogenation conditions. We show that surface silanols resulting from dissociative water adsorption at the most stable stoichiometric (001) and (111) surfaces prevent strong zinc-silica interactions.

Deposition of hydrogenated silicon clusters for efficient epitaxial growth.

Epitaxial silicon thin films grown from the deposition of plasma-born hydrogenated silicon nanoparticles using plasma-enhanced chemical vapor deposition have widely been investigated due to their potential applications in photovoltaic and nanoelectronic device technologies. However, the optimal experimental conditions and the underlying growth mechanisms leading to the high-speed epitaxial growth of thin silicon films from hydrogenated silicon nanoparticles remain far from being understood. In the present work, extensive molecular dynamics simulations were performed to study the epitaxial growth of silicon thin films resulting from the deposition of plasma-born hydrogenated silicon clusters at low substrate temperatures under realistic reactor conditions.

Structural, electronic and adhesion characteristics of zinc/silica interfaces: ab initio study on zinc/β-cristobalite.

The weak interaction between zinc and silica is responsible for a poor performance of anti-corrosive galvanic zinc coatings on modern advanced high strength steels. With the goal of identifying its microscopic origin, we report an extensive ab initio study on the structural, electronic, and adhesion characteristics of a variety of model zinc/β-cristobalite interfaces, representative for different oxidation conditions. We show that the weakness of the zinc-silica interaction at non polar interfaces is driven by the presence of surface siloxane rings.

Metallic-like bonding in plasma-born silicon nanocrystals for nanoscale bandgap engineering.

Based on ab initio molecular dynamics simulations, we show that small nanoclusters of about 1 nm size spontaneously generated in a low-temperature silane plasma do not possess tetrahedral structures, but are ultrastable. Apparently small differences in the cluster structure result in substantial modifications in their electric, magnetic, and optical properties, without the need for any dopants. Their non-tetrahedral geometries notably lead to electron deficient bonds that introduce efficient electron delocalization that strongly resembles the one of a homogeneous electron gas leading to metallic-like bonding within a semiconductor nanocrystal.

New routes for improving adhesion at the metal/α-Al2O3(0001) interface.

With the advent of new steel grades, galvanic protection by zinc coating faces a new paradigm. Indeed, enrichment in strengthening elements prone to oxidation, such as Al, Mn, and Si, leads to the formation of oxide films that are poorly wet by zinc. We study herein routes for the improvement of adhesion at the model Zn/α-Al2O3 interface by the addition of metals.

A deeper insight into strain for the sila-bi[6]prismane ( Si18H12) cluster with its endohedrally trapped silicon atom, Si19H12.

A new family of over-coordinated hydrogenated silicon nanoclusters with outstanding optical and mechanical properties has recently been proposed. For one member of this family, namely the highly symmetric Si19 H12 nanocrystal, strain calculations have been presented with the goal to question its thermal stability and the underlying mechanism of ultrastability and electron-deficiency aromaticity. Here, the invalidity of these strain energy (SE) calculations is demonstrated mainly based on a fundamentally wrong usage of homodesmotic reactions, the miscounting of atomic bonds, and arithmetic errors.

Temperature dependence of the radiative lifetimes in Ge and Si nanocrystals.

The effect of finite temperature on the optical properties of nanostructures has been a longstanding problem for their theoretical description and its omission presents serious limits on the validity of calculated spectra and radiative lifetimes. Most ab initio calculations have been carried out neglecting temperature effects altogether, although progress has been made recently. In the present work, the temperature dependence of the intrinsic radiative lifetimes of excited electron-hole pairs in Ge and Si nanocrystals due to classical temperature effects is calculated using ab initio molecular dynamics.