X-ray photoelectron spectroscopy and transmission electron microscopy studies of the NiAl/Al2O3 interfacial chemical compatibility

Abstract

β-NiAl thin films were prepared by physical vapor deposition (PVD) either on thin PVD Al2O3 films on Si substrates or on sapphire single crystals. These samples were characterized by x-ray diffraction and electron spectroscopies [Auger electron spectroscopy and x-ray photoelectron spectroscopy (XPS)]. Crystalline films were obtained after deposition at room temperature. XPS depth profiles and transmission electron microscopy cross sections show that the NiAl–Al2O3 interface is sharp (1 nm) and that NiAl oxidation occurs. Ni remains chemically unaffected by the presence of oxygen while the formation of Al3+ compounds is discussed. Within the film Al and Ni appear in a single chemical environment characterized by binding energies close to those of pure intermetallic compounds. Annealing of these wafers at 600 °C induces surface oxidation and, particularly, the formation of an Al2O3 protective layer.