Equilibrium segregation of Ti to Au-sapphire interfaces

Equilibrium segregation of Ti to Au-sapphire interfaces was measured from dewetted Au(Ti) films on the (0001) surface of sapphire. Quantitative energy dispersive spectroscopy was used to determine a Ti excess at the Au-sapphire interface of 2.2 Ti atoms/nm ², which together with an excess of 4.6 Ti atoms/nm ² at the (0001) sapphire surface, is associated with a decrease in the solid-solid Au-sapphire interface energy. Quantitative high resolution transmission electron microscopy showed that the segregated Ti is distributed within a 1.54-nm thick intergranular film at the Au-sapphire interface, which is not a bulk phase but rather an equilibrium interface state. As a result, Ti segregation without the formation of a bulk reaction at the interface is associated with a decreased interface energy, improved wetting, and may be an important part of the total complex mechanism responsible for improved wetting and spreading in "reactive" braze systems.