Characterization and properties of amorphous carbon coatings prepared by middle frequency pulsed unbalanced magnetron sputtering at different substrate bias

Abstract

The amorphous carbon (a-C) coatings were synthesized at different substrate bias using a middle frequency pulsed unbalanced magnetron sputtering technique. Some properties of the coatings were characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), nano-indentation tests, spectroscopic ellipsometry (SE). SEM measurement shows that the deposited a-C coatings are comparatively uniform. XPS and AES measurements show that sp3 content in a-C coatings changes with increasing substrate bias voltage. AES depth profile exhibits that the C element distributes uniformly across the coating thickness, and carbon atoms have penetrated into the Si substrate. Nano-indentation and spectroscopic ellipsometry tests indicate that the coating deposited at the substrate bias of 120V shows the optimized synthetic properties with higher nanohardness, higher elastic modus, higher refractive index and lower extinction coefficient. These results above are useful for the practical application of a-C as antireflection protection coatings. The influences of substrate bias on the sp3 fraction can be explanted by the sub-plantation model.