Chemical bonding of nitrogenated ultrananocrystalline diamond films deposited on titanium substrates by pulsed laser deposition

Ultrananocrystalline diamond (UNCD)/nonhydrogenated nitrogenated amorphous carbon (a-C:N) composite (UNCD/a-C:N) films were prepared on titanium substrates in a nitrogen atmosphere by pulsed laser deposition, and their adhesion to the titanium substrates was remarkably improved as compared with those of UNCD/hydrogenated nitrogenized amorphous carbon (a-C:H:N) composite films deposited in a nitrogen and hydrogen mixture atmosphere. Their chemical bonding structures were investigated in details by X-ray photoemission and near edge X-ray absorption fine structure spectroscopies with synchrotron radiation. The UNCD/a-C:N films exhibit an obviously enhanced formation of sp2 and sp bonding such as C=N and CßN bonds. It should be contributable to the adhesion improvement. Since its formation locally disconnects sp3 bonding networks in the films, an internal stress, which is the main reason for exfoliation, should be released.