The reaction of sputter deposited layers of Ti on the (001) surface of a synthetically grown single crystal type IIb boron doped diamond has been investigated using Auger electron spectroscopy with depth profiling, Rutherford backscattering spectroscopy (RBS) and Raman spectroscopy. Electrical characteristics of the contacts were measured usingI–Vdata and separated from substrate electrical effects using Hall measurements of the carrier concentration and mobility. Heat treatments above 425 °C were found necessary to cause the transition from a rectifying to an ohmic contact. Without a protective 150 nm layer of Au, oxidation of the Ti layer was observed atT≥425 °C, even for annealing in forming gas. This was detrimental to the adhesion of the layer and the long term stability of the ohmic contact resistance. With a protective Au film, low resistance, adherent ohmic contacts were observed even after 1 h at 750 °C, even though Ti diffused along Au grain boundaries to form nodules of TiO2at the Au/ambient interface. Interfacial carbides were detected by both Auger peak shape changes and RBS measurements for annealing temperatures as low as 500 °C, and their appearance correlated with the transition to ohmic contacts. The carbides increased in thickness to about 50 nm after 1 h at 750 °C.