Pulsed-laser deposition of diamond-like carbon: Relations between laser fluence, velocity of carbon ions, and bonding in the films

Abstract

In the pulsed-laser deposition process, high intensity laser pulses expel material from a solid target and form expanding plasma near the solid surface. The expansion of the plasma produces a forward-directed beam of ionized and neutral species with typical energies of 1–100 eV. In this study, amorphous diamond-like carbon (DLC) thin films were deposited onto silicon substrates at room temperature using an XeCl excimer laser (wavelength 308 nm, pulse length 20 ns) with laser fluences in the range 5–45 J cm−2, on a pyrolytic graphite target. The effect of laser fluence on the velocity and kinetic energy distribution of carbon ions was measured by time-of-flight (TOF) spectrometry using a system based on a Faraday cup with biased grids, and a multichannel plate based particle detector. We have found high kinetic energies, up to 500 eV, for expelled atomic species. In order to study the effect of the energy of the arriving ions on the structure of DLC, the bonding of carbon atoms in films, deposited under similar conditions as in the TOF measurements, was studied by x-ray absorption near-edge structure.