Characterization of laser vaporization plasmas generated for the deposition of diamond-like carbon

Abstract

Pulsed laser vaporization of graphite is rapidly emerging as an effective technique for the preparation of high quality diamond-like carbon films. However, the dynamics of the process and mechanisms by which diamond-like properties are obtained have not been well understood. The characteristics of the vapor plume generated by 248 nm KrF excimer laser irradiation of a graphite target are investigated using laser induced fluorescence and a Langmuir probe. It is found that the kinetic energy of the C2 molecule increases with laser fluence, reaching a value in excess of 12 eV in the moderate fluence range (3-5 J/cm2) employed for deposition. The Cn+ ions are 5-10 times more energetic and comprise ∼10% of the vapor flux. A notable finding is that irradiation of the surface at an angle of 70° with respect to the target normal increases the ion velocity when compared with 0° laser incidence at the same surface fluence. Analysis of the films prepared under such conditions supports the theory that diamond-like film character is directly related to the kinetic energy of the depositing species.