Complementary neutron and x-ray reflectivity studies of "near-frictionless" carbon films

Near-frictionless carbon, a form of amorphous hydrogenated diamond-like-carbon developed at Argonne National Laboratory, has been investigated by neutron and x-ray reflectivity under ambient conditions, in vacuum, and at elevated temperature. A series of films was made with different ratios of hydrogen to carbon in the plasma; the deuterated counterparts were also synthesized. The details of scattering length density profiles, thickness, and surface and interfacial roughness of the films were obtained from neutron and x-ray reflectivity profiles. This allowed us to calculate the mass density and hydrogen composition of the bulk carbon film, leading to insight into the frictional properties. From the analysis we found that the magnitude of the scattering length density of the top surface layer was greatly affected by the experimental atmosphere in which the films were contained although the trend with hydrogen in the plasma remained the same. All samples were fitted with a three-layer model in addition to the substrate. (c) 2007 American Institute of Physics.