Laser Raman and X-ray photoelectron spectroscopy of phosphorus containing diamond-like carbon films grown by pulsed laser ablation methods

Abstract

Mechanically hard, electrically conducting diamond-like carbon (DLC) films containing 0 to ∼26 at.% phosphorus have been deposited on both Si and quartz substrates by pulsed laser ablation of graphite/phosphorus targets (containing varying percentages of phosphorus), at a range of substrate temperatures ( T sub=25–400 °C), in vacuum. Laser Raman spectra (514.5 nm excitation wavelength) of the as-deposited films yield the band maxima and relative intensities of the D and G peaks ( I(D) and I(G), respectively), as a function of T sub, P:C ratio and incident laser fluence, F. Nanocrystalline graphitisation was deduced to occur at higher substrate temperatures, consistent with previous results for undoped DLC and CN x films. P containing DLC films deposited at lower T sub values exhibit higher I(D)/ I(G) ratios than the corresponding undoped DLC films. Measured trends in G-peak positions and I(D)/ I(G) ratios are consistent with values for the C-sp 3 content obtained by deconvoluting the C 1s peak in the corresponding X-ray photoelectron spectra. XPS also reveals a decrease in P content in films grown at higher T sub and at higher F, suggesting that P atoms are more mobile than C atoms, and thus less strongly accommodated, during the film growth process.