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

摘要

Diamond and diamond-like carbon (DLC) are used as coating materials fornumerous applications, ranging from biomedicine to tribology. Recently, it hasbeen shown that the hydrophilicity of the carbon films can be enhanced bysilicon doping, which highly improves their biocompatibility and frictionalperformances. Despite the relevance of these properties for applications, amicroscopic understanding on the effects of silicon is still lacking. Here weapply ab initio calculations to study the interaction of water molecules withSi-incorporated C(001) surfaces. We find that the presence of Si dopantsconsiderably increases the energy gain for water chemisorption and decreasesthe energy barrier for water dissociation by more than 50%. We provide aphysical rational for the phenomenon by analysing the electronic chargedisplacements occuring upon adsorption. We also show that once hydroxylated,the surface is able to bind further water molecules much strongly than theclean surface via hydrogen-bond networks. This two-step process is consistentwith and can explain the enhanced hydrophilic character observed incarbon-based films doped by silicon.