It has been extremely difficult for nanodiamond composite (NDC) films to be deposited on Ti due to a large thermal expansion coefficient difference. Native oxide layer on Ti is another problem preventing the appropriate adhesion of NDC films and subsequent delamination. In this work, innovative room temperature adhesion of 3μm NDC films with 54GPa hardness on Ti substrates was accomplished via a hybrid system of ion etching gun and coaxial arc plasma deposition (CAPD). Ar+ plasma etching is capable to terminate the superficial TiO2 layer and manipulate substrate morphology while, CAPD provides instantaneous deposition of NDC films at room temperature
In this study, we report on the novel growth of nanodiamond composite (NDC) films on 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 C+ ions 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 sp3
content (63%) and adhesion strength (16 N).
We report on negative bias-enhanced growth of quenched-produced diamond films on titanium using hybrid coaxial arc plasma deposition at room temperature. Optimizing the bias voltage to -40 V resulted in a spontaneous formation of a titanium carbide interfacial layer, which caused a significant increase in the adhesion strength from 16 to 48 N. Selective etching of undesired sp2-C bonded atoms and ultrafast quenching of the energetic carbon ions C+ promoted the growth of dense sp3-C bonded atoms, achieving a superhardness of 96 GPa, comparable to natural diamond. These pioneering findings have the potential to revolutionize multifunctional materials for biomedical applications
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