Insigths into the tribochemistry of silicon-doped carbon based films by ab initio analysis of water/surface interactions

TL;DR

This study uses ab initio calculations to reveal how silicon doping enhances water interaction and hydrophilicity of carbon-based films, explaining their improved tribological and biocompatible properties.

Contribution

It provides a microscopic understanding of how silicon doping affects water adsorption and dissociation on carbon surfaces, which was previously unclear.

Findings

Silicon increases water chemisorption energy gain.

Silicon decreases water dissociation energy barrier by over 50%.

Hydroxylated surfaces bind additional water molecules strongly through hydrogen bonds.

Abstract

Diamond and diamond-like carbon (DLC) are used as coating materials for numerous applications, ranging from biomedicine to tribology. Recently, it has been shown that the hydrophilicity of the carbon films can be enhanced by silicon doping, which highly improves their biocompatibility and frictional performances. Despite the relevance of these properties for applications, a microscopic understanding on the effects of silicon is still lacking. Here we apply ab initio calculations to study the interaction of water molecules with Si-incorporated C(001) surfaces. We find that the presence of Si dopants considerably increases the energy gain for water chemisorption and decreases the energy barrier for water dissociation by more than 50%. We provide a physical rational for the phenomenon by analysing the electronic charge displacements occuring upon adsorption. We also show that once hydroxylated, the surface is able to bind further water molecules much strongly than the clean surface via hydrogen-bond networks. This two-step process is consistent with and can explain the enhanced hydrophilic character observed in carbon-based films doped by silicon.