X-ray Photoelectron Spectroscopy Analyses of the Electronic Structure of Polycrystalline Ti1-xAlxN Thin Films with 0 ≤ x ≤ 0.96

Abstract

Metastable Ti 1-x Al x N (0 x 0.96) alloy thin films are grown by reactive magnetron sputter deposition using a combination of high-power pulsed magnetron (HIPIMS) and DC magnetron sputtering (DCMS). Layers are deposited from elemental Ti and Al targets onto Si(001) substrates at 500C. All Ti 1-x Al x N film surfaces are analyzed by x-ray photoelectron spectroscopy (XPS) employing monochromatic Al K a radiation (h = 1486.6 eV). Prior to spectra acquisition, TiAlN surfaces are sputter-cleaned in-situ with 4 keV Ar + ions incident at an angle of 70 with respect to the surface normal. XPS results reveal satellite structures on the high binding energy side of the Ti 2p, Ti 3s, and Ti 3p core-level signals. The intensities of the primary Ti features (Ti 2p, Ti 3s, and Ti 3p) decrease with increasing AlN concentration such that the satellite peaks dominate spectra from films with x ! 0.67. The density-of-states at the Fermi level also decrease with increasing x indicating that the satellite peaks are due to screening of core holes created by the photoionization event. Film compositions, obtained using XPS sensitivity factors, agree to within . Nevertheless, metastable NaCl-structure pseudobinary alloys can be obtained by physical vapor deposition (PVD) due to kinetically-limited low-temperature growth and low-energy ion-irradiation-induced dynamic mixing in the near-surface region. Reported kinetic AlN solubility limits in cubic Ti 1-x Al x N alloys are typically x max $ 0.50 for dc magnetron sputter (DCMS) deposition at film growth temperatures T s = 500 C (Refs. 8 and 9), while x max values up to 0.66 have been reported using cathodic arc evaporation (Refs. 10 and 11). However, the resulting films have very high compressive stresses, up to À5 GPa (Ref. 12) for DCMS and À9.1 GPa (Ref. 13) for arc-deposited films.Recently, we have shown that single-phase NaCl-structure Ti 1-x Al x N alloys with x 0.64, combining high hardness and low residual stress, can be grown by a hybrid technique consisting of reactive high-power pulsed magnetron sputtering (HIPIMS) of Al and DC magnetron sputtering (DCMS) of Ti targets (Al-HIPIMS/Ti-DCMS) (Refs. 14-16). In distinct contrast, Ti-HIPIMS/Al-DCMS Ti 1-x Al x N layers with x > 0.41 are two-phase mixtures, NaCl-structure Ti 1-x Al x N plus wurtzite AlN, which exhibit low hardness with high compressive stress due to an intense energetic Ti 2+ metal-ion flux incident at the growing film surface.Here, we employ x-ray photoelectron spectroscopy (XPS) to investigate the electronic structure of Ti 1-x Al x N alloy thin films with 0 x 0.96 grown by reactive hybrid Ti-HIPIMS/Al-DCMS co-sputtering. normal. Ti 2p, Ti 3s, Ti 3p, Al 2p, Al 2s, N 1s, and valence band spectra are presented. The Ti 2p core-level spectra exhibit a satellite peak on the high binding energy (BE) side of the Ti 2p 3/2 and Ti 2p 1/2 peaks in agreement with earlier XPS analyses of . The origin of this feature is widely discussed in the literature and several interpretations have been proposed including intra-band transiti...

Al capping layers for nondestructive x-ray photoelectron spectroscopy analyses of transition-metal nitride thin films

“…We select Al as the cap layer for the following reasons: (1) the Al native oxide, <2 nm thick at room temperature, is stable against spallation; 29 thus minimizing interfacial reactions; (3) and Al core-level peaks do not overlap with the primary Ti and N signals. We show that Al layers with thickness d Al ¼ 1.5 nm form a dense continuous, oxidized barrier that protects the TiN underlayer and allows for acquisition of high-resolution Ti 2p and N 1s core-level spectra, with clear pronounced satellite features, [30][31][32][33] which are in excellent agreement with those obtained from epitaxial TiN layers grown in-situ in an XPS system. 34 O 1s spectra reveal no evidence for Ti-O bonding.…”

Compositional and structural studies of ion-beam modified AlN/TiN multilayers

“…The Ti 2p 3/2 core levels recorded in point-B and D demonstrate the dramatic effects of ion irradiation. In the TiN layer a new lineshape of the Ti 2p slightly shifts to higher binding energies, and the shake-up peaks become more dominant in agreement with previously reported works [17,27]; a well spectral matching of the Ti 2p curve with reference spectrum [17] The irradiated sample still exhibits some form of a layered structure, but the layers become thicker and the contrast appears rather uniform, indicating that initially isolated phases become intermixed. A closer analysis shows that TiN layers appear to grow in thickness, consuming the adjacent AlN layers.…”

Effect of thermal treatments in high purity Ar on the oxidation and tribological behavior of arc-PVD c-Al0.66Ti0.33N coatings

“…In our case, the XRD reflexion at 37.5° of the eV and 461.36 eV correspond to Ti 2p3/2 and Ti 2p1/2 branchings, respectively. This is in agreement with the binding energy of Ti in the TiAlN structure [22,28], and no other signals of Ti-N bonds were found. The second doublet at 457.27 and 462.93 eV confirms the presence of TiOxNy bonds [28] and, the third doublet at 459.20 and 464.86 eV is associated with Ti-O bonds into TiO2 [29].…”

“…Fig. 2c displays the N 1s spectrum with three components at 396.59, 397.68 and 400.36 eV corresponding to Al-Ti-N, Al-Ti-O-N and N-C bonds [22,[26][27][28].…”