Investigation of anomalous physical properties of multilayer nanolaminate (TiAl)N/Cu coatings by electron spectroscopy techniques

In accordance with high-resolution transmission electron microscopy (HRTEM), (Ti₃₄Al₆₆)N/Cu physical vapour deposition (PVD) composite coating had a nanolaminated structure with 20 nm (Ti ₃₄Al₆₆)N and 2.0-5.0 nm fine grain recrystallized Cu layers. It was unexpectedly found that the coatings under investigation had a lower thermal conductivity coefficient of 25 to 450° C compared to the TiAlN single layer coating. The physical basis of thermo-barrier protective features of copper nanolayers was explained based on XPS and high-resolution electron energy losses spectroscopy (HREELS) data. The temperature dependence of the phonons and conducting electron vibrations was investigated for Cu bulk, (TiAl)N upper layer, and the intermediate Cu one. In comparison with Cu bulk reference sample, the intermediate Cu layers of complex PVD coating were characterized by the following features: size-dependent shift of Cu 2p_3/2 binding energy, reduced plasmon losses and acoustic mode phonon vibrations amplitudes, and increased intensities of the optical mode vibrations. These features of phonon and plasmon oscillations in the crystal lattice of Cu nanolayers do not completely explain the anomalies of the thermal conductivity of the (TiAl)N/Cu PVD coating. The thermal barrier properties of Cu nanolayers can be primarily attributed to the mirror effect or reflecting of the heat flux from the surface by metal layer with high concentration of conducting electrons.