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

Structural properties of polymer-like amorphous carbon (a-C:H) films grown in a dual-plasma (microwave (MW) assisted radio frequency (RF)) reactor hav e been investigated. An interesting transition appears as the film density increases due to increasing ion energy: (1) in situ infrared ellipsometry s hows 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 perfonned on a-C: H powders with densities increasing from 0.9 to 1.7 g cm(-3). This paper re ports on X-ray measurements performed in transmission geometry using the hi gh photon flux at LURE facilities. The data show differences between the sa mples in the structure factor, S(K), and in the pair correlation function, G(r). X-ray spectra have prepeaks in the vicinity of 1 Angstrom(-1), which change in position and shape with the density of the powders. The contracti on 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 term s of local co-ordination, in relation with the C-H bonding. (C) 2000 Publis hed by Elsevier Science B.V. All rights reserved.