Structure and growth of titanium buffer layers on Al2O3(0 0 0 1)

The structure of titanium films on α-Al2O3(0 0 0 1) surfaces at room temperature was investigated through in situ reflection high energy electron diffraction (RHEED). The α-phase of titanium was observed to grow with the Ti(0 0 0 1)∥Al2O3(0 0 0 1), Ti[1 1̄ 0 0]∥Al2O3[2 1̄ 1̄ 0] and Ti[1 0 1̄ 0]∥Al2O3[1 1̄ 0 0] epitaxy. For up to 6 nm thick films, an other structure was found to co-exist with α-Ti. Its presence has dramatic consequences for the wetting of silver, which partly explains the non-trivial buffer effect of titanium at the silver/alumina interface. From the RHEED data, the extra structure is assigned to the high-pressure hexagonal ω-Ti phase. This is supported by tight-binding total energy calculations that demonstrate that the ω phase could actually be stabilized by the α-Al2O3(0 0 0 1) substrate.