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

TL;DR

This study investigates the epitaxial growth and phase structure of titanium buffer layers on Al2O3(0001), revealing coexistence of ta and mbda phases and their effects on silver wetting, supported by experimental and computational analysis.

Contribution

It provides new insights into the phase coexistence and epitaxial relationships of titanium on Al2O3(0001), including stabilization of the mbda phase by the substrate.

Findings

ta-phase of titanium grows epitaxially on Al2O3(0001).

Coexistence of ta and mbda phases observed up to 6 nm thickness.

The mbda phase is stabilized by the substrate, affecting silver wetting.

Abstract

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.