The preparation of multifunctional copper-nanocrystalline diamond composite materials

Abstract

Deposition of adherent diamond films on copper is challenging due to a combination of high thermal mismatch and poor bonding. Therefore, pretreatment of copper by various techniques and its effect on diamond nucleation, growth, and adhesion were investigated. A combination of abrasion with microdiamond and deposition of a thin (200 nm) titanium interlayer was conducive for the final coating performance. Although ultrasonic nanodiamond seeding facilitates diamond growth, it does not significantly enhance the adhesion of the diamond coating. The mechanisms for improved film adhesion are based on anchoring due to introduction of surface roughness by abrasion and mechanical interlocking due to embedding of microdiamond in the copper surface and Ti interlayer. Furthermore, the Ti interlayer is able to form carbides and establish chemical bonding with the diamond film during hot filament chemical vapor deposition. The thermal stress was mitigated by combining a reduced deposition temperature (650 °C) with a Ti interlayer, which served as a compliant buffer for CTE mismatch. Diamond films grown for 12 h (with a thickness of approximately 10 micrometers) did not spontaneously delaminate after cooling, and the adhesion strength of the nanocrystalline diamond film was ca. 68.5 MPa. Furthermore, the diamond film features a high resistivity up to 1.51 × 1014 Ω·cm at 30 °C. The material’s high resistivity and superior thermal transport properties offer novel options for electronic circuit design, potentially improving heat dissipation and simplifying production.

Keywords

• adhesion
• copper substrate
• diamond nucleation and growth
• nanocrystalline diamond
• titanium