Pulsed laser deposition of diamond-like amorphous carbon films from graphite and polycarbonate targets

Abstract

Amorphous carbon (a-C) and amorphous hydrogenated carbon (a-C:H) films are produced by 248 nm pulsed laser ablation of graphite and polycarbonate targets in high vacuum conditions. Plasma plumes generated by target irradiation with different laser fluences are investigated with laser induced fluorescence spectroscopy and an electrostatic probe. Ions of C2+ with kinetic energies of several hundred eV are detected in the leading edge of the plasma plumes from both targets. These energetic species are proposed to be responsible for the formation of film structures corresponding to diamond-like carbon (DLC), as it is found from electron-energy-loss spectroscopy (EELS) and Raman investigations of 0.5 μm films deposited onto steel substrates. The validation of a laser wavelength/fluence region for DLC formation found earlier for graphite targets is discussed and expanded to polycarbonate targets. An increase in laser fluence leads to higher percentages of sp3 bonds in the a-C and a-C:H films. For the a-C:H films, the incorporation of large molecular conglomerates ejected from polycarbonate targets results in the formation of unique heterogeneous structures revealed from scanning electron microscopy (SEM) studies. The embedded conglomerates cause a decrease in the a-C:H film hardness to 15 GPa, in comparison to 60 GPa for the a-C films.