Superior wear resistance and low friction in hybrid ultrathin silicon nitride/carbon films: synergy of the interfacial chemistry and carbon microstructure

Abstract

Amorphous carbon-based films are commonly investigated as protective nanocoatings in macro- to nano-scale devices due to their exceptional tribological and mechanical properties. However, with further device miniaturization where even thinner coatings are required, the wear durability of the nanocoating rapidly degrades at the expense of lower thickness. Here we discover that for sub-10 nm coating thicknesses, a hybrid bi-layer film structure, comprising a high sp³-bonded amorphous carbon top layer and a silicon nitride (SiN_x) bottom layer, consistently outperforms its single-layer amorphous carbon counterpart in terms of wear durability on a commercial tape drive head, while exhibiting low, stable friction and excellent wear resistance on a flat ceramic substrate. The superior performance of the hybrid film is attributed to the constructive synergy of the sp³-rich carbon microstructure and an enhanced interfacial chemistry arising from additional interfacial bonding. Moreover, a high energy C⁺ ion treatment step, introduced either directly to the substrate or to the SiN_x layer before carbon deposition, also aids in increasing atomic mixing that contributes to further improvement in the wear resistance. This study highlights the importance of both the carbon microstructure and interfacial chemistry in the design of wear-durable nanocoatings at few-nanometer thicknesses, particularly for aggressive wear conditions.