Toward a Better Understanding of the Influence of the Hydrocarbon Precursor on the Mechanical Properties of a-C: H Coatings Synthesized by a Hybrid PECVD/PVD Method

In this work, we provide new insight on the influence of the precursor (CH₄ vs. C₂H₂) on the mechanical properties of a-C:H coatings synthesized in a hybrid PECVD/PVD process. For a given set of plasma parameters, the films synthesized in CH₄/Ar gas mixture are found harder than the ones prepared in C₂H₂/Ar atmosphere despite their lower sp³ density and similar hydrogen content. This unusual behavior is attributed to different molecular organization of the polymeric network constituting the films. The latter is explained considering the influence of the chemical nature of the film-forming species on the cross-linking and branching degree of the films. The whole set of our results unambiguously demonstrates that additional factors than the sp³ and hydrogen content have to be considered for explaining the mechanical properties of a-C:H layers. The purpose of this work is to enlarge the comprehension about the influence of the chemical precursor (CH₄ vs. C₂H₂) on the mechanical properties of amorphous hydrogenated carbon film (a-C:H) synthesized by a PECVD/PVD hybrid method. The whole set of our results enables to highlight the influence of other factors (e.g., cross-linking degree, branching character) than the sp³ and hydrogen content for determining the hardness of the a-C:H layers.