INTERFACE REACTIONS BETWEEN TITANIUM THIN-FILMS AND (112) SAPPHIRE SUBSTRATES

We have studied the reactivity of Ti with the R-plane (112BAR) of sapphire from room temperature to 1250-degrees-C by X-ray photoemission spectroscopy (XPS), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Rutherford backscattering spectroscopy (RBS). The combination of these techniques allowed the interface reactions to be studied from the monolayer regime up to the bulk regime. XPS showed that at room temperature, monolayer coverages of Ti reduced the sapphire surface to form Ti-O and Ti-Al bonds. TEM, XRD, and RBS showed that annealing of room-temperature deposited Ti resulted in an interfacial region consisting of two layers, a Ti3Al[O] layer adjacent to the sapphire and a Ti0.67[O0.33] layer at the free surface. The growth of the Ti3Al[O] layer had an activation energy of 103.4 +/- 25 kJ deg-mole. The nature of the interfacial reaction between Ti and sapphire was similar for Ti coverages from the monolayer to the bulk regime.