Solvothermal
growth of thin (1–2 μm thick), uniform
films of carbon phosphonitride on fused quartz substrates has been
achieved by self-reaction of 1 m P(CN)3 in diphenyl ether at 185 °C for 7 days in a sealed Teflon-lined
digestion bomb. The films are chemically similar to C3N3P powders thermoset from neat (solid) P(CN)3 based
on XPS and IR spectra. A difference in bulk elemental composition
relative to C3N3Preduced nitrogen and
increased oxygen contentis attributable to through-film (as
opposed to surface-confined) hydrolysis of unreacted nitriles (P–CN)
to hydroxyl species (P–OH). Nanoindentation analyses were performed
to assess the mechanical properties of these CPN films. Minimal dependence
of mechanical properties on thermal treatment was observed with annealing
temperatures in the 100–400 °C range, resulting in an
average reduced modulus of E
r = 26.5 ±
1.5 GPa and hardness of H = 1.5 ± 0.1 GPa, which
is on par with high performance polymers. Heating to 550 °C results
in higher modulus and hardness (E
r
550 °C =
51 ± 2 GPa, H
550 °C = 5.0 ± 0.4 GPa), likely due to an increased prevalence
of oligomeric phosphine oxide cross-links formed by dehydration of
P–OH functional groups.