Coating Morphology, Porosity, and Diffusional Property

An outstanding characteristic of DLC coating is its nanolevel smoothness and freedom of pinholes and other similar defects. From that standpoint, DLC is different from CVD diamond (see Ch. 13, Sec. 3.10). A 

DLC coating planarizes the surface, i.e., the coating surface is smoother than the substrate, with surface roughness measured at 0.28 nm for a 100 nm coating thickness. l The material is an excellent diffusion barrier to sodium, moisture, and most gases. l 

DLC converts to graphite at iower temperature than diamond. An initial transformation has been observed as low as 250°C. The transformation is rapid at 400°C and proceeds by loss of hydrogen and subsequent graphitization. A maximum long-term use temperature for DLC is 250 -300°C. 

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