Extreme durability composite diamond film

Abstract

A novel composite diamond film comprising of a relatively thick layer of UNCD (Ultrananocrystalline Diamond) with a Young's modulus of less than 900 GPa and a relatively thin MCD (microcrystalline diamond) outermost layer with a Young's modulus of greater than 900 GPa, has been shown to exhibit superior delamination resistance under extreme shear stress. It is hypothesized that this improvement is due to a combination of stress relief by the composite film with a slightly 'softer' UNCD layer, a disruption of the fracture mechanism through the composite layer(s), and the near ideal chemical and thermal expansion coefficient match between the two diamond layers. The combination of a thick but 'softer' underlying UNCD layer with a thin but harder overlying MCD layer provides an excellent compromise between the low deposition cost and smoothness of UNCD with the extreme hardness and unparalleled chemical, electrochemical and immunological inertness of even a thin layer of MCD. The MCD layer's roughness is minimized and its adhesion maximized by the use of a thin layer of MCD and its deposition on the smooth surface of the chemically nearly identical underlying UNCD layer. The composite film can be applied to any application currently utilizing a diamond or a similar hard film, including cutting tools, abrasive surfaces, electrochemistry, biomedical applications such as human implants or thermally conductive films and the like, requiring superior durability, chemical resistance and/or immunological inertness.