X-ray reflectivity was used to differentiate between two hydrogenated amorphous carbon (a-C:H) coatings with distinct Raman signatures proving that they are layered, with the top-layer characterized by a density that is either higher or lower than the averaged film density of the coating. The density of the upper-layer was found to be 1.3 g/cm(3) for the coating with the greater intensity ratio I-d/I-g [the intensity ratio of the raman D-band (1350 cm(-1)) and the G-band (1530 cm(-1))], as compared with 2.2 g/cm(3) for the "typical" a-C: H. The coating with the lower-density 8 nm top-layer was manufactured under conditions that allow for the trapping of physisorbed hydrogen. It is likely that this polymeric top-layer was necessary in trapping unbound hydrogen. This coating was also distinguished by a higher surface roughness of 0.98 nm as compared with 0.68 nm for the denser coating. A very low coefficient of friction, 0.02-0.04, was recorded during scratch testing using progressive loading. The critical load to failure was in the range of 28-40 N; and the failure mode was brittle as determined by the Si substrate. (C) 2004 American Vacuum Society.