Annealing effects on the mechanical properties of near-frictionless carbon thin films

In this work, the near-frictionless carbon (NFC) thin films developed at Argonne National Laboratory were annealed at 100 °C, 150 °C, 200 °C, 400 °C, and 600 °C in nitrogen atmosphere. The changes of the NFC mechanical properties were measured with both static and dynamic nanoindentation methods. It was found that the Young's modulus and hardness decreased with increasing annealing temperatures. Raman spectroscopy, atomic force microscopy (AFM), and scanning electron microscopy (SEM) were used to characterize the film's structural change before nanoindentation testing. Raman characterization indicated that the G peak shifted upwards as the annealing temperature was increased above 150 °C, which indicated decreasing sp3 content. The intensity of the D peak was shown to increase with annealing temperature indicating that the NFC film became more graphite-like. AFM analysis showed an increase of sp2 clustering with annealing temperature, which resulted in an increase in surface roughness. SEM characterization indicated that as the films were annealed large cracks and numerous pinholes were generated. The characterization results were in good agreement with the measured mechanical properties.