Microstructure And Mechanical Properties Of Amorphous Carbon Nitride Thin Films

Carbon nitride films and Ni doped carbon nitride films were fabricated by a DCfacing-target magnetron sputtering system at room temperature and were subsequentlyannealed at different temperatures. The surface morphology, composition,microstructure and nanomechanical properties were investigated by atomic forcemicroscopy (AFM), Raman spectroscopy, Fourier transform infrared spectroscopy(FTIR), transmission electron microscopy (TEM), high-resolution transmission electronmicroscopy (HRTEM) and nanoindentor.MORPHOLOGY A large number of self-assembling nanosized dots can beproduced on the surface of the pure C films deposited at appropriate sputtering powerand pressure. As for CN films, the average surface roughness increases with theincreasing N2 fractions (P_N) in the gas mixture. When the films deposited at a P_N of60% are annealed at 650℃, few pyramids are produced.COMPOSITION The N concentration of the films deposited at roomtemperature is not directly proportional to P_N, and it rises quickly to a saturate value of～33 at.% at a P_N of 20%. After being annealed, a dramatic N loss occurs in all the films,while the trend of the change in N concentration with the increasing P_N remainsunchanged.MICROSTRUCTURE With the increase of P_N, a graphitization progress,including the conversion from sp~3 C to sp~2 C, the increase of the number and size ofaromatic clusters, occurs in the CN films. The films deposited at different P_N showdifferent thermal stability. The structure modification induced by thermal annealingdepends on the bonding structure of the films determined by P_N. For the films depositedat high P_N, thermal annealing makes the structure looser, while for the films deposited atlow P_N, thermal annealing enhances the graphitization of the films. The relative thermalstability of various N bonds in the films deposited at different PN is also different. Forthe films deposited at high PN, with the increase of annealing temperature, the contentof N–sp2C bonds is unchanged, C≡N bonds appear, and N–sp3C bonds disappearcompletely. While for the films deposited at low PN, during the same annealing process,the content of N–sp2C bonds is unchanged, C≡N bonds do not appear, and N–sp3Cbonds decrease.EFFECTS of Ni DOPING The Ni doping in CN films greatly changes thesurface morphology of the films and makes the average roughness increase. At roomtemperature, the formation of Ni–N compound increases the N content. As theannealing temperature increases, the C–N bonds and Ni–N bonds decompose so that theN content in the Ni doped CN films decrease significantly. At 650 oC, the N content inNi doped CN film is only 1/3 of that in the pure CN films. At room temperature, Nidoping almost does not affect the microstructure of the CN films. When annealingtemperature increases, Ni doping improves the graphitization of a-CN. The catalysiseffect of Ni on the graphitization of a-CN, which is associated with annealingtemperature, leads to the formation of bamboo-shaped nanostructured CN at 650 oC.NANOMECHANICAL PROPERTIES The hardness of the CN filmsdecreases with the increasing PN due to the graphitization of sp2 C structure. It was alsofound that the hardness depends less on the bond structures of N atoms but more on thebond structures of C atoms. The incorporation of N changes the mechanical propertiesof the CN films through the modification of the bond structures of C atoms by Ndoping.