Grazing-angle x-ray reflectivity ͑XRR͒ is described as an efficient, nondestructive, parameter-free means to measure the mass density of various types of amorphous carbon films down to the nanometer thickness range. It is shown how XRR can also detect layering if it is present in the films, in which case the reflectivity profile must be modeled to derive the density. The mass density can also be derived from the valence electron density via the plasmon energy, which is measured by electron energy-loss spectroscopy ͑EELS͒. We formally define an interband effective electron mass m*, which accounts for the finite band gap. Comparison of XRR and EELS densities allows us to fit an average m*ϭ0.87m for carbon systems, m being the free-electron mass. We show that, within the Drude-Lorentz model of the optical spectrum, m*ϭ͓1Ϫn(0) Ϫ2 ͔m, where n(0) is the refractive index at zero optical frequency. The fraction of sp 2 bonding is derived from the carbon K-edge EELS spectrum, and it is shown how a choice of ''magic'' incidence and collection angles in the scanning transmission electron microscope can give sp 2 fraction values that are independent of sample orientation or anisotropy. We thus give a general relationship between mass density and sp 3 content for carbon films.

Structural and mechanical properties of diamond-like carbon films deposited by direct current magnetron sputtering J. Vac. Sci. Technol. A 21, 851 (2003); 10.1116/1.1575231Preparation and mechanical properties of composite diamond-like carbon thin films Ultrathin 2-nm-thick carbon coatings are needed to increase the storage density in magnetic hard disks. We show how x-ray reflectivity, surface Brillouin scattering, resonant Raman scattering, and electron energy loss spectroscopy can measure consistently the structural and mechanical properties of these thin films. 2 nm films retain a Young's modulus of 100 GPa.

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Grazing angle x-ray reflectivity (XRR) is used to study density, thickness, internal layering and roughness of a variety of carbon samples, with and without hydrogen and nitrogen. The bulk mass density of optimised tetrahedral amorphous carbon (ta-C) is 3.26 g/cm2, for which Electron Energy Loss Spectroscopy (EELS) found a sp3 fraction of 85%. Combining XRR and EELS we benchmark the dependence of sp3 fraction on density for hydrogen-free carbons. Hydrogenated ta-C (ta-C:H) deposited by electron cyclotron wave resonance (ECWR) reactor from acetylene gas, has a density of 2.35 g/cm3, 75% sp3 and ∼30% hydrogen. These data provide a similar validation for density and sp3 EELS data for hydrogenated DLCs. XRR can also reveal internal layering in films, and indeed less dense layers may be found at the surface or interface of ta-C films, but no such layers are found in ta-C:H films.

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