Mass density and hydrogen content of diamondlike carbon as related to the preparation by plasma-enhanced chemical vapor deposition

Combined neutron and x-ray reflectometry was used to determine mass density and hydrogen content for thin (less than 3000 Å) diamondlike hydrocarbon films on polished Si (100) substrates. The introduction of ‘‘twin’’ neutron reflectometry improved the accuracy of the measurements. Mass densities in the range of 1.60–1.84 g/cm3 and hydrogen contents of 31–36 at. % were determined together with the nucleus densities of hydrogen and carbon. A series of diamondlike carbon films prepared by plasma-enhanced chemical vapor deposition was investigated to analyze the effect of depositing films at different flow rates of methane precursor gas. The mass density was found to increase with flow in the range of 1–8 standard cm3/min (sccm). For higher flows the mass density was constant. The hydrogen content did not depend on the rate of flow in the interval of 2–30 sccm. Finally, results of the mass density measured in a simpler way, using a scanning electron microscope and a profilometer, were compared to the results obtained by neutron and x-ray reflectometry.