Ion beam analysis of diamond-like carbon films

Abstract

Diamond-like carbon films are deposited with a number of different methods. This results in a wide variety of different microstructures and even compositions of the films, which challenges characterization capabilities. Ion beam analysis can be used in many ways to probe the properties of the films. A classic application is the determination of hydrogen concentrations in hydrogenated amorphous carbon films, a-H : C. This is performed by using either a resonance of the nuclear reaction 1H( 15N, αγ) 12C or a forward recoiling technique. Diamond-like films have been doped with metals, Si, F, etc. in order to modify mechanical, tribological, or optical properties. Dopand concentrations can be qualitatively measured using either a backscattering or nuclear reaction analysis (NRA) method. A fairly trivial application is the utilization of either Rutherford or non-Rutherford backscattering to obtain the number of carbon atoms per square centimetre. Combined with other information on the chemical composition of the film and with the thickness obtained with a profilometer, for example, the density of the very thin films can be calculated. The density is an interesting parameter of the films and may vary considerably, depending on the hydrogen concentration and the structure of chemical bonding. If the thickness of the films is not constant or if a diamond-like material is just a deposition with an irregular shape, the above method cannot be utilized. The ion beam technique may still be useful and the Doppler shift attenuation of the resonance can be used. Resonance techniques are useful in analysing some other carbon related films, for example in analysing nitrogen in CN x films. In this paper, the most useful ion beam techniques for analysing diamond-like materials are given with examples.