The use of a biomolecular target for crystalline carbon nitride film deposition by Ar ion-beam sputtering without any other source of nitrogen

Carbon nitride films have been synthesized by argon ion-beam sputtering from a biomolecular compound target, 8-aza-6-aminopurine $({\mathrm{C}}_{\mathrm{4}}{\mathrm{N}}_{\mathrm{6}}{\mathrm{H}}_{\mathrm{4}}\mathrm{).}$ The compound has a six-membered ring structure similar to that existing in the hypothetical $\mathrm{\beta -}{\mathrm{C}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}}.$ Except for the target material, no other source of nitrogen was used during sputtering deposition. It was found that crystalline carbon nitride with high N/C atomic composition ratios of 0.43–0.56 can be formed even at room temperature. The infrared spectra of the film exhibit two peaks at 1383 and $\text{1643\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}},$ corresponding to C–N and $\mathrm{C=N}$ stretching modes, respectively. No detectable peak at $\text{2200\hspace{0.17em}}{\mathrm{cm}}^{\mathrm{-1}}$ $(\mathrm{C\equiv N}$ stretching mode) is observed. Both x-ray diffraction and transmission electron microscopy show a very strong broad peak at 3.2 Å, comparable to the $d$ spacing of the (110) orientation in the $\mathrm{\beta -}{\mathrm{C}}_{\mathrm{3}}{\mathrm{N}}_{\mathrm{4}}$ structure. However, it is suggested that the film contains a nanocrystalline phase with a crystal structure yet to be determined.