X-ray diffraction investigation of polymer-like hydrogenated amorphous carbon films

Abstract Structural properties of polymer-like amorphous carbon (a-C:H) films grown in a dual-plasma (microwave (MW) assisted radio frequency (RF)) reactor have been investigated. An interesting transition appears as the film density increases due to increasing ion energy: (1) in situ infrared ellipsometry shows a transition in the C–H bonding modes corresponding to carbon skeleton cross-linking, (2) a quenching of the photoluminescence (PL) efficiency is observed when film density is >1.3 g cm −3 . To analyze the origin of such an evolution, X-ray diffraction investigations have been performed on a-C:H powders with densities increasing from 0.9 to 1.7 g cm −3 . This paper reports on X-ray measurements performed in transmission geometry using the high photon flux at LURE facilities. The data show differences between the samples in the structure factor, S ( K ), and in the pair correlation function, G ( r ). X-ray spectra have pre-peaks in the vicinity of 1 A −1 , which change in position and shape with the density of the powders. The contraction of the first distances, C–C, is observed as the density increases, from 0.152±0.002 nm for transparent and soft films to 0.142±0.002 nm for the denser one. The evolution of C-skeleton structure is described in terms of local co-ordination, in relation with the C–H bonding.