Enhancing and manipulating the mechanical properties of graphene oxide (GO)-based structures are challenging because the GO assembly is easily delaminated. We develop nacre-like bionanofilms whose in-plane mechanical properties can be manipulated through water vapor annealing without influencing their mechanical properties in the thickness direction. These bionanofilms are prepared from GO, silk fibroin (SF), and cellulose nanocrystals (CNCs) via a spin-assisted layer-by-layer assembly. The postannealing mechanical properties of the films are determined with atomic force microscopy (AFM) bending and nanoindentation, and it is confirmed that the mechanical properties of the bionanofilms are altered only in the in-plane direction. While AFM bending shows Young’s moduli of 26.9, 36.3, 24.3, and 41.4 GPa for 15, 15 annealed, 30, and 30 annealed GO/SF/CNC trilayers, nanoindentation shows reduced moduli of 19.5 ± 2.6 and 19.5 ± 2.5 GPa before and after annealing, respectively. The unaltered mechanical properties of the bionanofilms along the thickness direction after annealing can be attributed to the CNC frame in the SF matrix acting as a support against stress in the thickness direction, while annealing reorganizes the bionanofilm structure. The tunability of the bionanofilms’ mechanical properties in only one direction through structure manipulation can lead to various applications, such as e-skin, wearable sensors, and human–machine interaction devices.

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Nitrogen doped diamond-like carbon (NDLC) is a candidate protective coating in state-of-the-art heat assisted magnetic recording (HAMR) media. To ensure the robustness of the media particularly at higher temperature applications, mechanical properties of ultra-thin sub 5-nm NDLC coatings are of great interest. Due to instrument limitations and very shallow films, it is very challenging to accurately measure sub-5 nm NDLC films and other HAMR components from experiments without substrate effects. In this study, very shallow nanoindentations were performed, and the results were fitted with finite element analysis using a modified indenter geometry to predict the elastic modulus and yield strength of NDLC films of two different thicknesses (3.5 and 4.5 nm) and other components without any substrate effect. Results showed that higher NDLC film thickness led to better elastic modulus and yield strength at 25 °C before and after heating and at 300 °C. Hardness to yield strength ratio (H/Y) for NDLC films was also determined and found within the range of 2.2–2.8, which is higher than the H/Y ratio of DLC films from earlier studies. This implied the dependence of H/Y ratio on the thickness, temperature conditions, and chemical structure of NDLC films. Results also showed that the yield strength of FeCo metal layer and glass substrate in HAMR media decreased at 300 °C, but almost fully recovered to their initial properties after removal of heat.