Influence of different pretreatments on the adhesion of nanodiamond composite films on Ti substrates via coaxial arc plasma deposition

In this study, we report on the novel growth of nanodiamond composite (NDC) films on titanium (Ti) substrates using the coaxial arc plasma deposition (CAPD) at room temperature, which offers several advantages over conventional growth techniques. CAPD employs a unique coaxial arc plasma gun structure that provides a supersaturated condition of highly energetic carbon ions (C+) for ultrafast quenching on the substrate, promoting the growth of nanodiamond grains. This allows for NDC films' growth on diverse substrates without the need for initial seeding or substrate heating. However, the growth of NDC films on Ti substrates at room temperature is challenging due to the native oxide layer (TiO2). Here, we grew NDC films on Ti substrates using three different pretreatments: (i) hydrofluoric acid (HF) etching, (ii) insertion of a titanium carbide (TiC) intermediate layer, and (iii) in situ Ar+ plasma etching. The morphology and structure of the grown NDC films were examined by 3D laser, high-resolution scanning electron microscopies (HR-SEM), Raman, and x-ray photoelectron (XPS) spectroscopies. Our results demonstrate that in situ Ar+ plasma etching is the most effective pretreatment method for completely removing the native TiO2 layer compared to the other two ex situ pretreatments, in which re-oxidation is more likely to occur after these pretreatments. Furthermore, NDC films grown using the hybrid Ar+ ion etching gun (IG) and CAPD exhibit the highest sp (3) content (63%) and adhesion strength (16 N).