Carbon nitride films have been synthesized by argon ion-beam sputtering from a biomolecular compound target, 8-aza-6-aminopurine (C4N6H4). The compound has a six-membered ring structure similar to that existing in the hypothetical β-C3N4. 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 1643cm-1, corresponding to C-N and CN stretching modes, respectively. No detectable peak at 2200cm-1 (CN 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 β-C3N4 structure. However, it is suggested that the film contains a nanocrystalline phase with a crystal structure yet to be determined.