Peculiar deformation characteristics of turbostratic boron nitride thin film

The deformation behavior of a textured turbostratic boron nitride thin film of 120 nm in thickness, with its c-axis parallel to the film surface, was investigated under nanoindentation. The load displacement response of the textured turbostratic boron nitride film was revealed to be loading rate dependent, and a creep-like phenomenon was observed under constant load. Moreover, the textured turbostratic boron nitride film was found to be able to recover with hysteresis, even when pressed to the maximum depth of approximately 20% of the film thickness. The apparent hardness and Young's modulus were estimated to be 1.5 and 30 GPa, respectively. The reversible hysteretic deformation, similar to that of a viscoelastic body, is clearly controlled by the bending of the sp2-bonded turbostratic boron nitride basal planes.