Large manipulation of competing bonding phases in ultrathin carbon layer system

N Dwivedi and SV Sunkara and C Dhand and R Yeo and AK Srivastava and SKRS Sankaranarayanan and D Dragoe and VA Esaulov and CS Bhatia, COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS, 714, 136548 (2025).

DOI: 10.1016/j.colsurfa.2025.136548

The extent of sp(3) bonding governs the functional properties of amorphous carbon films, by changing their density, Young's modulus and hardness, which in turn affects their corrosion resistance, tribological properties and more. However, the sp(3) bonding and other structural properties of such films at the ultrathin level, especially for sub-10 nm films, remain elusive. Here, we experimentally probe and quantify the bonding network of similar to 0.7-10 nm amorphous carbon films. With decreasing carbon thickness, the films undergo giant structural modification with a decrease in sp(3) bonding. Molecular dynamics simulations provide further insights into the observed variations in sp(2) vs. sp(3) bonding characteristics. We discover that the structural transformation is also substrate-dependent, with the films on metallic substrates yielding lower sp(3) bonding than on silicon. Moreover, engineering the film-metal substrate interface via atomically thin silicon nitride promotes the sp(3) bonding of < 3 nm-thick carbon films. We also observe that the sp(3) bonded carbon network is destroyed when ion bombardment or sputter-etching is performed. This work provides crucial fundamental insights into the structure-characteristics modifications that may arise when engineering sub-10 nm amorphous carbon based films.

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