High temperature nanomechanical properties of sub-5 nm nitrogen doped diamond-like carbon using nanoindentation and finite element analysis

Abstract

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.

Creep Behavior of Graphene Oxide, Silk Fibroin, and Cellulose Nanocrystal Bionanofilms

“…Following the work from Zhang et al. and Shakil et al., [ 25,26 ] the flat part length ( a ) was determined to be 12.5 nm for the indenter radius ( R ) of 80 nm. Further details of the indenter geometry determination and model validation are discussed in the appendix.…”

“…The axis of symmetry was constrained for rotations and lateral movements; and the bottom surface of the sample was constrained for rotations and vertical movements. Following the work from Zhang et al and Shakil et al, [25,26] the flat part length (a) was determined to be 12.5 nm for the indenter radius (R) of 80 nm. Further details of the indenter geometry determination and model validation are discussed in the appendix.…”

“…To determine the indenter geometry of the FEA model (Section 3.1), a standard fused quartz (FQ) sample with known elastic modulus of 72 GPa was used, following works from the literature. [25,26] First, very shallow nanoindentations were performed on the FQ sample so that the load-displacement response is elastic, as shown in Figure A1a. In this case, the indenter acted as a flat punch pushing the FQ sample without any plastic deformation.…”

“…[ 24 ] For predicting true properties of thin films from nanoindentation and FEA, the indenter geometry is also an important factor and needs to be considered in FEA. [ 25,26 ]…”

“…[24] For predicting true properties of thin films from nanoindentation and FEA, the indenter geometry is also an important factor and needs to be considered in FEA. [25,26] In this study, GO-SF-CNC nanocomposite films were fabricated using SA-LbL method and nanoindentation creep experiments were performed to investigate mechanical and creep behavior of GO-SF-CNC nanocomposite at different temperature conditions. Finite element method was also performed using modified indenter geometry to investigate creep properties of the nanocomposite.…”