Grazing-angle x-ray reflectivity (XRR) 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 (EELS). 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 $m^{*}=0.87m$ for carbon systems, m being the free-electron mass. We show that, within the Drude-Lorentz model of the optical spectrum, $m^{*}=\left[1-{n\left(0\right)\mathrm{}}^{-2}\right]m,$ where $n\left(0\right)\mathrm{}$ is the refractive index at zero optical frequency. The fraction of ${\mathrm{sp}}^2$ 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 ${\mathrm{sp}}^2$ fraction values that are independent of sample orientation or anisotropy. We thus give a general relationship between mass density and ${\mathrm{sp}}^3$ content for carbon films.

A comprehensive study of the stress release and structural changes caused by postdeposition thermal annealing of tetrahedral amorphous carbon (ta-C) on Si has been carried out. Complete stress relief occurs at 600–700 °C and is accompanied by minimal structural modifications, as indicated by electron energy loss spectroscopy, Raman spectroscopy, and optical gap measurements. Further annealing in vacuum converts sp3 sites to sp2 with a drastic change occurring after 1100 °C. The field emitting behavior is substantially retained up to the complete stress relief, confirming that ta-C is a robust emitting material.