Structure and growth of titanium buffer layers on Al2O3(0001)

The structure of titanium films on \alpha - Al2O3(0001) surfaces at room temperature was investigated through in situ reflection high energy electron diffraction (RHEED). The \alpha-phase of titanium was observed to grow with the Ti(0001) || Al2O3(0001), Ti[1100] || Al2O3[2110] and Ti[1010] || Al2O3[1100] epitaxy. For up to 6 nm thick films, an other structure was found to coexist with \alpha-Ti. Its presence has dramatic consequences for the wetting of silver, which partly explains the nontrivial buffer effect of titanium at the silver/alumina interface. From the RHEED data, the extra structure is assigned to the high-pressure hexagonal \omega-Ti phase. This is supported by tight-binding total energy calculations that demonstrate that the \omega phase could actually be stabilized by the \alpha - Al2O3(0001) substrate.