Structure and properties of diamond-like carbon thin films synthesized by biased target ion beam deposition

Biased target ion beam deposition (BTIBD) was firstly used to synthesize hydrogen free diamond-like carbon (DLC) thin films. The structure and properties of the synthesized films were characterized by atomic force microscopy (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), nanoindentation, and ball-on-disk testing. The effect of target bias voltage, ranging from − 200 to − 1000 V, on the structure and properties of the films was investigated. The results show that the sp3 bonding content increases from 20% to 60%, the root-mean squared (RMS) roughness decreases from 0.2 nm to 0.05 nm, the coefficient of friction (COF) decreases from 0.3 to 0.06, the hardness increases from 4.5 GPa to 15 GPa, and the Young's modulus increases from 65 GPa to 170 GPa with increasing the absolute value of target bias voltage from 200 V to 800 V. However, when the target bias voltage further increased to − 1000 V, the sp3 bonding content decreases to 44%, RMS roughness increases to 0.09 nm, COF raises to 0.11, hardness decreases to 12.9 GPa and Young's modulus is lowered to 150 GPa. It has been found that the higher the fraction of sp3 bonds, the lower the surface roughness and friction coefficient, and the higher the hardness and Young's modulus.

► DLC can be synthesized by sputtering of graphite without additional ion bombardment.
► DLC films with a RMS as low as 0.05 nm were synthesized with BTIBD technique.
► DLC films with a COF as low as 0.06 were synthesized with BTIBD technique.