Optical and luminescence properties of polymer-like a-C:H films deposited in a dual-mode PECVD reactor

Butane has been decomposed in the post-discharge of a helium-argon microwave plasma, assisted by a radiofrequency (rf) plasma. The ion bombardment on the substrate, monitored by the rf power, is found to control the optical and luminescence properties of hydrogenated amorphous carbon (a-C:H) thin films: the extinction coefficient of a-C:H increases with rf power while the photoluminescence efficiency decreases by three orders of magnitude. The parametrization of the dielectric function, using a three-phase effective medium approximation, is discussed in relation to the expected size effects on the dielectric function of the pi-bonded clusters.