SURFACE CHARACTERIZATION OF PLASMA-NITRIDED TITANIUM - AN XPS STUDY

DC plasma nitriding was applied to titanium metal sheets in a commercial cell using Ar + NH3 as the admixture and the nitrided surface investigated by means of XPS. As a comparison, in situ nitriding of a chemically pure Ti surface at room temperature was performed by N2+ ion bombardment (1-5 keV) in the electron spectrometer. Synthesis of the complex Ti2p envelope was accomplished using two sets of loss peaks, separated by 1.6 and 3.0 eV from the major Ti-N-type Ti2p3/2 and Ti2p1/2 components. A doublet at 458.8 and 464.5 eV was also included to account for a TiO2-type oxide. The sum of the main Ti TiN peak and the two loss peaks were taken to be representative of nearly stoichiometric TiN(x) with x ranging from 0.85 to 1.15. Further components derived from the peak synthesis were assigned to TiN(x)O(y) and Ti2O3. The stoichiometric nitride is represented by a Ti2p doublet at binding energies of 454.7 and 460.6 eV and a single sharp N 1s peak at 396.7 +/- 0.1 eV. On the superstoichiometric samples, especially after N2+ bombardment, a second peak appears at about 395.8 eV with a positive correlation between this peak concentration and the relative amounts of species (TiN(x)O(y), Ti2O3, TiO2) derived from Ti2p components and the surface O and N content. Consecutive Ar+, N2+ and (N2+ + O2+) bombardment leads to significant changes in composition together with rearrangement of short-range chemical structure which is reflected in peak-shape changes of the Ti2p and N 1s lines.