XPS, AFM and nanoindentation studies of Ti1−xAlxN films synthesized by reactive unbalanced magnetron sputtering

A combined investigation of chemical analysis and bonding states in Ti1−xAlxN films sputter-deposited on Si(1 0 0) in an Ar–N2 gas mixture by X-ray photoelectron spectroscopy and of surface morphology and mechanical properties by atomic force microscopy (AFM) and nanoindentation measurements is reported. It was found that a linear increase in the Al concentration of the films was observed with increasing Al target current up to 7 A, while the reverse trend was seen for the Ti concentration. The Al and Ti in the films presented in a form of stoichiometric TiN and AlN at different atomic concentration of Al. Several types of chemical states, such as Al2O3, TiNxOy, Ti2O3 and TiO2 have been identified. However, no unbound Al and Ti atomic species were detected in films. By applying the height–height correction functions to the measured AFM images, a steady growth roughness exponent α=0.94±0.03 was determined for all the Ti1−xAlxN films. The value of α is consistent with growth model predictions incorporating surface diffusion. It was also found that the improved mechanical properties of Ti1−xAlxN films with the addition of Al into TiN matrix were attributed to their densified microstructure with development of fine grain size and reduced surface roughness. The effect of aluminium in stabilizing the Ti–Al–N structure was also elucidated and explained on the basis of the adatom mobility and the surface diffusion of atoms.