Structural characterisation of CN_x thin films deposited by pulsed laser ablation

摘要

Carbon nitride (CN_x) film growth by 193 nm pulsed laser ablation of graphite in a low pressure of N_2 has been investigated both by studying optical emission from the plume and by analyses of the composition, structure and bonding of material deposited at a range of substrate temperatures. Spectral analysis of the emission reveals the presence of C~+ ions, C atoms, C_2 and CN radicals and N_2~+ molecular ions within the ablation plume travelling towards the substrate. Films deposited at low substrate temperature (T_(sub)) are amorphous, with an N/C ratio of approx 20 at. percent. Raman analysis shows CN_x films grown at higher T_(sub) to be increasingly nanocrystalline, but thinner, and suggests that N inclusion encourages nanocrystallite formation. X-ray photoelectron spectroscopy reveals that CN_x films grown at higher T_(sub) also have a reduced overall N content. The observations have been rationalised by assuming an increased propensity for sputtering or desorption of more labile CN species from the growing film surface at higher T_(sub), resulting in a higher fraction of C-C bonding-most probably in the form of graphitic nanocrystallites embedded in an amorphous matrix.